iran ilsf cdr
DESCRIPTION
iran synchrotronTRANSCRIPT
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TABLE OF CONTENTS
LIST OF CONTRIBUTORS .............................................................................................................................. 9
CHAPTER 1: INTRODUCTION .................................................................................................... 11
1.1 A LIGHT SOURCE FOR IRAN .............................................................................................................. 11 1.2 IRANIAN USERS ............................................................................................................................. 14 1.3 GAS-PHASE PHOTOEMISSION BEAMLINE ............................................................................................. 16 1.4 SOFT X-RAY TWIN-SPECTROMICROSCOPY BEAMLINE ............................................................................. 20 1.5 MACROMOLECULAR X-RAY CRYSTALLOGRAPHY USING SYNCHROTRON RADIATION ...................................... 23 1.6 INELASTIC X-RAY SCATTERING BEAMLINE FOR ILSF .............................................................................. 27 REFERENCES .......................................................................................................................................... 29
CHAPTER 2: CHOICE OF LATTICE ............................................................................................... 31
2.1 INTRODUCTION ............................................................................................................................. 31 2.2 GENERAL LAYOUT OF THE ACCELERATOR COMPLEX ............................................................................... 34
CHAPTER 3: BEAM DYNAMICS ................................................................................................. 37
3.1 ILSF STORAGE RING ....................................................................................................................... 37 3.1.1 Lattice structure .............................................................................................................. 37 3.1.2 Nonlinear beam dynamics .............................................................................................. 41 3.1.3 Choice of tune points and upgrade capabilities .............................................................. 45 3.1.4 Closed orbit ..................................................................................................................... 46
3.1.4.1 Closed orbit distortion ........................................................................................................ 46 3.1.4.2 Closed orbit correction ....................................................................................................... 47
3.1.5 Effects of insertion devices ............................................................................................. 48 3.1.5.1 Beta-beating and tune shift ................................................................................................ 49 3.1.5.2 Dynamic aperture reduction ............................................................................................... 51 3.1.5.3 Effects of radiation from ID ................................................................................................. 54
3.1.6 Multipole effects ............................................................................................................ 55 3.1.6.1 Systematic multiple errors .................................................................................................. 55 3.1.6.2 Multipole errors for dipole magnets ................................................................................... 56 3.1.6.3 Multipole errors for quadrupole magnets .......................................................................... 57 3.1.6.4 Multipole errors for sextupole magnets ............................................................................. 57 3.1.6.5 Systematic multipole errors for all magnets ....................................................................... 58 3.1.6.6 Measured multipole errors in ALBA .................................................................................... 59
3.1.7 Lifetime ........................................................................................................................... 63 3.1.7.1 RF system in ILSF storage ring ............................................................................................. 64 3.1.7.2 Quantum lifetime ................................................................................................................ 65 3.1.7.3 Touschek lifetime ................................................................................................................ 65 3.1.7.4 Gas scattering ..................................................................................................................... 66 3.1.7.5 Total lifetime ....................................................................................................................... 69
3.1.8 Injection into the ring...................................................................................................... 71 3.1.9 Specification of magnets................................................................................................. 73
3.1.9.1 Dipole magnets ................................................................................................................... 74 3.1.9.2 Quadrupole magnets .......................................................................................................... 74 3.1.10.3 Sextupole magnets .............................................................................................................. 75
3.2 BOOSTER ..................................................................................................................................... 76 3.2.1 Lattice structure .............................................................................................................. 76 3.2.2 Nonlinear beam dynamics .............................................................................................. 79 3.2.3 Magnets .......................................................................................................................... 81
3.2.3.1 Dipole magnets ................................................................................................................... 81 3.2.4.2 Quadrupole magnets .......................................................................................................... 82 3.2.3.3 Sextupole magnets .............................................................................................................. 83
3.2.4 Closed orbit ..................................................................................................................... 83 3.2.4.1 Closed orbit distortion ........................................................................................................ 83 3.2.4.2 Closed orbit correction ....................................................................................................... 83
3.2.5 Ramping effects .............................................................................................................. 85 3.2.5.1 Ramping of energy and RF voltage...................................................................................... 85
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3.2.5.2 Time evolution of beam emittance ..................................................................................... 86 3.2.5.3 Time evolution of energy spread ........................................................................................ 87
3.2.6 Eddy current effects ........................................................................................................ 88 3.2.6.1 Induced sextupole component in dipoles vacuum chamber .............................................. 88 3.2.6.2 Nonlinear optimization with chromaticity fixed at ............................. 90
3.2.7 Lattice alternative for the booster .................................................................................. 92 3.2.7.1 Nonlinear beam dynamics .................................................................................................. 93 3.2.7.2 Magnets .............................................................................................................................. 95
3.3 TRANSFER LINES ............................................................................................................................ 96 3.3.1 LTB transfer line .............................................................................................................. 96 3.3.2 BTS transfer line .............................................................................................................. 98
REFERENCES ........................................................................................................................................ 100 APPENDIX 3.1: ILSF LATTICE 1 ........................................................................................................ 101 APPENDIX 3.2: ILSF BOOSTER LATTICE .............................................................................................. 102 APPENDIX 3.3: ILSF LTB LATTICE ..................................................................................................... 103 APPENDIX 3.4: ILSF BTS LATTICE..................................................................................................... 104
CHAPTER 4: MAGNETS ........................................................................................................... 105
4.1 STORAGE RING LATTICE MAGNETS ................................................................................................... 105 4.1.1 Principal specifications of lattice magnets ................................................................... 105
4.1.1.1 Bending magnets .............................................................................................................. 106 4.1.1.2 Quadrupole magnets ........................................................................................................ 106 4.1.1.3 Sextupole magnets ............................................................................................................ 106
4.1.2 Dipole magnets ............................................................................................................. 107 4.1.2.1 Dipole design parameters ................................................................................................. 107 4.1.2.2 Pole and yoke geometry ................................................................................................... 107 4.1.2.3 Field Quality ...................................................................................................................... 111 4.1.2.4 Harmonic analysis ............................................................................................................. 112 4.1.2.5 Three-dimensional magnetic simulations ......................................................................... 113 4.1.2.6 Electrical and cooling parameters ..................................................................................... 114 4.1.2.7 Saturation ......................................................................................................................... 116 4.1.2.8 Engineering layout ............................................................................................................ 116
4.1.3 Quadrupole magnets .................................................................................................... 118 4.1.3.1 Quadrupole design parameters ........................................................................................ 118 4.1.3.2 Pole and yoke geometry ................................................................................................... 118 4.1.3.3 Field Quality ...................................................................................................................... 121 4.1.3.4 Harmonic analysis ............................................................................................................. 122 4.1.3.5 Electrical and Cooling Parameters .................................................................................... 123 4.1.3.6 Saturation ......................................................................................................................... 124 4.1.3.7 Engineering layout ............................................................................................................ 125
4.1.4 Sextupole Magnets ....................................................................................................... 126 4.1.4.1 Sextupole design parameters............................................................................................ 126 4.1.4.2 Pole and yoke geometry ................................................................................................... 126 4.1.4.3 Field Quality ...................................................................................................................... 129 4.1.4.4 Harmonic analysis ............................................................................................................. 130 4.1.4.5 Electrical and Cooling Parameters .................................................................................... 130 4.1.4.6 Sextupole Corrector coils .................................................................................................. 131 4.1.4.7 Saturation ......................................................................................................................... 133 4.1.4.8 Engineering layout ............................................................................................................ 133
4.1.5 Magnetic steel .............................................................................................................. 135 4.2 BOOSTER LATTICE MAGNETS .......................................................................................................... 136
4.2.1 Principal specifications of the lattice magnets ............................................................. 136 4.2.1.1 Bending magnets .............................................................................................................. 137 4.2.1.2 Quadrupole magnets ........................................................................................................ 137
4.2.2 Dipole magnet .............................................................................................................. 138 4.2.2.1 Dipole design parameters ................................................................................................. 138 4.2.2.2 Pole and yoke geometry ................................................................................................... 138 4.2.2.3 Field Quality ...................................................................................................................... 140 4.2.2.4 Harmonic analysis ............................................................................................................. 141 4.2.2.5 Electrical and cooling parameters ..................................................................................... 142 4.2.2.6 Saturation ......................................................................................................................... 143
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4.2.3 Quadrupole magnets .................................................................................................... 144 4.2.3.1 Quadrupole design Parameters ........................................................................................ 144 4.2.3.2 Pole and yoke geometry ................................................................................................... 144 4.2.3.3 Field Quality ...................................................................................................................... 147 4.2.3.4 Harmonic analysis ............................................................................................................. 148 4.2.3.5 Electrical and cooling parameters ..................................................................................... 149 4.2.3.6 Saturation ......................................................................................................................... 150
4.2.4 Magnetic steel .............................................................................................................. 151 REFERENCES ........................................................................................................................................ 151
CHAPTER 5: MAGNET GIRDERS .............................................................................................. 153
5.1 SCOPE ....................................................................................................................................... 153 5.2 STABILITY REQUIREMENTS AND POSITIONING TOLERANCES .................................................................. 153 5.3 THE ROLE OF GIRDERS .................................................................................................................. 153 5.4 PRIMARY DESIGN OF MAGNET-GIRDER SUPPORT SYSTEM ................................................................... 154
5.4.1 Girder Layouts ............................................................................................................... 154 5.4.2 Main design features .................................................................................................... 158 5.4.3 Alignment mechanism .................................................................................................. 159
5.4.3.1 Positioning ........................................................................................................................ 159 5.4.3.2 ILSF positioning and fixing system..................................................................................... 159
5.5 MECHANICAL STABILITY OF THE MAGNET–GIRDER SUPPORT SYSTEM ...................................................... 159 5.5.1 Static Stability ............................................................................................................... 161 5.5.2 Dynamic stability .......................................................................................................... 164
5.5.2.1 Vibrational stability ........................................................................................................... 164 5.5.2.2 Finite-element modal analysis .......................................................................................... 165
5.5.3 Thermal stability ........................................................................................................... 167 5.6 TEST AND QUALITY CONTROL ......................................................................................................... 169
5.6.1 Dimensional check ........................................................................................................ 169 5.6.2 Vibration tests............................................................................................................... 169
REFERENCES: ....................................................................................................................................... 170
CHAPTER 6: VACUUM SYSTEMS ............................................................................................. 171
6.1 VACUUM SYSTEM OF THE STORAGE RING .......................................................................................... 171 6.1.1 Design objectives .......................................................................................................... 171 6.1.2 General layout .............................................................................................................. 171 6.1.3 Vacuum chamber layout ............................................................................................... 172
6.1.3.1 Vacuum chamber profile ................................................................................................... 172 6.1.3.2 Vacuum chamber design ................................................................................................... 176
6.1.4 Construction material ................................................................................................... 181 6.1.5 Deformation of vacuum chambers ............................................................................... 181 6.1.6 The pressure calculations .............................................................................................. 182
6.1.6.1 The conductance and the effective pumping speed ......................................................... 183 6.1.6.2 Ray tracing of bending magnets’ synchrotron radiation in the horizontal plane .............. 183
6.1.7 Desorption .................................................................................................................... 184 6.1.7.1 Thermal desorption........................................................................................................... 184 6.1.7.2 Photon stimulated desorption .......................................................................................... 184
6.1.8 The pressure profile ...................................................................................................... 185 6.1.8.1 The base pressure ............................................................................................................. 185 6.1.8.2 Dynamic pressure ............................................................................................................. 185
6.1.9 Instrumentation ............................................................................................................ 187 6.1.10 Absorbers ................................................................................................................. 188
6.2 VACUUM SYSTEM OF THE BOOSTER ................................................................................................. 195 6.2.1 Booster’s layout ............................................................................................................ 195 6.2.2 Cross section of the vacuum chambers ......................................................................... 196 6.2.3 Supercell layout ............................................................................................................ 197 6.2.4 Vacuum chamber design .............................................................................................. 197 6.2.5 Pressure calculations .................................................................................................... 198
6.2.5.1 Gas sources ....................................................................................................................... 198 6.2.5.2 Thermal desorption........................................................................................................... 199
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6.2.5.3 Photon-stimulated desorption .......................................................................................... 199 6.2.6 The pressure profile ...................................................................................................... 199 6.2.7 The base pressure profile .............................................................................................. 200 6.2.8 Dynamic pressure profile .............................................................................................. 201
REFERENCES: ....................................................................................................................................... 201
CHAPTER 7: RF SYSTEMS ........................................................................................................ 203
7.1 FUNDAMENTALS OF AN RF SYSTEM ................................................................................................. 203 7.2 STORAGE RING RF SYSTEM ........................................................................................................... 207
7.2.1 Discussion of the optimum frequency ........................................................................... 207 7.2.1.1 Short review of RF frequencies of existing storage rings .................................................. 208 7.2.1.2 Theoretical consequences of the choice of RF frequency ................................................. 208 7.2.2.3 Practical consequences of the choice of RF frequency ..................................................... 213 7.2.2.4 Conclusion ......................................................................................................................... 214
7.2.3 Cavity considerations .................................................................................................... 214 7.2.3.1 Short review of existing cavities ........................................................................................ 214 7.2.3.2 Considerations of multi-bunch instabilities....................................................................... 216 7.2.3.3 Cavity and RF parameters ................................................................................................. 220 7.2.3.4 Cavity cooling system ........................................................................................................ 222 7.2.3.5 Beam-cavity interaction .................................................................................................... 222
7.2.4 High power RF Generator ............................................................................................. 226 7.2.4.1 Discussion of different technical options for high power RF generator ............................ 226 7.2.4.2 Solid-state high-power amplifier ....................................................................................... 227 7.2.4.3 Proposed system structure for ILSF solid-state amplifier ................................................. 230
7.2.5 Low-level RF system ...................................................................................................... 233 7.2.5.1 Various approaches for realizing LLRF systems ................................................................. 234 7.2.5.2 Frequency tuning loop ...................................................................................................... 236
7.2.6 Waveguide system ........................................................................................................ 237 7.2.7 Storage ring RF plant configuration .............................................................................. 239
7.3 BOOSTER RF SYSTEM ................................................................................................................... 240 7.3.2 Time structure ............................................................................................................... 241 7.3.3 Cavity Considerations ................................................................................................... 244 7.3.4 High-power RF generator ............................................................................................. 246 7.3.5 Low-level RF system ...................................................................................................... 246 7.3.6 Waveguide system ........................................................................................................ 246
REFERENCES: ....................................................................................................................................... 247
CHAPTER 8: POWER SUPPLIES ................................................................................................ 249
8.1 INTRODUCTION ........................................................................................................................... 249 8.2 POWER SUPPLY TOPOLOGIES.......................................................................................................... 249
8.2.1 Switched-mode power converter .................................................................................. 249 8.2.2 SMPS topologies ........................................................................................................... 250
8.3 SUBASSEMBLY OF POWER SUPPLIES ................................................................................................. 250 8.3.1 Input section ................................................................................................................. 250 8.3.2 Control assembly .......................................................................................................... 251 8.3.3 Converter assemblies and redundancies ...................................................................... 251 8.3.4 Display assembly and remote control ........................................................................... 251 8.3.5 Power supply interlocks ................................................................................................ 251
8.4 STORAGE RING POWER SUPPLIES .................................................................................................... 251 8.4.1 Dipole power supply ..................................................................................................... 251
8.4.1.1 Specification of power supply for dipole magnets ............................................................ 252 8.4.1.2 Selection of topology for dipole power supply ................................................................. 252
8.4.2 Quadrupole power supplies .......................................................................................... 254 8.4.2.1 Specifications of power supply for quadrupole magnets .................................................. 255 8.4.2.2 Selection of topology for quadrupole power supplies ...................................................... 255
8.4.3 Sextupole power supplies ............................................................................................. 256 8.4.3.1 Specification of power supply for sextupole magnets ...................................................... 257 8.4.3.2 Selection of topology for sextupole power supplies ......................................................... 257
8.5 RAMPING POWER SUPPLIES FOR BOOSTER MAGNETS .......................................................................... 257
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8.5.1 Dipole magnet power supply of booster ....................................................................... 259 8.5.1.1 Specifications of the power supplies for booster dipole magnets .................................... 259 8.5.1.2 Topology of the dipole magnets’ power supply ................................................................ 259
8.5.2 Quadrupole power supplies .......................................................................................... 260 8.5.2.1 Specifications of the power supply for quadrupole magnets ........................................... 260 8.5.2.2 Selection of topology for the quadrupole magnets’ power supply ................................... 260
REFERENCES: ....................................................................................................................................... 261
CHAPTER 9: DIAGNOSTICS...................................................................................................... 263
9.1 INTRODUCTION ........................................................................................................................... 263 9.2 DESCRIPTION OF THE DIAGNOSTICS ELEMENTS ................................................................................... 264
9.2.1 Fast current transformer (FCT) ..................................................................................... 264 9.2.2 DC current transformer (DCCT) ..................................................................................... 265 9.2.3 Annular electrode (AE) .................................................................................................. 266 9.2.4 Scrapers (SCR) ............................................................................................................... 267 9.2.5 Beam position monitors (BPM) ..................................................................................... 268 9.2.5 Stripine .......................................................................................................................... 269 9.2.7 Fluorescent screens (FS)/ Optical transition radiation (OTR) ........................................ 270 9.2.8 Synchrotron Radiation Monitor (SRM) ......................................................................... 272 9.2.9 Visible synchrotron radiation front-end ........................................................................ 272 9.2.10 X-ray synchrotron radiation front-end (pinhole) ...................................................... 273 9.2.11 Beam loss monitors (BLM) ....................................................................................... 274
9.3 BPM DESIGN FOR THE ILSF SYNCHROTRON ...................................................................................... 274 9.3.1 Storage ring BPMs ........................................................................................................ 275 9.3.1 Booster BPMs ................................................................................................................ 278
9.4 FAST POSITIONAL GLOBAL FEEDBACK FOR THE STORAGE RING ............................................................... 279 9.4.1 Global corrections ......................................................................................................... 280 9.4.2 Local corrections ........................................................................................................... 280 9.4.3 Local and global scheme comparison for fast corrections ............................................ 280 9.4.4 General guidelines ........................................................................................................ 281
9.4.4.1 Electron BPMs ................................................................................................................... 281 9.4.4.2 Photon BPMs..................................................................................................................... 281 9.4.4.3 Corrector magnets and power supplies ............................................................................ 281
9.5 TUNE MEASUREMENT................................................................................................................... 282 9.6 LIBERA BEAM POSITION PROCESSORS ............................................................................................. 283 9.7 DISTRIBUTION OF THE DIAGNOSTIC INSTRUMENTS IN THE STORAGE RING ................................................ 286 9.8 DISTRIBUTION OF THE DIAGNOSTIC INSTRUMENTS IN THE BOOSTER........................................................ 288 9.9 DISTRIBUTION OF DIAGNOSTIC INSTRUMENTS IN THE BOOSTER TO STORAGE RING (BTS) TRANSFER LINE ....... 289 9.10 CONCLUSION ......................................................................................................................... 290 REFERENCES: ....................................................................................................................................... 291
CHAPTER 10: PRE-INJECTOR ..................................................................................................... 293
10.1 INTRODUCTION ...................................................................................................................... 293 10.2 DEFINITIONS AND SPECIFICATIONS.............................................................................................. 293
10.2.1 Structure, RF frequency, and resonant mode........................................................... 293 10.2.2 Pulse length and charge per bunch .......................................................................... 294 10.2.3 Beam energy ............................................................................................................ 294 10.2.4 Energy spread .......................................................................................................... 294 10.2.5 Pulse to pulse energy variation ................................................................................ 295 10.2.6 Beam emittance ....................................................................................................... 295 10.2.7 Repetition Rate ........................................................................................................ 295 10.2.8 Pulse to pulse time jitter, beam position stability and single bunch purity .............. 296
10.3 PRE-INJECTOR STRUCTURE ........................................................................................................ 298 10.3.1 Lattice layout ........................................................................................................... 298 10.3.2 Main components .................................................................................................... 303
10.3.2.1 Electron gun ...................................................................................................................... 303 10.3.2.2 Linac structure .................................................................................................................. 306 10.3.2.3 Alpha magnet .................................................................................................................... 306
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10.3.2.4 Quadrupole magnets ........................................................................................................ 307 10.3.2.5 Steering magnets .............................................................................................................. 307
10.4 BEAM DYNAMICS CALCULATIONS ............................................................................................... 307 10.5 SPACE REQUIRED FOR THE PRE-INJECTOR SYSTEM .......................................................................... 313 REFERENCES ........................................................................................................................................ 313
CHAPTER 11: INSERTION DEVICES ............................................................................................ 315
CHAPTER 12: FRONT ENDS ....................................................................................................... 317
12.1 FRONT-END DESIGN ................................................................................................................ 317 12.1.1 General layout of a front end ................................................................................... 318 12.1.2 A particular front-end layout ................................................................................... 324 12.1.3 Cooling of front-end components ............................................................................ 327
CHAPTER 13: CONTROL SYSTEMS ............................................................................................. 329
13.1 INTRODUCTION ...................................................................................................................... 329 13.2 ARCHITECTURE ....................................................................................................................... 329 13.3 NETWORK ............................................................................................................................. 330
13.3.1 Ethernet-connected devices ..................................................................................... 331 13.3.2 Devices not connected by Ethernet .......................................................................... 332 13.3.3 Other points ............................................................................................................. 332
13.4 CONTROLS ADMINISTRATION .................................................................................................... 333 13.4.1 Development environment ...................................................................................... 333 13.4.2 Standard tool for maintaining versions of software packages installed .................. 333 13.4.3 Remote booting ....................................................................................................... 333
13.5 OPERATOR INTERFACES: TAURUS............................................................................................. 334 13.5.1 TAURUS’s look and feel ............................................................................................ 334
13.6 THE CONTROL SYSTEM CENTRAL MANAGING POINT: THE SARDANA “DEVICE POOL”. ............................. 334 13.7 BACKUPS, STORAGE, DATABASES, CENTRAL MANAGEMENT INFORMATION SYSTEM AND SYSTEM
ADMINISTRATION. ................................................................................................................................. 335 13.8 NAMING CONVENTIONS ........................................................................................................... 335
13.8.1 Coupling software naming conventions to hardware conventions .......................... 336 13.9 EQUIPMENT, CONTROLS AND ARCHIVING DATABASES ..................................................................... 337
13.9.1 Fast data logger. ...................................................................................................... 337 13.10 EQUIPMENT PROTECTION SYSTEM ............................................................................................. 338 13.11 MACHINE CONTROLS ............................................................................................................... 340
13.11.1 Subsystems ............................................................................................................... 340 13.11.2 Vacuum system requirements .................................................................................. 341 13.11.3 Power supplies ......................................................................................................... 343 13.11.4 Radiofrequency system (RF) ..................................................................................... 343 13.11.5 Diagnostics ............................................................................................................... 345
13.11.5.1 Beam position monitors .................................................................................................... 345 13.11.5.2 Beam loss monitors (BLMs) ............................................................................................... 345 13.11.5.3 Fluorescent screen ............................................................................................................ 346 13.11.5.4 Scrappers and other motions in the machine ................................................................... 346 13.11.5.5 Oscilloscopes ..................................................................................................................... 346
13.11.6 Insertion Devices ...................................................................................................... 346 13.11.7 Orbit correction ........................................................................................................ 347
13.12 MOTOR CONTROLLERS ............................................................................................................. 347 13.13 CALLS FOR TENDERS AND OUTSOURCING. .................................................................................... 347
13.13.1 Structure .................................................................................................................. 348 13.14 TIMING SYSTEM ..................................................................................................................... 348 13.15 PERSONNEL SAFETY SYSTEM (PSS) ............................................................................................ 350 13.16 BEAMLINES ........................................................................................................................... 350
13.16.1 Control interfaces between the machine and the beamlines ................................... 351 13.16.1.1 Front-end .......................................................................................................................... 351 13.16.1.2 EPS Front End – Beamline communications ...................................................................... 351
13.17 ORGANIZATION AND ECONOMICAL ASPECTS ................................................................................. 352
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CHAPTER 14: CONVENTIONAL FACILITIES ................................................................................. 355
14.1 INTRODUCTION ...................................................................................................................... 355 14.2 GOALS.................................................................................................................................. 355 14.3 BUILDINGS AND INSTALLATIONS ................................................................................................. 355 14.4 SITE SELECTION ...................................................................................................................... 357
14.4.1 Technical requirements ............................................................................................ 357 14.4.1.1 Geological and vibrational requirements .......................................................................... 357 14.4.1.2 Environmental requirements: ........................................................................................... 357 14.4.1.3 Economic requirements: ................................................................................................... 357
14.4.2 Analysis of the proposed sites .................................................................................. 357 14.5 GROUND VIBRATIONS .............................................................................................................. 359
14.5.1 The measurements ................................................................................................... 359 14.5.2 Analysis of results..................................................................................................... 361
14.6 GEOTECHNICAL SURVEY ........................................................................................................... 362 14.6.1 Site's geology ........................................................................................................... 362 14.6.2 Geotechnical characterization tests ......................................................................... 363 14.6.3 Geotechnical analysis ............................................................................................... 364
14.7 FOUNDATION STABILITY REQUIREMENTS ...................................................................................... 364 14.8 ARCHITECTURE ....................................................................................................................... 365
14.8.1 Sustainable architecture .......................................................................................... 365 14.8.2 Buildings ................................................................................................................... 366
14.8.2.1 Types of buildings ............................................................................................................. 366 14.8.2.2 Duration of use ................................................................................................................. 366 14.8.2.3 Occupancy and projected surface area ............................................................................. 366 14.8.2.4 Main building .................................................................................................................... 366 14.8.2.5 Laboratories ...................................................................................................................... 368 14.8.2.6 Utility building ................................................................................................................... 368 14.8.2.7 Administrative Office building .......................................................................................... 369 14.8.2.8 Guest house and recreational facilities ............................................................................. 369 14.8.2.9 Parking .............................................................................................................................. 369
14.8.3 Architectural design ................................................................................................. 369 14.8.4 Site Plan ................................................................................................................... 372
14.9 STRUCTURAL SYSTEM .............................................................................................................. 372 14.9.1 Building Design Codes .............................................................................................. 372 14.9.2 Building Design Loads .............................................................................................. 373 14.9.3 Main building structural design ............................................................................... 374
14.10 MECHANICAL SYSTEMS ............................................................................................................ 377 14.10.1 Codes and standards ................................................................................................ 377 14.10.2 Design constraints .................................................................................................... 377
14.10.2.1 Outdoor design ................................................................................................................. 377 14.10.2.2 Indoor design .................................................................................................................... 377 14.10.2.3 Pressure ............................................................................................................................ 378
14.10.3 Mechanical utilities .................................................................................................. 378 14.10.3.1 Cooling System .................................................................................................................. 379
14.11 ELECTRICAL INSTALLATIONS ...................................................................................................... 385 14.11.1 Required electrical installations ............................................................................... 385 14.11.2 Estimation of electrical power requirement............................................................. 385
REFERENCES: ....................................................................................................................................... 386
CHAPTER 15: RADIATION SAFETY AND SHIELDING ................................................................... 387
15.1 IONIZING RADIATION HAZARDS .................................................................................................. 387 15.1.1 Bremsstrahlung ................................................................................................................ 387 15.1.2 Neutron production .................................................................................................. 388
15.1.2.1 Giant resonance neutrons (GRNs) ..................................................................................... 388 15.1.2.2 High energy neutrons (HENs) ............................................................................................ 388
15.1.3 Induced Radioactivity ............................................................................................... 388 15.1.4 Synchrotron radiation .............................................................................................. 388
15.2 SHIELDING OBJECTIVES............................................................................................................. 388
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15.2.1 Analytical methods .................................................................................................. 389 15.2.2 Simulation methods ................................................................................................. 389
15.3 BEAM LOSS CALCULATIONS ....................................................................................................... 389 15.3.1 Linac ......................................................................................................................... 390 15.3.2 Booster ..................................................................................................................... 390 15.3.3 Storage ring ............................................................................................................. 391
15.4 SHIELDING WALL THICKNESSES................................................................................................... 393 15.4.1 Linac ......................................................................................................................... 393 15.4.2 Linac-to-booster transfer line ................................................................................... 394 15.4.3 Booster ..................................................................................................................... 395 15.4.4 Booster-to-storage ring transfer line ....................................................................... 395 15.4.5 Storage ring ............................................................................................................. 396
15.5 SHIELDING CALCULATIONS FOR ILSF ........................................................................................... 397 15.5.1 Forward side direction ............................................................................................. 397 15.5.2 Forward direction ..................................................................................................... 398 15.5.3 Upward and downward directions ........................................................................... 399
15.6 SHIELDING CALCULATION OF ILSF BEAM STOP .............................................................................. 400 15.7 INVESTIGATION OF RADIATION STREAMING AND SHIELDING CALCULATIONS FOR ILSF MAZE ................... 404
15.7.1 Monte Carlo simulations .......................................................................................... 404 15.7.2 Comparison of the results from different methods .................................................. 407
15.8 GAS BREMSSTRAHLUNG IN ILSF INSERTION DEVICES ...................................................................... 408 15.9 RADIATION SAFETY .................................................................................................................. 411
15.9.1 Personnel protection system .................................................................................... 411 15.9.2 Radiation monitoring system ................................................................................... 411
REFERENCES: ....................................................................................................................................... 411
CHAPTER 16: TIME SCHEDULE/BUDGET ................................................................................... 413
16.1 INTRODUCTION ...................................................................................................................... 413 16.2 SCOPE OF THE PROJECT ............................................................................................................ 413 16.3 WORK BREAKDOWN STRUCTURE ................................................................................................ 413 16.4 COST AND SCHEDULE ............................................................................................................... 414
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List of contributors
All chapters of the CDR were written under direct supervision and guidance of Dieter Einfeld from ALBA Synchrotron Facility ,Spain, who has also written Chapters 2 and 12. Helmut Wiedemann (Stanford Synchrotron Radiation Laboratory, USA) and Albin Wrülich (Paul Scherrer Institute, Switzerland) have also reviewed all or most of the chapters of the CDR and have provided valuable suggestions. In addition Ernst Weihreter (Synchrotron Radiation Source BESSY II – Helmholtz Center, Germany) has read and given advice on RF systems (Chapter 7); Kay Wittenburg (DESY, Germany) and Peter Forck (GSI Helmholtz Center for Heavy Ion Research, Germany) have read the chapter on diagnostic systems (Chapter 9) and provided valuable suggestions. Ronald Frahm (University of Wuppertal, Germany) was involved in the discussions on the day-one beamlines during the Third Users' Meeting held at IPM in Tehran and provided valuable advice on the choice of beamlines. Members of the technical staff of ILSF involved in writing various chapters are:
Esmaeil Ahmadi
Hasan Ajam
Gholam-Reza Aslani
Sedigheh Azizi
Alireza Babaei
Hamideh Beigzadeh Jalali
Ghader Faraji
Hossein Farrokhpour
Samira Fatehi
Mohammad Fereidani
Hossein Ghasem
Nader Heydari
Amin Iraji
Morteza Jafarzadeh
Hamid-Reza Kalhor
Babak Kamkari
Shima Kashani
Mohammadreza Khabazi
Sharmin Kharrazi
Hossein Khosroabadi
Fatemeh Mousavi
Saeid Pirani
Javad Rahighi
Mohammad Ali Rahimi
Mehdi Rasouli Ghahroudi
Arash Sadeghipanah
Farhad Saeidi
Reza Safian
Ehsan Salimi
Khorshid Sarhadi
Omid Seify
Mehdi Shafiee
Zahra Shahveh
Amin Shahverdi
Solmaz Vejdani
Shaghayegh Zihajehzadeh
Vahid Moradi and Donya Shirangi have contributed drawings to various chapters. The whole text of the CDR was edited and corrected by Nader Heydari.
10
11
CHAPTER 1: Introduction
1.1 A light source for Iran
With the advent of several dedicated synchrotron radiation sources since about 1980,
synchrotron radiation, as a versatile research tool, has experienced an unprecedented
expansion. Today, a large and continuously growing community of researchers
representing a variety of disciplines depends on light sources as an essential part of
their research programs. In order to meet the demands of cutting-edge research,
increasingly advanced synchrotron radiation facilities have been constructed around
the world. The number of such synchrotron radiation facilities now exceeds 75 with
more than 20,000 users per year; it is predicted that these numbers will continuously
grow in the future. Standard research can be performed using different conventional
light sources whose radiations span different parts of the electromagnetic spectrum
from the infrared to visible to UV up to the hard X-rays, but synchrotron radiation due
to its extremely high intensity, continuous spectrum and well-defined properties often
leads to cutting-edge research. It has to be emphasized that all conventional light
sources are restricted to certain wavelengths or limited wavelength ranges, whereas
synchrotron radiation allows the selection of any desired wavelength. Thus – in
popular language – synchrotron allows shedding light on samples in full color,
whereas conventional light sources only give a black-and-white view of a given
sample. Synchrotron radiation is generated in particle accelerators, and thus its
success is based on the improvements in accelerator physics.
Unfortunately, Iran is lagging in this important field. The lack of a national facility
which can provide the numerous academic institutes and industrial establishments in
the country, with the many benefits of accelerated particle beams is deeply felt. The
academic institutes of Iran have close to 20000 faculty members in science and
engineering, who are responsible for teaching and supervising the work of some
90000 graduate students, about 10000 of whom are enrolled in PhD programs [1.1].
These numbers indicate a great potential for the establishment and utilization of a
large national scientific facility.
Through several official meetings and many informal discussions among the Iranian
academics active in the field of accelerators and their applications [1.2], the consensus
has been reached that under the present circumstances, the establishment of a National
Accelerator Laboratory with a synchrotron light source facility dedicated solely to
research, is the best option that entails the greatest benefit to the scientific community
of Iran. The other option would have been the establishment of a national facility for
high-energy physics research – even though at present, several Iranian high-energy
physicists are collaborating with CERN through IPM, establishing such a laboratory
with the existing number of users which is not likely to grow drastically in the
foreseeable future could not have been a priority.
Iran is a member of SESAME (Synchrotron-light for Experimental Science and
Applications in the Middle East). During the last decade many Iranian scientists and
engineers have undergone training in both the field of accelerators and the
12
applications of synchrotron radiation within the framework of the training programs
of SESAME. Most of the trainees have demonstrated a great degree of talent working
in synchrotron laboratories around the world. In addition many Iranian universities
and research institutes have actively joined this national endeavor towards building a
light source and utilizing the possibilities synchrotron radiation has to offer by
training research students in the related fields. We will have to take advantage of their
expertise at various stages of the design and construction of the Iranian Light Source
Facility. In addition, the design and construction process of SESAME synchrotron is a
great opportunity for our accelerator physicists and engineers in Iran. Once SESAME
becomes operational, the ensuing international scientific collaboration can
undoubtedly contribute greatly to the capacity building and scientific development of
all the countries of the region including Iran. However, this facility alone cannot serve
to achieve Iran’s strategic goals of scientific development within the future decades.
A synchrotron light source would also serve as a significant impetus for
multidisciplinary collaboration between scientists from different research areas and
from different institutions. The benefits of such scientific cross-pollinations are huge.
As an example, the rapid development of the macromolecular field would not have
been possible without synchrotron-related collaboration between physicists and
biologists. Even outside of research-driven industry the need for personnel trained in a
multidisciplinary environment is ever increasing. Currently, the only way for Iranian
scientists to access such advanced facilities is to go overseas. However, this limits the
scientific research to whatever – sometimes very limited – possibilities that are
available, and the research cannot be optimized for the specific needs of Iranian
scientists and the developments within the Iranian science scene.
A synchrotron is a highly complex machine comprised of many parts. Building a
synchrotron requires the utilization of various advanced technologies including the
manufacture of magnets, ultra high-vacuum systems, RF technology, X-ray optics, X-
ray and electron spectroscopy, control and data acquisition, and it will be an instance
of the management of a scientific project on an unprecedented scale for Iran. These
include:
- component placement and alignment with mirco- and nano-meter precision,
- machining with such precisions,
- isolation and reduction of vibrations to nano-meter levels
- design of heat absorbers which have to deal with heat loads higher than that on the
surface of the Sun,
- radiation shielding,
- computer-aided design and manufacturing,
- control of data and signals on an unprecedented scale (simultaneous monitoring of
more than 100000 input and output signals as well as simultaneous calculations
based on 350000 variables to maintain stable operating conditions),
- manufacture of RF cavities as well as utilization of high-power semi-conductor
amplifiers and combiners with application in radio/TV communications and
airport radars,
- construction of buildings immune to environmental vibrations and highly stable
internal temperatures.
The Iranian Light Source Facility (ILSF) is an open project fully complying with the
international scientific codes and standards. All the design and progress reports will
13
be presented at local and international conferences and published in international
journals accessible to scientists all over the world.
To realize this project, the intention is to work and collaborate with other light sources
around the world. Users from abroad shall be welcome to set up their experiments in
this new facility upon the acceptance of their proposals by the appropriate review
boards. The layout and performance of the planned facility shall be based on the most
recent advances and significantly improved with respect to other facilities which were
planned many years ago and realized only recently. This will add to the attractiveness
of ILSF for outside users, and improves the possibilities for multinational
collaborations. An international Machine Advisory Committee has been set up to
provide consultation on the design of the accelerator complex and to follow up on the
design of the different components as well as the construction of the complex. An
international Scientific Advisory Committee (SAC) will also be set up to discuss the
scientific case and the layout of the beamlines, and to follow up the progress during
their installation.
In order to perform cutting-edge research in the next 2 or 3 decades, the machine
should be capable of providing intense synchrotron radiation with an emittance lower
than 3 nm.rad. In order to perform cutting-edge research, among other parameters
such as energy, circumference and number of beamlines available to the users, the
machine should be capable of providing intense radiation in the few hundred eV to
few tens of keV photon energy range.
Scientific cases are to be detailed in close collaboration with the user community.
Prior to putting together detailed engineering design, making precise cost estimates
and drawing a detailed construction schedule, development of prototypes must be
carried out to validate the proposed technical solutions. This is particularly relevant to
the design of various types of magnets (bending dipole, quadrupole and sextupole
magnets) used in the storage ring lattice, high power solid state RF amplifiers which
will replace klystrons and electron tubes, and also to the high-stability magnet power
supplies. Once the critical components or subsystems are identified, development
prototype work must be carried out.
This document describes the preliminary design parameters for the Iranian Light
Source Facility (ILSF). It corresponds to the first milestone noted in the following
chart (Fig. 1.1). It is important to note that at each of the subsequent steps, many of
the features and specifications may change based on the input received from the
users’ community as well as from the results from the prototypes,.
14
1.2 Iranian users
The completion of a project of such a large scale involves a series of phases along
which increasing co-operation and involvement is expected both from governmental
funding bodies and the users’ community. Currently about 50 Iranian users have been
identified in Iran and abroad, and hundreds more are potential users of synchrotron
radiation. Currently, the interests of the users include:
X-ray powder diffraction (XRD)
Single-crystal X-ray diffraction
X-ray reflectivity (XRR)
X-ray magnetic circular dichroism (XMCD)
X-ray fluorescence (XRF)
Inelastic X-ray scattering (IXS)
Photoelectron spectroscopy (PES)
Electron spectroscopy for chemical analysis (ESCA)
Photoelectron emission microscopy (PEM)
Macromolecular crystallography
Small-angle X-ray scattering (SAXS)
Figure 1.1 Various stages and milestones of the ILSF project.
15
Extended X-ray absorption fine structure (EXAFS)
Medical applications
Through several meetings held since the initiation of ILSF with participation of
foreign guests, the consensus was reached for the establishment of several beamlines
collectively named as day-one beamlines; these are listed in Table 1.1 along with their
specifications.
Table 1.1 Day-one beamlines
No. Beamline Source
Energy
Range
(eV)
Photon
Flux
(p/s)
Resolution/
Resolving
power
Spot size
(µm)
1 Powder Diffraction Bending
Magnet 6-30 k 10
12 10
-4 100 ×100
2 Single-Crystal X-ray Diffraction for
small molecules
In-vacuum
Undulator 5-25 k 10
13 10
-4 50 × 50
3 EXAFS Wiggler 3-35 k 1013
10-4
Few µm
4 Gas phase photoemission
(XPS, AES, ARPES)
Electromagnetic
Undulator
15-
1000 10
11 10000
5 Solid-State Electron Spectroscopy Electromagnetic
Undulator
10-
1500 10
12 10000
6 Spectromicroscopy
SPEM
(+ARPES) Helical
Undulator
10-
2000 10
13 >8000 Few µm
PEEM
(+ XMCD)
7 Macromolecular Crystallography Wiggler 3-25 K 1012
In what follows some of these beamlines as well as one other proposed beamline are
briefly described and their use is explored.
16
1.3 Gas-phase photoemission beamline
Study of atoms and molecules in gas phase is of direct relevance in important fields
such as chemistry, surface chemistry, atmospheric chemistry, radiation damage
(specific and controlled energy deposit in complex molecules), plasma studies,
astrophysics and astrochemistry. For example, the most important environmental
phenomena such as global warming and ozone depletion depend on the chemical
properties and reactivity of the atoms, molecules and radicals involved in the related
gas phase reactions.
In Iran at present, various groups of researchers in chemical physics and biology, do
an ever-increasing number of numerical and simulation studies leading to a large
number of published articles. Investigation of atoms, molecules, ions, clusters, and
complex molecular systems (liquids and solutions) in gas phase is carried out with
different software packages and different properties such as ionization spectra,
excitation of valence electrons as well as electrons in inner shells, and the dynamics
of dissociation are studied by such methods. What this research lacks are
experimental data which could add a great deal to the quality of research. This
research can be backed up by experiments which can be performed in a gas-phase
photoemission beamline.
For these experiments, the samples can be ionized or their valence and inner
electronic states can be excited by using VUV and soft X-ray radiation. Synchrotron
radiation in the VUV and soft X-ray range is the best tool for studying the electronic
structure of atoms, molecules, ions, clusters and complex molecular systems because
of its high brilliance, tunability and collimation. Brilliance is mainly important for
gas-phase experiments where the target density is very low. Study of electronic
structure of species in gas phase is important because it determines the largest number
of physical and chemical properties of substances and provides the information
necessary to understand more complex systems such as macromolecules, molecules
adsorbed on the surface of solids.
The transition from atoms and molecules to solid can be examined by looking at free
clusters of variable sizes in the gas phase. This investigation is very important for
producing materials with new functionality.
Recently, there has been a lot of interest in the study of the dynamics of processes
such as dissociation of molecules or clusters after ionization or excitation. Dynamical
studies focus on photon/target interaction and the objective is the description and
understanding of processes and their extrapolation from well-defined isolated systems
to the solid state. A short summary on the scientific arguments related to the
experiments in the gas phase photoemission beamline is given below.
Atoms, Molecules and Ions: X-ray photoelectron and absorption spectroscopy
determine the lifetime and energetic information of the core-hole ionized and excited
states, respectively. Core-hole states are characterized by short lifetime and large
spectral width but, this limitation can be overcome by using synchrotron radiation
with high flux and photon bandwidth that are much narrower than the lifetime width
of the core-hole state. This phenomenon is seen in resonant Raman scattering
(relaxation via fluorescence and Auger) and yields high-resolution spectra in deep X-
ray region. Fig. 1.2 shows the high-resolution resonant Auger spectrum of formic acid
after excitation of the first oxygen resonance (CO) [1.3]
17
Also, inner-shell ionization and excitation can provide information about the chemical
environment of each atom in a molecule which is very important in chemistry. The
energies of core-level excitations depend on the atom in question and also on its
chemical environment. The shifts in core excitation energies allow the specification of
chemical states. The chemical bonding energy shifts can be very accurately
determined by precise modeling of the spectra which provides information on
chemical activation energies at different atomic sites [1.4].
Multiple ionization of atoms and molecules by a one-photon process is of
fundamental interest because it is directly related to electron correlations which
determine the electronic description of both discrete and continuum states. It is a
rapidly developing field as seen by numerous recent publications on triply-differential
cross section (TDCS) on Helium double ionization. Multiple ionization experiments
are difficult to perform because of the rapidly decreasing cross section as the
ionization degree is increased. A third generation source like ILSF will be very useful
for developing such experiments. Fig. 1.3 shows the TDSC of He2+
(1S
e) and
Ar2+
3s03p
6 (
1S
e) in equal energy sharing at 20 eV above their respective thresholds
measured in the gas phase photoemission beamline [1.5].
Study of amino acids in gas phase, has attracted considerable interest in the last few
years, due to the fundamental importance of these molecules, which may be
considered as the building blocks of proteins [1.6]. Recently, core ionization
spectroscopy with the aid of theoretical calculations have been employed to study and
determine the percentage of conformations and tautomers of biological molecules
such as amino acids and nucleotides in gas phase. Also, photoionization and
excitation studies of these molecules provide the understanding for the photostability
and photo degradation in the VUV and soft X-ray region. Photoionization and
excitation of a molecule can lead to chemical reactions such as dissociation and
produce ionic and neutral fragments. Dissociation product can be determined using
time-of-flight mass spectrometry and coincidence techniques. This information is of
key importance in astrophysics and photochemistry, since amino acids have been
Figure 1.2 Resonant Auger spectrum of formic acid after oxygen , compared with theoretical calculations [1.3].
18
found in the interstellar medium and meteoritic materials. This field of research is
growing rapidly and has a great potential for high-quality research in the field of
biochemistry and biophysics.
There is a considerable lack of experimental data (absolute cross sections, electron
spectroscopy, etc.) on ions, due to the very low density with which they can be
produced. Laser spectroscopy is the main method to obtain experimental information
about the ions (positive and negative). But, there is an upper limit in the photon
energy that produced by standard lasers and in order to access VUV and soft X-ray
light, synchrotron radiation is necessary. Experiments on photoionization of ions have
been basically limited up to now to total ionization cross section of low-charge
species.
Clusters: Experiment on clusters is a field of research where one tries to understand
how the behavior of matter changes in transition from single atom to solids; it has a
large fundamental and applied interest. The study of free clusters is a rapidly
developing field. There are some new physical phenomena such as interatomic
Coulombic decay (ICD) which cannot take place in free atoms and molecules. In ICD,
an inner valence hole undergoes ultrafast relaxation due to energy transfer to a
neighboring atom followed by electron emission from a neighboring site. Synchrotron
radiation can be used, at least, in two different ways for clusters: the photoionization
in the valence shell for species which cannot be easily ionized by lasers because of
their high ionization potential and multiply-charged species of particular interest for
their stability can be obtained. The photoionization in the inner-shells allows the
observation of shape resonances which are very useful for probing the structure of
clusters locally. Signals from the clusters are weak and therefore it is necessary to
have a high photon flux. Fig. 1.4 shows the 2p photoelectron spectrum of Argon
clusters with a cluster size of 250 at a photon energy of 280 eV [1.6][1.7].
Complex molecular systems: Complex molecular systems are of great importance in
the science of biosphere, as well as in chemistry and biology. Their properties are
determined by their interconnected electronic and geometric structure. Both these
structures, and hence the properties, of a molecule, are strongly affected by the
surroundings. Examples of this are liquids and formation of ions and de-protonated
species upon solvation in water.
Figure 1.3 Triply differential cross section of He2+ (1Se) and Ar2+3s03p6 (1Se) in equal energy sharing at 20 eV above their respective threshold [1.5]. The full line is the fit to experimental data
19
Recent developments of micro-jet techniques have made the studies of liquids and
solutions feasible. The aim of this kind of experiment is the study of complex
molecular systems, i.e. molecules in different environments, dissolved in water (or
some other liquid), and adsorbed on the surface of liquid water or solid ice. The same
molecule is studied both in free form, and in e.g. water solution. Comparison between
theseenvironments will help isolate the effects of solvation. Fig. 1.5 shows the effect
of the hydrogen bonding on the 1s ionization energy of atomic oxygen in liquid water
[1.8]. Other scientific aspects that can be studied in liquid and solution phases are
liquid surface science, femtosecond charge-transfer processes and ultra-fast relaxation
mechanisms.
Figure 1.4 2p photoelectron spectrum of argon clusters with a cluster size of 250 at a photon energy of 280 eV using time-of-flight [1.7].
Figure 1.5 O1s photoelectron spectrum of liquid water measured at 600 eV photon energy at two different maximum and minimum overlap between the liquid microjet and synchrotron radiation [1.8].
20
Beamline specifications: In this part we give a brief summary of the beamline
specification and its layout. The source will be an undulator. The proposed energy
range of the spectrum is 10-1000 eV. The resolving power should be between 10000
and 25000, and linearly polarized or circularly polarized light is most appropriate for
the experiments. The photon flux of the beamline should be about 1013
-1015
because
some of the experiments in this beamline need high photon flux. This beamline should
operate with two experimental stations. A typical optical layout of the gas phase
beamline is shown in Fig. 1.6
1.4 Soft X-ray twin-spectromicroscopy beamline
Nanoscience, as the ability to manipulate and probe material properties at nanoscale,
deals with understanding the behavior of materials at low dimensions.
Nanotechnology, as a rapidly growing field, promises development of advanced
materials and devices for technological applications such as development of new
catalysts, sensors etc.
Nanoscience and nanotechnology in Iran is supported by the Iranian Nanotechnology
Initiative Council (INIC) as well as other programs sponsored by various ministries.
The nanoscience/nanotechnology community in Iran is actively involved in
conducting cutting-edge research and in 2011 Iran ranked 12th
in the number of papers
published in nanoscience field [1.10].
The ultimate goal of nanoscience is to understand the chemical, electronic and
magnetic properties of nanostructures as well as manipulating their sizes and shapes.
High-resolution microscopy techniques such as TEM, AFM and STM provide no
spectroscopic information, and spectroscopy techniques such as FTIR and PES suffer
from poor lateral resolution. Therefore, it is essential to apply microscopy techniques
based on spectroscopy techniques which promise high spatial resolution as well as
chemical information. Photoemission is a very good example of the evolution from
spectroscopy to spectromicroscopy. High lateral resolution can be achieved with
either photoelectron emission microscopy (PEEM), or scanning photoemission
microscopy (SPEM) [1.3][1.11], [1.12], [1.13], and [1.14]. These techniques enable
one to analyze the core-level peaks and derive local chemical properties such as the
presence of elements corresponding to the detected core levels, or their chemical
bonding status, and also to obtain chemical map by detecting the intensity of a given
core-level peak. While PEEM has a better resolution in imaging (in principle less than
10 nm) SPEM has a better spatial resolution in micro-spectroscopy mode. Energy
Figure 1.6 Optical layout of a typical gas phase beamline [1.9].
21
resolution of SPEM can be as small as 10 meV, about 2 orders of magnitude less than
that of PEEM.
SPEM can only image slow processes due to sequential scanning, while PEEM is a
parallel process which can be applied for the detection of fast dynamic processes like
surface growth or catalytic reactions. The water formation reaction on Rh(110)
modified with sub-ML Au has been investigated by using SPELEEM (Fig.1.7).
The domain structure in ferromagnetic materials strongly depends on the shape of the
sample, defects or strain. Therefore it is essential to study the magnetic structure at
microscale or even nanoscale. As can be seen in Fig. 1.8, by tuning the photon energy
to the absorption edge of elements (for example LIII edge of 3d elements) and by
using polarized X-rays, it is possible to obtain X-ray magnetic circular dichroism
XMCD-PEEM images or XMLD-PEEM which can be applied for element-specific
imaging of ferromagnetic and antiferromagnetic domains, respectively [1.16].
While PEEM is highly sensitive to surface roughness, SPEM can be applied for
measurements on rough surfaces and samples of arbitrary shape and size. Therefore
for the nanomaterials in the powder form, prepared ex-situ, SPEM is a much better
choice.
The PEEM microscopes can image the entire momentum space with energy resolution
in the range up to 0.3 eV [1.17], thus implementing a microscopic approach to angle-
resolved photoelectron spectroscopy (micro-ARPES) measurements (Fig. 1.9).
Similarly, PEEM microscopes enable micro-probe X-ray photoelectron diffraction
(micro-XPD), for probing the short-range order around the emitter.
Figure 1.7 (Top) Au 4f images illustrating how Au–O, preserved in oxygen ambient, is dissolved under reduction conditions. (Bottom) Au 4f7/2 average intensity in the areas labeled (A) and (B) (see top), as a function of time. As can be seen, the Au 4f7/2 intensity measured in (A) and (B) equalizes quickly after imposing reduction [1.15].
22
A soft X-ray twin spectromicroscopy beamline will offer the possibility of performing
PEEM, SPEM, XMCD, XMLD, and ARPES to a large community of users including
researchers working in the fields of nanomaterials, magnetism, strongly-correlated
electron systems, catalysis, etc.
Beamline specifications – Spatial and time resolution of SPEM and PEEM can be
complementary in various multi-disciplinary studies. Therefore we find it essential to
opt for twin spectromicroscopies at ILSF. The two microscopes (PEEM and SPEM)
can share the source (two helical undulators) but in separate lines. It is highly desired
to have a high photon flux of 1015
photon/s or even higher to have better results
(images of higher resolution), especially if aberration correction or minimization in
PEEM is to be carried out. The energy range required is 10-1500 eV to an energy
resolution of better than 10-4
.
Figure 1.9 An XPEEM image of the diffraction plane at 0.3 eV below the Fermi level. The curves in (b) are cross-sections along the GKMG directions in the space, obtained from a sequence images
acquired at different electron kinetic energies, where the bright areas represent the p bands. The s bands are weak, barely visible in the lower part of the plot. The curves in (c) are cross-sections of the same ARPES dataset along , i.e. across the directions indicated by the straight lines in (b) [1.18].
Figure 1.8 Example of layer-resolved magnetic domain imaging by XMCDPEEM. (a) and (b) show the magnetic domain images of the FeNi and the Co layer, respectively, of an FeNi/Cu/Co trilayer on FeMn/Cu(001) after application of an external magnetic field of 340 Oe in the direction indicated by “H” [1.16].
23
1.5 Macromolecular X-ray crystallography using synchrotron radiation
Over the last decade, research and development in biological sciences has experienced
a fast-paced growth in Iran, especially in areas such as biotechnology, stem-cell
biology, and nanobiotechnology. Furthermore, biological sciences are directly related
to the health and well-being of our nation through the development of appropriate
drugs for fighting common diseases as well as studies related to ecosystems,
especially marine ecosystems and forests. To understand the function of
biomacromolecules, one of the main approaches in modern biology has been to find
their three-dimensional molecular structure. Using the information extracted from this
structure, one becomes able to elucidate the role that the biomolecule plays in a cell
and in body. X-ray crystallography has been the main approach in obtaining structural
information about proteins, arguably the most important biomolecules.
The advent of synchrotron radiation has immensely improved and enhanced the
efficiency and speed of protein structure identification. Indeed, without the use of
synchrotron radiation in protein crystallography, the advances in determining protein
structure would have been very limited and cumbersome.
In Iran, there are over one hundred laboratories involved in studying protein structure,
protein folding, and enzyme action mechanism which could benefit from the protein
crystallography studies. At the moment, obtaining the 3D structure of a protein is only
possible through collaboration with researchers from other nationalities. To be truly
independent in biological research, our nation needs to tap the seemingly unlimited
opportunities that synchrotron radiation can offer especially in the biological sciences.
Pharmaceutical companies have been one of the major users of protein structural
information in order to search for inhibitory drugs for a number of human pathogens
Figure 1.10 Layout of the ESCA-Microscopy beamline (SPEM) at ELETTRA [1.19].
24
and diseases, and indeed the pharmaceutical industry in Iran can be a major
beneficiary of an Iranian light source.
X-ray crystallography allows scientists the elucidation of the molecular structure of
the proteins down to a resolution of one angstrom i.e. down to atomic sizes, thus when
the size of protein is so large that other methods like NMR are not capable of
providing atomic structural data, X-ray crystallography with synchrotron radiation is
the only option.
Obtaining a protein structure begins with obtaining a decent amount of protein. The
recombinant technology has immensely helped in generating recombinant proteins in
bacteria that can be purified to a high degree of homogeneity.
The next step in the protein structure pipeline is the generation of protein crystals.
Crystals with good qualities and appropriate sizes are needed for structure
determination. During the past decades, a number of procedures had to be developed
in order to obtain crystals of right qualities and sizes. Subsequently, the protein
crystals are used to obtain diffraction data which can be used to determine the electron
density. However, to deduce the electron density of atoms in the crystal, the phase of
the diffracted X-rays needs to be determined. At the end, the atomic structure of the
protein is solved and reported to the appropriate databases such as “pdb”.
Synchrotron radiation has revolutionized the field of protein crystallography. As
shown in Figure 1.11, the number of structures that have been determined using
synchrotron radiation far exceeds the conventional methods. There are several reasons
for the greater utility of synchrotron radiation in finding the atomic structure of the
proteins. Synchrotron radiation is 100-1000 times more brilliant than conventional
radiation sources. The synchrotron radiation beam also has a very small cross section
(spot size); it has been possible to produce micron-size beams [1.20]. Exploiting these
advantages, scientists have been able to diffract microcrystals as small as five
microns.
Moreover, unlike conventional X-rays, the synchrotron radiation is a tunable light
source. In recent years, biologists have used the tunability of the synchrotron
radiation in a procedure called multiple-wavelength anomalous diffraction (MAD) for
solving the phase problem [1.21]. Using MAD, solving the phase problem in
crystallography has become much easier and faster.
Figure 1.11 Protein Structural deposits data taken from conventional method (orange) and synchrotron sources (blue) [1.21].
25
Major breakthroughs in macromolecular crystallography using synchrotron
radiation: One of the earliest breakthroughs in structural biology was obtaining the
structure of the nucleosomes. The DNA of eukaryotes is wrapped inside a set of
proteins known as histones, leading to a specific structure known as nucleosome. For
years, scientists had tried to obtain the molecular structure of nucleosome at the
atomic scale, but they were not successful until 1997 when the structure of this unique
biological complex was determined using synchrotron radiation [1.23]. After
resolving the molecular structure of nucleosome, it became clear how the histone tails
are capable of influencing the structure of nucleosome and gene expression in general
(Fig. 1.12).
Another breakthrough in structural biology was solving the structure of
RNA polymerase II (Pol II) enzyme. Pol II plays pivotal role in the transcription of
cellular RNA. Understanding its structure and function has been of essential
importance to a number of disciplines in biology. For example, in many cases of
cancer, the transcription of an oncogene could be elevated. Central to these type
regulations is Pol II enzyme by which the oncogene is transcribed. The determination
of structure of Pol II had been a major hurdle and its successful completion was called
a “technical tour de force”. Roger Kornberg using the instruments at Stanford
Synchrotron Radiation Laboratory (SSRL) was able to obtain the crystal structure of
Pol II which led to his Nobel prize in 2006 [1.24]. The X-ray structure of the Pol II
along with its numerous details (Fig. 1.13) has been essential for understanding the
function and biochemical mechanisms of Pol II.
Figure 1.12 Structure of nucleosome obtained by X-ray crystallography: the histone tail is the disordered structures protruding out of the DNA molecule e.g. the tail at the upper left [1.23].
26
Another major breakthrough in macromolecular crystallography has been the
elucidation of the structure of ribosome. Ribosome is a nanofactory whose function
within the cell is synthesizing proteins. This huge megadalton structure is made of
several RNAs and proteins. For years scientists have tried to obtain the atomic
structure of ribosome but it was not until the biologists used synchrotron radiation that
they were able to solve the structure of this important macromolecule. Indeed, it was
through the collaboration of three synchrotron laboratories that the three-dimensional
structure of this ribosome was finally deciphered. Determination of the structure of
ribosome led to the 2009 Nobel Prize in chemistry (Fig. 1.14).
Beamline specifications: As shown in Fig. 1.15, the X-ray beamline at DIAMOND is
comprised of several parts including pre-focusing and post-focusing mirrors, and
focusing monochromators. In most recent macromolecular X-ray beamline,
undulators are used. Using undulators one is able to produce highly brilliant light
without projecting a great amount of power into the optics of the beamline.
Figure 1.14 Crystal structure of ribosome, the nano-factory of protein synthesis, the proteins of large subunits are depicted as green, rRNA molecules are colored orange, and the proteins of small subunits are colored blue [1.25].
Figure 1.13 Crystal structure of Pol II [1.24].
27
1.6 Inelastic X-ray Scattering Beamline for ILSF
Inelastic X-ray scattering is a very powerful method for measuring the electronic and
dynamic properties of a large variety of materials in a wide range of energies and
energy resolutions. Due to the need for different range of energies and resolutions
required for measuring the properties of phonons and photoelectron using inelastic X-
ray scattering, two different beamlines has to be set up for each purpose. Both types
of information are very important for determining the phonon properties and sound
velocities in liquids and solids, and for measuring the wide range of electronic
structures such as energy band structure, electron density of states, and Fermi surface
which are very important for the determination of the phonon and electronic structure
of materials. In the following we shall briefly describe some of the areas where such
an experimental facility will be of great utility.
Strongly-correlated systems: Phonons have been found to play an important role in
the renormalization of the electronic properties; their role in normal superconductivity
is well-known and it is being investigated for high-temperature superconductivity.
Theoretical work in this area can be checked with this facility. At present about a
hundred researchers in Iran are working on high-temperature superconductivity and
such a facility will benefit both the theorists and experimentalists working in this area.
Metals, semi-metals, semiconductors, insulators: The energy distribution and the
frequency intervals of the phonons play a decisive role in the electronic, optical, and
heat-conduction properties of these materials. Properties such as the specific heat
capacity and heat conductivity are easily calculable when the phonon spectrum is
known. Knowing these properties is very important since all of these types of material
play important role in many of today’s technologies.
Materials under extreme conditions: Geologists as well as material engineers are
interested in the behavior of materials under very high temperatures and pressures.
Such knowledge is of great use in studying the propagation of sound waves and heat
conduction in the inner layers of the Earth, and the properties of the inner cores of
planets.
Wave propagation in liquids, molten material, and solutions: Because of limitations
associated with neutron scattering methods, inelastic X-ray scattering is the only
method that can be used for this kind of studies.
Figure 1.15 Typical X-ray beamline for molecular crystallography [1.22]
28
A typical study – One of the most important types of studies done with this beamline
concentrates on determining the dispersion relation of optical phonon branches of
high-temperature superconductors whose theory is yet to be developed. Experiments
have shown an anomalous phonon softening which indicates the role of electron-
phonon interactions in high-temperature superconductor materials. Other type of
studies which can be carried out with this beamline concentrates on phonon dispersion
measurements in single crystals of simple metals or semiconductors where large
single-domain crystals are not available for inelastic neutron scattering measurements.
Phonons play an important role in the physical properties of large-gap semiconductors
such as their specific heat, thermal conductivity, thermal expansion coefficient, etc.
Phonon dispersion curves for such materials (e.g. 3C-SiC, 4H-SiC, GaN, AlN) have
been measured in similar beamlines and good agreements have been obtained with
other experimental and computational studies. Other systems that can be studied with
this beamline are quantum systems such as 3He and
4He in the superfluid states where
due to large absorption cross sections neutron scattering cannot be used to measure
the collective phonon modes. These studies have been done successfully with this
type of beamline. Strongly-correlated systems such as superconductors, magnetic
materials, charge-density-ordered systems, compounds of heavy elements, etc. can
also be studied in this beamline. In these materials phonons play an important role in
the electronic and other underlying transport properties. The phonon measurement of
these systems especially when large single crystals are not available has been
extensively carried out in similar beamlines. A detailed review of these studies can be
found in the review paper by E. Burkel [1.27]. Figure 1.16 shows the results of one of
a study of a high temperature superconductor using one such beamline [1.28]. Such a
beamline would be an unprecedented facility in Iran where at present no experimental
facility for this type of studies exists. This would fill the vacuum of experimental data
and would prove a boon to experimental science in Iran whose practitioners suffer
from a lack of adequate experimental facilities and laboratories.
Beamline specifications – Due to the need for very high brilliance and hard X-rays
this beamline needs a standard undulator as source. The energy and energy resolution
Figure 1.16 Phonon measurement of La2-xSrxCuO4 high temperature superconductor: Dots and lines are the experimental data and fitted curves respectively [1.28].
29
(dE/E) need to be in the range of 15-25 keV and 10-7
-10-8
, respectively. Typical spot
size of the X-ray at the sample position should be around 100 mm × 100 mm. Such a
beamline will be comprised of three hutches: the optics hutch, the backscattering
hutch, and the analyzer hutch. The optics hutch consists of a double crystal
monochromator Si(1,1,1) to produce a monochromatic X-ray beam with about 1 eV
resolution. In the backscattering hutch, a backscattering monochromator could be
adjusted in different configurations such as Si(7,7,7), Si(8,8,8) and Si(9,9,9) to
produce X-rays with meV resolution which is needed for phonon measurements. The
sample could be in liquid or solid phase and the sample temperature could be
controlled and adjusted over a wide range of temperatures (10-1000 K). The analyzer
hutch is comprised of several slits, 12 Si energy analyzers and
12 detectors to measure the energy and intensity of the scattered photons. Two
different arms can be used for horizontal and vertical polarizations of the phonon
wave vectors. Due to the high energy and intensity of the X-ray beam, all the optical
and measurement components are controlled by electronic motors driven by
computerized controls. Figure 1.17 shows a schematic layout of such a
beamline [1.26].
References
[1.1] Institute for Higher Education Research and Planning, Ministry of Science,
Research, and Technology, private communication; the data cited are for the
educational year 2009-2010, .
[1.2] Summary of Decisions reached by The Interim Council meetings of Iranian
National Accelerator Project, ILSF, Institute for Research in Fundamental
Sciences, October 2010 (available upon request).
[1.3] U. Hergenhahn, A. Rudel, K. Maier, A. M Bradshaw, R. F. Fink, A. T.Wen,
Chemical Physics 289 (2003) 57-69.
[1.4] L. J. Saethre, T. D. Thomas et al., Phys. Chem. Chem. Phys. 6 (2004) 4254.
[1.5] P. Bolognesi, M. Coreno, G. Alberti, R. Richter, R. Sankari, L. Avaldi., J.
Elect. Spect. Rel. Phenom. 141 (2004) 105-119.
Figure 1.17 The layout of Inelastic x-ray scattering beamline [1.26].
30
[1.6] S. Pilling, D. P. P. Andrade, R. T.Marinho, E.M. do Nascimento, H.M.
Boechat-Roberty, R. B. de Castilho, G. G. B. de Souza, L. H. Coutinho, R. L.
Cavasso-Filho, A. F. Lago, A. N. de Brito, Astrobiology Science Conference
2010 (2010).
[1.7] Journal of Physics:Conference Series 194 (2009) 022108.
[1.8] B. Winter, E. F. Aziz, U. Hergenhahn, M. Faubel, I. V. Hertel., J. Chem.
Phys. 126 (2007) 124504.
[1.9] http://www.elettra.trieste.it/beamline/GAPH.
[1.10] http://en.nano.ir/index.php/main/page/17; Michael M. Grieneisen, Minghua
Zhang, “Nanoscience and Nanotechnology: Evolving Definitions and
Growing Footprint on the Scientific Landscape”, Small
DOI: 10.1002/smll.201100387
[1.11] S. Günther, B. Kaulich, L. Gregoratti and M. Kishkinova, Prog. Surf. Sic. 70
(2002) 187.
[1.12] G. Margaritondo, J. Elect. Spect. Related Phenom. 178-179 (2010) 273.
[1.13] T. Yokoyama, T. Nakagawa and Y. Takagi, Int. Rev. Phys. Chem. 27 (2008)
449.
[1.14] E. Bauer, J. Elect. Spect. Related Phenom. 114-116 (2001) 975.
[1.15] A. Locatelli, S. Heun, M. Kishkinova, Surf. Sci. 566-568 (2004) 1130.
[1.16] H. A. Dürr et al., IEEE Trans. Magn. 45 (2009) 15.
[1.17] A. Locatelli, E. Bauer, J. Phys.:Condens. Matter 20 (2008) 093002.
[1.18] A. Barinov et al., Nucl. Instr. Method. Phys. Res. A601 (2009) 195.
[1.19] ELETTRA website, BL 2.2. L ESCA microscopy:
http://www.elettra.trieste.it/experiments/beamlines/esca/index.html.
[1.20] R. Moukhametzianov et al. (2008) “Protein crystallography with a
micrometre-sized synchrotron-radiation beam”, Acta Crystallographica
Section D, D64 (2008) 158–166.
[1.21] A. A. McCarthy et al. “A decade of user operation on the macromolecular
crystallography MAD beamline ID14-4 at the ESRF”, J. Synchrotron Rad 16
(2009) 803–812.
[1.22] E. Girard et al. “Instrumentation for synchrotron-radiation macromolecular
crystallography”, Acta Cryst D62 (2006) 12-18.
[1.23] K. Luger, A. W. Mader, R. K. Richmond, D. F. Sargent, T. J. Richmond,
“Crystal structures of the nucleosome core particle at 2.8 A resolution”,
Nature 389 (1997) 251-260.
[1.24] A. L. Gantte, P. Cramer, J. Fu, D. A. Bushnell, R. D. Kornberg, “Structural
Basis of Transcription: An RNA Polymerase II Elongation Complex at 3.3 Å
Resolution”, Science 292 (2001) 1844-1846.
[1.25] A. Ben-Shem, L. Jenner, G. Yusupov, M. Yusupova, “Crystal Structure of the
Eukaryotes Ribosome”, Science 330 (2010) 1203-1209.
[1.26] Beamline 35XU of Super Photon Ring-8 Gev (SPring-8),
http://www.spring8.or.jp/
[1.27] E. Burkel, Rep. Prog. Phys. 63 (2000) 171-232.
[1.28] T. Fukuda et al., Phys. Rev. B71, (2005) 060501.
31
CHAPTER 2: Choice of lattice
2.1 Introduction
A modern synchrotron light source is usually designed to produce extremely bright
synchrotron radiation covering a wide range of the electromagnetic spectrum. This
radiation, which is generated from deflecting a low-emittance electron beam within
the bending magnets or insertion devices, is characterized by its spectral range,
photon flux, photon flux density, brilliance and polarization. Photon flux is defined as
the overall flux collected by an experiment, photon flux density is the photon flux per
unit area at the sample, and brilliance is the photon flux per unit area and unit opening
angle of the source. The relation between the brilliance of the emitted photons and the
characteristics of electron beam is given below
(2.1)
where is the emission rate of photons, σx and σy are the beam size in the
horizontal (x) and vertical (y) directions, σx' and σy' are the beam divergences in the
transverse plane, and Δω/ω is the FWHM (full-width half-maximum) bandwidth in
units of 0.1% or 10-3
. This equation indicates that in order to have high-brilliance X-
ray pulses, beam size and beam divergence must be as small as possible at the
radiator. Transverse beam emittance can be expressed as a function of beam size and
beam divergence (εx=σx σx' and εy=σy σy'), Eq. 2-1 can be rewritten as
(2.2)
where εx and εy are horizontal and vertical emittance, respectively. As the vertical
emittance can be expressed in terms of horizontal emittance by a coupling factor of k:
(2.3)
the brilliance of the emitted X-ray pulses is given by
(2.4)
In most of the cases for a 3rd
generation synchrotron light source, the emittance in the
vertical direction is already diffraction limited, which means it is given by the
radiation coming from the insertion devices. In this case the brilliance goes with
(2.5)
Emittance of the electron beam which is constant in a storage ring depends on the
parameters of the magnetic elements in the lattice. Natural horizontal beam emittance
in a storage ring is given by
(2.6)
where γ is the relativistic factor, Jx is the horizontal damping partition number which
is almost equal to 1, θ (rad.) is the bending angle, F is a value which depends on the
behavior of the beta functions and the dispersion function within the bending
magnets, and Cq is a constant (Cq = m). In Eq 2-6, the factor F is given
32
by the design of the storage ring, a small number means a good design. For the
comparison of the design of the different storage rings it is sometimes worthwhile to
introduce the so called normalized emittance:
(2.7)
Since beam emittance grows with the second power of beam energy and the third
power of bending angle, in a light source of intermediate energy it is desirable to have
short bending magnets hence small bending angles in order to get a small emittance.
For some experiments the brilliance is not as important as the photon flux density:
(2.8)
A synchrotron light source is an accelerator complex existing of a pre-injector, an
injector, a storage ring and the transfer lines between the different accelerators. The
synchrotron light will be emitted from the bending magnet of the storage ring and the
insertion devices installed in the straight sections of the storage ring. Most important
are the straight sections for the insertion devices. In the design of a storage ring one
tries to get a small emittance for high brilliance and many long straight sections for
the installation of insertion devices. A synchrotron light source should provide the
photon beam for a many users and this is possible with more straight sections. Overall
this means that a high brilliance light source supporting many beamlines will have a
storage ring with a large circumference and therefore will be expensive.
Table 2.1: Characteristics of the latest-built synchrotron light sources.
Source Lattice Energy Emitt. ID-Length Angle Circumf. Perc. Nor.- Em. Tot. Brill
( GeV ) nmrad ( m) ( rad) ( m) ( % ) **)
MAX II DBA 1.5 9 31.4 0.3142 90 34.9 129.0 116
ALS TBA 1.9 5.6 81 0.1745 196.8 41.2 291.9 611
BESSY II DBA 1.9 6.4 89 0.1963 240 37.1 234.4 550
ELETTRA DBA 2 7 74.78 0.2618 258 29.0 97.5 404
INDUS II DBA 2 44 36.48 0.3927 172 21.2 181.6 12
SLS TBA 2.4 5 63 0.244 288 21.9 59.8 563
NSLS-xray DBA 2.5 44.5 18 0.3927 170.08 10.6 117.6 6
SESAME TME 2.5 26 54.56 0.3927 133.2 41.0 68.7 41
SOLEIL DBA* 2.75 3.72 159.6 0.1963 354 45.1 65.0 2224
CLS DBA 2.9 18.2 62.4 0.2618 170.4 36.6 120.6 80
ROSY DBA* 3 28.5 44.8 0.3927 148.11 30.2 52.3 29
SPEAR III DBA 3 18.2 67 0.16535 234.13 28.6 447.3 86
ASP DBA 3 6.88 76.72 0.2244 216 35.5 67.7 425
DIAMOND DBA 3 2.74 218.2 0.1309 561.6 38.9 135.7 4811
ALBA DBA* 3 4.29 103.44 0.1963 268.8 38.5 63.0 1164
CANDLE DBA 3 8.4 76.8 0.1963 216 35.6 123.4 315
SIRIUS TBA 3 1.9 154.8 0.1047 460.6 33.6 183.9 5911
MAX IV MBA 3 0.328 55.2 0.0748 528 10.5 87.1 29385
NSLS-II DBA 3 2.24 94.56 0.10472 780.3 12.1 216.7 2821
TPS DBA 3 1.6 198 0.0524 518.4 38.2 1235.6 9783
PAL-II MBA 3 5.6 118.92 0.2618 281.82 42.2 34.7 897
SSRF DBA 3.5 3.9 152 0.1571 432 35.2 82.1 1974
ILSF-II-2 DBA 3 1.598 130.13 0.1428 326.4 39.9 61.0 6442
Norm.-Emittance = Emitt. /((E^2)*(Angle^3)), Tot. Brill.=(Circumf.*Percent.)/(Emitt.^1.5)
33
Table 2.1 lists the characteristics of the latest built synchrotron light sources. In this
table the important entries are the normalized emittance, the percentage of the
circumference devoted to straight sections and the total brilliance. A small normalized
emittance means a state-of-art design. In Table 2.1 one can see that this value has to
be around 60 or smaller. The possible candidate for the ILSF project is the lattice
ILSF II-2 which has a value of 61. A high number of the percentage means a state of
the art design too, according to table 2-1 this value should be around 40%. The lattice
ILSF II-2 has a value of 39.9 %, which is relatively good.
The extremes in Table 2.1 are the designs of SLS and MAX-IV, both of which have
pretty good normalized emittances but a very low percentage of the circumference is
devoted to the long straight sections. Because of the small emittance MAX IV has the
highest total brilliance. The total brilliance of the lattice ILSF II-2 is 6442, which
according to Table 2.1 is a pretty good number.
For the design of the ILSF lattice three lattices were used as the starting point: ALBA,
ASP and PAL-II. The characteristics of the different lattices which have been
investigated are given in Table 2.2. Because of the highest total brilliance the lattice
ILSF-II-2 is the best candidate.
Table 2.2: Characteristics of the lattices investigated for the ILSF project.
Also for the total flux density (see Table 2.3), the lattice ILSF II-2 has the highest
value. Hence the best candidates for the lattice of the ILSF storage ring are ILSF I-2
and ILSF II-2. Both lattices will be described in the following sections.
Source Lattice Energy Emitt. ID-Length Angle Circumf. Perc. Nor.- Em. Tot. Brill
( GeV ) nmrad ( m) ( rad) ( m) ( % ) **)
ALBA DBA* 3 4.29 103.44 0.1963 268.8 38.5 63.0 1164
XXX-5 DBA 3 4.68 83.832 0.1963 249.6 33.6 68.7 828
XXX-7 DBA 3 5.46 82.128 0.2244 249.6 32.9 53.7 644
XXX-10 MBA 3 3.25 123.8 0.1963 297.6 41.6 47.7 2113
PAL-XXX MBA 3 5.42 100.26 0.2618 257.14 39.0 33.6 794
PAL-XXX-II MBA 3 5.47 93.928 0.2618 249.6 37.6 33.9 734
PAL-XXX-III MBA 3 9.64 94.888 0.31416 249.6 38.0 34.6 317
PAL-XXX-IV MBA 3 8.16 94.888 0.31416 249.6 38.0 29.3 406.9
Javad-ALBA DBA 3 3.54 130.6 0.1963 297.6 43.9 52.0 1961
Javad-PAL-II DBA 3 3.11 145.2 0.1963 318.9 45.5 45.7 2647
XXX-19 MBA 3 3.3 131.522 0.19635 297.5 44.2 48.4 2194
ASP-Iran DBA 3 2.06 116.77 0.1428 297.6 39.2 78.6 3949
ILSF-0 DBA 3 1.74 128.68 0.1428 326.4 39.4 66.4 5606
ILSF-I DBA 3 3.282 129.4 0.19635 297.6 43.5 48.2 2176
ILSF-I-2 DBA 3 3.14 143.36 0.19635 316.8 45.3 46.1 2577
ILSF-II DBA 3 1.956 106.2 0.1428 297.6 35.7 74.6 3882
ILSF-II-2 DBA 3 1.598 130 0.1428 326.4 39.8 61.0 6435
TBA-II TBA 3 1 122.8 0.1047 326.4 37.6 96.8 12280
Norm Emitt = Tot. Brill. =nm*rad/((E^2)*(Angle^3)) (Circumf*Percent.) /[(Emitt)^1.5]
34
Table 2.3: Flux density of the lattices investigated for the ILSF project.
2.2 General layout of the accelerator complex
The general layout of the Iranian Light Source Facility (ILSF) is shown in Figure 2.1.
As shown, the approximate diameter of facility will be 230 m. An electron beam
produced with an electron gun, is accelerated by a traveling wave linear accelerator
(linac) to the energy of 150 MeV. Then the electrons enter into the booster
synchrotron via linac-to-booster transfer line (LTB). The booster accelerates the
electron beam to the energy of 3 GeV using a radio frequency (RF) cavity with the
frequency of around 0.5 GHz. After reaching the target energy, the electron beam is
transferred from the booster to the storage ring through an almost 40 m transfer line
(BTS).
The arrangement of the different accelerators (pre-injector, booster synchrotron and
storage ring is completely different from other 3rd
generation light sources. Other light
sources as SLS, ALBA and TPS have the booster synchrotron in the same tunnel as
the storage ring. Diamond, Soleil and SSRF attached the booster synchrotron to the
storage ring.
Source Lattice Energy Emitt. ID-Length Angle Long Medium Short SUM
( GeV ) nmrad ( m) ( rad) **) **) **) **)
ALBA DBA* 3 4.29 103.44 0.1963 7316 49304.0 4377.0 6.1E+04
XXX-5 DBA 3 4.68 83.832 0.1963 5796 38329.0 4.4E+04
XXX-7 DBA 3 5.46 82.128 0.2244 7659 38011.0 4.6E+04
XXX-10 MBA 3 3.25 123.8 0.1963 12858 111734.0 1.2E+05
PAL-XXX MBA 3 5.42 100.26 0.2618 8563 26941.0 3.6E+04
PAL-XXX-II MBA 3 5.47 93.928 0.2618 12288 29668.0 4.2E+04
PAL-XXX-III MBA 3 9.64 94.888 0.31416 3693 17085.0 2.1E+04
PAL-XXX-IV MBA 3 8.16 94.888 0.31416 3987 27182.0 3.1E+04
Javad-ALBA DBA 3 3.54 130.6 0.1963 11639 56471.0 11518.0 8.0E+04
Javad-PAL-II DBA 3 3.11 145.2 0.1963 11106 93979.0 7804.0 1.1E+05
XXX-19 MBA 3 3.3 131.522 0.19635 7960 55972.0 16056.0 8.0E+04
ASP-Iran DBA 3 2.06 116.77 0.1428 73611 7.4E+04
ILSF-0 DBA 3 1.74 128.68 0.1428 65333 180282.0 2.5E+05
ILSF-I DBA 3 3.282 129.4 0.19635 8066 60332.0 14038.0 8.2E+04
ILSF-I-2 DBA 3 3.14 143.36 0.19635 7254 86172.0 9.3E+04
ILSF-II DBA 3 1.956 106.2 0.1428 54381 5.4E+04
ILSF-II-2 DBA 3 1.598 130 0.1428 70333 196282.0 2.7E+05
TBA-II TBA 3 1 122.8 0.1047 174180 1.7E+05
**): Flux density = (ID-length)/ (Sigma_x*Sigma_y)
35
For the ILSF project the booster synchrotron is in a separated tunnel next to the
service area (see Fig.2.1). The reason is to assemble and commission the booster
synchrotron independently from the storage ring. The building needed for the booster
synchrotron is a very simple one and therefore the additional costs are marginal. The
booster to storage ring transfer line is pretty long, but it takes away far less space from
the service area as an attached booster to the storage ring.
Figure 2.1 General layout of ILSF’s accelerator complex.
36
37
CHAPTER 3: Beam dynamics
3.1 ILSF storage ring
3.1.1 Lattice structure
In order to meet the future demands of the users, the ILSF storage ring has to be
designed to provide high brilliance radiation from an electron beam with a small
emittance. Since we are interested in high-energy photons with high brilliance in
several beamlines, we aimed to have several straight sections of different lengths to
accommodate various required insertion devices. Thus a four-fold symmetric ring
with 32 straight sections was a good choice for our lattice. The ring consists of 4
superperiods, each designed with three double bends. Achromat unit cells and
matching sections were added to optimize the machine functions. The circumference
of the storage ring in this design is 297.6 m and the linear lattice functions are well-
matched to the requirements of a small emittance and small beam size at the radiators.
The simulation tools which were used for linear and nonlinear lattice optimization and
particle tracking have been OPA [3.1], ELEGANT [3.2], MADX [3.3] and BETA
[3.4]. An overview of storage ring based on this design (named ILSF Lattice 1) is
shown in Figure 3.1 and its major lattice parameters are listed in Table 3.1.
Figure 3.1 Layout of the storage ring in ILSF Lattice 1 design.
38
Table 3.1: Main parameters of the storage ring based on ILSF Lattice 1.
Parameter Unit Value
Energy GeV
Circumference m
Number of superperiods -
Current mA
Horizontal emittance nm.rad
Harmonic number -
RF frequency MHz
Tune ( ) -
Natural energy spread -
Natural chromaticity ( ) -
Momentum compaction ( ) -
Radiation loss per turn MeV
No. of dipoles -
No. of quadrupoles -
No. of sextupoles -
The four-fold symmetric configuration provides four 7.88 m long straight sections to
accommodate long insertion devices (ID) and injection elements. There are 16 straight
sections of medium length, each 4 m long, which can be used for insertion devices up
to 3.5 m long. Moreover, 12 short straight sections with a length of 2.82 m are
reserved for placing diagnostic equipment, kickers for feedback system, RF cavities
and short IDs. The ratio of the total length of the straight sections to the circumference
of the ring (percentage of storage ring) is 43.46% which is pretty good in comparison
with other light sources. As shown in Figure 3.2, each superperiod is composed of
two matching cells at the beginning and the end and three unit cells located in
between. The two matching cells and three unit cells are also shown in Figure 3.1
represented by two red triangles and three blue triangles respectively.
Lattice functions in matching and unit cells of ILSF-Lattice-1 are shown in Figure 3.3
and they are depicted in one superperiod in Figure 3.4. In order to obtain low beam
dimensions and to minimize the undesirable effects of IDs on the optics, we have
considered 4 straight sections of medium length with low beta functions in each
Figure 3.2 Arrangement of magnets in one superperiod (top), the matching cell (center), the unit cell of ILSF-Lattice-1 (bottom).
39
superperiod to accommodate the wigglers and undulators. Optical functions at the
center of straight sections are given in Table 3.2. The structure of ILSF Lattice 1 is
given in Appendix 3.1.
Table 3.2: Optical functions at the center of long,
medium, and short straight sections of ILSF Lattice 1.
Parameter Long Medium Short
(m) 14.001 2.370 7.813
(m) 4.200 1.433 2.888
(m) 0.247 0.124 0.182
As a good working tune point in a stable area on the tune diagram is desirable for the
ring stability, the linear parts of lattice have been optimized to find a tune point far
away from major resonance lines. Working tune point in tune diagram containing
resonance lines up to the 5th
order is shown in Figure 3.5. The tune point is
Figure 3.3 Optical functions in a matching cell (left), and a unit cell (right) of ILSF Lattice 1.
Figure 3.4 Optical functions in one superperiod of ILSF Lattice 1.
40
represented by the blue circle and the corresponding equation for each resonance line
has been given.
The cross section of the electron beam within one quadrant of ring is given in
Figure 3.6. Two factors determine the beam size: (i) the monochromatic beam width
which is equal to the square root of the product of the beta function and the emittance,
and (ii) the chromatic correction equal to the product of the dispersion function and
the energy spread. A main criterion in the design is to make the emittance as small as
possible; the value found for the ILSF Lattice 1 is 3.278 nm.rad. The smallest
horizontal cross section in the straight sections is obtained with this lattice at the
medium straight section with the above mentioned emittance and a beta function of
roughly 2.370 m.
Figure 3.6 Beam size in one quadrant of ILSF Lattice 1.
Figure 3.5 Tune point for the storage ring of ILSF Lattice 1.
41
We have specified transverse beam envelope at the straight sections in Table 3.3. For
the purpose of beam envelope calculation a 1% coupling was assumed.
Table 3.3: Beam envelope at the center of long, medium, and short straight sections.
Parameter Long Medium Short
333.93 156.18 250.12
11.72 6.85 9.80
3.1.2 Nonlinear beam dynamics
The strong focusing magnets required for a small beam emittance result in a large
chromatic aberration and negative natural chromaticity. In order to avoid large tune
spread due to energy errors and to suppress the transverse head-tail instabilities, this
natural chromaticity should be corrected and brought close to zero by sextupole
magnets. However, the nonlinearities of strong sextupole magnets affect the dynamic
aperture. These effects can be suppressed by placing the sextupoles at suitable
locations in the ring with proper phase advances. Having 9 families of sextupoles in
ILSF Lattice 1 were sufficient for this purpose.
Since the electron beam envelope and the quality of radiation have indirect effects on
machine functions, the distortion of optical functions due to energy deviation is very
crucial and must be kept as small as possible through nonlinear optimization.
Variation of lattice functions after chromaticity correction for on-momentum
electrons and electrons with an energy deviation of ±3% is shown in Figure 3.7. It has
been found that after chromaticity correction, main parameters of storage ring do not
change appreciably due to energy error. Changes of the ring’s major parameters due
to energy deviations up to 3% are given in Table 3.4.
Figure 3.7 Variations of machine functions in one quadrant of ILSF Lattice 1 due to energy deviations up to 3%.
42
Table 3.4 Changes of ILSF-Lattice-1 storage ring parameters due to energy deviation.
Parameters Unit
Horizontal emittance nm.rad
Tune ( ) -
Natural energy spread -
Corrected chromaticity -
Momentum compaction -
Radiation loss per turn MeV
at center of
medium straight sec. m
Figure 3.8 Phase space tracking at the center of long straight section: (top) on-momentum particles (center) +3% off-momentum particles (bottom) -3% off-momentum particles
43
For more reliable results, we have tracked the on/off-momentum electrons for many
turns in the storage ring using ELEGANT. The SDDS TOOLKIT [3.5] program is
used to plot the results of ELEGANT. Phase-space tracking of particles helps us find
the stable boundaries of particle orbits everywhere in the ring. Phase space of on-
momentum particles and particles with ±3% energy deviation after tracking 3000
turns are shown in Figure 3.8. The corresponding dynamic apertures are shown in
Figure 3.9.
A smooth tune shift with energy deviation keeps the working tune points of off-
momentum particles far away from dangerous resonance lines up to energy
acceptance. Figure 3.10 shows the fraction of transverse tune shift for energy
deviations up to 3%.
Figure 3.9 Dynamic aperture at center of a long straight section in ILSF-Lattice-1 storage ring.
Figure 3.10. Fraction of tune shift vs. energy deviation.
44
One of the favorable results of nonlinear optimization of ILSF Lattice 1, as seen in
Figure 3.10, is that the tune shift with energy is very small. The related tune shift in
tune diagram containing resonance lines up to the 5th
order is shown in Figure 3.11.
The color maps of dynamic aperture for on-momentum electrons are shown in
Figure 3.12.
In addition to energy, we have also studied the shift of tune with transverse amplitude.
This has been investigated for on-momentum particles and Figure 3.13 shows how the
fraction of transverse tune shifts due to amplitude. The corresponding tune diagram is
also depicted in Figure 3.14.
Figure 3.11 Tune shift vs. energy deviation up to 3% in the tune diagram.
Figure 3.12 Color maps of dynamic aperture show the variations in the fractional part of horizontal (left) and vertical (right) tunes for on-energy electrons after tracking them for 3000 turns.
45
3.1.3 Choice of tune points and upgrade capabilities
As seen in the previous section, the working tune point ( ) designed for ILSF
Lattice 1 is 18.265/11.328 and the natural emittance is 3.278 nm.rad. This point for
working tune works well, however we need to find other tune points near the main
tune and study how the ring works. These new tune points are found by modifying the
magnets of ILSF Lattice 1 particularly the quadrupole magnets. The strength of quads
are changed in such a way that the requirements of low emittance, low natural
chromaticity, low beta functions, high beam size at the radiators, high beta functions
at injection and other important issues in lattice design for a light source are still
satisfied. Several tune points near the original tune have been found and the
performance of the storage ring has been optimized both linearly and nonlinearly for
the new tunes. We have called the modifications separate modes of the
ILSF Lattice 1. The parameters of the storage ring that work with the new tunes after
optimization are listed in Table 3.5.
Figure 3.13 Transverse tune shift as a function of amplitude.
Figure 3.14 Color map of tune shift in tune diagram vs. transverse amplitude: (left) x coordinate (right) y coordinate.
46
Table 3.5 Main parameters of storage ring with modification in ILSF-Lattice-1.
ILSF Lattice 1
(original mode)
Mode 1 Mode 2
Tune ( )
Emittance (nm.rad)
Chromaticity ( ) -
Mom. compaction
( )
Energy spread ( )
Dyn. Aper. (H/V)
(mm)
-30 to 25 / -11 to 11 -40 to 28 / -15 to15 -28 to 20 / -8 to 8
The results of these optimizations which we have not shown here indicate that the
new tune points are as good as the original tune. These results reveal that
ILSF Lattice 1 can easily operate at the new tune points.
3.1.4 Closed orbit
In the high intensity storage rings, there are many sources of errors which can cause
closed orbit distortion (COD). One of the sources of COD is error in the field of
dipole magnets which kicks out the particles. Other sources of COD are displacement
and roll of magnetic elements which can be caused by girder deformation or
misalignment of the magnets. The most severe effects come from the misalignment of
quadrupoles where the resulting dipole field is proportional to both gradient and
misalignment errors. This section gives effects of errors in closed orbits.
3.1.4.1 Closed orbit distortion
To study the total effect of errors on a closed orbit, different types of expected
misalignments and field errors were imposed randomly in the lattice of ILSF storage
ring. It is worthwhile to mention that each error has been separately studied and we
found that which one has the most effect on closed orbit. The errors which are listed
in Table 3.6 have been utilized in our calculations. The relative field error of
is also assumed in dipoles.
Table 3.6 The utilized errors for COD calculation of the ILSF storage ring.
Type of error Error value
Displacement and roll of dipole with respect to girder Δx = Δy = 30 μm
Δφs = 100 μrad
Displacement and roll of quadrupole with respect to girder Δx = Δy = 30 μm
Δφs = 100 μrad
Displacement and roll of sextupole with respect to girder Δx = Δy = 30 μm
Δφs = 100 μrad
Displacement and roll of BPM with respect to girder Δx = Δy = 30 μm
Δφs = 100 μrad
Girder transverse displacement and roll Δx = Δy = 100 μm
Δφs = 100 μrad
47
The orbit distortion evaluated numerically with ELEGANT code is given in
Figure 3.15.
3.1.4.2 Closed orbit correction
In order to correct COD, 128 horizontal and 128 vertical corrector coils in each plane
of the sextupole magnets have been distributed around the whole ring. Moreover, we
have assumed 128 beam position monitors (BPM) to observe the beam and study its
orbit. They are placed at beginning and end of the straight sections and between the
magnets. Locations of the BPMs and the correctors in half a superperiod of the ILSF
ring are shown in Figure 3.16. The corrected closed orbit in the transverse plane as
shown in Figure 3.17 indicates a very good orbit with deviations below 0.06 mm in
transverse plane. Figure 3.18 shows the strength of kicker magnets around the ring
with a maximum strength of 0.3 mrad.
Figure 3.15 Distorted horizontal (left) and vertical (right) closed orbits in one superperiod for 200 seeds.
Figure 3.16 Location of BPMs and correctors in half a superperiod of ILSF lattice.
48
3.1.5 Effects of insertion devices
The radiation coming from a dipole magnet of a storage ring is very useful for a broad
range of applications, but the insertion devices (IDs) are indispensable parts of a
modern 3rd
generation synchrotron light source. They are used for special experiments
which need hard x-rays, monochromatic radiation of higher brightness, elliptically
polarized radiation, etc.
There are two major effects due to the perturbation of the electron beam by insertion
devices (IDs) in a ring that usually need to be considered. The first is the shift of the
tune due to the magnetic field of the IDs, which results in beta beating and a smaller
dynamic aperture. The second is the change in emittance and energy spread of the
electron beam due to the energy radiated from the IDs. In this section we evaluate
analytically the effects of the IDs in the ILSF storage ring and compare it with the
simulation results. The primary ILSF beamlines will be based on conventional
parameters of planar IDs used in ALBA [3.6][3.7] as listed in Table 3.7. Devices with
Figure 3.17 Corrected horizontal (left) and vertical (right) closed orbits in one
superperiod of the ILSF storage ring for 200 seeds.
Figure 3.18 Strength of correctors in the ILSF ring.
49
very similar parameters are widely used in synchrotron radiation facilities around the
world.
Table 3.7 Main parameters of primary insertion devices.
IVU-21 W80 SC-W31
21.6 80 31 λ (mm)
92 12 60 N period
2.1 1 1.9 L (m)
0.79 1.73 2.10 By (T)
5.7 12.5 12.4 Gap (mm)
1.60 12.98 6.30 K (T.cm)
Planar/Pure Planar/Hybrid Planar/Superconductive Type
To simplify the calculations, we consider planar insertion devices whose poles are
parallel and produce a sinusoidal magnetic field.
3.1.5.1 Beta-beating and tune shift
The quadrupole effect associated with an insertion device causes tune shift and beta-
beating [3.8]. For a planar insertion device, we have [3.9], [3.10]
(3-1)
(3-2)
where By is the magnetic field of ID and is vertical beta function at the location of
ID. Due to different values of the optical functions in the straight sections of the ILSF,
the IDs would have different effects on the beam parameters. Due to the lower values
of the optical functions, the IDs will have no significant effect in medium straight
sections in comparison with long and short straight sections (Eq. 3.1 and Eq. 3.2).
Since the SCW-31 has the highest value of magnetic field, we expect the strongest
effects on the beam parameters from SCW-31. In the following we study the effects
of high field superconducting wiggler magnet (SCW-31) with the length of 1.9 m and
maximum field of 2.1 T (see Table 3.7) which we assume as placed in one of the
medium straight sections of ILSF lattice. In the presence of SCW-31, only changes in
vertical beta function were observed while horizontal beta function did not change.
The distorted beta function in the presence of SCW-31is depicted with BETA code in
Figure 3.19. The effect of IDs on transverse tune have summarized in Table 3.8.
Table 3.8: Effect of IDs on vertical tune.
ΔQy(Theory) ΔQy(BETA) Qy Qx
Without ID SC-W31
W80
IVU-21
50
The agreement between the simulation and analytic calculations as seen in Table 3.8
is very good.
Beta-beating can be defined as below
Beta-beating
(3-3)
One can then calculate how much the SCW-31 affects the optics. The distorted optical
functions are compensated by four quadrupoles adjacent to ID while the regular
quadrupoles adjust the tune to its original value. The strengths of the quadrupoles
nearest to SCW-31 before and after beta correction are listed in Table 3.9. As
calculated, the maximum relative verified gradient is less than 1.4 %. The corrected
optical functions in presence of SCW-31 are given in Figure 3.20. The calculated beta
beating due to SCW-31 before and after correcting is shown in Figure 3.21. It is
obvious that the beta beating after correction is less than 1% in both horizontal and
vertical directions except at the ID location.
Table 3.9: Gradient of adjacent quadrupoles to SCW-31 before and after beta beating correction.
Relative Change (%)
Gradient with SCW31 (T/m)
Original gradient (T/m)
-0.420 1.894 1.902 QF2W
+1.398 -1.740 -1.716 QD2W
+1.232 -2.136 -2.110 QD3W
-0.300 1.994 2.000 QF3W
Figure 3.19 Effect of SCW-31 on the optical functions in one quadrant of the ILSF ring: SCW-31 is represented by the green box in a medium straight section.
51
3.1.5.2 Dynamic aperture reduction
In addition to the focusing effect, the IDs shrink the dynamic aperture. The other
source of dynamic aperture shrinkage is the perturbed symmetry of the lattice due to
the low value of the beta function in the medium straight sections [3.6], [3.11].
Figure 3.22 shows the effect of SCW-31 on the dynamic aperture for on-momentum
electrons.
Figure 3.20 Optical Functions of ILSF lattice with one SCW-31 after beta correction in one quadrant of the ring. The green box represents the SCW-31 ID.
Figure 3.21 Beta-Beating along the ring with one SCW-31 in a medium straight section before and after correction. The peak points represent beta beating in SCW-31.
52
It should be pointed out that study of dynamic aperture for off-momentum particles
showed a significant reduction of dynamic aperture in particular for -3% energy
deviation which was not seen in bare lattice (see Figure 3.23). This effect is again
caused by the symmetry breaking of the sextupoles [3.9]. Three resonance islands
(Figure 3.24) appear in the phase space of particles with -3% energy deviation while
they do not appear in the bare lattice. To clarify this effect, the working tune point of
the machine in the presence of ID is plotted in Figure 3.25 which indicates that the
tune point for -3% energy deviation is near the third dangerous resonance
( ).
Figure 3.22 Dynamic aperture at the center of long straight section of ILSF ring with and without SCW-31.
Figure 3.23 Dynamic aperture with SCW-31 at the center of a long straight section. The on/off-momentum particles have been tracked 3000 turns through the ring.
53
A possible cure could be either in small modifications of tune or in fine optimization
of sextupole magnets.
Figure 3.24 Horizontal phase space with SCW-31 present in the ring for a particle with -3% energy deviation.
Figure 3.25 Working tune point with SCW-31 for on/off-momentum particles.
54
3.1.5.3 Effects of radiation from ID
The other major effect of the IDs is the change in emittance and energy spread due to
radiation. The changes in energy spread, emittance and energy loss per turn for
different planar IDs in ILSF ring obtained from OPA simulations are listed in the
Table 3.10.
Table 3.10: Effect of installation of IDs in a medium straight section of ILSF ring
on energy spread, emittance and energy loss per turn.
Emittance (nm.rad) Energy loss per turn (Kev)
Energy spread (10-3
)
3.278 1016.7 1.041 Without ID
3.701 1063.9 1.043 SC-W31
3.381 1031.3 1.040 W80
3.293 1024.2 1.038 IVU-21
For the case of SCW-31, relative energy spread and emittance as a function of field of
SCW-31 (installed in a medium straight section) is shown in Figure 3.26 and
Figure. 3.27 respectively and a very good agreement is observed between analytic
calculations and simulation results.
Figure 3.26 Relative energy spread versus SCW-31’s magnetic field calculated by theory and OPA code.
55
3.1.6 Multipole effects
The main limitation of dynamic aperture arises from the chromaticity of sextupoles.
However, small multipole errors in magnetic elements can reduce the dynamic
aperture by generating high-order resonances at the aperture boundaries. Field errors
in iron magnets have two distinct sources: finite pole width, and, tolerances in
mechanical manufacturing and assembly. From symmetry arguments, field errors due
to the finite pole width produce specific multipole components. The manufacturing
and assembly errors, however, do not have any symmetry and can cause the
appearance of any multipole component.
3.1.6.1 Systematic multiple errors
The ILSF dynamic aperture in the presence of magnetic multipoles was studied and
simulated by BETA tracking code and the results are presented in this section.
Systematic multipole errors of compound bending magnet due to finite pole width
occur for n = 3, 5, 7, 9, 11, 13... So, the expansion of bending magnet field that
includes the systematic errors is of the form
(3-4)
The relative multipole errors for a combined bending magnet are as follows:
Figure 3.27 Relative emittance of ILSF lattice versus the magnetic field of SCW-31 calculated by theory and OPA code.
56
The expansion of quadrupole field with systematic multipole components is
(3-5)
The field quality is given by
with n = 6, 10, 14,…
The expansion of sextupole field with systematic multipole components is
(3-21)
And the field quality in this case is
with n = 9, 15, 21, …
3.1.6.2 Multipole errors for dipole magnets
The systematic multipole components of the magnetic flux for two families of ILSF
storage ring bending magnets with good field region of ±10 mm have been estimated
in the median plane by Fourier analysis using 2-D POISSON code. Figure 3.28
compares the dynamic aperture of ILSF ring with the case where multiple errors are
taken into account. The reduction in dynamic aperture is seen to be negligible.
Figure 3.28 Dynamic aperture of ILSF ring with and without multipole errors in the dipole magnets.
57
3.1.6.3 Multipole errors for quadrupole magnets
Since only infinitely wide hyperbolic poles create a pure quadrupole field, we expect
the appearance of higher multipole field components due to finite pole width. The
systematic multipole contents of the magnetic flux in the good field region of ±18 mm
have been estimated by a Fourier analysis of the flux distribution in the median plane
of a quadrupole magnet. The effect of multipole errors for quadrupole magnets on the
dynamic aperture is shown in Figure 3.29. Again the effect is seen to be insignificant.
3.1.6.4 Multipole errors for sextupole magnets
Reduction of dynamic aperture due to the relative multipole components for ILSF
sextupoles at ±12 mm good field region as shown in Figure 3.30 is not significant.
Figure 3.29 Dynamic aperture for the two cases where multipole errors of the quadrupoles are and are not taken into account.
Figure 3.30 Dynamic aperture for the two cases in which multipole errors of sextupoles are and are not taken into account.
58
3.1.6.5 Systematic multipole errors for all magnets
The systematic errors in the magnets will decrease the dynamic aperture especially in
the vertical direction. Figure 3.31 shows the dynamic aperture by tracking 3000 turns
of on- and off-momentum electrons with multipole errors for all magnets taken into
account. Shrinkage of dynamic aperture due to all systematic errors is not
considerable and there is no need to re-optimize the dynamic aperture. To clarify
these effects, Figure 3.32 and Figure 3.33 show and compare the transverse tune shift
with amplitude for bare ILSF lattice and ILSF lattice with higher multipole errors.
Figure 3.31 Dynamic aperture of on- and off-momentum electrons with multipole errors for all magnets by 3000 turns tracking.
Figure 3.32 Tune shift with horizontal amplitude with and without multipole errors for on-momentum particles and 3000 turns tracking.
59
3.1.6.6 Measured multipole errors in ALBA
To get a realistic idea of the effects of multipole errors we have looked at the
measurement of magnetic components at ALBA [3.12][3.12] [3.13], a modern light
source similar to ILSF, and simulations by MAD-X tracking code. Rotating coil
measurements, performed by the manufacturer (BINP) in all the 120 ALBA
quadrupoles (4 magnet types: Q200, Q260, Q280, Q500 with different lengths) and
112 sextupoles (2 types: S150, S220 also with different lengths) at R=25mm, are
plotted in Figure 3.34 and Figure 3.35 respectively and the main relative component
of ALBA magnets are listed in Table 3.11 in which Bn and An denote the normal and
skew relative components, respectivley.
Table 3.11: Measured relative multipole components in ALBA’s quadrupole and sextupole magnets
104/Bmain S150 S220 Q200 Q260 Q280 Q500
B1 -22.2 -21.5 0.6 -1.3 -0.8 1
B2 0.1 3.3 104 1.0×10
4 1.0×10
4 1.0×10
4
B3 1.0×104 1.0×10
4 0.6 0.9 1.5 -0.4
B4 -0.7 -0.5 0.0 -0.3 -1.4 -1.5
B5 -1.3 -1.6 -0.3 -0.1 0.1 0.1
B6 0.2 -0.1 0.9 -1 -0.6 -0.9
B9 -4.3 -3.8 -0.1 0 0 0.1
B10 0.2 0 -3.5 -2.9 -2.9 -2
B14 0.2 0 -0.7 -0.8 -0.8 -0.7
B15 2.3 2.2 -0.1 0 0 0.1
A1 2.4 -0.2 3.5 2.6 2.3 4.1
A2 4.1 3.4 0.1 -0.8 0.2 -0.2
A3 1 -0.4 -1.4 0.8 0.1 0.4
A4 -0.7 0 0.3 0 -0.3 0.1
A5 1.1 -0.3 -0.1 -0.5 -0.1 0
A6 1.6 -0.1 0.3 -0.3 -0.2 0
Figure 3.33 Tune shift with vertical amplitude with and without multipole errors for on-momentum particles and 3000 turns tracking.
60
Figure 3.34 Measured higher-order relative multipole errors in ALBA’s quadrupoles [3.13].
61
In the ILSF storage ring 104 quadupole magnets of 3 types with different magnetic
lengths (530 mm, 310 mm and 260 mm) and 128 sextupole magnets of 2 types with
different magnetic lengths (150 mm and 220 mm) will be distributed around the ring.
To study the effects of multipole errors in the ILSF storage ring, the Q500, Q280 and
Q260 errors measured at ALBA for quadrupoles and the S150 and S220 errors
measeured for sextupoles have been simulated for the ILSF magnets. Figure 3.36
shows dynamic aperture of ILSF lattice without any multipole errors for on/off
momentum particles as simulated by MAD-X tracking code. The effect of real
multipole errors on the dynamic aperture is shown in Figure 3.37.
Figure 3.35 Measured higher-order relative multipole Errors in ALBA’s sextupoles [3.13].
Figure 3.36 Dynamic aperture of ideal lattice for on- and ±3% off-momentum electrons.
62
To figure out the maximum acceptable multipole errors, we have investigated the
scaling effect of relative multipole errors on the ILSF lattice. Figure 3.38 shows the
scaling effect of multiplying the multipole errors by a factor 1, 5, and 10 for on-
momentum particles. The resulting dynamic apertures are comparable with bare
reference dynamic aperture (without any multipole errors). Figure 3.39 and
Figure 3.40 show the scaling effect for ±3% off-momentum electrons. The effect on
the dynamic aperture for the reference case of the multipoles is minimal, even with a
10-fold increase in the value of the multipole components[3.14]. The maximum effect
of multipole errors occurs for factor of 10 and for on- and ±3% off-momentum
electrons.
Figure 3.37 Dynamic aperture in the presence of real multipole errors for on- and off-momentum electrons.
Figure 3.38 The effect of scaling multipole errors on the dynamic aperture of ILSF storage ring for on-energy electrons.
63
3.1.7 Lifetime
Another requirement for 3rd
generation light source is a long beam lifetime. The
lifetime is usually determined by the cross section of the different interaction
processes of the stored electron beam with the atoms and molecules within the
vacuum chamber, Eq. 3-7
Figure 3.39 The effect of scaling multipole errors on the dynamic aperture of ILSF storage ring for electrons with +3% energy deviation.
Figure 3.40 The effect of scaling multipole errors on the dynamic aperture of ILSF storage ring for electrons with -3% energy deviation.
64
..
1
cnτ (3-7)
where σ is the cross section of the interaction, n is the particle density in the vacuum
chamber and c is the speed of light. The loss processes which dominate the beam
lifetime in a storage ring are quantum excitation, intra-beam scattering (Touschek
effect), elastic and inelastic scattering against gas molecules at rest which are
respectively called Coulomb and bremsstrahlung scatterings. Each loss mechanisms
contributes to the total beam lifetime τ and the total lifetime is given by
(3-8)
where τq is the quantum lifetime, τT is the Touschek lifetime, τCo is the Coulomb
lifetime and τBr is the Bremsstrahlung lifetime. This section gives an evaluation of
lifetime in the ILSF storage ring.
3.1.7.1 RF system in ILSF storage ring
In a storage ring, an RF cavity must be employed to compensate the energy loss of
electrons due to radiation. As specified in Table 3.1, the natural energy loss per turn
due to the dipole radiation from ILSF is around 1 MeV. However, the total radiation
loss per turn (dipoles + IDs) would be between 1.3 MeV to 1.5 MeV. Since the length
of each pair of EU cavities (as the main part of RF system, see Table 7.4) for the
[3.15] [3.16] is almost 2 m, we have decided to distribute the RF system in the 3 short
straight sections.
The momentum acceptance of a storage ring is usually limited longitudinally by the
RF system and Touschek scattering increases in inverse proportion with the
momentum acceptance [3.17]. Thus, one needs to operate the accelerating cavity at an
optimum value of voltage to have a long beam lifetime as well as acceptable beam
parameters. Several values for the peak RF voltage have been investigated and as
shown in Figure 3.41 a 3.6 MV RF voltage yields a momentum acceptance of 3%
which is the desirable value for the ILSF storage ring.
Figure 3.41 Momentum acceptance as a function of total energy loss for various peak RF voltages.
65
3.1.7.2 Quantum lifetime
The electron beam lifetime due to the quantum character of synchrotron radiation is
given by
(3-9)
where τs is the longitudinal damping time and ξ is defined as
where is the momentum acceptance and is the energy spread. Longitudinal
damping time in the ILSF is 4.6 ms and the natural energy spread as given in
Table 3.1 is almost 0.1%. Thus for the momentum acceptance of 3%, ξ ≈ 450 and
using Eq. 3-9 one finds a quantum beam lifetime due to synchrotron radiation that is
very large and can be neglected in the evaluation of total beam lifetime.
3.1.7.3 Touschek lifetime
The figures of merit of the ILSF storage ring are a low natural emittance, high beam
current and a low beam cross section at the insertion devices (IDs). These make the
Touschek effect as the major factor responsible for particle loss. High bunch density
in low-emittance electron storage rings leads to a strong collisions between electrons
within the bunch. This scattering of charged particles in a stored beam causes an
exchange of energy between transverse and longitudinal motions and is referred to as
Touschek effect. By increasing the small transverse momentum as a result of
scattering, electrons scatter out of RF bucket or momentum acceptance and are lost. In
the ILSF storage ring, the circumference is 297.6 m and for 500 MHz RF frequency
with a filling factor of 0.8, number of bunches in the ring would be 400. On the other
hand, for a 400 mA beam current, each bunch has a current of 1 mA and in a bunch
with a length of several millimeters, the number of electrons would be roughly 1010
.
Such a high bunch density makes the Touschek lifetime the significant part of total
lifetime. The Touschek lifetime is not given by a simple formula but has to be
calculated as an integral over the ring circumference involving local beam parameters
and local energy acceptances, which can be either determined by the RF voltage or by
the lattice off-energy acceptance [3.17][3.18]. The Touschek lifetime can be
expressed as
(3-10)
where <σxσy>σl is proportional to the average bunch volume, γ is the relativistic factor
E/E0, re is the classical electron radius, Nb is the number of electrons per bunch and
D(ε) is the function
])2ln3(2
1ln
22
3[)( du
u
edue
u
ueD
uu
with ε defined as
66
2
22
1m
x
x
where εx is the horizontal emittance and <βx> is the average horizontal beta function.
For a beam current of 400 mA and RF filling factor of 0.8, the Touschek beam
lifetime is plotted versus momentum acceptance in Figure 3.42.
3.1.7.4 Gas scattering
Interaction between electrons of a bunch with residual gas molecules in the vacuum
chamber through elastic (Coulomb) and inelastic (bremsstrahung) scattering, can
cause deviation of electrons from limited closed orbit and result in beam loss [3.19].
The rate of loss due to these mechanisms obviously depends on the amount of residual
gas particles present in the beam pipe and is therefore proportional to the pressure.
The residual gas in the vacuum pipe will be a mixture of different compounds, and
this combination will be different depending on the commissioning of the storage
ring. Gas type, temperature, shape of vacuum chamber and ring acceptance are the
other factors which strongly affect the gas scattering.
Coulomb lifetime: The beam lifetime due to Coulomb elastic scattering for the
residual gas pressure P is given by [3.8], [3.19], and [3.20]
(3-11)
where re ( m) is the classical radius of electron, γ is the Lorentz
factor, NA is the Avogadro's number ( mol-1
), R is the ideal gas constant
(8.134 J.mol-1
.K-1
), c is the speed of light, T is the temperature, <β > is the average
beta function around the ring, εA is the ring acceptance, Zi is the average atomic
number, Ni is number of atoms per molecule and rpi represents partial fractions of the
different gasses composing the residual gas. The function F(R') is related to the shape
of the vacuum chamber and if we assume a chamber which is 3 times wider in the
Figure 3.42 Touschek lifetime vs. momentum acceptance.
67
horizontal plane compared to the vertical plane, meaning R'=1/3 as is the case for
ILSF vacuum chamber, the function 2π/F(R') would be very close to 2 giving
(3-12)
or
. (3-13)
The residual gas in vacuum chamber consists of H2, O2, N2 and a little ratio of organic
compounds. Because of high atomic number of N2 compared with others, it has the
strongest effects on lifetime. If we assume nitrogen gas, N2 (Z=7, N=2,rp=1) and
temperature of 300 K
then Eq. 3-13 can be rewritten as
(3-14)
or
(3-15)
In order to calculate the Coulomb lifetime at specific pressure we need to find out ring
acceptance,
2
A
g (3-16)
where g is the half gap width of the vacuum chamber and β is the beta function.
Rough profile of the half gap of the vacuum chamber in 1/8 of ILSF ring is shown in
Figure 3.43, see Table 3.12.
Table 3.12: Half aperture in the straight sections and magnets of ILSF ring.
gx (mm) gy (mm)
Long S.S. Injection 15 7.5
IDs 10 3.5
Medium S.S. 7.5 2.8
Short S.S. 10 7.5
Dipole 35 11.1
Quadrupole 35 12
Sextupole 35 12
68
Since the half gap width in horizontal direction is roughly 3 times that in the vertical
direction, the vertical acceptance would be dominant in Coulomb scattering. Thus the
Eq. 3-15 can be rewritten as
(3-17)
The minimum value of ring acceptance in ILSF ring is 1.55 mm.mrad at the end of the
long straight sections and the average value of vertical beta function is 7.42 m. So for
the 3 GeV ILSF ring Coulomb lifetime as a function of pressure would be
, (3-18)
the corresponding plot is shown in Figure 3.44.
Figure 3.43 Half of transverse gap width of the vacuum chamber in half a superperiod.
Figure 3.44 Coulomb lifetime vs. pressure.
69
This plot indicates that even at the pressure of 2.5 nTorr, the Coulomb lifetime is still
as much as 17 hours.
Bremsstrahlung lifetime: Inelastic scattering (bremsstrahlung) is rapid deceleration
and photon emission of the beam particles as a result of interaction with the residual
gas atoms. The lifetime due to bremsstrahlung scattering is given by
, (3-19)
where
)183ln(
)1440ln(3/1
3/2
i
i
z
z .
Bremsstrahlung lifetime in the ILSF storage ring as a function of pressure is shown in
Figure 3.45. Similar to the previous part, it has been assumed that the only residual
gas in the vacuum chamber is nitrogen gas.
3.1.7.5 Total lifetime
Obviously pressure affects only elastic scattering and bremsstrahlung lifetimes,
whereas the Touschek lifetime stays unchanged (Figure 3.46). The total lifetime as a
function of pressure is given in Figure 3.47.
Figure 3.45 Bremsstrahlung lifetime vs. pressure.
70
Figure 3.46 Lifetime in the ILSF storage ring vs. pressure within the pipe; momentum acceptance is 3.067% in this calculation.
Figure 3.47 Total lifetime in the ILSF storage ring vs. pressure within the pipe.
71
3.1.8 Injection into the ring
In order to inject the 3 GeV electron beam transferred from the booster into the
storage ring of the ILSF via BTS transfer line, we need kickers and a septum magnet
as the injection elements. The kicker magnet produces a bump to capture the beam
and the septum brings the injected beam into the vacuum chamber of the storage ring.
It is worthwhile to mention that all the bump and injection equipment will occupy a
7.88 m long straight section (LSS) of the ILSF storage ring for efficient and safe
injection.
To have a smooth orbit near to the septum magnet, we use four kicker magnets and
optimize them to observe successive bumps of the stored beam. These kickers are
named K1, K2, K3, K4 respectively and the septum magnet will be placed between
K2 and K3. Moreover, the phase-space coordinates of the beam at several watch-
points are monitored in our simulation to obtain the transverse phase space of the
bunched electrons. A schematic drawing of the kickers, septum and bumped orbit is
presented in Figure 3.48 with the relevant distances given in meters.
The stored beam receives a 5.2 mrad kick from the first kicker magnet and is bumped
10 mm in the 1.5 m drift space to K2. Locations of the stored, bumped and injected
beams in the vacuum chamber are shown schematically in Figure 3.49. The distances
between the injected beam, bumped beam and stored beam can be seen in Figure 3.49.
The width of septum is assumed to be 3 mm and the injected beam is at a distance of
1 mm from the septum.
The half-waveform of the kicker magnets is shown in Figure 3.50. As seen, the kicker
pulse is an 8 μs half sinusoidal [3.21] which is roughly 8 times longer than the
Figure 3.48 Layout of the injection system.
Figure 3.49 Injected, bumped and stored beams.
72
revolution time. Specifications of the kickers are given in Table 3.13. All the kickers
have a length of 85 cm and each one produces a 6.7 mrad kick.
Table 3.13: Specification of the kicker magnets.
Kicker magnets
Length (m) Angle (mrad)
K1 0.85 6.7
K2 0.85 -6.7
K3 0.85 -6.7
K4 0.85 6.7
The horizontal trajectory of bumped orbit due to the kicker magnets after 20 turns
tracking through the ILSF ring is shown in Figure 3.51.
In order to simulate the injection process, we tracked one bunch of electrons at a
distance of 19 mm from the reference orbit and observed what happened to the bunch.
The tracking results are shown in Figure 3.52.
Figure 3.50 Normalized half-waveform of the kicker magnets.
Figure 3.51 Horizontal trajectory of bunched centroid for 20 passes.
73
3.1.9 Specification of magnets
The general expansion for the magnetic field is
, (3-20)
or
, (3-21)
where and indicate the quadrupole field gradient and sextupole components
respectively. K and M are the strengths of quadrupole and sextupoles and are defined
as below
(3.22)
(3.23)
The field at the pole tip of the magnetic element can be calculated if one knows the
aperture radius using
(3.24)
where n is the order of the magnet and R is the aperture radius. For quadrupole and
sextupole magnets this reduces to
(3.25)
(3.26)
Figure 3.52 Horizontal phase space monitored at the injection point (colors indicate the number of turns).
74
3.1.9.1 Dipole magnets
The arrangement of dipole magnets in half a superperiod of ILSF-Lattice-1 is shown
in Fig. 3.53.
There are two dipole magnets at the beginning and at the end of one superperiod
called BE1 (part of the matching cells) and 6 dipole magnets placed between them
called BE2 (part of unit cells). The main parameters of dipole magnets are given in
Table 3.14. The only difference between these two types is in the defocusing
quadrupole component (quadrupole field gradient). The K parameter in BE1 and BE2
are -0.3835 and -0.5835 respectively.
Table 3.14: Main parameters of dipole magnets in ILSF Lattice 1.
Parameters Unit Value
Magnetic field T 1.42
Length m 1.38
Deflecting angle Deg. 11.25
Bending radius m 7.04
Half gap height mm ±16
Good field region (BE1/BE2) mm ±3.98/±4.89
Magnetic field gradient (BE1/BE2) T/m -3.837/-5.839
K (BE1/BE2) m-2
-0.383/-0.583
Totally 32 dipole magnets are used in the ring.
3.1.9.2 Quadrupole magnets
There are nine families of quadrupole magnets in ILSF ring. Locations of the
quadrupole magnets in half a superperiod are given in Fig. 3.54 and their main
parameters are given in Table 3.15.
Figure 3.54 Arrangement of magnets in half a superperiod of ILSF Lattice 1. The red arrows show the locations of quadrupole magnets
Figure 3.53 Arrangement of magnets in half a super-period of ILSF Lattice 1. The blue arrows show the locations of the dipole magnets.
75
Table 3.15: Main parameters of the quadrupole magnets in ILSF-Lattice-1 (aperture radius = 30 mm).
3.1.10.3 Sextupole magnets
In order to correct the natural chromaticity of the storage ring and also to perform
nonlinear optimization of the lattice, nine families of sextupole magnets are
employed. Locations of sextupole magnets in half a superperiod of the storage ring
are shown in Figure 3.55 and their main parameters are listed in Table 3.16. Totally
128 sextupoles will be in the ring.
Table 3.16: Main parameters of sextupole magnets in ILSF Lattice 1
(aperture radius =34 mm).
SEXT. Length (m) M (m-3
) B" (T/m2) Bpole (T)
Good field
region
(mm) SF1 0.15 19.685 196.991 0.113 ±17.78
SF2 0.22 53.055 530.919 0.310 ±9.98
SF3 0.15 30.341 303.623 0.176 ±11.75
SF4 0.22 53.532 535.694 0.301 ±13.07
SD1 0.15 -47.393 -474.258 -0.275 ±5.99
SD2 0.22 -37.652 -376.783 -0.218 ±7.67
SD3 0.22 -67.447 -674.946 -0.390 ±6.76
SD4 0.15 -52.521 -525.578 -0.304 ±7.53
SD5 0.22 -49.516 -495.510 -0.286 ±8.99
QUAD. Length (m) K (m-2
) Gradient
(T/m) Bpole (T) Good field
region (mm)
QF1 0.31 2.120 21.217 0.637 ±16.00
QF2 0.53 1.900 19.020 0.571 ±11.53
QF3 0.53 2.001 20.022 0.601 ±11.70
QF4 0.31 2.000 20.064 0.602 ±13.05
QF5 0.53 1.986 19.871 0.596 ±10.93
QD1 0.26 -1.404 -14.053 -0.422 ±8.69
QD2 0.26 -1.713 -17.141 -0.514 ±8.83
QD3 0.26 -2.111 -21.121 -0.634 ±9.72
QD4 0.26 -2.131 -21.321 -0.640 ±9.78
Figure 3.55 Arrangement of magnets in half a superperiod of ILSFLattice 1. The yellow arrows show the locations of sextupole magnets
76
3.2 Booster
The main task of the injectors in ILSF storage ring is to generate and accelerate the
electrons to the target energy of 3 GeV. The ILSF injector consists of four main
systems.
Linac
Transfer line from Linac to booster (LTB)
Booster synchrotron
Transfer line from booster to storage ring (BTS)
An electron beam produced with an electron gun, is accelerated by a traveling wave
linear accelerator (linac) to the energy of 150 MeV. Electrons then enter the booster
synchrotron via LTB. The booster accelerates the electron beam to 3 GeV using a
radio frequency (RF) cavity with a frequency of around 500 MHz. After reaching he
target energy, the electron beam is transferred from the booster to the storage ring
through an almost 40 m long BTS transport line. The specifications of the injectors to
the storage ring based on the ILSF Lattice 1 will be described below.
3.2.1 Lattice structure
The booster has four-fold symmetry and a diameter of 59 m. Each superperiod starts
and ends with two matching cells and there are 5 unit cells between them. The
circumference of the booster in this design is 192 m and the length of the straight
sections is 4.5 m. One superperiod of the booster is shown in Figure 3.56. The main
parameters of the booster are given in Table 3.17. The optical functions in one
superperiod of the lattice of booster are shown in Figure 3.57.
Figure 3.56 Matching and unit cells in one quadrant of the booster.
77
Table 3.17: Main parameters of the booster.
Parameter Unit Value
Energy at injection GeV
Energy at extraction GeV
Circumference m
Number of super-period -
Maximum current mA
Hor. Emittance nm.rad
Harmonic number -
Tune ( ) -
Natural energy spread -
Natural chromaticity -
Momentum compaction ( ) -
Radiation loss per turn MeV
Rep. rate Hz
Damping times ms
Revolution frequency MHz
The dispersion function in the straight section is nonzero and has a low negative value
of m. Optical functions at the center of the straight sections are listed in
Table 3.18 and the lattice structure of the booster with a circumference of 192 m is
given in Appendix 3.2. The working tune point within a tune diagram that includes
resonance lines up to the 5th
order is shown in Figure 3.58.
Table 3.18: Optical functions at the center of the straight sections.
Parameter Straight section
(m)
(m)
(m)
Figure 3.57 Optical functions in one quadrant of the booster.
78
Beam envelope in one quadrant of booster at the extraction energy of 3 GeV is shown
in Figure 3.59 and the beam size at the straight section is given in Table 3.19.
Table 3.19 Beam size at the center of the straight section (at extraction energy of 3 GeV) .
Parameter Unit Value
Figure 3.58 Tune diagram of the ILSF booster (the red circle represents the tune point).
Figure 3.59 Beam size in one quadrant of the booster at the extraction energy of 3 GeV.
79
3.2.2 Nonlinear beam dynamics
We have used just one type of combined dipole magnet without a quadrupole
component but with a sextupole component. Three combined quadrupole magnets
with sextupole components are also used to correct the natural chromaticity. Two
individual sextupoles are reserved for correction of eddy current effects during
ramping. Variation of lattice functions in the booster after chromaticity correction for
on-momentum electrons and electrons with energy deviation of ±3% is shown in
Figure 3.60. No big changes of optical functions are observed in one quadrant of
booster especially in the straight sections. Changes in booster main parameters up to
3% energy deviation are given in Table 3.20.
Table 3.20: Change of booster parameters for energy deviations up to 3%
Parameter Unit
Horizontal emittance nm.rad
Tune ( ) -
Natural energy spread -
Corr. chromaticity ( ) -
Momentum compaction -
Radiation loss per turn MeV
at Str. Sec. m
A smooth tune shift versus energy deviation keeps the working tune points of off–
momentum particles far from dangerous resonance lines. Transverse tune shift vs.
energy deviation up to 3% as shown in Figure 3.61 is very small. The corresponding
tune shift in the tune diagram containing resonance lines up to the 5th
order is shown
in Figure 3.62.
Figure 3.60 Machine functions in one quadrant of booster for electrons with ±3% energy deviation and on-momentum electrons.
80
For more reliable results, we have tracked the on-/off-momentum particles for many
turns in the booster (Figure. 3.63). For this purpose, an electron has been tracked 3000
turns through the booster. Dynamic aperture calculation for electrons with ±3%
energy deviation and on-momentum electrons after 3000 orbits is shown in
Figure 3.64. These graphs indicate that the dynamic aperture is large enough even for
off-momentum electrons.
Figure 3.61 Fraction of tune shift vs energy deviation.
Figure 3.62 Tune shift due to energy deviation up to 3%.
81
3.2.3 Magnets
3.2.3.1 Dipole magnets
For linear and nonlinear optimization, one type of combined dipole magnet with
sextupole component has been employed. A total of 48 dipole magnets are used in the
booster. Locations of the dipole magnets in one quadrant of booster are shown in
Figure 3.65 and their specifications are given in Table 3.21.
Figure 3.63 Phase-space tracking of on/off-momentum electrons at the center of the straight section.
Figure 3.64 Dynamic aperture at the center of straight sections in the booster.
82
Table 3.21: Main parameters of dipole magnets in the booster.
3.2.4.2 Quadrupole magnets
Six families of quadrupole magnets have been used in one quadrant of the booster.
Since the dipoles have no quadrupole components, we have used one quadrupole
magnet at the center of the unit cell (QD3). In addition to the sextupole components of
the dipoles, three combined quadrupoles with the same sextupole component have
been utilized to correct the chromaticity. Major parameters of quadrupoles at
extraction energy of 3 GeV are given in Table 3.22.
Table 3.22: Main parameters of quadrupole magnets in booster at 3 GeV.
QUAD. No. Type Length (m) Gradient (T/m) M (m-3
)
QD1 8 Quadrupole
QD2 8 Quadrupole
QD3 20 Quadrupole
QF1 8 Combined
QF2 8 Combined
QF3 40 Combined
Parameters Unit Value
Magnetic field at injection T
Magnetic field at extraction T
Length m
Deflecting angle Deg.
Bending radius m
Gap mm
Magnetic field gradient ( ) T/m
Quad. strength ( ) m-2
Sextupole component ( ) T/ m-2
Sextupole strength ( ) m-3
Figure 3.65 Arrangement of magnets in one superperiod (top), the matching cell (center), the unit cell (bottom) of the booster.
83
3.2.3.3 Sextupole magnets
Two separate families of sextupoles in the matching cells are reserved to correct and
compensate for eddy current effects. Their length is 0.15 m and we have denoted them
by SF and SD. The main parameters of the sextupoles are given in Table 3.23.
Table 3.23: Main parameters of booster’s quadrupole magnets at 3 GeV.
Sextupole No. Type Length M (m-3
)
SF 8 Sextupole 0.15 1.5466
SD 8 Sextupole 0.15 -19.186
3.2.4 Closed orbit
3.2.4.1 Closed orbit distortion
The distributed errors in the lattice of the booster are listed in Table 3.24 and the
distorted orbit due to these errors is shown in Figure 3.66. A relative field error of
0.001 is assumed in our calculations.
Table 3.24: Distributed errors in booster.
Error type Error value
Dipole
Quadrupole
Sextupole
3.2.4.2 Closed orbit correction
The orbit correction system of the booster synchrotron consists of 36 beam position
monitors (BPM), 36 horizontal correctors (HC) and 28 vertical correctors (VC). The
Figure 3.66 Closed orbit distortion: (left) horizontal, (right) vertical.
84
distribution and number of correctors have been chosen so as to provide good COD
correction with a reasonable value of corrector’s strength. The location of BPMs, HCs
and VCs along the phase advance of electrons in one supperperiod of the booster is
shown in Figure 3.67. The SVD method has been used for correction and the orbit
after correction is shown in Figure 3.68. We have summarized the results of closed
orbit correction in the ILSF booster in Table 3.25.
Figure 3.67 Position of horizontal and vertical correctors and BPMs in one superperiod of the booster.
Figure 3.68 Closed orbit of electrons after correction for the ILSF booster.
85
Table 3.25: Closed orbit correction results
After correction Before correction
Vertical horizontal vertical horizontal
MAX CO (mm)
AVG .rms Co (mm)
MAX cor Angle (mrad)
Avg.cor Angle (mrad)
3.2.5 Ramping effects
3.2.5.1 Ramping of energy and RF voltage
The repetition rate in the ILSF booster is 2 Hz which means that a bunch of electrons
after injection into booster with an energy of 150 MeV will be extracted from the
booster after 250 ms with an energy of 3 GeV. The RF system of booster must
provide adequate energy and power to compensate the energy loss due to synchrotron
radiation and to accelerate the electron beam to the target energy of 3 GeV. To have
0.7% energy acceptance at extraction point, the required RF voltage is 1.445 MV.
Since the synchrotron radiation at injection energy is very close to zero, the RF
voltage is just determined by the size of RF bucket and the energy acceptance of more
than 2% is required to capture the injected electrons from the linac. The energy
ramping of electrons behaves sinusoidally and is given by
(3.27)
where the f is repetition frequency and the coefficients α and E0 are given by the
initial and final energies
Ramping of energy and RF voltage in half the ramping time is shown in Figure 3.69
and Figure 3.70 respectively.
Figure 3.69 Ramp of energy in the ILSF booster during half of ramping time.
86
3.2.5.2 Time evolution of beam emittance
Beam parameters like emittance, energy spread and bunch length will change during
acceleration. The equilibrium emittance is defined as the n the balance between
radiation damping and quantum excitation:
time evolution of emittance due to radiation damping:
time evolution of emittance due to quantum excitation:
so
(3.28)
where Cq is m/(GeV)3. However, for the booster synchrotron we need
also to consider the adiabatic damping of beam emittance particularly for low
energies. Thus the time evolution of beam emittance during the energy ramping in
booster would be a superposition of adiabatic damping, synchrotron radiation
damping and quantum excitation. Adiabatic damping of emittance is given by [3.22]:
time evolution of emittance due to adiabatic damping:
(3.29)
Therefore time evolution of emittance in the booster is given by
2
52 )(212)(
)(
1
I
ItC
Jdt
td
tdt
dq
xxx
(3.30)
The radiation integrals in the ILSF booster are:
I1 =
I2 =
Figure 3.70 Ramp of RF voltage in the ILSF booster during half of ramping time.
87
I3 =
I4 =
I5 =
Using Eq. 3-30, the evolution of emittance during ramping time is shown in
Figure 3.71. It should be mentioned that emittance of the beam emerging from the
linac is assumed to be 80 nm.rad [3.23]. At the low energies, a huge reduction of
beam emittance is seen which is mostly due to adiabatic damping and at the high
energies the quantum excitation is dominant. As seen after half ramping time a final
emittance of roughly 32 nm.rad will be achieved.
3.2.5.3 Time evolution of energy spread
Another beam parameter which changes during ramping process is the energy spread.
Following the same steps as the derivation of time evolution of beam emittance in
consequence of adiabatic damping, radiation damping, and quantum excitation we
arrive at the following equation:
2
2
32
.
2
))(
)(
12(
2)(
dt
td
tI
I
JtC
dt
d
zzz
q
eq
(3.31)
where and are longitudinal damping partition number and damping time
respectively. Figure 3.72 shows the time evolution of energy spread in the ILSF
booster during the ramping.
It has been assumed that the energy spread coming from the linac at injection point is
0.4% [3.23]. As seen the equilibrium value of the energy spread is 0.08% which is in
agreement with result of OPA code for ILSF booster.
Figure 3.71 Time evolution of the beam emittance during ramping in the booster.
88
3.2.6 Eddy current effects
Time-varying fields in booster dipole magnets induce eddy currents in the vacuum
chambers which in turn induce multipole components in the dipole vacuum chambers.
The most important multipole produced by eddy current is the sextupole component
which changes the natural chromaticity of the booster. We will neglect the
quadrupoles and high order multipoles created by eddy currents in dipole’s vacuum
chamber. Another major effect of the eddy currents is the vacuum chamber wall
heating. However because of low repetition rate and small size of the booster vacuum
chamber the dissipated power will be negligible.
In this section, we estimate the strength of induced sextupole components in the
dipole vacuum chambers and its effect on the natural chromaticity of the booster. By
resorting to two individual sextupoles which have been reserved for chromaticity
correction during the lattice design, the induced chromaticity will be compensated.
Calculations have been done for the repetition rate of 2Hz.
3.2.6.1 Induced sextupole component in dipoles vacuum chamber
For a sinusoidal ramp of the dipole magnetic field, we have
(3.32)
where
,
and is the booster repetition rate. From Faraday’s law this time-varying field
generates longitudinal electric fields along the vacuum chamber inside the bending
magnets. The induced electric field will set up eddy currents in the vacuum chamber
Figure 3.72 Time evolution of energy spread during ramping process.
89
walls. The general equation which describes the induced sextupole field by eddy
currents is given by [3.24]
(3.33)
where
is the vacuum permeability
is the stainless steel vacuum chamber conductivity
is the vacuum chamber half-width
is the vacuum chamber half-height
is the bending magnet radius
is the vacuum chamber thickness
and,
is a function of vacuum chamber
ellipticity.
After substituting for using Eq. (3.49), from Eq. (3.61) we get
(3.34)
For ILSF booster: , , and
. During the
ramping process a time-varying sextupole component will be induced in the vacuum
chamber. Figure 3.73 shows the variation of the sextupole component induced by
eddy currents in the vacuum chamber wall. As once can see the maximum sextupole
component generated by eddy currents occurs after 0.04 seconds. At this instant, the
energy of electrons is 325 MeV.
In the ILSF booster, the embedded sextupole components in bending and focusing
quadrupole magnets have been used for correcting the natural chromaticity and
optimizing the dynamic. However, the induced sextupole components will change the
sextupole strength which in turn will change the chromaticity during the ramping
process. By using two separate families of focusing and defocusing sextupoles we
will fix the chromaticity during ramping.
Dynamic aperture optimization and natural chromaticity correction in the presence of
eddy currents have been done for two scenarios where in the first the chromaticity
during ramping is fixed at , and in the second the chromaticity of r
is fixed at In the next two sections, we shall investigate the details
of the nonlinear behavior of electrons for these two scenarios.
90
3.2.6.2 Nonlinear optimization with chromaticity fixed at
Figure 3.74 shows the variation of natural chromaticity of booster during ramping.
As can be seen, the chromaticity in direction is positive during ramping process.
This means we do not need a strong focusing sextupole to push the chromaticity to a
small positive value. On the other hand, the chromaticity in direction, as expected;
suddenly decreases to negative values at the beginning of ramp. Therefore, to
compensate the negative chromaticity in direction we need a strong defocusing
sextupole. By using Beta and OPA codes, we evaluated the required strength of
sextupoles to compensate the induced chromaticity in and directions. Figure 3.75
shows the strengths of SF and SD sextupoles during ramping. As seen, the strength of
Figure 3.73 Variation of integrated sextupole strength induced by eddy currents during ramping.
Figure 3.74 Variation of chromaticity during ramping .
91
focusing quadrupole remains relatively constant during ramping process. The
integrated strength of SF during ramping peaks at 0.232 T/m2 for
E = 325 MeV. Consequently it does not affect the dynamic aperture significantly. On
the other hand, the strength of defocusing sextupole SD changes dramatically during
the ramping time. When the energy of electrons reaches 325 MeV, the required
integrated strength of SD for pushing the chromaticity to +1 in y direction is
-2.878 T/m2. A large reduction of dynamic aperture in direction can be expected.
The dynamic aperture of on-energy particles with and without eddy currents present is
depicted in Figure 3.76. The dynamic aperture tracking has been done for the worst
case namely when the energy of electrons is 325 MeV. As seen, eddy currents lead to
dynamic aperture shrinkage but the dynamical aperture is still adequately larger than
the physical aperture.
Figure 3.75 Strength of SF and SD during the ramping process .
Figure 3.76 Dynamic aperture of booster with and without eddy currents present with .
92
3.2.7 Lattice alternative for the booster
Based on the previous design and as a new alternative for the booster magnets, in
addition to the sextupole component, we add quadrupole components to all the
dipoles and remove the defocusing quadrupoles in the unit cells. Instead of the
defocusing quadrupoles in the unit cells, focusing quadrupoles with sextupole
components are used which helps nonlinear optimization. The booster in the new
design has the same circumference of 192 m. One quadrant of the booster is shown in
Figure 3.77 and the optical functions are plotted in Figure 3.78.
The main parameters of the booster are given in Table 3.26.
Several tune points have been investigated for the new alternative and the best one is
given in Figure 3.79 along with resonance lines up to the 5th
order.
Figure 3.77 One quadrant of the alternative design of the booster.
Figure 3.78 Optical functions in one superperiod of booster.
93
Table 3.26: Main parameters of the booster (new alternative).
Parameter Unit Value
Energy GeV
Circumference m
Number of super-period -
Maximum current mA
Hor. Emittance nm.rad
Harmonic number -
Tune ( ) -
Natural energy spread -
Natural chromaticity -
Momentum compaction ( ) -
Radiation loss per turn MeV
Rep. rate Hz
Damping times ms
Revolution frequency MHz
3.2.7.1 Nonlinear beam dynamics
In order to study energy deviation effects in the new design, we correct the natural
chromaticity, bringing it close to zero, and investigate the tune shift, phase space, and
dynamic aperture. Tune shift due to energy, shown in Figure 3.80, indicates a very
promising behavior and smooth variation up to 3% energy deviation. The
corresponding tune diagram is shown in Figure 3.81.
Figure 3.79 Tune point of the alternative design for booster lattice.
94
To observe the stable boundary of particles, results of 3000-turn phase-space tracking
of on-momentum electrons have been plotted in Figure 3.82. Dynamic aperture as a
result of nonlinear optimization of sextupole components in focusing quadrupoles and
dipoles (Figure 3.83) shows a very large stable area for the electrons.
Figure 3.80 Tune shift due to energy deviation.
Figure 3.81 Shift of tune point in the tune diagram; resonance lines up to 5th order are also shown in the diagram.
Figure 3.82 Phase space of on-energy particles.
95
3.2.7.2 Magnets
Arrangement of magnets in a superperiod is shown in Figure 3.84. As can be seen the
booster is composed of 36 dipole magnets and 88 quadrupole magnets. Their main
parameters and specifications are given in Table 3.27 and Table 3.28.
Table 3.27: Main parameters of the dipole magnets (alternative design).
Parameters Unit BE
Magnetic field at injection T 0.058
Magnetic field at extraction T 1.165
Length m 1.5
Deflecting angle Deg. 10
Bending radius m 8.594
Magnetic field gradient ( ) T/m -4.372
Quadrupole strength ( ) m-2
-0.437
Sextupole strength ( ) m-3
-3.672
Figure 3.83 Dynamic aperture for the alternative design of the booster.
Figure 3.84 Arrangement of magnets in one superperiod (top), the matching cell (center), the unit cell of the booster (bottom).
96
Table 3.28: Main parameters of quadrupole magnets 3 GeV (alternative design).
QUAD. No. Type Length (m) Gradient (T/m) M (m-3
)
Q12 8 Quadrupole 0.25 -1.333 0.000
Q21 8 Combined 0.25 1.328 3.928
Q11 8 Combined 0.50 1.340 3.928
Q22 8 Combined 0.25 1.178 3.928
Q31 56 Combined 0.25 1.364 3.932
3.3 Transfer lines
There are two transfer lines within the ILSF accelerator complex. The first transfer
line (T-line) links the linac to booster (LTB) transferring the electron beam from the
pre-injector system to the booster. The second line connects the booster to the storage
ring (BTS).
3.3.1 LTB transfer line
The LTB transfer line guides the beam from 150-MeV linac to the booster
synchrotron. The LTB transfer line provides for matching of beam parameters from
the exit of the linac to the booster synchrotron injection septum. Based on the first
layout for the storage ring and booster in which the booster is turned by 36 degrees
relative to the storage ring and for horizontal injection scheme, the LTB does not have
vertical bending magnets. In this design it is assumed that the linac is located inside
the service area. In this case the best configuration is having the linac parallel to a
long straight section of the storage ring. Figure 3.85 shows the linac, LTB, and
booster surrounded by the shielding walls and indicates the useful space in the service
area. Figure 3.86 is the mechanical drawing of LTB.
Five dipole magnets are employed to guide the beam to a straight section of the
booster. One of them will be used to guide the electron beam into the diagnostic line.
The other four dipoles are used to guide the beam into the booster. Three of them
bend the beam positively and the last one gives a negative deflection to the electrons.
Figure 3.85 LTB transfer line within the service area surrounded by the shielding walls.
97
In addition, a septum magnet with a negative deflection of 12 degrees has been used
to inject the beam into the booster. To meet the matching conditions, several
quadrupole magnets have been employed between the dipole magnets in the LTB.
Matching of optical functions was performed in six-dimensional phase space. Thus
strengths of the quadrupoles and dipoles in LTB have been optimized to match the
optical function at the end of the LTB to booster. Table 3.29 gives the optical
functions assumed for the linac. Fig 3.87 is a plot of the optical functions for the case
of no alpha and 5 m beta function. Specifications of the LTB magnets are given in
Appendix 3.3.
Figure 3.87 Optical functions in LTB.
Figure 3.86 Mechanical drawing of LTB.
98
Table 3.29: Optical functions after linac.
βx/βy (m) 5/5 7/7 10/10 10/10 7/7 10/10 15/15
αx/αy 0/0 0/0 0/0 1/1 -1/-1 -1/-1 0/0
ηx (m) 0 0 0 0 0 0 0
η'x (m) 0 0 0 0 0 0 0
3.3.2 BTS transfer line
As mentioned before, booster and storage ring have the same center in x-y coordinates
but the booster is turned by 36 degrees relative to the storage ring. In order to extract
the electron beam from the booster, an extraction kicker magnet with a kick strength
of 8.73 mrad is used. The extracted beam is then bent with a septum with a negative
angle of 23.5 degrees. So for the injection of the electrons into the ring an injection
septum with a positive deflection of 24 degrees is employed. To bring about the
remaining 36 degrees of deflection between the booster and the storage ring 4 dipole
magnets with deflection angles of 18 degrees and lengths of 1.5 m will be used. One
of them causes a negative deflection after the extraction septum and the remaining
three dipoles deflect the beam positively prior to the injection septum. In addition to
the dipoles several quadrupoles have to be used to match the machine functions of the
booster to those of the storage ring. The mechanical drawing of the BTS is shown in
Figure 3.88. Each quadrupole has length of 0.36 m and the total length of the BTS
line will be 31.965 m.
Figure 3.88 Mechanical drawing of the BTS line.
99
There are two matching points in the BTS. The first point is the extraction point from
booster to the ring after the kicker magnet (matching point I) and the second is at the
injection point into the storage ring (matching point II). The matching values of the
optical functions at each of these points are given in Table 3.30. The optimized optics
through the BTS line is shown in Figure 3.89 and the main parameters of the dipoles
and quadrupole magnets used for the BTS line are given in Appendix 3.4.
Table 3.30: Optical functions at two matching points.
At extraction: matching point I
At injection matching point II
βx/βy (m) 11.960/2.935 14.003/4.208
αx/αy -0.107/-0.576 -0.013/-0.043
ηx (m) -0.084 0.247
η'x (m) 0.0 0.0
Figure 3.89 Optical functions in the BTS transfer line.
100
References
[3.1] [email protected], http://slsbd.psi.ch/_streun/opa/opa.html.
[3.2] M. Borland, elegant: A flexible sdds-compliant code for accelerator
simulation, Argon National Laboratory Advanced Photon Source Report, No.
LS-287 (2000).
[3.3] http://mad.home.cern.ch/mad/.
[3.4] L. Farvacque, T.F. Guenzel, J.L. Laclare, ESRF, Grenoble, third edition, July
2001.
[3.5] M. Borland, “A self-describing file protocol for simulation, integration, and
shared post-processors”, Proceedings of the Particle Accelerator Conference
(PAC, Dallas, Texas, 1995) p. 2184.
[3.6] D. Einfeld, E. Levichev, P. Piminov, Influence of Insertion Devices on the
ALBA Dynamic Aperture, EPAC08, p2279.
[3.7] P. Elleaume, D. Einfeld, State of the Art Insertion Device, Tehran, 10th
December (2010).
[3.8] H. Wiedemann, Particle Accelerator Physics, Springer, New York, 2007.
[3.9] L. Smith, Effect of Wigglers and Undulators on Beam Dynamics, LBL-ESG-
24,1986.
[3.10] Candle light source conceptual design report.
[3.11] M. H. Wang, S. Y. Lee, “Quadrupole-bend achromatic low emittance lattice
studies”, Review of scientific instruments, Vol.78, (2007) 055109.
[3.12] D. Einfeld, “Higher multipoles in quadrupoles and sextupoles”, NSLS-II
ASAC Meeting, 2008.
[3.13] Z. Martí, M. Muñoz, D. Einfeld, “Simulated influence of the measured
multipoles on the ALBA lattice”, Nonlinear Beam Dynamic Workshop II.
[3.14] Z. Martí, M. Muñoz, D. Einfeld, G. Beneditti, “Predicted effect of the
measured high-order magnetic multipoles in the ALBA storage ring”, IPAC
2010, Kyoto, Japan.
[3.15] F. Marhauser, E.Weihreter, “First Tests of a HOM Damped High Power 500
MHz Cavity”, Proceedings of the European Particle Accelerator Conference,
Lucerne, Switzerland, EPAC (2004).
[3.16] E.Weihreter, IPM, Tehran, Iran (2009).
[3.17] H. S. Kang, J. Y. Huang, S. H. Nam, “Measurment of Touschek lifetime in
PLS storage ring”, Proceedings of the Second Asian Particle Accelerator
Conference, Beijing, China, APAC (2001) 314.
[3.18] W. T. Liu, H. P. Chang, H. C. Chao, P. J. Chou, C. C. Kuo, G. H. Luo, H. J.
Tsa, M. H. Wang, Proceedings of the Particle Accelerator Conference June
25–29, 2007, Albuquerque, New Mexico, U.S.A., PAC (2007) 1094.
[3.19] A. Streun, Beam Lifetime in the SLS Storage Ring, SLS-TME-TA-2001-0191,
(2001).
[3.20] Spring-8 Project, Part I, Facility Design, February 1991.
[3.21] Private communication with the Power Supplies team.
[3.22] Andy Wolski, “Low-emittance machines”, CAS, Daresbury, UK, September
2007.
[3.23] Private communication with the RF team.
[3.24] F. Lazzourene, “Updated lattice for the ELETTRA Booster synchrotron”,
ST/M-00/2 April 2001.
101
Appendix 3.1: ILSF Lattice 1
Name Length (m) Def. angle (Deg.) K (m-2
) M (m-3
)
Drift
D11 0.2
D12 0.43
D13 0.26
D21 0.37
D22 0.175
D23 0.165
D31 0.175
D 41 0.54
L-L 3.9403
L-M 2
L-S 1.41334
Dipole BE1 1.383684 11.25 -0.383500
BE2 1.383684 11.25 -0.583500
Quadrupole
QF1 0.31 2.120220
QF2 0.53 1.900630
QF3 0.53 2.000750
QF4 0.31 2.004980
QF5 0.53 1.985710
QD1 0.26 -1.404340
QD2 0.26 -1.712880
QD3 0.26 -2.110620
QD4 0.26 -2.130580
Sextupole
SF1 0.15 19.685333334
SF2 0.22 53.05472728
SF3 0.15 32.62196
SF4 0.22 53.5319091
SD1 0.15 -47.3926
SD2 0.22 -37.65192728
SD3 0.22 -67.44731818
SD4 0.15 -52.52102666
SD5 0.22 -49.51634546
Lattice
Block1 L-L, SF1, D11, QF1, D12, QD1, D13, SD1, D14
Block2 D21, SD2, D22, QF2, D23, SF2, D24, QD2,L-M
Block3 L-M, QD3, D31, SF2, D32, QF3, D33, SD3, D34
Block4 D41, SD4, D42, QF4, D43, SF3,L-S
Block5 D21, SD5, D22, QF5, D23, SF4, D24, QD4,L-M
Oct Block1, BE1, Block2, Block3, BE2, Block4, -Block4, BE2, Block5, -Block5,
BE2, Block4 Quad Oct, -Oct
Ring 4*Quad
102
Appendix 3.2: ILSF booster lattice
Name Length (m) Defl. angle (Deg.) K (m-2
) M (m-3
)
Drift
D11 2.25
D12 0.275
D13 0.2
D21 0.2
D22 0.15
D23 0.9552
D24 0.15
D25 0.25
D31 1.5
D32 0.2
Dipole BE 1.1908 7.5 0.0 -1.602346
Quadrupole
QF1 0.5 1.3887 3.224
QF2 0.25 1.49265 3.224
QF3 0.25 1.1915 3.227412
QD1 0.5 -1.1989 0.0
QD2 0.5 -0.456585 0.0
QD3 0.25 -1.3478 0.0
Sextupole SF 0.15 0.0
SD 0.15 0.0
Lattice
Block1 D11, QF1, D12, QD1, D13
Block2 D21, QD2, D22, SD, D23, SF, D24, QF2, D25
Block3 QF3, D31, BE, D32, QD3, D32, BE, D31, QF3
Match Block1, BE, Block2
Super Match, 5*Block3,Match
Ring 4*Super
103
Appendix 3.3: ILSF LTB lattice
Length (m) Def. angle (Deg.) Strength (m-2
)
Drift 2
Quadrupole 0.12 -6.08989
Drift 0.52
Quadrupole 0.12 3.78916
Drift 1.195
Dipole 0.3334 37.4
Drift 0.3
Quadrupole 0.12 10.24909
Drift 0.2
Quadrupole 0.12 -10.30140
Drift 3.5095
Quadrupole 0.12 4.90722
Drift 0.62
Dipole 0.3761 37.4
Drift 3.5
Quadrupole 0.12 -4.96685
Drift 0.2
Quadrupole 0.12 -10.0541
Drift 0.2
Quadrupole 0.12 14.49414
Drift 3.5
Dipole 0.1422 -9
Drift 0.3
Quadrupole 0.12 8.81684
Drift 0.59
Quadrupole 0.12 -7.84672
Drift 4.74
Dipole 0.6112 -12
104
Appendix 3.4: ILSF BTS lattice
Length (m) Def. angle (Deg.) Strength (m-2
)
Kicker -0.5
Drift 0.8
Septum 1.9528 -23.5
Drift 1
Quadrupole 0.36 1.66237
Drift 0.40
Quadrupole 0.36 -2.02266
Drift 0.40
Dipole 1.5 -18
Drift 0.6
Quadrupole 0.36 0.69141
Drift 5.2616
Quadrupole 0.36 2.14086
Drift 0.40
Quadrupole 0.36 -1.87196
Drift 2.401
Dipole 1.5 18
Drift 0.40
Quadrupole 0.36 1.60131
Drift 0.40
Dipole 1.5 18
Drift 0.40
Quadrupole 0.36 -0.83685
Drift 0.40
Dipole 1.5 18
Drift 1.07
Quadrupole 0.3 0.71851
Drift 5.2
Dipole 2 24
105
CHAPTER 4: Magnets
4.1 Storage ring lattice magnets
The 3 GeV storage ring, based on ILSF Lattice 1, consists of 32 combined bending
magnets of 2 types, 104 quadrupoles in 9 families and 128 sextupoles in 9 families.
The dipoles and each family of sextupoles are planned to be run in series with a
common power supply while the quadrupoles are individually powered.
4.1.1 Principal specifications of lattice magnets
The storage ring magnets are to be designed so that the bending magnets provide the
guiding field, quadrupoles provided the necessary focusing/defocusing, and
sextupoles correct chromaticity aberrations. Moreover, one can use combined
magnets which result in a more compact lattice. For example combined bending
magnets that are used in ILSF lattice can bend the beam as well as perform vertical
defocusing.
The magnets within a half superperiod of ILSF (Iranian Light Source Facility) lattice
are shown in Figure 4.1; the specifications of the magnets are given in Table 4.1 ,
Table 4.2, Table 4.3
It should be pointed out that magnet parameters are based on the following equations:
(4.1)
(4.2)
where K is the strength of the quadrupole, M is strength of the sextupole, B is the
field gradient and B denotes the sextupole component. The last two parameters are
the coefficients defined in the following expansion:
(4.3)
Figure 4.43 Arrangement of the magnets in half a superperiod of ILSF storage ring
106
4.1.1.1 Bending magnets
The specifications of bending magnets 1 and 2 are given in the following table.
The general layout of both types of bending magnets is the same, and only the
pole profile is changing because of the different required gradients.
Table 4.1: ILSF dipole parameters
Field
quality
in GFR
Magnetic
length
(m)
Total
gap
(mm)
Field
gradient
(T/m)
Field
(T)
Deflecting
angle
Bending
radius
(m)
QTY Magnet
type
1.384 32 -3.837 1.42 11.25 7.047 8 BE 1
1.384 32 -5.839 1.42 11.25 7.047 24 BE 2
In order to have the desired quadrupole component with the desired field uniformity,
the following equation was used [4.1]:
(4.4)
4.1.1.2 Quadrupole magnets
The specifications of all quadrupoles are given in the Table 4.2. The general
layout of the quadrupoles as well as the pole profile will be the same, but the
lengths will be different.
Using the following equation, for the area around the midplane,
(4.5)
pole profile coordinates can be obtained.
Table 4.2: ILSF quadrupole parameters
4.1.1.3 Sextupole magnets
The specifications of all sextupoles are given in Table 4.3. The general layout of
the sextupoles as well as the pole profile will be the same, but the lengths will be
different.
Magnetic
Length (m)
Sextupole component (Tesla/m
2)
Aperture radius (mm)
Maximum Gradient field
(Tesla/m)
Total QTY
No. of families
Quadrupole family
0.31 0 30 21.20 32 2 Qx-310
0.26 0 30 21.31 40 4 Qx-260
0.53 0 30 20.01 32 3 Qx-530
107
Table 4.3: ILSF sextupole parameters
Magnetic
Length (m)
Maximum Sextupole
component (T/m
2)
Aperture radius (mm)
QTY No. of
families Sextupole
family
0.15 513.8 34 40 3 Sx-150
0.22 630.0 34 88 6 Sx-220
The pole profile in the area around the midplane can be calculated using the following
formula.
(4.6)
This chapter presents the designs developed for the dipole, quadrupole and sextupole
magnets required for the ILSF (Iranian Light Source Facility) storage ring lattice.
4.1.2 Dipole magnets
4.1.2.1 Dipole design parameters
It was decided to use a C-type parallel-ends combined bending magnet that can be
opened in half. This permits easier installation and servicing of the vacuum chamber.
The main parameters of the bending magnets are given in Table 4.1.
Using combined magnets in lattice leads to more compact and cost-effective designs.
In combined dipole magnets, field uniformity is the most important item; the required
accuracy for field uniformity is over the specified good-
field region.
4.1.2.2 Pole and yoke geometry
Using the two-dimensional, non-linear, finite-element magneto-static code Poisson, a
pole and yoke geometry was developed for the dipole which met the operational
requirements for the magnet. The pole face has a broad low shim at the pole edge, to
maintain the field homogeneity over the full horizontal aperture. Outside the shims,
the pole is followed by a linear taper to the pole root. The dipole will be curved, to
follow the path of the circulating beam, so it is not necessary to increase the radial
aperture of the magnet to accommodate the beam sagitta. This choice also lowers the
weight and therefore the cost of the magnet. Calculations are done according to the
main parameters brought in Table 4.4 for BE.1 and . Results for the BE.1
bending magnet are presented in this report:
108
Table 4.4 Bending magnet main parameters
Parameter Unit ILSF BE 1 ILSF BE 2
Field Tesla 1.42 1.42
Deflecting angle Deg. 11.25 11.2
Gradient Tesla/m -3.837 -5.839
Gap mm 32 32
Horizontal good-field region mm ±10 ±10
The pole was designed to have a field uniformity of 10-4
within a ±10 mm horizontal
good-field region using Eq.4.4 But the profile given by Eq 4.4 is only correct if the
pole profile extended to infinity. Because the pole width is finite, magnet codes
(Poisson, etc.) have to be used for correct calculation of the pole profile. Also using
shims is the way to reach the desired field quality within the good-field region and
reduce the residual higher-order field components. These shims are added to the pole
ends and should be designed using an iterative process [4.1], [4.2], [4.4]. Table 4.5
shows the coordinates of the optimized pole profile:
Table 4.5: Dipole pole profile coordinates
NO. (mm) (mm) NO. (mm) (mm) NO. (mm) (mm)
1 54.000 60.00 24 10.000 16.444 47 -13.000 15.457 2 50.174 21.770 25 9.000 16.399 48 -14.000 15.417 3 49.770 20.670 26 8.000 16.354 49 -15.000 15.377 4 49.229 19.620 27 7.000 16.308 50 -16.000 15.337 5 48.200 18.840 28 6.000 16.264 51 -17.000 15.297 6 46.800 18.340 29 5.000 16.219 52 -18.000 15.258 7 42.985 18.040 30 4.000 16.175 53 -19.000 15.219 8 41.790 17.940 31 3.000 16.131 54 -20.000 15.180 9 40.559 17.878 32 2.000 16.087 55 -21.000 15.134 10 30.376 17.360 33 1.000 16.043 56 -22.000 15.095 11 24.029 17.143 34 0.000 16.000 57 -25.000 14.978 12 22.863 17.100 35 -1.000 15.957 58 -27.000 14.902 13 22.053 17.060 36 -2.000 15.914 59 -28.000 14.864 14 20.000 16.914 37 -3.000 15.871 60 -29.000 14.827 15 19.000 16.866 38 -4.000 15.829 61 -30.400 14.300 16 18.000 16.818 39 -5.000 15.787 62 -33.00 13.600 17 17.000 16.770 40 -6.000 15.745 63 -35.000 13.600 18 16.000 16.723 41 -7.000 15.703 64 -36.600 14.065 19 15.000 16.676 42 -8.000 15.661 65 -37.944 14.733 20 14.000 16.629 43 -9.000 15.620 66 -39.428 15.948 21 13.000 16.582 44 -10.000 15.579 67 -41.313 17.7222 22 12.000 16.536 45 -11.000 15.538 68 -51.733 29.740 23 11.000 16.490 46 -12.000 15.498 69
109
Moreover the calculated pole profiles of ILSF bending magnets, and are
compared and sketched in the Figure 4.3.
As shown in the Figure 4.3 above, the applied shims to the ILSF pole profiles have
almost the same shapes. The difference in pole profiles is due to different gap heights
and gradients. Using steel type , the averaged quantity of the magnetic
field in different parts of the magnet and also magnet dimensions are demonstrated
below. Magnetic properties of the type of steel used in the simulation are given in
Table 4.16, Section 4.1.5.
Figure 4.2 The pole profile calculated for ILSF bending magnet compared with theory.
Figure 4.3 Shape of the ILSF bending magnets’ pole profile.
110
The gap of the magnet was determined after discussion with the vacuum group to
ensure that it will accommodate the vacuum chamber.
The results for field and field gradient obtained using "Poisson" are also shown in
Figure 4.6 and Figure 4.7:
Figure 4.4 Simulated fields in one half of a dipole magnet: The field lines were calculated using "Poisson", the field values have been specified at some points.
Figure 4.5 Dipole dimensions for ILSF dipole: (a) General dimensions for both BE1 and BE2 (b) BE1 pole profile (c) BE2 pole profile
111
4.1.2.3 Field Quality
Field uniformity is defined as
(4.7)
where is the field gradient at Field uniformity is shown for the good field
region (extending from to ) in Figure 4.8.
(m) (T) (T) (T/m)
-0.010 -1.3813 -1.4200 -3.837 1.9 × 10-4
0.010 -1.4582 -1.4200 -3.837 1.0 × 10-4
Figure 4.6 Vertical dipole field versus horizontal coordinate (x).
Figure 4.7 Vertical field gradient ( ) versus horizontal coordinate
( )
112
4.1.2.4 Harmonic analysis
Higher multipole components due to finite pole profile or saturation of iron in pole
tips affect the dynamic aperture. The multipole coefficients are defined by the
following equation:
(4.8)
A combined dipole magnet ideally should only have dipole and quadrupole field
components so we have: . In this formula x is the horizontal and y is the
vertical direction. Table 4.6 shows the field coefficients at a normalization radius of
in CGS units obtained from the Poisson code.
Table 4.6: The multipole coefficients of ILSF dipole magnet’s field
n type Bn (15mm)
(Tesla) |Bn/B0| (15mm) bn
(T/mn-1
)
1 B
2 Q
3 B
5 B
6 Q
7 B
9 B
10 Q
11 B
13 B
14 Q
Figure 4.9 Field tolerance versus x (boundaries of the good field region are shown in red).
-0.025
-0.02
-0.015
-0.01
-0.005
0
-40 -30 -20 -10 0 10 20 30 40
DB
/B0
X[mm]
113
4.1.2.5 Three-dimensional magnetic simulations
The 3D magnetic simulations have been carried out with RADIA using a straight-
magnet model, see Figure 4.10. The magnetic length of the bending magnet is
1384mm. The chamfers of the magnet’s ends have been made to achieve the “same”
effective magnetic length along the transverse position of the electron beam, i.e.
within ±10mm at the nominal excitation of the magnet (3 GeV beam energy).
The optimized end chamfer for the nominal excitation level of the magnet makes a
45-degree angle with the zy-plane and a 6.8-degree angle with the zx-plane
(see Figure 4.11).
Figure 4.11 Absolute normalized multipoles' errors at the 15 mm good field region. Dipolar and quadrupolar components (n =1, 2) are not shown.
Figure 4.10 1384 mm straight-magnet model of the ILSF bending magnet.
114
The vertical component of the field in the longitudinal direction is shown in
Figure 4.12. The designed 3D chamfer is a primary design and optimization of the
field is still in progress.
4.1.2.6 Electrical and cooling parameters
Storage ring dipoles are designed so that bending magnets are connected in series
with a single power supply. Minor differences between the bending angles shall be
corrected by independently powered trim coils located on each dipole [4.1]. The coil
specifications for both ILSF dipoles as well as electrical and cooling parameters, are
compiled in Table 4.7.
The chosen current density in the copper conductor represents a rough compromise
between lifetime operational costs of the facility, and the initial capital costs. The
optimization curve is generally at its minimum between and . Based on
this optimization, the current density is taken to be [4.2] [4.4].
The coil geometry is shown in Figure 4.13
Figure 4.11 Shape (left) and dimensions (right) of the end chamfer for the dipole magnet.
Figure 4.12 Central vertical field component versus longitudinal direction Z.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
-1200 -900 -600 -300 0 300 600 900 1200
By
[T]
Longitudinal position Z [mm]
115
Table 4.7: Electrical and cooling parameters for ILSF’s dipole magnets
Parameter Unit BE1 BE2
Magnetic length m 1.384 1.384
Total amp-turns per coil At 18445.00 18450.00
Operating current A 461.12 461.25
Number of turns per coil - 40 40
Number of pancakes per coil - 4 (each has 2 layers) 4 (each has 2 layers)
Turns per pancake - 10 10
Conductor dimensions mm2 14.3 x 11.4 14.3 x 11.4
Water cooling tube diameter mm 6 6
Copper area mm2 134.75 134.75
Current density in copper A/mm2 3.42 3.42
Voltage drop V 19.27 19.27
Resistance m 42 42
Power KW 8.89 8.89
Number of water circuits - 4 (each coil has 2) 4 (each coil has 2)
Water temperature rise C 8.80° 8.80°
Cooling water speed m/s 4.27 4.27
Pressure drop Bar 8.86 8.87
Reynolds number. - 6398 6401.5
Electrical calculations were based on four pancakes with two layers and ten turns
each. In order to have the optimum current density, conductor dimensions have been
chosen to be with a cooling hole of 6 mm, resulting in two cooling
Figure 4.13 Coil cross section for bending magnets.
116
circuits with an water temperature rise. The total pressure drop required to
provide the necessary flow is expected to be roughly equal to bars.
Since for active cooling, turbulent flow within the cooling channels is required, taking
proper values for “Reynolds number” and the critical water speed is also of a great
importance. Both criteria are fulfilled with the proposed design. [4.1] [4.5] [4.6].
4.1.2.7 Saturation
Saturation test was done by sketching the field B and its normalized values versus
current I, as shown in Figure 4.14. Saturation occurs when the magnetic flux does not
increase as the current is increased. According to the figures, there is approximately
no saturation for the fields below the (including and current of
which are the nominal field and current).
4.1.2.8 Engineering layout
Below in Figure 4.15, Figure 4.16 and Figure 4.17 the isometric view, general
drawing and coil drawing of ILSF prototype dipole are shown. The dipole has parallel
ends and a curved yoke to follow the beam path. The magnet is a C type magnet and
its opening points toward outside the ring in order to ease beam extraction. It also can
be opened from the middle to facilitate vacuum chamber installation.
(a) (b)
(c) (d)
Figure 4.14 Field vs. current: (a) Actual field, (b) normalized field, (c) field gradient, and (d) normalized field gradient vs. current.
117
Figure 4.15 Isometric view of ILSF dipole magnets.
Figure 4.16 General drawing of ILSF prototype dipole.
118
4.1.3 Quadrupole magnets
4.1.3.1 Quadrupole design parameters
The parameters for ILSF quadrupole magnets are tabulated in Table 4.2. The design
should be accurate enough so that over the specified good field
region.
4.1.3.2 Pole and yoke geometry
Using the two-dimensional Poisson software, a pole and yoke geometry was
developed for the quadrupole magnets which met the operational requirements.
Simulations were done for a quadrupole with a field gradient of and magnetic
length of which will be the maximum possible field gradient and length in the
lattice. The other quadrupoles, according to Table 4.2, can be easily simulated by
reducing the ampere-turns. The main parameters for the ILSF quadrupole are given in
Table 4.8:
Table 4.8: ILSF quadrupole main parameters
Parameter Unit Value
Field gradient-g T/m 23.00
Aperture radius mm 30
Horizontal good field region mm ±18
Magnetic length m 0.53
Figure 4.17 Coil drawing of ILSF prototype dipole.
119
The following equation gives the curve for a pole profile that extends to infinity:
(4.9)
To obtain the required field tolerances within the good field region, some shimming is
required. Table 4.9, gives the coordinates for one eighth of the magnet pole profile
after shimming:
Table 4.9: Pole profile coordinates for 1/8 of a quadrupole magnet
No. (mm) (mm) No. (mm) (mm) No. (mm) (mm)
1 21.213 21.213 19 28.413 15.838 37 35.613 12.636
2 21.613 20.821 20 28.813 15.618 38 36.013 12.495
3 22.013 20.442 21 29.213 15.404 39 36.413 12.358
4 22.413 20.078 22 29.613 15.196 40 36.813 12.224
5 22.813 19.726 23 30.013 14.994 41 37.213 12.093
6 23.213 19.386 24 30.413 14.796 42 37.613 11.964
7 23.613 19.057 25 30.813 14.604 43 38.013 11.838
8 24.013 18.740 26 31.213 14.417 44 38.413 11.715
9 24.413 18.433 27 31.613 14.235 45 38.813 11.594
10 24.813 18.136 28 32.013 14.057 46 39.213 11.476
11 25.213 17.848 29 32.413 13.883 47 39.613 11.36
12 25.613 17.569 30 32.813 13.714 48 40.013 11.246
13 26.013 17.299 31 33.213 13.549 49 40.397 10.423
14 26.413 17.037 32 33.613 13.388 50 40.721 10.000
15 26.813 16.783 33 34.013 13.230 51 42.500 10.000
16 27.213 16.536 34 34.413 13.076
17 27.613 16.297 35 34.813 12.926
18 28.013 16.064 36 35.213 12.779
Figure 4.18 ILSF quadrupole pole profile compared with theory
120
Using steel type , (see Table 4.16) the averaged quantity of the
magnetic field in different parts of the simulated sample and magnet dimensions are
shown below (Figure 4.19 and Figure 4.20):
The obtained field and field gradient are shown in Figure 4.21 and Figure 4.22
respectively,
Figure 4.19 Field lines inside 1/2 of a quadrupole magnet as simulated in "Poisson"; magnetic field intensities are shown at several points.
Figure 4.20 Dimensions of ILSF quadrupole.
121
4.1.3.3 Field Quality
For field uniformity the following formula was used:
(4.10)
Field gradient tolerance is shown in Figure 4.23:
(mm) (T/m) (T/m)
-18 23.000 23.008 < 4 × 10-4
18 23.000 23.008 < 4× 10-4
Figure 4.21 Vertical field versus horizontal distance x.
Figure 4.22 Field gradient versus x.
22.88
22.92
22.96
23
-30 -20 -10 0 10 20 30
dB
y / d
x [
T/m
]
X [mm]
122
As can be seen, in the good field region up to , the field tolerance is on the
order of .
4.1.3.4 Harmonic analysis
Table 4.10 tabulates some field coefficients defined by the following equation,
obtained from Poisson.
(4.11)
where the normalization radius has been taken as .
Table 4.10: ILSF quadrupole field coefficients
n type Bn (20 mm)
Tesla |Bn/B2| (20 mm) bn (T/m
n-1)
Figure 4.23 Field gradient tolerance versus x.
-0.005
-0.004
-0.003
-0.002
-0.001
0
0.001
0.002
-30 -20 -10 0 10 20 30
DB
'/B
'0
X (mm)
123
4.1.3.5 Electrical and Cooling Parameters
Table 4.11 gives the coil specifications. Coil geometry is shown in Figure 4.25.
Table 4.11: Quadrupole electrical and cooling parameters
Parameter Unit ILSF
Magnetic length m 0.53
Total Amp-turns per coil At 8410
Operating current A 168.2
Number of turns per coil - 50
Number of pancakes per coil - No pancakes
conductor dimensions mm 8 x 8
Water cooling tube diameter mm 4
Copper area mm2 51.43
Current density A/mm2 3.27
Resistance m 119
Voltage drop V 20.05
Power per magnet KW 3.37
Number of water circuits - 4
Water temperature rise C 10.0°
Cooling water speed m/s 1.6
Pressure drop bar 9.71
Reynolds number. - 3204.5
Figure 4.24 Absolute normalized multipole errors in the 20 mm good field region: quadrupolar component (n = 2) is not shown.
124
4.1.3.6 Saturation
To test for saturation the field gradient ' was sketched versus current I, the resulting
curves are shown in Figure 4.26:
Figure 4.25 Coil cross section for quadrupole magnets.
Figure 4.26 Field (top) and normalized field gradient (bottom) vs. current.
125
Saturation occurs where the field gradient, B', ceases to be increasing as a function of
current. Therefore approximately there is no saturation at . This is the
nominal current used for creating a field gradient.
4.1.3.7 Engineering layout
A quadrupole needs to have specific designed spacers in order to allow separation of
its two halves, and provide the path for beam extraction in different quadrupoles.
Spacers are needed to provide a precise assembly to avoid occurrence of unwanted
harmonics. Figure 4.27, Figure 4.28 and Figure 4.29 show the mechanical layout of an
ILSF quadrupole magnet.
Figure 4.27 Isometric view of ILSF prototype quadrupole.
Figure 4.28 General drawing of an ILSF dipole.
126
4.1.4 Sextupole Magnets
4.1.4.1 Sextupole design parameters
The sextupole magnets are required to generate the second-order fields needed for
chromaticity correction and non-linear effects. In addition, these magnets are suitable
for applying static or slowly varying correction fields.
The parameters for the sextupoles magnets proposed for ILSF are summarized in
Table 4.3. The design should be accurate enough so that over the
specified good-field region.
4.1.4.2 Pole and yoke geometry
Using two-dimensional Poisson software, a pole and yoke geometry was developed
for the sextupole which met the operational requirements for the magnet. Simulations
were done for a sextupole with a sextupole component of and a magnetic
length of which will be the maximum possible sextupole component and
length in the lattice for the sextupoles. The other sextupoles listed in Table 4.3, can be
easily simulated by reducing the ampere-turns.
Table 4.12 contains the specifications of the ILSF sextupole:
Figure 4.29 Drawing of the ILSF quadrupole’s coil.
127
Table 4.12: The main parameters for ILSF’s sextupole magnets
Parameter Unit Value
Sextupole Component T/m2
700
Aperture Radius mm 34
Pole tip field T 0.41
Horizontal Good Field Region mm ±16
Magnetic Length m 0.22
Using Eq. 4.6, in the area around the midplane, one-twelfth of pole profile coordinates
are given below in Table 4.13.
Table 4.13: Pole profile coordinates of 1/12 of the sextupole magnet
No. (mm) (mm) No. (mm) (mm)
1 29.445 17.000 13 32.211 13.400
2 29.622 16.700 14 32.516 13.100
3 29.808 16.400 15 32.835 12.800
4 30.003 16.100 16 33.169 12.500
5 30.206 15.800 17 33.519 12.200
6 30.419 15.500 18 33.884 11.900
7 30.642 15.200 19 34.268 11.600
8 30.875 14.900 20 34.669 11.300
9 31.119 14.600 21 35.091 11.000
10 31.374 14.300 22 35.533 10.700
11 31.641 14.000 23 35.997 10.400
12 31.920 13.700 24 46.000 10.400
As seen in Figure 4.30, the shape of the pole profile is cubic at the pole center region
with a straight line on each side which is similar to the TPS sextupole pole profile
[4.6]
Using steel type , (see Table 4.16), the averaged simulated magnitude
of the magnetic field in different parts of the sample is shown in Figure 4.31 . Figure
4.32 shows the magnet’s dimensions.
128
Figure 4.30 Sextupole pole profile and comparison with theory.
Figure 4.31 Magnetic field inside one twelfth of the sextupole magnet as simulated by "Poisson"; the magnitude of the field is given at several points.
Figure 4.32 Sextupole dimensions.
129
The vertical field of the sextupole magnet has been plotted vs. horizontal distance in
Figure 4.33.
4.1.4.3 Field Quality
For field uniformity the following formula was used:
(4.12)
Figure 4.34 shows field tolerance vs. x :
(mm) (T/m2) (T/m
2)
-16 700.00 699.70 < 4 × 10-4
16 700.00 699.70 < 4× 10-4
The figure shows that the field tolerance is of the order of in the good field
region up to .
Figure 4.33 Sextupole vertical field versus horizontal distance x.
Figure 4.34 Sextupole field tolerance versus x.
130
4.1.4.4 Harmonic analysis
In Table 4.14 the field coefficients as defined by
(4.13)
are listed. The harmonics obtained from the Poisson code at the normalization radius
of are given below in Table 4.14:
Table 4.14: ILSF sextupole magnet multipole field coefficients
n type Bn (20mm)
Tesla |Bn/B3| (20mm) bn (T/m
n-1)
3 S
9 S
15 S
21 S
27 S
4.1.4.5 Electrical and Cooling Parameters
Coil dimensions were based on the data in Table 4.15:
Figure 4.35 Absolute normalized mulipoles' errors in the 20 mm good field region (sextupolar component n = 3 is not shown).
131
Table 4.15: Sextupole electrical and cooling parameters
Parameter Unit Value
Magnetic length m 0.22
Total Amp-turns per coil A 3780
Operating current A 111.18
Number of turns per coil - 34
Number of pancakes per coil - No pancakes
conductor dimensions mm 7 x 7
Water cooling tube diameter mm 3.5
Copper area mm2 39.38
Current density A/mm2 2.82
Voltage drop V 9.5
Power KW 1.056
Number of water circuits - 2
Water temperature rise C 10°
Cooling water speed m/s 1.31
Pressure drop bar 8.87
Reynolds No. - 2290
Figure 4.36 shows the conductor’s cross-section
The selected aperture allows the placement of the vacuum chamber.
4.1.4.6 Sextupole Corrector coils
In addition to sextupole coils, horizontal and vertical dipolar correction and skew
quadrupole coils will also be embedded in the sextupole magnets. Six air-cooled coils
will be winded around the main sextupole water-cooled coils.
Figure 4.36 Coil cross section for sextupole magnets.
132
In order to produce the maximum horizontal and vertical deviation of 0.3 mrad at
3 GeV beam energy, six horizontal steering trim coils (red coils in Figure 4.37) will
be used on each pole and four vertical steering trim coils (blue coils in Figure 4.37)
will be located on 30°, 150°, 210° and 330° poles.
The skew quadrupole field is also generated in the sextupole magnets by using the air-
cooled windings located on 90° and 270° poles..
The current configurations for having horizontal steering, vertical steering and skew
quadrupolar correction are shown in Figure 4.38. For horizontal steering the windings
at 30°, 90°and 150° poles are excited by a current of opposite polarity to that of 210°,
270° and 330° poles (Figure 4.38 (a)). Vertical steering is generated by having
currents at 150° and 210° poles flow opposite to that of 30° and 330° poles (Figure
4.38 (b)). For skew quadrupolar correction all auxiliary windings are energized with
the same polarity (Figure 4.38 (c)) [4.1][4.8].
Figure 4.37 Schematic of the horizontal dipolar (red), vertical dipolar (blue), and skew quadrupole (yellow) coils.
(a) (b) (c)
Figure 4.38 Coils' current configurations for (a) horizontal steering; (b) vertical
steering; (c) skew quadrupole correction. Green and orange colors
represent positive and negative current flux in each coil respectively.
133
4.1.4.7 Saturation
The sextupole component, , and normalized sextupole component, , versus
current I, were tested for saturation. The results are shown in Figure 4.39. Saturation
occurs where the Sextupole component, , ceases to increase as a function of
current. Therefore no saturation occurs at , which is the nominal current
used for creating the sextupole component.
4.1.4.8 Engineering layout
A sextupole needs to have specific designed spacers in order to allow separation of its
two halves and provide the path for beam extraction. Spacers are needed to provide a
precise assembly to avoid occurrence of unwanted harmonics. Figure 4.40,
Figure 4.41 and Figure4.42 show the mechanical layout of ILSF’s sextupole magnet.
Figure 4.39 Sextupole components vs. current: (top) actual component (bottom) normalized component.
134
Figure 4.40 Isometric view of ILSF prototype sextupole.
Figure 4.41 General drawing of ILSF sextupole.
135
4.1.5 Magnetic steel
Carbon percentage is one of the important factors in choosing yoke material,
increasing the carbon percentage causes saturation at lower fields and increases the
hardness. Therefore lower carbon percentage is preferred.
Using silicon also results in higher punchability and fewer burrs. It is expected that
steel coated with Stabolit , STABOCOR from EBG,
will be used at ILSF. This is a low-carbon steel with medium silicon
content . Table 4.16 contains the data for the B-H curve of steel
which were fed to Poisson code.
Table 4.16: Points of steel 1200-100 B-H curve
Magnetic field (A/m) Minimum induction parallel
to rolling direction (T) Relative dc permeability
116 0.50 3430
208 1.0 3826
300 1.3 3448
597 1.5 1999
1343 1.6 948
3236 1.7 418
6855 1.81 210
12490 1.91 122
Figure 4.42 Coil drawing for the ILSF sextupole.
136
Yoke is considered to be a collection of laminations which have nominal thicknesses
of 1 mm. The use of laminations will keep the magnetic properties constant along the
magnet’s length; it also makes the magnets more uniform [4.3]. To produce yokes,
these laminations can be stacked and glued or stacked and welded. Stacking and
gluing can be a better choice since gluing avoids distortions in the core assemblies
caused by the thermal effects of welding [4.7].
In addition one should ascertain that during the manufacturing process of this type of
steel:
The coercivity in a single sample does not exceed ; where coercivity is
defined as the field required to produce zero induction after saturating with a field
.
Maximum variation from the mean is less than .
4.2 Booster lattice magnets
The booster is supposed to work at an injection energy of 150 KeV and increase the
energy of the electrons to the ring energy of 3 GeV. It consists of 48 combined
bending magnets of the same type, 92 quadrupoles in 6 families, and 16 sextupoles in
2 families. The dipoles will run in series with a common power supply while for the
quadrupoles and sextupoles within each family will be connected in series.
4.2.1 Principal specifications of the lattice magnets
Combined magnets will be used in the booster. The bending magnets are to provide
the guiding field as well as correct chromaticity aberrations while quadrupoles which
are for focusing/defocusing purposes, also have an integrated sextupole component.
The magnets within a superperiod of ILSF lattice are shown in Figure 4.43; the
specifications of the magnets are summarized in Table 4.17 and Table 4.18.
Figure 4.43 Arrangement of magnets in one superperiod (top), the matching cell (center), and the unit cell (bottom) of the booster.
137
The magnet parameters are based on the following equations:
(4.14)
(4.15)
where K is the strength of the quadrupole, M is the strength of the sextupole, B is the
field gradient and B denotes the sextupole component. The last two parameters are
the coefficients defined in the following expansion:
(4.16)
4.2.1.1 Bending magnets
The specifications of bending magnets are given in the following table. The general
layout and the pole profile for all dipole magnets are the same.
Table 4.17: ILSF booster dipole parameters
Field
quality
in GFR
Magnetic
length
(m)
Total
gap
(mm)
Sextupole
component
(T/m2)
Field
(T)
Deflecting
angle
Bending
radius
(m)
Qty Type
1.2 22.6 16.03 1.10 7.50 9.09 48 BE 1
In order to have the desired sextupole component with the desired field uniformity,
the following equation was used [4.1]:
(4.17)
4.2.1.2 Quadrupole magnets
The specifications of all quadrupoles are given in Table 4.18 Full specifications are
given in Table 3.22 and Appendix 3.2. The general layout of the quadrupoles is the
same but the lengths are different. There will be 4 different pole profiles for the
specified families. QD1, QD2 and QD3 families in Table 3.22 which are pure
quadrupoles (no sextupole component) and are denoted in our Table 4.18 as Qx1-500
and Qx1-250 according to their lengths, have a common pole profile. Each of the
QF1, QF2 and QF3 families, denoted as Qx2-500 and Qx2-250 types in Table 4.18,
has its own gradient but the same sextupole component so there should be 3 different
pole profiles, one for each family.
Pole profile coordinates can be obtained from the following equation:
(4.18)
but in order to have a combined sextupole-quadrupole magnet some asymmetries
should be imposed.
138
Table 4.18: ILSF booster’s quadrupole parameters
Quadrupole type Unit Qx1-500 Qx1-250 Qx2-500 Qx2-250
No. of families - 2 1 1 2
QTY - 16 20 8 48
Maximum gradient field (Tesla/m) 11.99 13.487 13.897 14.937
Sextupole component (Tesla/m2) 0 0 3.22 3.22
Aperture radius (mm) 18 18 18 18
Magnetic Length (m) 0.50 0.25 0.50 0.25
4.2.2 Dipole magnet
4.2.2.1 Dipole design parameters
After evaluations, in order to reduce costs and have higher mechanical stability, H-
type combined bending magnet with following parameters is chosen. A combined
magnet acts as a dipole and having a weak sextupole component can also work as a
sextupole. Using combined magnets in lattice leads to more compact and cost
effective designs. In dipoles, field uniformity is one of the most important items.
Required accuracy for field uniformity is ΔB/B < ±0.01% over the specified good
field region.
4.2.2.2 Pole and yoke geometry
Using the two-dimensional code Poisson, an optimized pole and yoke was designed
for the dipole. The steel in the pole and back-leg was modeled. The pole face has a
broad, low shim at the pole edge, to maintain the field homogeneity over the full
horizontal aperture. The dipole will be curved, to follow the path of the circulating
beam. Simulations were done for the parameters given in Table 4.17 and a horizontal
good field region of ±10 mm. Figure 4.44 shows the pole profile and
Table 4.19 gives the coordinates of the optimized pole profile:
Figure 4.44 The pole profile calculated for ILSF bending magnet and comparison with theory.
139
Table 4.19: Pole profile coordinates for booster’s dipole magnet
The averaged quantity of the magnetic field in different parts of the magnet at
extraction/ injection for steel type is shown in Figure 4.45. Figure 4.46
shows the dimensions of the magnet. The field obtained from "Poisson" is plotted in
Figure 4.47. For the magnetic properties of the type of steel used in the simulation see
Table 4.26.
No. (mm) (mm) No. (mm) (mm) No. (mm) (mm)
1 0.000 11.300 16 15.000 11.319 31 28.737 11.168
2 1.000 11.300 17 16.000 11.321 32 29.829 10.990
3 2.000 11.300 18 17.000 11.324 33 30.220 10.930
4 3.000 11.301 19 18.000 11.327 34 31.000 10.860
5 4.000 11.301 20 19.000 11.330 35 31.780 10.790
6 5.000 11.302 21 20.000 11.333 36 32.560 10.720
7 6.000 11.303 22 21.000 11.336 37 33.330 10.650
8 7.000 11.304 23 22.000 11.340 38 34.110 10.600
9 8.000 11.305 24 23.000 11.344 39 34.890 10.580
10 9.000 11.307 25 24.000 11.347 40 35.670 10.590
11 10.000 11.308 26 25.000 11.351 41 36.440 10.670
12 11.000 11.310 27 26.000 11.356 42 37.220 10.830
13 12.000 11.312 28 27.110 11.353 43 38.000 11.090
14 13.000 11.314 29 27.637 11.334 44 49.000 68.000
15 14.000 11.316 30 28.018 11.286 45 53.000 70.000
Figure 4.45 Simulated fields in one half of a dipole magnet calculated using "Poisson"; the field values have been specified at some points for both extraction/injection.
140
4.2.2.3 Field Quality
Field uniformity is defined as:
(4.19)
where is the sextupole component at x=0. Figure 4.48 shows the field tolerance
obtained from this equation, for both injection and extraction in the ±10 mm good
field region:
(mm) (T) (T) (T/m)
extraction -10 1.099 1.1 -16.03 <1 × 10
-4
10 1.099 1.1 -16.03 <1 × 10-4
injection -10 0.05557 0.05554 -0.76 <1 × 10
-4
10 0.05557 0.05554 -0.76 <1 × 10-4
Figure 4.46 Dimension of ILSF booster’s dipole magnet.
Figure 4.47 Vertical dipole field versus horizontal coordinate (x).
141
4.2.2.4 Harmonic analysis
Higher multipole components due to imperfections in pole profile or saturation of iron
in pole tips affect the dynamic aperture. The multipole coefficients defined by the
following equation:
(4.20)
as obtained from Poisson code are listed in Table 4.20 where . In this
formula denotes the horizontal direction and denotes the vertical direction. The
normalization radius is taken to be
Table 4.20: ILSF dipole magnet’s field multipole coefficients
n type Bn(1cm) Gauss lBn/B0l (1cm) bn(T/mn-1)
1 B
3 B,S
5 B
7 B
9 B,S
11 B
13 B
Figure 4.48 Field tolerance versus x (boundaries of the good field region are shown as green dots).
142
4.2.2.5 Electrical and cooling parameters
Booster dipoles will be connected in series with a single power supply. The coil
specifications are given in Table 4.21 as well as the electrical and cooling parameters.
The coil geometry is shown in Figure 4.50
Table 4.21: Dipole electrical and cooling parameters for ILSF
Parameter Unit ILSF
Total Amp-turns per coil At 10480.00
Operating current A 524.00
Number of turns per coil - 20
Number of pancakes per coil - 2 (each has 2 layers)
Turns per pancake - 10
Conductor dimensions mm2
12 x 12
Water cooling tube diameter mm 4 .00
Current density in copper A/mm2
3.99
Resistance mΩ 17.80
Voltage drop V 9.42
Inductance mH 13.61
Power (AC) KW 4.94
Number of water circuits - 4 (each coil has 2)
Water temperature rise C 8.00°
Cooling water speed m/s 1.46
Pressure drop bar 3.20
Reynolds number. - 2931.44
Figure 4.49 Absolute normalized multipole errors at the 10 mm good field region. Dipolar and sextupolar components (n =1, 3) are not shown.
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
5 7 9 11 13
lBn
/B0l
n
143
Electrical calculations were based on two pancakes with two layers and ten turns
each. In order to have the optimum current density, conductor dimensions have been
chosen to be with a cooling hole of 4 mm. keeping the number of
cooling circuits down to 2 and having a water temperature rise. The total pressure
drop required to provide the necessary flow is expected to be roughly equal to
bars [4.4] [4.5].
4.2.2.6 Saturation
Figure 4.51 shows the plots of the field and the normalized field versus current. As
can be seen, there is approximately no saturation for fields below (including
and current of which are the nominal field and current).
Figure 4.50 Coil cross section for bending magnets.
144
4.2.3 Quadrupole magnets
4.2.3.1 Quadrupole design Parameters
The parameters for ILSF booster’s quadrupole magnets are given in Table 4.18. The
design should be accurate enough so that over the specified good
field region.
4.2.3.2 Pole and yoke geometry
Using the two-dimensional Poisson software, a pole and yoke geometry was
developed. Simulations were done for a maximum field gradient of and an
integrated sextupole component of . Also cooling calculations were done
for a maximum magnetic length of which will be the maximum possible
length in the lattice. The main parameters for the ILSF quadrupole are specified in
Table 4.22 below:
Figure 4.51 Field vs. current: (top) actual field, (bottom) normalized field.
145
Table 4.22: ILSF quadrupole main parameters
Parameter Unit Value
Field Gradient-g T/m 14.93
Sextupole component T/m2
3.22
Aperture Radius mm 18,18.2
Horizontal Good Field Region mm ±10
Magnetic Length m 0.500
Because of an integrated sextupole component the pole profiles are rotated by 0.467º
counterclockwise, but this rotation causes an unwanted dipolar component in the
center. In order to eliminate this dipolar component two different apertures, 18 mm
and 18.2 mm, are imposed on the left and right poles (see Figure 4.52).
To obtain the required field tolerances within the good field region, some shimming is
required and two different shims are imposed on each side. Table 4.23, contains the
coordinates for one half of the magnet pole profile after shimming:
Table 4.23: Pole profile coordinates for 1/2 of a quadrupole magnet
146
The result of the simulation for the the magnetic field, using t steel type ,
is shown in Figure 4.53. The obtained vertical field and field gradient are shown in
Figure 4.54 and Figure 4.55 respectively
Figure 4.52 ILSF quadrupole pole profile and comparison with theory
Figure 4.53 Field lines inside 1/2 of a quadrupole simulated in "Poisson",
the numbers are indicative of the dimensions of the magnet.
147
4.2.3.3 Field Quality
Field uniformity is defined as follows:
(4.21)
The resulting field gradient tolerance is shown in Fig. 4.56:
(mm) (T) (T/m)
-10 14.9 -32.22 <5 × 10-4
10 14.9 -32.22 <5 × 10-4
Figure 4.54 Vertical field versus horizontal distance x.
Figure 4.55 Field gradient versus x.
148
4.2.3.4 Harmonic analysis
Table 4.24 shows the field coefficients obtained with Poisson as defined in
(4.22)
and . The normalization radius is taken to be .
Table 4.24 ILSF quadrupole field coefficients
n type Bn(10 mm) Gauss lBn/B0l(10 mm) bn(T/mn-1)
2 Q
3 S
6 Q
9 S
10 Q
14 Q
Figure 4.56 Field gradient tolerance versus x.
Figure 4.57 Absolute normalized multipole errors in the 10 mm good field region; quadrupolar and sextupolar components (n = 2, 3) are not shown.
1.00E-16
1.00E-14
1.00E-12
1.00E-10
1.00E-08
1.00E-06
1.00E-04
6 9 10 14
Bn
/B0l
n
149
4.2.3.5 Electrical and cooling parameters
Table 4.25 gives the specifications of the coil [4.4][4.5]. The coil geometry is shown
in Figure 4.58.
Table 4.25: Quadrupole electrical and cooling parameters
Parameter Unit ILSF
Length m 0.500
Total Amp-turns per coil At 2078.00
Operating current A 122.20
Number of turns per coil - 17
Number of pancakes per coil - No pancakes
Conductor dimensions mm2
5 x 5
Water cooling tube diameter mm 3 .00
Current density in copper A/mm2
6.8
Resistance mΩ 15.96
Voltage drop V 19.5
Inductance mH 6.28
Power (AC) KW 2.38
Number of water circuits - 2
Water temperature rise C 8.0°
Cooling water speed m/s 2.52
Pressure drop bar 7.16
Reynolds number. - 3780
Figure 4.58 Coil cross section for quadrupole magnets.
150
4.2.3.6 Saturation
To test for saturation the field gradient ' and normalized field gradient was
sketched versus current I, the resulting curves are shown in Figure 4.59:
Saturation occurs when the field gradient, B’, ceases to be increasing as a function of
current. Therefore approximately there is no saturation at . This is the
nominal current used for creating a field gradient.
There are also pure quadrupoles in the booster lattice which are supposed to have the
same dimensions as the combined quadrupoles with an aperture of r =18 mm.
Figure 4.59 Field gradient (top) and normalized field gradient (bottom) vs. current.
151
4.2.4 Magnetic steel
Choice of material affects the saturation characteristics of the magnet and its
suitability for particular applications. Iron with high purity should not be used in the
booster ring, due to its high electrical conductivity. Alternating currents result in
alternating flux which induces an emf in the core and eddy currents. Eddy currents
decrease the flux, produce heat and power loss proportional to the square of current’s
amplitude. To avoid eddy currents, one should use 3% silicon-steel with lower
electrical conductivity. Addition of silicon increases resistivity, decreases hysteresis
loss, increases permeability, and virtually eliminates aging.
The primary way to decrease eddy current loss is to make the core out of thin sheets,
or laminations parallel to the alternating field lines. If these sheets are electrically
insulated from one another, the eddy currents are limited to laminations and charge
buildup suppresses the eddy currents [4.9].
Therefore in order to reduce the eddy currents and keep the magnetic properties
identical along the magnet length, yoke should be a collection of laminations, with
nominal thickness of 0.5 mm.
Table 4.26 shows some points of B-H curve for steel type M270-50A used in our
simulations, which is one of the main silicon steels and is coated on both sides with an
insulating coating. This table gives the minimum values of induction at the stated
values of field parallel to the rolling direction. Induction measured perpendicular to
the rolling direction should be more than 80% of the values given in the table below.
Table 4.26: Points of steel M270-50A’s B-H curve
Magnetic field (A/m) Minimum induction parallel
to the rolling direction (T)
2500 1.49
5000 1.60
10000 1.70
To produce yokes, these laminations can be stacked and glued or stacked and welded.
Stacking and gluing is a better choice since gluing avoids distortions in the core
assemblies caused by the thermal effects of welding.
References
[4.1] Jack Tanabe, Iron-Dominated Electromagnets Design: Fabrication, Assembly
and Measurements, (World Scientific, 2004).
[4.2] G. E. Fischer. Iron Dominated magnets, Stanford Linear Accelerator Center,
Stanford University, Stanford, CA 94305, July1985
[4.3] D. Einfeld. M. Pont, Specifications Quality Control Manufacturing Testing
(part I) Lecture, CAS, Bruges, June. 2009
[4.4] D. Einfeld, Magnet (warm) lecture. CAS, Frascati, Nov. 2008.
[4.5] D. Tommasini, Magnet (warm) lecture. CAS, Varna, Sep. 2010.
152
[4.6] Th. Zickler, Basic design and engineering of normal conducting, iron-
dominated electromagnets, Bruges, Belgium, 16-25 June 2009.
[4.7] C. H. Chang, C. S. Hwang, W.P. Li, M. H. Huang , H. H. Chen, T. C. Fan, , F.
Y. Lin, Hui-Chia Su, “Conceptual design of magnet systems for the Taiwan
photon source”, Particle Accelerator Conference, Knoxville, Tennessee,2005.
[4.8] Gautam Sinha, Gurnam Singh, “Design and characterization of combined
function multipole magnet for accelerators”, Review of Scientific Instruments
79 (2008) 123302.
[4.9] B. D. Cullity, C. D. Graham, Introduction to Magnetic materials (Wiley,
2011).
153
CHAPTER 5: Magnet girders
5.1 Scope
This chapter describes positioning tolerances, role of girders, stability requirements,
and the preliminary design of the storage ring support and alignment system.
5.2 Stability Requirements and positioning tolerances
The alignment of the storage ring magnets affects the ring performance in several
ways. Magnet alignment is necessary in order to store the electron beam with the
designed emittance and lifetime (i.e., sufficient dynamic aperture, DA). The magnets
can be misaligned because their central axes could be at different heights from the
reference surface of the girder. There are also alignment requirements for the angle
between the ends of the girders, their longitudinal positions, and roll angles (six
parameters). Any girder misalignment translates into a correlated offset for the
magnets [5.2].
The stability of closed-orbit position is critical to providing a constant flux in the
users' beamlines. There are several factors that cause large closed-orbit motion
(relative to the users' beamline) [5.2]: power supply fluctuations, energy modulations,
and changes in alignment due to vibrations of the magnets. The magnet motions that
are of most concern are changes in quadrupole transverse positions, dipole
longitudinal positions, and dipole roll angles. Here we will discuss the time variation
of the beam orbit due to quadrupole and dipole motions and the impact this has on the
users' beamlines.
In general, the largest allowable static or dynamic displacement of the beam should be
less than 10% of the RMS size of the beam. However corrector magnets placed
around the ring prevent major displacements of the beam. After considering all these
factors alignment tolerances as required by beam dynamics calculations turn out to be
±50µm and ±50µrad.
5.3 The role of girders
A platform called girder has several roles in synchrotron facilities. It provides a stable
platform not only for assembling the magnets but also for aligning them outside the
tunnel. Precise tolerances are fulfilled by precision alignment techniques requiring
out-of-tunnel assembly and alignment. The magnet alignment must remain unchanged
during the transportation and installation process. Speed of installation and alignment
and ease of operations must be considered in the design of girder. The nominal beam
height is usually 1.3-1.6 m, and the girders raise the center of magnets to the beam
height. In general it should be as low as possible.
154
Girder also provides a stable support to fulfill alignment requirements during both
initial and further dynamic alignments if needed. Girder structure design is of
importance in that it must meet dynamic stability requirements under ambient floor
motion, flow-induced vibrations and temperature fluctuations of the tunnel's air.
5.4 Primary Design of Magnet-Girder Support System
5.4.1 Girder Layouts
Layout of girders is usually classified as 4 types as listed below:
Type 1: Dipole, quadrupole and sextupole magnets are mounted on one girder
(ALBA, see Figure 5.1).
Type 2: Quadrupole and sextupole magnets are mounted on one girder and dipole
magnet is mounted on two sequential girders (NSLS, SLS, see Figure 5.2).
Type 3: Quadrupole and sextupole magnets are mounted on one girder and dipole
magnet is mounted on a separate girder, because of their height difference and less
stringent alignment and stability requirements (ANKA, Australian Syn., see
Figure 5.3).
Type 4: Quadrupole and sextupole magnets are mounted on one girder and dipole
magnet is mounted on a separate concrete girder (SSRF, see Figure 5.3).
Figure 5.1 Magnet-girder support system of ALBA [5.5].
155
Various solutions have been adopted at accelerator facilities around the world to
support the elements of the machine. The individual support stands are generally used
when the accelerator components are spread out, while girders are the preferred
solution when a set of components has to be mounted on a common platform. The
storage ring girders provide common mounting platforms for different sets of
magnets, as illustrated in Fig.5.4. In order to reduce the misalignment errors in most
of third generation light sources many magnets are loaded on the same support
(girder). This support is mechanically machined with a high precision of and
the locations of the magnets are fixed by accurate positioning of the pins. Considering
ILSF girders of the storage ring in Fig.5.5, two possible type of girders layout are
types 1 and 3. Because of further dynamic alignment requirements and ease of
operation, type 1 was selected to be the layout for ILSF girders.
Figure 5.4 ILSF girders in one eighth of a lattice.
Figure 5.3 Magnet-Girder Support system of SSRF [5.7]
Figure 5.2 Magnet-girder support system of SLS [5.6]
156
ILSF storage ring lattice has 4-fold symmetry, and each superperiod has 3 unit cells
and 2 matching cells. Girders of matching cells are longer than those of unit cells.
Therefore, there are two types of girders in terms of length in each cell of ILSF
storage ring: type 1 for the matching cells (the longer ones) and type 2 for the unit
cells (the shorter ones). Consequently, the storage ring has 8 girders of matching cell
type, 24 girders of unit cell type and 32 girders overall. Initially a single type of girder
of constant length was to be used for the storage ring, but since there a considerably
more unit cells than matching cells, it was decided that two types of girders will be
used. Table 5.1 lists the dimensions of ILSF girders for half of a superperiod.
Figure 5.5 ILSF girders in one quarter of the lattice.
157
Table 5.1: ILSF girders’ dimensions in one cell of the storage ring
Drift l.id 3.9403 3.9403
M
atc
hin
g C
ell
sf10 0.15
5.541453
U
nit
Cell 1
– S
eco
nd
Part
sf30 0.15
5.156453
Drift d11 0.2 Drift d43 0.165
qf1 0.31 qf4 0.31
Drift d12 0.43 Drift d42 0.54
qd1 0.26 sd40 0.15
Drift d13 0.2 Drift d41 0.26
sd10 0.15 be2 1.381453
Drift d14 0.26 Drift d21 0.26
be1 1.381453 sd50 0.22
Drift d21 0.26 Drift d22 0.37
sd20 0.22 qf5 0.53
Drift d22 0.37 Drift d23 0.175
qf2 0.53 sf50 0.22
Drift d23 0.175 Drift d24 0.165
sf20 0.22 qd4 0.26
Drift d24 0.165
qd2 0.26 Drift m.id 2 4 m.id 2
Drift m.id 2 4
m.id 2
U
nit
Cell 2
– F
irst
Pa
rt
The s
am
e a
s th
e U
nit C
ell
1 –
First
Part
.
U
nit
Cell 1
– F
irst
Pa
rt
qd3 0.26
5.156453
Drift d31 0.165
sf20 0.22
Drift d32 0.175
qf3 0.53
Drift d33 0.37
sd30 0.22
Drift d34 0.26
be2 1.381453
Drift d41 0.26
sd40 0.15
Drift d42 0.54
qf4 0.31
Drift d43 0.165
sf30 0.15 Drift s.id 1.41334 1.41334
Drift s.id 1.41334 2.82668
s.id 1.41334
158
5.4.2 Main design features
A typical girder body is shown in Fig 5.6. The nominal lengths are about to
The girder’s body is approximately wide and high. They are
fabricated by welding commercially available plates (St 37-2) of thicknesses ranging
from to millimeters. The top and bottom surfaces of the girder are made of 40
mm thick plates and side plates are thick. As shown in Fig. 5.6, there are
thick plates inside the girder body. Internal rips are created angularly inside
the girder body to increase the twist strength of the body. The overall weight of the
girder and the pedestals assembly is about 7.3 tons. After welding, the girders are
stress-relieved by stress-relief equipment either thermally or vibrationally.
The girders are mounted on three pedestals that are fastened to the floor. For
mounting and height adjustment, 12 bolts and six jacks are to be used. The girders are
over-constrained in order to minimize static deflection and to raise the first natural
frequency of the magnet–girder assembly.
It must be noted that the longer type of girders (type 1) were used in mechanical
analyses since the stability problems associated with larger length are more severe,
and all undesired deformations will be less severe for shorter lengths. Table 5.1 lists
the magnetic lengths of the magnetic elements and distances between them that were
used in the preliminary design.
Figure 5.6 Primary design of ILSF girders body.
159
5.4.3 Alignment mechanism
5.4.3.1 Positioning
A girder in 3D space has six degrees of freedom (DOF) shown in Fig 5.7.
Displacement DOFs include x, s and z and the rotational DOFs are θx, θs and θz. For a
fully positioned girder and magnet assembly, one must limit all DOFs with fixation
mechanisms after positioning.
In different light sources, many different systems for positioning and fixation of a
girder have been used. After an extensive study of these systems we chose to use
ALBA type adjusting mechanism in ILSF.
5.4.3.2 ILSF positioning and fixing system
From a mechanical engineering point of view, positioning and fixing of a body are
two different concepts though sometimes there are a few designs where both tasks are
performed simultaneously. Fixation must be done after positioning in a way that the
positioning is not disturbed. Figures 5.8 (a) and (b) show the girder and positioning
and fixation system used for ILSF.
To constrain the vertical (z) and θx and θs rotational DOFs six spherical-end screw
jacks and to constrain the transverse horizontal (x) and θz rotational DOFs two struts
with two universal joints at the two ends will be used. In the beam direction (s) one
strut jack is used.
After precise positioning of the girder body, all six DOFs are fixed using bolts and
nuts.
5.5 Mechanical stability of the magnet–girder support system
In the design of third-generation synchrotron-light sources and related experimental
infrastructure, there is a wide range of mechanical engineering tasks to be performed.
The elements of the machine have to be positioned with ultra-high precision and one
Figure 5.7 Definition of the degrees of freedom.
160
has to deal with accuracies and resolutions in nanometer and μrad range. The
machining tolerance of the final pieces of equipment has to be in micrometers.
Theoretical studies by beam dynamic group define allowable total deviation from
ideal beam trajectory. The allowable total deviation was reported to be ±50μm. It
means that all the cumulative deviation from the girder assembly components (such as
pedestal deformation and manufacturing tolerances, adjusting mechanism
manufacturing and positioning tolerances, static and dynamic deformations of the
(a)
(b)
Figure 5.8 ILSF positioning and fixation systems for constraining of 6 DOFs.
161
girder, manufacturing tolerances of the girder, residual stress effects, magnet-girder
positioning errors, deviation between magnetic and mechanical centers, positioning
errors in alignment of girders relative to each other and etc.) must not exceed from
±50μm:
A: Flatness of the girder.
B: Girder body and pedestals deformations including static, thermal and dynamic
deformations.
C: Adjusting mechanism manufacturing tolerances and positioning errors.
D: Magnet-Girder positioning errors.
E: Deviation between magnetic and mechanical centers.
F: Residual stress effects.
Thus, the factors affecting mechanical stability of the Magnet–Girder support system
can be divided into two main groups: static sources of misalignment such as static
deformations, manufacturing tolerances, etc.,and time-varying sources of
misalignment, the latter are related to the stability of the supporting system.
5.5.1 Static Stability
In order to investigate static deformations of supporting system under the load of
mounted magnets, a finite-element analysis was carried out to extract deflection
values of the supporting system. The static FE analysis was performed on preliminary
design using ANSYS commercial finite element code. Figure 5.9 shows 3D view of
the magnet-girder supporting system. The following tables list some of the relevant
information:
Table 5.2: Material properties Structural steel st-37 (DIN 1.0037)
Young’s Modulus (MPa)
Poisson’s Ratio
Compressive Yield Strength (MPa)
Tensile Yield Strength (MPa)
Tensile Ultimate Strength( MPa)
Density (kg.mm-3
)
Coefficient of Thermal Expansion (C-1
)
|A ± B ± C ± D ± E ± F ± …|< 50μm
162
Figure 5.10 illustrates the meshed geometry of the magnet-girder support system. The
geometry was meshed using coarse elements automatically.
Figure 5.9 3D-view of the Supporting system
Figure 5.10 Meshed model of girder assembly
163
As for boundary conditions, the bottom faces of the pedestals are taken as fixed
(Figure 5.11) and all contacts (between plates and all other components) are taken to
be bonded contacts which are not separable.
With known density of the material, Standard Earth Gravity in vertical direction
(9.8066 m/s2 in y direction) was applied to all loads of magnetic elements on the
girder top surface.
Table 5.3 Summary of results for maximum and minimum deformations
Total deformation Deformation along z-axis (GPS) Location
Minimum pedestal
Maximum Sd20
Figure 5.12 shows the static deformation of the assembly in vertical direction.
Maximum Static deformation in vertical direction is about 12.23 µm.
Figure 5.11 Fixed supports.
164
5.5.2 Dynamic stability
Sources affecting the mechanical stability of the support system include ground
settlement, ambient floor motion, flow-induced vibrations, and thermal transients.
These sources can be categorized in terms of the frequency range as low (< 10 Hz),
medium (for frequencies between 10 and 100 Hz), and fast (> 100 Hz).
Sources are also categorized based on the time-scale of the excitation, as being short
(< 1 hour), medium-term (< 1 week), or long-term (> 1 week). Short-term sources
include natural and agricultural ground vibrations, flow-induced vibrations, and
power supply jitters. Thermal transients due to temperature changes of the cooling
water or the tunnel air constitute medium-term sources. Floor settlement or seasonal
temperature changes, which may have direct impact on the position of components,
are considered to be long-term effects.
5.5.2.1 Vibrational stability
The magnet–girder assembly fastened to the pedestals is dynamically complex,
however, a simple 1-D oscillator show in Figure 5.13 will be useful to model the
important design features of such a complex system; the relevant parameters are:.
the natural frequency:
amplification (ratio of the system’s response Y to the external excitation X):
Figure 5.12 Static deformation of the ILSF magnet–girder assembly in vertical direction.
165
critical damping constant:
where k [N/m], c [N.s/m or kg/s], and m [kg] represent respectively the effective
spring coefficient, damping ratio, and mass.
The value of the damping ratio determines the behavior of the system. A damped
harmonic oscillator can be: (a) overdamped ( the system returns (exponentially
decays) to equilibrium without oscillating; for larger values of the system returns to
equilibrium more slowly; (b) critically damped ( ): the system returns to
equilibrium as fast as possible without oscillating; (c) underdamped ( ): the
system oscillates (at a reduced frequency compared to the undamped case) with the
amplitude of the oscillation gradually decreasing to zero; (d) undamped ( ): the
system oscillates at it natural resonance frequency ( ).
As shown in Fig. 5.12, There is no significant vibration amplification
(amplification ) when the natural frequency, , is substantially greater than the
excitation frequency, .
Several finite-element modal analyses were performed on different designs of
magnet-girder assembly to extract its dynamic response. Results of analyses of the
last (but not the final) design are discussed below.
5.5.2.2 Finite-element modal analysis
Modal FE analysis was also carried out on the preliminary design using ANSYS code.
All the parameters in setting up modal analysis (material properties, boundary
conditions, etc.) are the same as those of the static analysis.
Finite-element modal analysis of the ILSF magnet–girder assembly shows that the
two lowest natural frequencies are and . The corresponding mode
Figure 5.13 One dimensional oscillator and amplification plot.
166
shapes are rolling of the girder and magnet oscillations. Figure 5.14.illustrates the first
six mode shapes. The six natural frequencies corresponding to these modes are listed
in Table 5.4.
Mode 1
Mode 2
Mode 3
Mode 4
Mode 5
Mode 6
Figure 5.14 The first six natural modes.
167
Natural frequencies predicted by finite-element analysis aren’t usually the exact real
natural frequencies due to certain assumptions made in the simulation e.g. the contacts
and joints being ideal. It must be noted that no matter what type of adjusting
mechanisms are used, the first natural frequency of the magnet-girder assembly of
most synchrotron facilities is less than except for SOLEIL due to the existence
of a locking system which enforces stiffness of the assembly.
Table 5.4 The first six natural frequencies
Mode 1 2 3 4 5 6
Frequency (Hz) 70.85 81.18 85.99 87.97 89.94 91.06
5.5.3 Thermal stability
Thermally induced deformations of support systems are unavoidable. Most important
sources of temperature variation are ambient air, cooling water, heat dissipation of
magnets etc. Tunnel air temperatures are restricted to range of 25±0.1ºC. This ensures
permissible thermal deformations of the ring components. To investigate the effect of
temperature gradients, finite-element analyses were performed based on the maximum
temperature variation that is possible. It must be noted that over-constraining each
girder to its pedestal at six locations minimizes the distortion effects.
All the parameters in setting up the modal analysis (material properties, boundary
conditions etc.) are the same as those in the static analysis except for ramped thermal
loading to 24.9 oC (for the lower limit) and 25.1
oC (for the upper limit).
Figure 5.15 Static-thermal deformation of the supporting system in vertical direction
(Temperature variation: 25→24.9 C (lower limit))
168
Figures 5.15 and 5.16 depict static-thermal deformation of the magnet–girder
assembly in vertical direction at the lower limit of temperature variation (24.9 C) and
upper limit of temperature variation (25.1 C), respectively.
Table 5.5 Summary of results for static-thermal deformation (ramping down to the lower limit)
Total deformation Deformation along z-axis (GPS) Location
Minimum pedestal
Maximum Sd20
Table 5.6 Summary of results for static-thermal deformation (ramping up to the higher limit)
Total deformation Deformation along z-axis (GPS) Location
Minimum pedestal
Maximum Sd20
Figure 5.16 Static-thermal deformation of the supporting system in vertical direction
(Temperature variation: 25→25.1 C (upper limit))
169
5.6 Test and quality control
All dimensions and tolerances such as flatness etc. must be checked by optical
instruments. To check the tolerances and dimensions of the girder assembly laser
tracker has to be used. At the time of mounting dummy magnets on the girder
assembly, mechanical and thermal deformations will occur. These deflections must be
in the allowable range and will be measured by laser tracker. Two different surface
2D curves resulting from girder body before and after deformation will be compared.
Modal tests are carried out to obtain the natural frequencies along with dynamic
deflections. These values must be within the allowable range.
5.6.1 Dimensional check
The geometrical measurements are carried out using laser tracker in conjunction with
a corner cube reflector which are used for surveying [5.3]. The measurements are
done on the specified surfaces with a flatness of ±15µm and the position of the pin
holes defining the positioning of the magnets with tolerance of ±15µm on the top
surface of the girder.
If these are out of tolerance range for the specified surface flatness or the position of
the pinholes, several solutions can be followed to improve the accuracy of the surface
machining and position machining of the pinholes [5.3]:
Refurnishing of the milling machine.
Realignment and re-machining of the machine axis.
Improvement of the machine base rigidity and planarity.
Replacement and calibration of the CNC optical rules.
Construction of a controlled temperature room around the machine.
Machining temperature should be 23 ± 0.75 ºC.
Strict control of the temperature on the machine and the pieces along the process.
5.6.2 Vibration tests
The following equipment is usually necessary for vibration tests:
Accelerometers: An accelerometer is a device that measures acceleration.
Accelerometers can be used to measure vibration on cars, machines, buildings,
process control systems and safety installations. They can also be used to measure
seismic activity, inclination, machine vibration, dynamic distance and speed with
or without the influence of gravity.
Triaxial seismometers [5.3] (one on the girder surface, one on the floor):
Seismometers are instruments that measure motions of the ground, including those
of seismic waves generated by earthquakes, volcanic eruptions, and other seismic
sources. Records of seismic waves allow seismologists to map the interior of the
Earth, and locate and measure the size of these different sources.
Geophones [5.3] placed on: pedestal platform, the surface of the girder, and on the floor to evaluate the
transfer function of the girder structure, surface of the girder and the magnet dummies to evaluate the transfer function
between the girder and the magnet dummies.
170
on the left- and rightmost corners of the girder surface to look for any twist modes
that may appear.
Geophone is a device which converts ground movement (displacement) into
voltage, which may be recorded at a recording station. The deviation of this
measured voltage from the baseline is called the seismic response and is analyzed
for structure of the earth.
Data acquisition system
The structure of supporting system is impacted in different points/directions and
vibrations are measured at different points (three axes at each point). Some of the
points will be on the girder structure and others on the magnets. Therefore, the natural
frequencies and corresponding mode shapes can be extracted.
The ILSF magnet-girder support system has greatly benefited from the knowledge
obtained from other facilities.
References:
[5.1] A. Lestrade, Principles & Status Of Soleil Alignment System,.IWAA2004
(CERN, Geneva, 4-7 October 2004).
[5.2] NSLS-II Preliminary Design Report.
[5.3] Lluis Miralles, Lidumila Nkitina, Iouir Nikitine, Mechanical aspects of the
design of third generation synchrotron light source storage ring girder system,
(June 10 2008).
[5.4] TPS Design Handbook, Design considerations and characteristics of TPS
(2008).
[5.5] Technical Specifications for the Manufacturing of the ALBA Storage Ring
Giders, END-SR-GI-TSEN-0002.
[5.6] S. Zelenika, “Mechanical Aspects of the Design of Third-Generation
Synchrotron Light Sources”, http://bib.irb.hr/datoteka/245477.p337.pdf.
[5.7] Xiao Wang, Lingshan Bu, Hanwen Du, Zhongbao Yan,
“Dynamic test of SSRF storage ring girder-magnet assembly”,
http://medsi2006.spring8.or.jp/proc/18.pdf.
171
CHAPTER 6: Vacuum systems
6.1 Vacuum system of the storage ring
A good storage ring vacuum system is necessary for beam’s long lifetime, good beam
quality and low bremsstrahlung radiation generated by collisions between the
electrons and the residual gases inside the vacuum chamber. A good vacuum is also
required for a stable beam size and position. The storage ring operates in the ultra
high vacuum (UHV) pressure region. At this pressure level, the beam lifetime has to
be longer than 10 hours with a beam current of about 400mA.
This section considers the vacuum systems of the ILSF storage ring. It will include
some discussion of the vacuum profile calculations, photon flux and the construction
materials needed for the vacuum vessels etc.
6.1.1 Design objectives
The vacuum system has to satisfy the following requirements:
Average pressure at the operation should be around mbar that allows a
lifetime of more than 10 hours
Accommodate other systems (especially magnets)
Vacuum chambers must utilize the inter-polar space of the electromagnets to the
fullest possible degree without distortion of the magnetic field in the gap
Residual gases in vacuum chamber must have lowest possible effect on the
circulating beam.
Lowest possible outgassing rate (thermal and photon-stimulated desorption)
Highest possible pumping speed
Sufficient cooling to remove the thermal power generated by the synchrotron
radiation
Maximum operational time (fast recovery and conditioning i.e. reliability, stability
and flexibility)
Lowest possible impedance (for this purpose, the internal surface of vacuum
chamber must be very smooth).
Capable of being built with standard and commercially available components and
proven materials, design methods and techniques
Efficient and not labor-intensive construction and operation
Amenable to future upgrade and changes
Reasonable cost
6.1.2 General layout
We shall consider ILSF storage ring based on ILSF-1 lattice that is an expanded
double bend achromat structure and has a nominal emittance of 3.2 nm.rad. The
circumference of the storage ring is 297.6 m and its energy is 3.00 GeV with a
172
maximum current of 400 mA. The lattice has four-fold symmetry and includes 4
superperiods each of which includes 2 matching cells and 3 unit cells (Figure 6.1 and
Table 6.1). The machine has 4 long 7.9 m straight sections (LSS), 16 medium 4 m
straight sections (MSS) and 12 short 2.8 m straight sections (SSS).
Table 6.1 The main parameters of ILSF storage ring.
Parameter Unit Value
Energy GeV
Design current mA
Circumference m
Number of dipoles
6.1.3 Vacuum chamber layout
6.1.3.1 Vacuum chamber profile
There are three possible configurations for the vacuum chambers: first, stainless steel
vacuum chamber with keyhole profile and ion pumps (as in ALBA); second, stainless
steel vacuum chamber with keyhole profile and NEG strips or liner ion pumps in
antechamber (as in DELTA); and third, NEG coated aluminum vacuum chamber with
elliptical or octagonal cross section (as in SOLEIL and MAX IV). For technical
reasons we will discuss only the first configuration; the other configurations are under
investigation. For this case, the vacuum chamber consists of an electron beam channel
and a photon channel or antechamber. Synchrotron radiation will be produced in the
electron beam channel and will pass through a slot to the antechamber to strike the
absorbers or go to beamlines.
Figure 6.1 Magnet layouts of unit cell (top) and matching cell (bottom).
173
Having an antechamber will
increase the conductance of the vacuum chamber;
result in photons hitting the absorbers in the antechamber; therefore, desorbed
gases have less influence on the electron channel pressure. Hence the radiation can
hit the absorbers with higher doses and conditioning and cleaning time will
decrease;
allow the installation of pumps’ flanges and other instruments in the photon
channel therefore their influence on impedance and electron channel pressure will
decrease.
increase the overall surface and therefore thermal desorption will increase too.
The vacuum chamber profile has been optimized in order to accommodate the
magnets, beamlines and satisfy injection requirements and also to achieve efficient
conductance and heat transfer.
Beam lifetime is a critical parameter for determining the size of the electron chamber.
There are 4 loss mechanisms that affect the lifetime as described by the following
formula:
Where τq is the quantum lifetime, τT is the Touschek lifetime, τCo is the Coulomb
lifetime and τbr is the bremsstrahlung lifetime [6.10][6.12]. The relation between
Coulomb lifetime and the shape of the vacuum chamber is given by the following
formula:
where E is the nominal beam energy, P is the pressure, εA is the ring acceptance, <β>
is the average of the vertical beta function which is 7.68 m for ILSF ring and the
function F(R) depends on the shape of the vacuum chamber; εA is the ring acceptance,
given by:
where g is the half-gap of the vacuum chamber and β is the vertical beta function. The
lowest value of the ring acceptance corresponds to the lowest value for Coulomb
lifetime.
As shown in Figure 6.2, the critical points for the electron chambers occur in the first
dipole’s vacuum chamber.
The height and length of the slot between electron chamber and antechamber plays an
important role in vacuum design. By decreasing the height and increasing the length,
the conductance of the slot will decrease and therefore pressure difference between
electron chamber and antechamber will increase.
To increase the height and decrease the length of the slot, the magnets need to have
larger aperture; this will increase the production and operational costs of the magnets.
174
For optimizing the size of the slot, the probability of gas molecules passing through
the slot was studied for different cases (see Figure 6.5). Relation between the passing
probability of slot and the slot's height and length are shown in Figure 6.6.
Figure 6.3 Vacuum chamber inside a quadrupole magnet (right) and a sextupole magnet (left).
Figure 6.4 Vacuum chamber inside a dipole.
Figure 6.2 Optical functions in half a superperiod of the ILSF ring.
175
Figure 6.5 Model for the effect of slot size on vacuum chamber pressure
Figure 6.6 Effect of height and length of the slot on passing probability (Ratio of the number of molecules that can pass through the slot to the total number of molecules). The specified point belongs to ALBA profile that has a 10mm high and 20 mm long slot.
Figure 6.7 Pressure profile along the cross section for different slot heights ( in
mm) and 20mm slot length. The base pressure is torr (in the left side). Vertical axis uses logarithmic scale. This figure shows that
when we need torr, the slot height must be higher than 10 mm.
176
Considering the cross section of the magnets and above discussion, the best cross
section for ILSF straight sections is shown in Figure 6.8. The width of antechamber
can be changed to increase the total conductance of the profile. The conductance of
ALBA profile is given in Table 6.2 for comparison.
Table 6.2: Conductance calculation for 3 cross sections
Total width
(mm)
Transmission
probability
Conductance
(liter/sec.m)
Area
(cm2)
Perimeter
(cm)
ILSF-
Straight 180 0.058 26.5 38.63 40.46
ILSF-Dipole 180 0.058 25.8 37.98 40.38
ALBA 180 0.060 28.7 40.80 41
6.1.3.2 Vacuum chamber design
The storage ring consists of 136 vacuum chambers that can be divided into 10
families, 8 of which are used in the straight sections and 2 in dipole magnets.
Figure 6.9 and Figure 6.10 show the arrangement of vacuum chambers in one
quadrant and one octant of the storage ring respectively.
Figure 6.8 Cross section of the vacuum chamber inside an ILSF dipole (top) and in other parts (bottom).
177
Figure 6.9 One quadrant of the storage ring.
Figure 6.10 One octant of the storage ring.
Figure 6.11 Dipole vacuum chamber (type I).
178
Figure 6.12 Dipole vacuum chamber (type II)
Figure 6.13 SB21 vacuum chamber.
179
Figure 6.14 SB31 vacuum chamber.
Figure 6.15 SB22 vacuum chamber.
180
Figure 6.16 SA2212 vacuum chamber.
Figure 6.17 SA13 vacuum chamber
181
6.1.4 Construction material
One of the major decisions concerning the vacuum system for a synchrotron light
source is the material from which the vacuum chambers are to be fabricated.
Important points to be taken into consideration are properties of the material (vacuum
and mechanical) and the economics.The chamber material must be radiation-resistant
and should provide small outgassing and penetrability as well as small magnetic
permeability.
Synchrotron light source vessels are fabricated mainly from either stainless steel or
aluminum. Copper and titanium are also good candidates but they are expensive for
general use. Copper and GlidCoptm
are used internally in photon stoppers or radiation
absorbers where high heat loads have to be dissipated.
Several suitable grades of stainless steel include, inter alia, 304, 304L, 304LN, 316,
316L and 316LN. Suitable grades of aluminum include, 4043, 6061, 6063
(extrusions), 2219 (commercial aluminum Conflat™ flanges) and where high strength
is needed and tempering is to be avoided 5052, 5083 and 5086 [6.2].
Based on the above, it has been decided that the machine will be constructed from
316LN stainless steel. However, aluminum can be considered as an alternative.
6.1.5 Deformation of vacuum chambers
Vacuum chambers deform due to atmospheric pressure and their own weight. The
total deformation is one of the most important parameters since it affects tolerance
and clearance between magnet poles and vacuum chamber. In order to calculate these
deformations finite element analysis (FEA) has been performed. To avoid large
Figure 6.18: Straight section vacuum chambers for long (top), medium (middle), and short (bottom) sections.
182
deformations in vacuum chambers, one or more ribs can be welded onto the vacuum
chambers in the space between the magnets.
The FEA results for SB22 vacuum chamber are shown in Figure 6.19. The figure at
top shows the deformation of the SB22 vacuum chamber without any ribs due to
gravity. It is clear that the deformation is negligible. The middle figure shows total
deformation due to both atmospheric pressure and gravity also without any ribs. The
maximum deformation is about 1.7 mm which occurs in the antechamber and near the
location of the slot between chamber and the antechamber. This value for deformation
is not acceptable. Therefore we consider the case where two ribs are attached to the
vacuum chamber. The result is shown in the figure at bottom. The maximum total
deformation is reduced to 0.4 mm, which is close to the nominal tolerance of 0.5 mm.
6.1.6 The pressure calculations
The pressure in vacuum chamber is determined by the thermal and photon-stimulated
outgassing of the vacuum chamber, the cross section and conductance of the vacuum
chamber, the pumping speed, location of the pumps, and some other factors. Vacuum
systems of synchrotrons fall under the category of conductance-limited systems. The
pressure affects the bremsstrahlung and Coulomb scattering of the electron beam and
hence the contribution of these two scattering mechanisms to the reduction of beam
lifetime. The Coulomb lifetime is an important factor in determining the shape of the
cross section of the vacuum chamber. Bremsstrahlung or inelastic scattering is the
rapid deceleration of electrons and emission of photons to beam interaction with the
residual gas atoms. Therefore, a longer bremsstrahlung lifetime is equivalent to less
harmful (bremsstrahlung) radiation.
(a)
(b)
(c)
Figure 6.19 Deformation (left) and Von Mises stress (right) of SB22 vacuum chamber due to (a) gravity (no ribs), (b) gravity and atmospheric pressure (no ribs), (c) gravity and atmospheric pressure (ribbed vacuum chamber).
183
The total lifetime of the beam is however dominated by Touschek lifetime which is
not related to pressure.
There are some analytical and numerical methods to calculate the pressure in the
vacuum chamber. In what follows two different approaches will be used for
calculating the pressure: MOLFLOW software that is based on the dynamics of
kinetic theory of gases; solving the mass balance equation [6.4]. Later we will
calculate conductance, photon flux, and thermal and photon-stimulated desorption
then calculate pressure profile for different cases.
6.1.6.1 The conductance and the effective pumping speed
To accommodate magnets, pumps are located in the space between magnets. The best
designs for pumping ports to guarantee the highest conductance are under
investigation. For initial calculations, a configuration like that of ALBA was used i.e.
pumps connected to the vacuum chamber through elbows with mm cross
sections. The pumps will be installed with a holder on one side of the girders.
For the purpose of calculating the pressure profile, it was assumed that the pumps will
be working at 75% of their nominal pumping speed in the 10-9
mbar pressure range.
6.1.6.2 Ray tracing of bending magnets’ synchrotron radiation in the horizontal plane
Ray tracing has been performed for the synchrotron radiation coming from the
bending magnets in the horizontal plane; crotch absorbers will be used solely all
around the ring. These absorbers have been located and distributed in such a way that
they cast a shadow on the next section.
To avoid any radiation hitting the vacuum chamber walls, the clearance between
vacuum chamber walls and photon rays must not be less than 5 mm in all parts.
In order to find the best place for photon absorbers, we have relied on two in-house
computer codes as well as a detailed drawing.
Figure 6.20 Ray tracing in the first block.
184
6.1.7 Desorption
6.1.7.1 Thermal desorption
The importance of thermal desorption is its role in determining the base pressure in a
vacuum system. Thermal desorption is described by outgassing rate (the quantity of
gas released from a unit area of a solid surface in unit time) or thermal desorption
yield (number of molecules released from a unit area of a solid surface in unit time).
As shown in [6.5], outgassing rate (or thermal desorption yield) decrease
exponentially with pumping time. Normally, it is estimated to be about
mbar.l/(sec.cm2) for cleaned and baked stainless steel. But after a hundreds hours of
pumping and for carefully chosen and well-prepared materials it will reduce to
mbar.l/(sec.cm2). Accurate analyses can be found in [6.5] and [6.6].
6.1.7.2 Photon stimulated desorption
A beam of photons directed at a surface can set up excited vibrational states in the
adsorbed molecules, which may lead to desorption or dissociation. Sometimes
incident photons can produce photoelectrons which cause electron-stimulated
desorption (ESD). ESD occurs mostly for electrons whose energy is less than 500 eV.
A variety of processes can occur where an electron strikes a molecule bound to a
surface. The molecule may dissociate; conversion of one binding state to another or
desorption of neutral or charged molecules and atoms.
By the way, PSD described by photon stimulated yield ( ), the number of gas
molecules released per incident photon, decreases with photon dose as shown in
Figure 6.21 and pumping time.
Figure 6.21 PSD yield for CO for baked and unbaked stainless steel [6.7].
185
6.1.8 The pressure profile
6.1.8.1 The base pressure
The base pressure is determined by the thermal outgassing of the vacuum chamber
and pumping speed and the location of pumps. Thermal outgassing can be calculated
from the following formula [6.8]:
Where: Q is the thermal outgassing, and
: is the specific outgassing rate after 1 h of pumping
: is the geometrical surface area
: is the time
: is the decay exponent
In a less rigorous way, the above formula can be written as
obtained form the formula above by setting ( is the thermal desorption yield).
MOLFLOW software that is based on dynamics of kinetic theory of gases was used to
calculate pressure profile of 6m of storage ring. The result is shown in Figure 6.22. As
discussed before ηt is taken to be mbar.l/(sec.cm2).
6.1.8.2 Dynamic pressure
During the operation of synchrotron, the most important source of outgassing is
photo-stimulated desorption (PSD). Total outgassing is calculated from
Figure 6.22 Base pressure in 6 m of storage ring.
186
The first part of this equation is due to thermal desorption and second part is due to
photon-stimulated desorption. PSD occurs in photon absorbers strongly and also in all
parts of a vacuum chamber due to scattering. PSD measurements of a copper crotch
absorber are described by Anashin et al. [6.9].
As discussed above, changes with time and photon dose. Therefore pressure
calculation must be done in different cases. Figure 6.23 shows the result of
calculations at first injection ( photon/m) and a current of 100 mA.
Ray tracing has been used to calculate photon flux in each part. In calculations it was
assumed that 10% of radiation is scattered all over the circumference of the storage
ring and the whole radiation produced by the dipoles is absorbed.
In Figure 6.24, mol/ph, and the machine works under full load (400mA,
1000Ah).
Figure 6.23 Pressure profile in 6 m of storage ring, first injection.
Figure 6.24 Pressure profile in 6 m of storage ring under conditions of full
operation ( mol/ph, 400mA, 1000Ah).
187
6.1.9 Instrumentation
To achieve appropriate pressure, we need an efficient system of pumping, monitoring
and control. Therefore many instruments such as different gauges, valves, pumps,
controllers, etc will be used in the ILSF vacuum system. It is preferred to use standard
components available in the market because of cost, availability of spare parts and
maintenance.
Figure 6.25 Pressure texture induced by ABS12.
Figure 6.26 Pressure texture induced by ABS11.
188
Since the final pressure is very low, two stages of pumping will be required, a
portable roughing station for pumping down from atmosphere to mbar and UHV
pumps to achieve and maintain mbar.
The roughing station includes a backing pump which works in atmosphere down to
mbar and a turbomolecular pump that will pump down the machine after the
backing pumps to mbar where the ion pumps will be switched on.
Several pumps will be used as UHV pumps in ILSF vacuum system. Sputter ion
pumps (SIP) are the main UHV pumps because of their good pumping speed for all
gases. Titanium sublimation pumps (TSP) will be used at the locations of high
outgassing. NEG pumps will be installed where there are space limitations.
Storage ring pressures will be measured in two stages too: in the atmosphere the
pressure is measured by Pirani gauges up to mbar, cathode gauges will be used
for measuring in the range of to mbar. Also, the current from SIPs can be
used for pressure measurement.
Quadrupole radio frequency mass spectrometers will be applied as residual gas
analyzer (RGA) in ILSF to measure partial pressure in storage ring. Measuring partial
pressure is a vital diagnostic tool used on all synchrotron light source vacuum
systems. Figure 6.27 shows the location of the valves, instrumentations and pumps in
one octant of ILSF storage ring.
6.1.10 Absorbers
Only crotch photon absorbers will be used in the ILSF vacuum system. Photon
absorbers need to be designed so that they can withstand high temperatures and high
temperature differences, and the corresponding thermal stresses under high thermal
loads. Therefore the locations of photon absorbers must be determined carefully.
Figures 6.28 and 6.29 show a typical ILSF absorber. Figures 6.30 and 6.31 show the
results of FEA for deformation of and stress in the lower jaw due to gravity.
Figure 6.27 The location of the valves, instrumentation and pumps in ILSF storage ring [6.1].
189
Figure 6.29 3D model of the lower jaw of ABS11.
Figure 6.28 3D model of ABS11 (a typical ILSF absorber).
Figure 6.30 Deformation of lower jaw due to gravity.
190
The total radiation power produced by bending magnets is about 407 kW. Most of this
synchrotron radiation is absorbed in photon absorbers. The power density of
synchrotron radiation that reaches the absorbers has a major role in creating
temperature gradients in absorber components. To determine the best location for
placing the absorbers and the power density that reaches them, a program was written.
The results of power calculations are shown in Figures 6.33 to 6.36 while the main
parameters of the absorbers in first block are listed in Table 6.3.
Table 6.3: Parameters of absorbers in block 1
Abs.# Effective
length*
(mm)
Effective
angle**
(mrad)
Total
power (W)
Total Flux
(ph/sec)
Minimum
distance
(cm)
Maximum
power
density
ABS11 173 61.4 3978 9.5+E18 117 183701268
ABS12 100 72 4679 1.1+E19 114 194635422
ABS13 117 43 2796 6.7+E18 256 38584724
ABS14 96 16.2 1050 2.5+E18 588 7327407
* Length of absorber exposed to synchrotron radiation
** Angle of radiation fan incident absorber
Figure 6.31 Stress in lower jaw due to gravity.
Figure 6.32 The location of the absorbers along the vacuum chamber.
191
Figure 6.33 Angular power density versus vertical angle for bending magnet.
Figure 6.34 Power density along absorbers of the first block
0.00E+00
5.00E+07
1.00E+08
1.50E+08
2.00E+08
2.50E+08
0 5 10 15 20
Po
we
r D
en
sity
(W
/m2
)
Unit lenght of the Absorber (cm)
ABS11 ABS12 ABS13 ABS14
192
Figure 6.35 Effective width along the absorbers of the first block.
0
0.5
1
1.5
2
2.5
3
3.5
4
0 5 10 15 20
Effe
ctiv
e w
idth
(m
m)
Unit lenght of the Absorber (cm)
ABS11 ABS12 ABS13 ABS14
Figure 6.36 Real power density on ABS12.
193
Figure 6.37 Thermal distribution in the lower jaw.
Figure 6.38 Distribution of Von Mises stress in the lower jaw.
194
Figure 6.39 Strain distribution in the lower jaw.
Figure 6.40 Water flow in the pipes of absorber ABS11.
195
6.2 Vacuum system of the booster
This section considers the vacuum system of the ILSF booster and its pressure profile
calculations. The booster ring pressure is in ultra-high vacuum region in which some
requirements must be considered. The vacuum chamber is a continuous pipe which
passes through several devices of different dimensions and cross sections, so the
dimensions of this pipe changes through this path. In addition, in order to reduce the
weak field effects, it is so important to reduce its thickness. The electron beam
circulates in the booster ring for a very short time, so there is no need to reduce its
pressure as much as that of the storage ring.
6.2.1 Booster’s layout
The total circumference of the ILSF booster is 192m. This booster has a four-fold
symmetry. There are 7 sections in each segment. Each segment is consists of 5 unit
cells and 2 matching cells. The main parameters of the ILSF booster are listed in
Table 6.4.
Table 6.4: Main parameters of the booster
Injection Energy 150 MeV
Extraction Energy 3 GeV
Horizontal emittances 32.42 nm.rad
Repetition Rate 2 MHz
Nominal Current 10 mA
Figure 6.41 Temperature distribution in ABS11.
196
6.2.2 Cross section of the vacuum chambers
ILSF Booster vacuum chamber has a circular cross section (Figure 6.42) except in
parts where the bending magnets surround the chamber. In these parts because of the
shape of the gap between the poles, the cross section of the vacuum chamber has to be
elliptical as shown in Figure 6.43.
Some main parameters for the circular and elliptical chamber cross sections in the
booster ring are listed in Table 6.5.
Table 6.5: Parameters of the vacuum chamber of the
booster ring at different cross sections
Radius
(cm)
Passing
Probability
Conductance
(liter//sec)
Area
(cm2)
Perimeter
(cm)
Circular 1.45 0.0359 2.75 6.60 9.1
Elliptical 0.88 × 2.3 0.033 2.44 6.36 10.5
Figure 6.42 Booster’s vacuum chamber cross section inside a quadrapole within a straight section.
Figure 6.43 Booster’s vacuum chamber cross section inside a bending magnet.
197
6.2.3 Supercell layout
This booster has a fourfold symmetry containing 4 segments in which there are 7
sections. Each segment is consisted of 5 unit cells and 2 matching cells. In each cell
there are “straight” and “curved” sections.
6.2.4 Vacuum chamber design
There are 4 different vacuum chambers having different lengths and cross sections.
The vacuum chamber has a circular cross section except in parts which are located
inside the bending magnets.
These chambers will be made of stainless steel 316 which is appropriate for UHV
conditions.
Figure 6.44 Arrangement of magnets in one superperiod (top), the matching cell (center) and the unit cell (bottom).
Figure 6.45 Booster’s lattice.
198
6.2.5 Pressure calculations
6.2.5.1 Gas sources
Before pumping the system, in addition to the volume of the gas already present, there
are several other sources which may increase the pressure inside it. Gases entering
into the system through permeation processes and leaks can be neglected because
these can be considerable only for pressures lower than 10-12
Torr at elevated
temperatures. The internal gas sources such as gas molecules released from the
surface and the bulk of the vacuum chamber walls mainly affect the pressure inside
the system.
Figure 6.46 Vacuum chamber in a matching cell.
Figure 6.47 Vacuum chamber in a unit cell.
Figure 6.48 Vacuum chamber in a matching cell.
Figure 6.49 Vacuum chamber in a unit cell.
199
6.2.5.2 Thermal desorption
Under equilibrium conditions, rate of gas molecules leaving the surface is balanced by
the rate of those arriving at the surface. This rate can only change because of a change
in temperature.
There are several factors that determine the total amount of adsorbed (and absorbed)
gases. The surface conditioning is a major factor that determines the total amount of
adsorbed gas molecules. Physical and chemical adsorption occur on the surface and
the amount of gases adsorbed is proportional to the real microscopic surface area, not
the geometric area. Outgassing is described by the following formula [6.14]:
where
is the outgassing
= 10 -11
[molecule/sec.cm2]
is the surface area which desorbs molecules
6.2.5.3 Photon-stimulated desorption
When system is exposed to the beam radiation, more deeply absorbed molecules are
released through photon-stimulated desorption. Photon stimulated desorption yield
has been studied experimentally. Generally, in a vacuum chamber, photon-stimulated
desorption yield, , decreases with accumulated photon dose and is proportional to
in which is the accumulated photon dose and the exponent is between
, at room temperature.
The (experimental) results of the desorption yield as a function of beam dose for CO
(mass 28) for unbaked in-situ and in-situ baked vacuum chamber has been shown in
Figure 6.42.
6.2.6 The pressure profile
Inside a vacuum chamber the equation for gas dynamic balance is [6.3]:
in which:
is the gas volume density [molecule m-3
]
is the longitudinal axis of the vacuum chamber [m]
vacuum chamber volume [m3]
flux of gas desorption [molecule sec-1
]
distributed pumping speed [m2 sec
-1]
The specific vacuum chamber molecular gas flow conductance per unit
axial length [m4 sec
-1] in which is the vacuum chamber cross section [m
2] and
is the Knudsen diffusion coefficient [m2sec
-1]
In the quasi-equilibrium state when V
, then the equation can be changed to:
200
It is well known that the outgassing rate (for both thermal desorption and photon-
stimulated desorption) depends on the surface conditions. The amount of total thermal
outgassing is achieved by the product of thermal outgassing rate and the total surface
area. The unit for the rate of thermal outgassing is expressed as "Torr liter per second
per cm2" while the gas load due to the photon-stimulated desorption is "Torr liter per
second."
Three main parameters in a vacuum calculation are conductance and the outgassing
rate and pumping speed. The conductance is considered as flow rate of gas molecules
limited by the geometry of the vacuum ducts. The outgassing is described by the
formula:
where:
is the out gassing rate [torr lit sec-1
]
is 10-11
[molecule sec-1
cm-2
]
is the photon flux of synchrotron radiation,
is the photon stimulated desorption yield
is the surface of the material which desorbs gas molecules [cm2].
6.2.7 The base pressure profile
Base pressure profile of the booster ring calculated by Vaccalc program is shown in
Figure 6.60. The average pressure of the chamber is 2.15 nTorr
Figure 6.50 Base pressure profile as calculated by VacCalc program.
201
6.2.8 Dynamic pressure profile
The dynamic pressure profile of the booster is shown in Figure 6.61 The average
pressure inside the chamber in this case is 1276.9 nTorr.
References:
[6.1] E. Al-Dmour, The vacuum system design for ALBA storage ring
(ALBA CDR, 2004).
[6.2] CAS course, Vacuum in Accelerators (CERN, 2006).
[6.3] Diamond vacuum design (2002).
[6.4] R. Kersevan, MOLFLOW program and user guide, (Sep. 1991).
[6.5] K. Akaishi et al., Vacuum 47 (1996) 741.
[6.6] J. Gómez-Goñi, “Temperature Dependence Of The Electron-Induced Gas
Desorption Yields from 316 L+N Stainless Steel, OFHC, Cu and Al
Samples”, Vacuum Technical Note 94-16, (July 1994).
[6.7] C.L. Foerster et al., J. Vac. Sci. Technol. A8(3) (1990) 1990-2856.
[6.8] James M. Lafferty, Foundations of Vacuum Science and Technology (Wiley,
1998) p. 513.
[6.9] V. Anashin et al., Proc. EPAC-98 Vol. 3 (Stockholm, 1998) 2163.
[6.10] H. Wiedemann, Particle Accelerator Physicsi (Springer-Verlag, 2007).
[6.11] H. Wiedemann, Synchrotron Radiation (Springer-Verlag, 2003).
[6.12] G. Rumulo, M. Munoz, Lifetime issues in ALBA (2005).
[6.13] Coulomb lifetime calculations for ILSF.
[6.14] C. Liu, J. Noonan, Advanced Photon Source Accelerator Ultrahigh Vacuum
Guide, ANL/APS/TB-16 (1994).
Figure 6.51 Dynamic pressure profile calculated by VacCalc program.
202
203
CHAPTER 7: RF systems
The main function of RF systems in accelerators is to capture the particle beam and
increase the energy of the particles by providing an adequate accelerating voltage
across the cavities. In the storage ring, this energy is required to compensate the
energy lost due to the synchrotron radiation emitted by the beam as it passes through
the bending magnets and insertion devices (IDs). In the booster, the RF system should
accelerate the injected beam of particles to the energy of the storage ring before they
are extracted and fed into the storage ring. RF systems basically consist of cavities,
RF amplifiers, low-level control systems and waveguides. High-power RF amplifiers
provide the required power and voltage across the cavities. Low-level RF systems
consist of different loops that control and stabilize the field inside the cavity.
Waveguide systems are employed to connect the different parts of an RF system.
Figure 7.1 shows the block-diagram of an RF system. The conceptual designs of
different parts of RF systems for ILSF storage ring and booster are explained in this
chapter. First, we will briefly introduce fundamentals of cavities and RF systems in
light sources.
7.1 Fundamentals of an RF system
To compensate the energy losses due to the emission of synchrotron radiation in a
storage ring, an electric field should be established across the cavity. This field must
alternate in time so that its direction will be opposite to the velocity of the electrons
that pass through the cavity. The standing wave electric field in the cavity can be
simply written as:
( , , ) ( , )sin( )z zE r z t E r z t (7.1)
Figure 7.1 Block diagram of an RF system in a light source.
204
where r represents the distance to the axis of the cavity, z the longitudinal distance
from the entrance of the cavity, the RF angular frequency, and is an arbitrary
phase. The energy gain on the cavity axis over the acceleration gap distance g, is
sinRFW eV D (7.2)
/2
/2(0, )cos
g
RF zg
V E z t dz
(7.3)
where is the maximum accelerating voltage of the RF cavity. To make sure that
the electrons get back their energy loss per turn, U01, they should reach the cavity at a
specific phase which is called the synchronous phase, and calculated from the
relation below [7.1]:
sin o rs
RF RF
U V
eV V (7.4)
The over-voltage factor is defined correspondingly as:
1
sin
RF
r s
Vq
V (7.5)
As shown in Figure 7.2, the electrons with the nominal energy, E0, reach the cavity at
the synchronous phase and gain the energy they have lost. An electron with a higher
energy travels a longer orbit and thus reaches the cavity later. In order to capture this
electron in the RF bucket along the nominal orbit, a lower amount of energy should be
given to this electron so that its energy decreases gradually and reaches the nominal
value. The opposite holds true for the electron with a lower energy. In order to have
this phase focusing action, the synchronous phase needs to be designed at the falling
slope of the RF voltage. Moreover, the electron revolution time should be an integer
multiple of the RF voltage period. This number is called the harmonic number and is
usually suggested to be divisible by many small factors due to flexibility
considerations in the timing system. Harmonic number shows the number of RF
buckets in the ring.
RF
rev
fh
f (7.6)
1 U0 is the electron energy loss per turn in Joules and Vr is in eV.
Figure 7.2 Synchrotron phase and phase focusing [7.1].
205
Once a standing wave is established in the cavity, the resistance of its walls causes
power dissipation. Shunt impedance, defined as:
2
2
RFs
Diss
VR
P (7.7)
represents the power efficiency of the cavity, therefore it becomes the key parameter
for cavity optimization. The shunt impedance of the fundamental mode should be
designed to be as high as possible while the higher-order modes (HOM) shunt
impedances should be minimized. The maximum tolerable HOM shunt impedances in
a storage ring with electron energy of and beam current of bI are specified by
stability thresholds, both in longitudinal and transverse directions [7.2]:
.
||
||,
2thresh s
c HOM b s
EQZ
N f I (7.8)
.
, ,
2thresh
c rev b x y x y
EZ
N f I
(7.9)
where Qs is the synchrotron tune, τx,y,s are the damping times and βx,y are beta
functions at the cavity. More explanations about these thresholds are given in
Section 7.2.1.
Other important cavity parameters are resonant frequency, quality factor, and
normalized impedance. Resonant frequency is an intrinsic characteristic of the cavity
which is determined by its geometrical dimensions. Resonant frequency of the cavity
should be determined based on the RF frequency of the accelerator. The coupling
factor ( ) which indicates the amount of coupled power to the cavity, can be
described as the ratio of the intrinsic quality factor (Q0) to the external quality factor
(Qext):
ext
o
Q
Q (7.10)
The intrinsic and external quality factors of a resonant cavity are defined as:
o
Diss
UQ
P
(7.11)
ext
ext
UQ
P
(7.12)
where ω is the cavity’s angular frequency,U is the stored energy of the mode in the
cavity,DissP the power dissipated in the cavity walls, and
extP the power coupled to the
matched waveguides out of the cavity (when there is no beam in the cavity). 0Q
depends on the cavity geometry while
extQ depends on coupling too. The choice of
206
the coupling depends on the cavity operational condition when a beam is present.
Loaded quality factor, loadQ is defined as
0
1 1 1
load extQ Q Q (7.13)
The normalized impedance is cavity’s geometry figure of merit which should be high
for the fundamental mode:
2
s RFR V
Q U (7.14)
To specify an RF system, first the RF voltage and frequency should be chosen. The
choice of RF frequency is explained in detail in Section 7.2.1. As the longitudinal
energy acceptance of the machine is limited by the RF parameters, RF voltage should
be selected in such a way that it will provide the desirable longitudinal energy
acceptance which should be the same as the transverse acceptance achieved by beam
dynamics. According to [7.1], the energy acceptance is expressed by:
2 r rev r
RF
RF
V F q f V F q
h E f E
(7.15)
where,
2 1 1( ) 2 1 cos ( )F q qq
(7.16)
and q is the over-voltage factor. It is worth noting that the selected voltage should also
result in a proper lifetime. To build up the RF voltage across the cavity, the power fed
to the cavities should be high enough to provide the power dissipated in the cavities as
well as the required beam power. Thus, the total required RF power can be calculated
as following:
RFTotal Beam DissTotalP P P (7.17)
where,
Beam r bP V I (7.18)
and DissTotalP is the dissipation power of all the cavities placed in the storage ring. Power
dissipated in a cavity depends on its voltage and shunt impedance:
2
2
cavDiss
s
VP
R (7.19)
One should note that by increasing the number of cavities (Nc) in a lattice, each cavity
voltage drops by factor of Nc, and so does the total dissipated power:
2 2
2 2
cav RFDissTotal c
s c s
V VP N
R N R (7.20)
The above-mentioned calculations have been done for ILSF storage ring and booster
and are presented with other considerations in the next sections.
207
Table 7.1: RF related lattice parameters of ILSF storage ring (ILSF1 lattice).
Parameters ILSF1 Lattice
Energy (GeV), 3
Beam current (mA), 400
Circumference (m), Cir 297.6
Energy loss per turn
(MeV), Vr
Dipoles radiation loss 1.0167
IDs radiation loss and
parasitic loss 0.4
Total loss 1.4
Momentum compaction factor, α 7.621×10-4
Energy spread, σE 1.0408×10-3
Revolution frequency(MHz), frev 1.0074
Transverse damping
time
(ms) 5.858
(ms) 3.386
Longitudinal damping time, τs (ms) 4.614
Short straight Sections
(Considered for
Cavities)
Number of 12
Length (m) 2.82
βx (m) 7.813
βy (m) 2.888
7.2 Storage Ring RF System
As discussed in the chapter on beam dynamics, ILSF1 lattice is the design most likely
to be used for the ILSF storage ring. Therefore, the conceptual design of the RF
system presented in this section is done based on this lattice. The RF-related beam
parameters are shown in Table 7.1.
7.2.1 Discussion of the optimum frequency
RF frequency is one of the main parameters of a synchrotron light source. The choice
of RF frequency does not seem straightforward, since it appears in the determination
of many other synchrotron parameters. One has to take the theoretical issues as well
as other practical concerns into consideration in order to choose an RF frequency,
which may not necessarily be the universally optimum choice, but will be the
optimum choice for the specific situation under consideration. In this part, a short
review and discussion of the main considerations that should be taken into account
concludes with the choice of RF frequency for ILSF storage ring.
208
7.2.1.1 Short review of RF frequencies of existing storage rings
RF frequencies of some 3rd
generation synchrotron light sources are listed in
Table 7.2. The widely used RF frequency of 500MHz seems a proper choice as a
considerable amount of experience exists for this frequency which can be utilized in
ILSF. But before making such a choice, the theoretical and practical consequences
should be assessed.
7.2.1.2 Theoretical consequences of the choice of RF frequency
Although the choice of frequency cannot be done solely based on theoretical issues,
they should be taken into account. The main parameters that are influenced by RF
frequency are[7.1]:
(a) RF voltage: As explained earlier, RF voltage should be selected in order to
provide the desirable energy acceptance and lifetime (especially Touschek lifetime).
Looking at Equation 7.15 for energy acceptance, it is obvious that for a given storage
ring in order to get a fixed energy acceptance at higher frequencies, higher RF
voltages are required. Although this means that more power is required, one cannot
conclude that lower frequencies are necessarily better since providing power may be
cheaper and easier at higher frequencies [7.1].
RF voltages required to provide different energy acceptances (1%, 3% and 5%) for
ILSF lattice have been calculated and plotted versus RF frequency in Figure 7.3. It
shows that a higher RF voltage is required for operation at higher frequencies as well
as for achieving larger acceptance values.
In addition to energy acceptance, Touschek lifetime also depends on RF frequency
and RF voltage but not in an explicit way.
Figure 7.3 RF voltage versus RF frequency for different energy acceptances in ILSF lattice.
0 100 200 300 400 500 600 700 800 900 10001
2
3
4
5
6
7
8
9
10
11
12
RF frequency(MHz)
RF
Voltage(M
V)
RF=1%
RF=3%
RF=5%
209
We have:
(7.21)
where,
(7.22)
, and is the number of electrons per bunch
which depends on the filling factor (F).
It is shown in [7.3] that for a given storage ring and energy acceptance Touschek
lifetime increases moderately with RF frequency and approaches a nearly constant
value at higher frequencies. This can be seen in Touschek lifetime plots computed for
ILSF lattice and depicted in Figure 7.4. Thus, contrary to what is sometimes
suggested, higher frequencies would be preferable as far as Touschek lifetime is
concerned, however Touschek lifetime is not a major factor in the selection of RF
frequency.
Figure 7.4 Touschek lifetime versus RF frequency for different energy acceptances in ILSF lattice.
0 100 200 300 400 500 600 700 800 900 10000
10
20
30
40
50
60
70
80
90
RF frequency(MHz)
Touschek L
ifetim
e(h
)
RF=1%
RF=3%
RF=5%
210
Table 7.2: RF frequencies and the cavities for some light sources (NC & SC denote
normal conducting and superconducting cavities respectively).
Bunch length: Bunch length is also influenced by RF voltage and frequency as can
be seen in the following formula:
2
1
2 1 1l E
RF revRF
Ec
f f V q
(7.23)
The bunch length in the ILSF lattice is plotted versus RF frequency in Figure 7.5 for
different energy acceptances. By decreasing the RF frequency or voltage, the bunch
length increases which results in a reduction of the bunch particle density, the intra-
beam scattering, and the induced fields in the vacuum chambers [7.4]. Although these
are helpful in decreasing multi-bunch instabilities, a long bunch length is not
appropriate for all users. If the users are interested in time-resolved measurements, it
is necessary to have the shortest possible bunch lengths and hence a high RF
2 There is no booster in MAX IV light source and the linac is the full-energy injector.
3 There is no booster in PLS II light source and the linac is the full-energy injector.
Synchrotron
light source
Energy
(GeV)
RF frequency
(MHz) Storage ring cavity Booster cavity
ALBA 3.00 499.654 NC EU-Cavity (DAMPY) Petra 5cell
SOLEIL 2.75 352.200 SC LEP CERN-LEP 5cell
Cu
SLS 2.40 500.000 NC ELETTRA single cell NC ELETTRA
single cell
TPS 3-3.3 499.654 SC KEK Petra 5cell
NSLS-II 3.00 499.680 SC CESR-B Petra 5cell or 7cell
ESRF 6.00 352.200 NC EU-Cavity (DAMPY) LEP type cavity
CANDLE 3.00 499.654 NC ELETTRA single cell DORIS 6cell
SESAME 2.50 499.954 NC ELETTRA single cell
Diamond 3.00 500.000 SC CESR modified Petra
ELETTRA 2.40 499.654 NC ELETTRA single cell Petra 5 cell
MAX IV 3.00 100.00 NC MAX LAB single cell __2
CLS 2.90 500.000 SC CESR modified Petra
PLS II 3.00 499.973 SC CESR __3
211
frequency [7.1]. In this case, feedback systems with higher bandwidth are used to
damp multi-bunch oscillations.
Synchrotron oscillations: The number of synchrotron oscillations per orbit should be
small so as not to limit the available tune space for the working point. According to
the expression of synchrotron tune [7.1],
cos
2
RF RF ss
rev
f VQ
f E
(7.24)
lower RF frequency and voltage are preferred but in the case of very low momentum
compaction factor α, as in modern lattices, small synchrotron tune is available
regardless of RF frequency. Thus, this parameter does not affect the choice of RF
frequency for ILSF either as its momentum compaction factor is 7.621×10-4
which is
low enough to have low synchrotron tunes in the order of 10-3
for different RF
frequencies as shown in Table 7.2. We should note that in both cases these tunes have
been calculated when 3% acceptance is provided by RF voltage.
Instabilities: Single-bunch and multi-bunch instabilities are the fundamental
instabilities in the synchrotron light sources. In general, a higher threshold for single-
bunch instabilities is obtained with longer bunch length. Multi-bunch instabilities are
more easily canceled out when fewer bunches exist which corresponds lower RF
frequency as well. Nevertheless these points are not critical since RF buckets can be
not fully filled in the multi-bunch case and sufficient high single-bunch current may
be attainable even at high RF frequency.
In order to show the effect of RF frequency on multi-bunch instabilities, the
longitudinal stability threshold impedances of ILSF have been compared for 100 MHz
and 500 MHz RF systems. These thresholds are calculated by expressions (7.8) and
(7.9) for the lattice parameters given in Table 7.3. However one should note that in
order to see the effect of RF frequency on multi-bunch instabilities it is not
appropriate to compare these thresholds as a function of frequency, rather one should
Figure 7.5 Bunch length versus RF frequency for different energy acceptances in ILSF lattice.
0 100 200 300 400 500 600 700 800 900 10000
5
10
15
20
25
30
35
40
RF frequency(MHz)
Bunch L
ength
(mm
)
RF=1%
RF=3%
RF=5%
212
compare the dependence of these thresholds on the ratio N of frequency to the RF
frequency RFN f f . Figure 7.6 (a) and (b) show the above-mentioned
comparisons. At first, looking at Figure 7.6(a), one could wrongly conclude that the
instability is more critical at lower RF frequencies since ILSF stability threshold with
100MHz is lower than 500 MHz over the whole frequency range (see the green curves
in Figure 7.6 (a). Such a comparison would mean that, for example, at 1 GHz one may
be comparing the threshold for the tenth unwanted HOM of ILSF 100 MHz cavity
with that for the second unwanted HOM of ILSF 500 MHz cavity. However in
Figure 7.6 (b) where the thresholds have been plotted versus N the two curves have
switched their positions. This indicates that the instabilities are less serious at lower
RF frequencies as the thresholds of MAX IV and ILSF with 100 MHz RF systems are
higher than those of BESSY II, ALBA and ILSF with 500 MHz RF systems.
Table 7.2: Parameters of MAX IV, ALBA, BESSY II and ILSF SR sources
involved in calculation of stability threshold impedances.
Parameters MAX IV ALBA BESSY II
ILSF
100 MHz
RF system
500 MHz
RF system
(MHz) 100 500 500 100 500
(GeV) 3 3 1.7 3
(mA) 500 400 250 400
2×10-3
8.34 ×10-3
6.16×10-3
2.406×10-3
8.051×10-3
6 6 4 6
(MHz) 0. 56779 1.12 1.25 1.0074
3.07×10-4
8.59×10-4
7.3×10-4
7.621×10-4
(ms) 5.2 3.106 8 5.858
(ms) 3.07 4.077 16 3.386
(ms) 8.2 5.289 16 4.614
(m) 2.8 8 1 7.813
(m) 6.3 3.2 1.2 2.888
213
7.2.2.3 Practical consequences of the choice of RF frequency
Practical issues that should be considered for selecting the RF frequency are mainly
technical considerations in availability and cost of the main components of the RF
system i.e. the cavity and RF power amplifier.
Cavity: In general, cavity dimensions put practical limits on the RF frequency. The
frequency should not exceed the upper limit at which the cavity stops providing the
required voltage across the accelerating gap and instead its field propagates down the
beam pipe. Moreover, in order to have high shunt impedance, the wavelength of the
upper limit must be greater than twice the largest dimension of the pipe which yields a
maximum frequency of less than 1 GHz [7.1]. The lower limit of frequency is
determined by the cavity’s shunt impedance, cost, design complexity and also the
available space. Generally, the cavity shunt impedance increases with the square root
(a)
(b)
Figure 7.6 Longitudinal stability threshold impedances of ILSF when using 100 MHz and 500 MHz RF frequency (a) versus frequency, (b) versus distance from RF frequency.
0 0.5 1 1.5 2 2.5 3 3.50
2
4
6
8
10
f (GHz)
Z|| (
k
)
ILSF (f
rf=500MHz)
ILSF (frf
=100MHz)
ALBA
BESSY II
MAX IV
0 1 2 3 4 5 6 7 8 9 100
2
4
6
8
10
Z|| (
k
)
N= f / frf
ILSF (frf
=500MHz)
ILSF (frf
=100MHz)
ALBA
BESSY
MAX IV
214
of the RF wavelength. However, in practice the available space is actually always
limited, and also, the cavity design becomes more complex at lower frequencies, thus
modest dimensions/frequencies are of interest. Table 7.2 establishes these practical
points as 100, 352 and 500MHz i.e. the RF frequencies already used in 3rd
generation
SR sources. Beyond these frequencies, the cavity of a same design inevitably has
larger dimensions at a lower frequency and hence entails more mechanical complexity
in fabrication.
RF power amplifier: The main consideration regarding the RF power amplifier and
frequency is the availability of adequate RF power sources. This means choosing
either a frequency which is used in other light sources or the one used for other
applications such as radio and TV transmitters that are commercially produced [7.1].
For typical frequencies up to 250 MHz, tetrode amplifiers are commonly used
whereas for higher frequencies klystron and IOT transmitters are more suitable. Solid-
state amplifiers are recently utilized in SR sources at higher frequencies (352 and 500
MHz) because of their advantages explained in Section 7.2.1. The power combiners
of these high-power solid-state amplifiers would become very large and mechanically
complex at lower frequencies although transistors with higher power are available at
these frequencies. According to the above-mentioned points, selecting the type of a
power amplifier which is usually done on the basis of accessibility and cost, dictates
the range of the RF frequency. Since most of the light sources have used higher
frequencies, the amplifiers at higher frequencies are probably more readily available
and preferred in practice.
7.2.2.4 Conclusion
The previous discussion shows that there is no optimum choice for the RF frequency
though it has important effects on the design and behavior of the machine. Although
theoretical issues seem to be mostly in favor of low frequencies, in the new generation
of synchrotron light sources as listed in Table 7.2 the higher frequency of 500MHz is
often chosen due to practical issues, and the possibility of compensating for the
theoretical problems, and utilizing the experience of other light sources. The latter is
one of the most important factors in this regard because many of previously tested
designs and fabricated components could be utilized in addition to the practical
knowledge. Consequently for ILSF, on the basis of the above-mentioned points, as
well as the local expertise in the field of solid-state amplifiers and in order to keep
open the possibility of time-resolved measurements for users, 500 MHz is chosen as
the RF frequency.
7.2.3 Cavity considerations
7.2.3.1 Short review of existing cavities
To determine the proper cavity for ILSF, first we shall review the existing cavities in
this section. Generally two categories of cavities exist, superconducting (SC) and
normal-conducting (NC). Having extremely high shunt impedances, the power
dissipated in SC cavities is negligible. As a result, higher RF voltages can be applied
per cell, which allows the minimization of the number of cells. This makes SC
cavities a preferred choice for storage rings especially those operating at higher
energies and currents. Since SC cavities have wide beam tubes, HOMs would not be
trapped in the cavity. Therefore HOM damping in SC cavities is not as critical as in
215
the NC cavities. There are three types of SC cavities which are now used in light
sources, CESR, KEKB and LEP cavities. The CESR cavity is a 500 MHz single-cell
cavity that has been adopted for CLS4[7.5], TLS[7.6], DIAMOND[7.7] and
SSRF[7.8]5. In the LEP-type cavity used for SOLEIL[7.2], a single cryostat houses
two 352 MHz cavity cells with a beam tube of 400 mm diameter between the two
cells. Two versions of KEKB cavities at frequencies of 508MHz and 500MHz are
available, the latter being used in the Beijing collider [7.9]. Despite being HOM-free
and having high shunt impedance, SC cavities are more complex requiring an
extensive cryogenic system. They are therefore less reliable which means more
average trip rates in comparison to NC cavities as reported in [7.9] and they usually
require more resources. However, the situation is improving and these factors are not
the deciding factors.
The main problem in using SC cavities is that they require longer straight sections
which are reserved for IDs in some lattices. SC cavities thus occupy the space usually
occupied by IDs and reduce the number of IDs and the beam lines. In ILSF1, the
medium straight sections with small beam size are reserved for IDs and the 2.82-
meter length of the short straight sections is not enough for a SC cavity.
Consequently, SC cavities are ruled out for ILSF1 lattice. For other ILSF candidates,
SC cavity could be considered as a choice
Considering NC cavities, several room-temperature single-cell copper cavities have
been developed for light source applications e.g. EU, ELETTRA, PEP II, KEK-PF,
DAPHNE, Spring 8, and MAX IV. The characteristics of these cavities and two SC
cavities are compared in Table 7.4. Since the resonance frequency of only EU,
ELETTERA, PEP II, KEK-PF, and SPring 8 cavities is 500 MHz, they could be
considered as candidates for the ILSF storage ring. Figure 7.7 shows these cavities.
Table 7.3: General specifications of different NC and SC cavities.
Resonant frequency
(MHz)
Shunt Impedance
6
(MΩ)
Unloaded Quality factor
Length (m)
Nominal Voltage
(kV)
Max. power @ coupler
(kW)
EU 500 3.3 30000 0.5 [7.2] 700 150
ELETTRA 500 3.3 39000 0.9 [7.30] 650 NA
PEP-II 479 3.8 33000 1.5 [7.2] 800 500
KEK-PF (ASP version)
500 3.57 39000 1 [7.23] 750 150
Daphne 368 2 33000 1.9 [7.2] 250 NA
SPring8 508.5 2.8 40000 0.44 [7.24]
530 NA
Max IV 100 1.6 20000 0.5 [7.26] 350 NA
CESR 500 89000 --- 2.9 [7.2] 3000 NA
4 Canadian Light Source
5Shanghai Synchrotron Radiation Facility
6 Rs = V
2 / 2.P
216
7.2.3.2 Considerations of multi-bunch instabilities
As mentioned before, unlike SC cavities, HOM damping is crucial in NC cavities.
Generally, HOMs induced by the beam inside the cavity is the most important factor
contributing to an increased emittance in both transverse directions through transverse
coupled-bunch oscillations, increasing the energy spread through longitudinal
coupled-bunch oscillations, and potentially limiting the beam current because of very
large oscillation amplitudes.
Thus in modern storage rings it is vital to damp the HOMs in order to limit any
increase in the emittance to within tolerable bounds and prevent beam instabilities
from spoiling the low emittance which is produced at a large cost. The HOM
spectrum of the cavity resonators is broad up to very high frequencies. The modes
above the cut-off frequency of the vacuum chamber (typically in the range of 3 GHz
for 3rd
generation synchrotron radiation sources) are not trapped in the cavity. They
propagate down the vacuum chamber and are damped by the surface resistance of the
chamber walls. Therefore cavity HOM damping is relevant in the frequency range
above the fundamental mode up to the vacuum chamber cut-off frequency. Various
methods have been applied to decrease the HOMs in the cavities so they would be
under the tolerable thresholds for the onset of coupled-bunch instabilities. The main
ones are[7.2]:
Detuning of the most dominant HOM away from its driving beam frequency using
a second tuner and/or by changing the cavity temperature (used in Elettra)
(a) (b) (c)
(d) (e)
Figure 7.7 NC cavity candidates for ILSF storage ring: (a) ELETTRA, (b) EU, (c) PEP II, (d) KEK-PF, (e) Spring8
217
Using narrow-band damping antennas to damp one or a few major HOMs
(MAX IV and KEK-PF)
Using higher and lower harmonic RF systems for Landau damping and decoupling
of the synchrotron tune of neighboring bunches respectively
Using broadband bunch-to-bunch feedback systems
Using broadband waveguides to take out the HOMs from the cavity and damp
them in the absorbers placed at waveguides’ endings (PEP II and EU)
To make sure that the effect of cavity HOMs is sufficiently reduced, the HOM
impedances should be lower than the stability threshold impedances. These thresholds
indicate the maximum cavity impedance allowable in a storage ring with a given set
of parameters, both in longitudinal and transverse directions and calculated by
Equations 7.8 and 7.9 respectively. ILSF storage ring parameters are given in
Table 7.3 and its longitudinal threshold has been compared with other light sources in
Figure 7.6. The stability thresholds in both directions are then calculated for 500 MHz
RF frequency and compared with HOMs of the cavity candidates in Figure 7.8. All
HOMs are given in Table 7.5 and Table 7.6. Although, lower values of beta function
at cavities result in higher thresholds which is better from the point of view of HOM
damping in transverse direction, short straight sections with medium values of beta
function have been considered for cavities to save the low beta straight sections for
insertion devices.
Table 7.5: Longitudinal HOM impedances of ILSF cavity candidates
EU7 ELETTRA[7.10] CESR[7.9] PEP II [7.28] KEK-PF (ASP)
8
f(MHz) R(kΩ) f(MHz) R(kΩ) f(MHz) R(kΩ) f(MHz
)
R(kΩ) f(MHz) R(kΩ)
499.5 3534 499.7 3400 1081.3 0.486 476 3809 500 3840 619.7 0.335 949.50
6
1017 2932.3 0.353 758 0.809 784.9 2300
625.8 0.136 1057.1
99
24 4127.9 0.874 1009 0.055 791.1 2100
620.1 0.153 1421.4
56
197 4210.5 0.669 1283 1.736 1314.1 0.18
625.8 0.628 1514.6
38
85 4259.8 0.743 1295 2.287 1314.9 0.17
639.4 0.179 1606.3
48
165 4298.8 0.329 1595 0.729 1354.9 700
643.9 1.574 1876.9
71
12 4352.3 0.434 1710 0.141 1357.6 680
654.6 1.091 1948.4
75
60 4574.4 0.477 1820 0.07 1719.6 80
670.0 2.000 2072.0
36
1 4617.9 0.316 1898 0.442 1780 8
812.5 0.174 2124.7
92
208 2121 0.616 1810 0.4
1024.2 0.222 2160 0.006 1840 0.8
1037.7 0.002 2265 0.126 1870 0.011
1057.5 0.456 1960 0.3
1083.7 0.088 2000 0.8
1533.8 0.548
1578.4 1.134
1338.9 0.370
2284.4 0.626
1384.7 0.092
7Private communication.
8Private communication.
218
Table 7.6: Transverse HOM impedances of ILSF cavity candidates.
EU ELETTRA CESR PEP-II KEK-PF (ASP)
f
(MHz)
R
(kΩ/m)
f
(MHz)
R
(kΩ/m
)
f
(MHz)
R
(kΩ/m)
f
(MHz)
R
(kΩ/m)
f
(MHz)
R
(kΩ/m
) 619.7 21.980 743.169
2900 679.4 12.885
6
792 42 692.3 105
625.8 63.652 743.303
2900 1138.5 0.8514 1063 38 704.6 103
1024.2 48.401 745.28 8700 1206.8 1.5272 1133 1.82 707.9 103
1029.3 43.315 746.463
8900 1240.6 3.1536 1202 12.2 797.6 1300
1037.7 58.640 1114.274
11200 1327 76.7 1005 6000
1057.5 31.752 1114.706
10800 1420 126.9 1005.8 6000
1083.7 45.211 1241.307
2100 1542 0.89 1250 20
1511.1 15.162 1242.237
2100 1595 1.39 1360 90
1533.8 29.718 1304.342
200 1676 64.5 1450 1
1384.7 23.110 1749 2.31 1480 0.25
1522 1.3
1580 5
1610 0.4
1680 2.8
1750 0.25
1850 1.3
1910 5.5
1950 12
1980 3.5
EU, PEP II, and ASP cavities are nose-coned cavities while Spring8 and ELETTRA
have bell-shaped cavities. According to the discussions in [7.27] compared to nose-
coned cavities, bell-shaped cavities have worse HOM problems, and to use them in
rings with high beam currents (about 400 mA), one has to resort to complicated HOM
damping techniques such as frequency shifting based on fine temperature tuning. This
technique has been successfully used in ELETTRA and has provided a current of 400
mA in ELETTRA and SLS ring without instabilities. However, SPring8 HOM
damping characteristics are not good enough for a 400 mA ring and therefore it has
been eliminated from the list of ILSF cavity candidates. Looking at Figure 7.8(a) EU
and PEP II longitudinal HOM impedances are lower than the threshold for ILSF,
while ELETTRA and ASP impedances are higher. By using temperature tuning which
has already been utilized in ELLETRA and SLS rings, the HOMs of ELETTRA
cavity can be moved away from the critical frequencies to avoid instabilities. In the
ASP cavity, HOM damping is achieved with damping antennas. This method can
assure stability up to 200 mA (ASP and KEK-PF rings), but it has to be checked for
400 mA. PEP II and EU cavities are equipped with three broadband waveguides to
damp the HOMs, and HOM damping is more efficient and less operationally
complicated since it does not require accurate tuning as in ELETTRA. This can be
seen in Figure 7.8 where the longitudinal HOMs of EU and PEP II cavities are
significantly lower than the stability threshold of ILSF. However, in the transverse
direction, the measured HOMs of the NC cavities exceed the thresholds at some
points. This is not a serious problem as it can be dealt with by a feedback system. The
figure also shows that HOM damping is not an issue for CESR SC cavity as its HOM
219
impedances are greatly lower than the threshold. Consequently, EU, PEP II, and
ELETTRA cavities are appropriate from the stability point of view and can be used in
the ILSF storage ring. ASP cavity could be used to provide 200 mA of beam current
but further investigation is necessary to ascertain the lowering of HOM impedance
below 400 mA. In addition to damping efficiency and operational complexity, cost
will be a deciding factor for the final selection of a cavity for ILSF.
(a)
(b)
Figure 7.8: Comparison of HOM impedances of cavity candidates with ILSF threshold impedance: (a) longitudinal impedances. (b) transverse impedances.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 550.01
0.1
1
10
100
1000
10,000
Frequency (GHz)
ZII (
k
)
ILSF ZIIThreshold
EU cavity ZIIHOM
ELETTRA ZIIHOM
CESR ZIIHOM
PEP-II (SPEAR3) Z||HOM
KEK-PF(ASP version) Z||HOM
0 0.5 1 1.5 2 2.5 3 3.5
0.1
1
10
100
1,000
10,000
Frequency (GHz)
Z(k
/m)
ILSF Z
Threshold
EU Cavity Z
HOM
ELETTRA Z
HOM
CESR Z
HOM
PEP-II (SPEAR3) Z
HOM
KEK-PF(ASP version) Z
HOM
220
7.2.3.3 Cavity and RF parameters
As calculated in Chapter 3, a total RF voltage of 3.6 MV is required to provide the
desirable energy acceptance and lifetime in ILSF storage ring. In the following, the
number of cavities and the RF power that should be fed to them are calculated for
different cavity candidates based on their specifications given in Table 7.4. The power
calculations have been done using Equations (7-17)-(7-20) for ILSF cavity candidates
and the results are presented in Table 7.7. It should be noted that the total energy loss
of 1.4 MeV also includes the parasitic loss caused by RF-resonator-like components
of the vacuum chamber in addition to the beam energy loss due to synchrotron
radiation from bending magnets and insertion devices. In order to deliver the requisite
RF power to a cavity, at least 10 percent more power should be generated at the RF
generator output regarding the transfer losses of the waveguide system. The number
of cavities should be such that the voltage on each cavity is acceptable. Accordingly,
6 cavities would be required if EU or ELETTRA cavities are selected, whereas 5
cavities will be sufficient in case of PEP-II. For ASP cavities, the maximum power
that can be maintained at the coupler is another factor that has to be taken into
account. By using five cavities, a power of 180 kW should be fed to each cavity but
the existing ASP coupler can only tolerate a maximum power of 150 kW. Therefore 6
ASP cavities are assumed in the calculations of Table 7.7. We also assumed 400 mA
is achievable without instability excitation by the HOMs of the ASP cavities.
Table 7.7: RF power considerations for ILSF storage ring cavity candidates
EU ELETTRA PEP-II
KEK-PF
(ASP
version)
Beam current (mA) 400 400 400 400
Beam loss per turn (keV) 1400 1400 1400 1400
Beam power (kW) 560 560 560 560
Total RF voltage (MV) 3.6 3.6 3.6 3.6
Over-voltage factor (q) 2.57 2.57 2.57 2.57
Shunt impedance (MΩ) 3.3 3.3 3.8 3.6
No. of cavities 6 6 5 6
Occupying Space 3 short S.S. 3 short S.S. 5 short S.S. 3 short S.S.9
RF voltage per cavity (kV) 600 600 720 600
Dissipation power per
cavity (kW) 54.6 54.55 68.3 50
RF power per cavity (kW) 148 148 180 143
Total RF power + 10%
transmission loss (kW) 978 978 990 946
9 Straight section
221
According to Table 7.7, the total required power is in the same range for all cavity
candidates. Thus, the cost of cavities and the other required components (waveguides,
LLRF systems and amplifiers) would be an important deciding factor in each
scenario. The space the cavities occupy in the storage ring tunnel should also be
considered because it affects the amount of space available for the insertion devices.
Two EU, ELETTRA, or ASP cavities fit in one short straight section so a total of 3
short straight sections are required for these cavities. However, PEP-II cavity has a
longer length and requires one short straight section per cavity, hence five short
straight sections would have to be used for PEP-II cavities.
As for the delivery of RF power to the cavity, it is necessary to consider the coupler
and transition from waveguide to coupler. The input coupler must be capable of
feeding CW RF power (forward) into the cavity and handling the full reflection.
Proper cavity couplers have been designed for each of the ILSF cavity candidates:
except for the PEP-II cavity which requires an iris coupler, all the other cavities work
with a coaxial loop coupler. Figure 7.9 shows both of these two coupling systems.
(a) (b)
Figure 7.9 Storage ring cavity coupler configurations: (a) coaxial loop coupler, (b) iris coupler.
Figure 7.10 Schematic view of waveguide to coaxial transition (WATRAX).
222
In order to connect the waveguide to coaxial cavity couplers it is necessary to
implement a waveguide to coaxial transition. The particular design (WATRAX) at
ALBA (Figure 7.10) has been tested successfully and operated routinely up to 150
kW [7.26].
7.2.3.4 Cavity cooling system
Transferring high power RF energy into the cavity would results in its overheating.
Cavity overheating would cause vacuum leakage, shift in cavity’s resonant frequency
and instability in beam current which are undesirable. Establishing a cooling system is
required to prevent such unwanted effects and this is done by water and air cooling.
Water circuits are used to maintain temperature rise less than 10°C across the storage
ring cavity. Expression for volume flow rate needed to absorb a specific heat can be
calculated by [7.12]:
(7.25)
where P is the dissipated power in watts, ∆T is the temperature drop and n is the
number of cooling circuits. Each of the cavity candidates has its own cooling system.
Table 7.8 lists the characteristics of each of these systems. The ELETTRA cavity has
a complex cooling system which in addition to removing the the dissipated power,
must allow a tight regulation of the surface temperature. This is required for
temperature tuning to prevent the coupled bunch instabilities.
Table 7.8: The cooling systems of different cavity candidates [7.13][7.15].
EU Elettra [7.14] PEP II ASP
Water flow (lit/min) 181 [7.13] 250 N.A N.A
Handeled power (kW)
54.5 60 69 73
Cooling pass for cavity body
4 12 6 [7.15] N.A
Water condition
Demineralised (deionized),
Conductance of 0.2 µS/cm
Demineralised (deionized),
Conductance of 1 mS/cm
N.A N.A
7.2.3.5 Beam-cavity interaction
To deliver the maximum power from the generator to the cavity, their impedances
should be matched by adjusting the coupling loop in the cavity. There is, however, the
complication that the beam current and synchronous phase angle affect the
transformed cavity impedance seen by the generator and therefore the optimum
matching should vary in a manner consistent with the presence of the beam inside the
cavity. But this is not possible as turning the coupling loop in the cavity will break the
vacuum. Thus, the coupling is usually optimized for the storage ring nominal beam
current and the reflected power corresponding to all other beam currents has to be
dealt with. To show the beam loading effect quantitatively, the cavity impedance seen
by the generator and the reflection coefficient will be calculated in this section.
223
The cavity equivalent circuit for the frequencies in the neighborhood of the
fundamental resonance is shown in Figure 7.11. The admittance of the beam-loaded
cavity seen by the generator can be written as
The second term is the beam loading effect whose real and imaginary parts can be
written in terms of the synchronous phase , the phase angle between the
synchronous particle and zero crossing of the RF cavity voltage:
whereby one obtains the following expression for the input admittance:
The matching condition occurs when the generator’s output admittance equals the
cavity admittance seen by the generator. This can be achieved for the nominal beam
current by adjusting the coupling coefficient to the value
Using the above value one obtains the following for the complex reflection
coefficient:
where . As can be seen, by adjusting the coupling factor,
only the real parts of the impedances will be matched at the nominal current and in
order to have the imaginary parts cancel each other out matching the cavity resonance
frequency should be detuned. This can be done by the cavity plunger and the detuned
resonance frequency will be
L2 L1 CRs
RA
IB
Yin
+
Vcav
-
Figure 7.11 Equivalent circuit of a resonant cavity near its fundamental resonance frequency.
224
By detuning the cavity, no power will be reflected from the cavity at the nominal
beam current and all the power is transferred to the cavity. The reflected beam power
and correspond voltage standing-wave ratio (VSWR) for other beam currents can be
simply calculated from the following formulas:
For the ILSF RF system the relevant parameters are , ,
, , (linac definition), ,
. With these values the coupling factor for optimum matching at 400
beam current evaluates to 2.71. The reflected power for different have been plotted
for different beam currents in Figure 7.12.
The amount of cavity detuning which is the frequency difference between the detuned
resonance frequency and the generator frequency (nominal cavity resonance
frequency) is plotted in Figure 7.13. For full matching at 400 mA, the cavity should
be detuned o 499.9704 MHz, which 33.8 kHz lower than the generator frequency.
Detuning the cavity to a frequency lower than the generator frequency also ensures
Robinson stability i.e. the particles with higher energy travel longer circumferences
and thus have a frequency component lower than the reference particle. Therefore the
high-energy particles see a higher cavity impedance and their energy gain is less than
the reference particle. The opposite happens for particles with lower energies than the
Figure 7.12 Cavity reflected power versus beam current.
0 100 200 300 400 500 6000
10
20
30
40
50
60
70
80
Beam Current (mA)
Refl
ecte
d p
ow
er
(kW
)
Cavity @ 500MHz
Detuned cavity
225
reference particle. Figure 7.14 shows the impedance seen by particles with different
energies under Robinson-stable condition.
Figure 7.13 Detuning frequency for impedance matching at different beam currents.
0 100 200 300 400 500 600-60
-50
-40
-30
-20
-10
0
X: 400
Y: -33.78
Beam Current (mA)
Detu
nin
g f
req
uen
cy,
f-f
res
-de
tun
ed(k
Hz)
Figure 7.14 Robinson-stable condition when cavity is detuned to a lower frequency than the generator.
Reference
particle
High-energy
particle
Low-energy
particle
226
7.2.4 High power RF Generator
High-power RF generators provide the necessary radio frequency power for the linear
accelerator, booster and storage ring. The power in the linear accelerator is in the form
of pulses with very high peaks. Currently the only sources for these pulses are
microwave tubes such as Klystron. In the case of the booster and storage ring the RF
sources are CW sources with much lower peaks compared to linear accelerators.
Historically microwave tube amplifiers were the only sources, but in recent years
solid-state amplifiers have successfully been used in some accelerator facilities. The
linear accelerator RF amplifier is not discussed here since it is included in the linear
accelerator package from the supplier. But booster and storage ring amplifiers are
built separately. In the following we discuss briefly different options for the booster
and storage ring amplifiers.
7.2.4.1 Discussion of different technical options for high power RF generator
The extremely high power required in synchrotron light sources leaves few options as
to what can be used as RF generators. Most of these options such as klystron and IOT
are different versions of a vacuum tube. In electronics, a vacuum tube is a device used
to amplify or switch an electrical signal by controlling the movement of electrons in a
low-pressure space. Most of the production of vacuum tubes is intended for the
market of television broadcast transmitters (wideband amplifiers with an output power
of about 50 kW). In this area IOT is progressively replacing the klystron. For
accelerator applications, which require higher average power (several hundred kW),
klystrons have generally been used, but the accelerator community, has also started to
convert to the use of IOTs in order to adapt to the marketplace. As a result, high
average power klystrons are disappearing in the marketplace. Two to four IOTs are
generally combined in order to achieve the power plant requirements (a few 100 kW).
For instance, DIAMOND, ALBA, and ELETTRA have opted for this solution [7.16].
Although microwave amplifier tubes such as klystron are still at the heart of most
accelerators, in recent years the cost of these high power RF transmitters has tripled.
Also only a few manufacturers can currently supply these amplifiers. Using klystrons
will result in continued reliance on vacuum tube technology, provided by a single
supplier, which could possibly drop it from its product line. Therefore, it is crucial to
the accelerator operation to start exploring alternative technologies for the production
of high power RF. Recent success at the SOLEIL light source in utilizing high power
solid-state technology for RF amplifier is very encouraging. The Brazilian
Synchrotron Light Laboratory (LNLS) has also implemented the solid-state RF
amplifier. The ESRF and SLS facilities are also proposing the utilization of solid-state
RF amplifier as part of their RF system upgrade program.
Solid-state RF amplifiers are being considered for an increasing number of accelerator
applications, both circular and linear. Their capabilities extend from a few kW to
several hundred kWs, and from less than 100 MHz to above 1 GHz. However, for
high-power ones, higher frequencies are preferable considering the component sizes
and the required space. Solid-state power amplifiers are very attractive for
individually-driven independently-phased superconducting cavities in accelerators
due to the following features:
227
Modularity, (which allows for easier and quicker maintenance and the possibility
of reduced power operation in case of failure)
Low-phase noise
Reliability
Safety (due to absence of high biasing voltages)
Low maintenance cost
Long lifetime
In SOLEIL, 5 solid-state amplifier towers provide the required RF power at 352 MHz;
these include a single 35 kW amplifier tower in the booster and four 190 kW
amplifiers in the storage ring. All these amplifiers consist of combinations of a large
number of 330 W unit amplifiers (147 modules in the booster and 4 towers of 724
modules in the storage ring), based on a design developed in-house, with
MOSFETs10
, integrated circulators, and individual power supplies. The following
table shows the parameters of the booster amplifier in SOLEIL.
Table 7.4: General specifications of the SOLEIL
booster amplifier modules [7.17].
In view of the above-mentioned points, and also the existence of local expertise in
design and fabrication of low-power solid-state amplifiers, ILSF has decided to
develop solid-state amplifiers for the booster and storage ring RF systems. This would
result in a lot of domestic R&D activities.
7.2.4.2 Solid-state high-power amplifier
Solid-state amplifiers are based on transistors instead of vacuum tubes as active
devices. First RF silicon devices were bipolar junction transistors (BJT). Vacuum
tubes were then generally preferred for medium- and high-power applications and
solid-state amplifiers were mainly used as driver stages with output CW power up to
some hundreds of watts at few tens of MHz. With the development of the integrated
circuit technology, MOSFETs could be used, which have higher gains, lower noise
levels and stand higher VSWR compared to BJTs.
The LDMOS is a member of the Enhancement-Metal-Oxide-Semiconductor FET
group. There are several features, which improve RF and power properties of typical
low-power MOSFET transistors. The LDMOS has a higher breakdown voltage.
GaAs-based MESFETs are used in high frequency operations e.g. telecommunication
applications. Nowadays an interest in Si-LDMOS is growing in the area of
10
Metal-Oxide-Semiconductor Field-Effect Transistors
228
telecommunication. Since Si is a developed material the structure of LDMOS gives
both good high-frequency and high-power characteristics [7.18].
Unit Amplifier’s building blocks: Unit amplifier is a RF amplifier which consists of
only one transistor. The most convenient way to evaluate a power transistor is to
design a class-A or class-AB power amplifier (PA) for it. The design is comprised of
several blocks for adjusting the conditions for the proper operation of the transistors
in accordance to the requirements. The block diagram (Figure 7.15) represents a
typical circuit considered in the design process. There are bias network (BN), input
matching network (IMN), output matching network (OMN), accessories networks
(AN) and the input and output ports that are assumed to be 50 Ohm.
In order to operate a transistor for a certain class, the gate and drain DC voltages have
to be biased carefully to a certain operating point (quiescent point or q-point). The
reason is that the choice of the q-point greatly influences linearity, power handling
and efficiency. In addition, the choice of optimal q-point is important for operation at
a particular frequency.
Combining unit amplifiers – A single transistor in a unit amplifier can deliver a
limited amount of power, therefore, to achieve high RF power we need to combine
several unit amplifiers. This task is done by power combiners. Power combiners and
dividers are major parts of solid-state power amplifiers. A combiner combines the
output power of all the individual power amplifiers and delivers it to the next
amplifying step or output terminal. A power divider delivers the required driving RF
power to individual amplifiers. With many power amplifiers to interconnect, the
physical shape and configuration of the combiner become major design parameters.
Most power amplifier modules can be grouped in rather flexible configurations that
will satisfy system requirements such as cooling, replaceability and power
connections. However, finding a mechanical space relationship that permits direct,
equal-length connection to low loss RF power combiner limits that flexibility. The
combiner may be binary in form, using two-to-one junctions in cascade. In this case
the number of inputs must be equal to a power of two. Some combiners using non-
binary structure combine the input power at one step. This type of combiners has
arbitrary number of inputs (3, 5, 7 and etc.). There are several basic requirements that
a power combiner network must meet:
Figure 7.15 Typical circuit considered in the design process [7.18].
229
The combiner should have low RF insertion loss so that the output power of
amplifiers is not wasted in the combining process.
The combiner should have sufficient RF isolation between input connections so
that the interaction between amplifiers becomes negligible. This item may be
omitted when modules are protected with isolators such as in SOLEIL power
amplifier system.
The combiner should not modify the characteristics of the power amplifiers, such
as phase and frequency response.
The reliability of power combiner should be acceptable.
The combiner should exhibit a “graceful degradation” feature and the ability to
remain online during replacement of each module or power amplifiers.
The mechanical packaging of the combiner should be such that it will fit well with
the rest of components comprising the amplifier tower.
Accelerators require a high power transmitter. To achieve the very high powers
required for this application, it is necessary to combine coherently the output power of
many lower-power solid-state devices known as unit amplifiers. Binary and serial
power combiners may be utilized to increase amplifier output power; however, circuit
losses impose an upper bound on the number of amplifiers that may be efficiently
combined in this manner. Losses following the outputs of combined amplifier devices
have a significant impact upon overall power amplifier efficiency. When efficiency is
a major concern, these losses must be minimized as a decrease in efficiency requires
additional power, which in turn requires a larger power source, a larger power supply
for the amplifiers, and additional cooling systems to discharge waste heat, all
translating into larger size and weight.
The radial power combiner (micro-strip, waveguide/micro-strip, TE01 cavity type and
etc.), by nature of its geometry, tends to minimize loss. So we use this type of power
combiner to gather the output power of modules or power amplifier at each
amplifying step. This type of power combiner is used without any isolation resistor,
so each module must be protected with an isolator to decrease the interaction between
adjacent modules.
High power solid state amplifier architecture [7.19]: RF MOSFETs have very low
input and output impedances which does not allow direct paralleling of several
transistors. In most cases, the elementary RF brick, called pallet, is based on 1 or at
most 2 transistors, mounted on a highly conducting metallic ground plane and
equipped with their biasing network and with input- and output-matching passive
stages. Several of these blocks are then combined to obtain higher output power, in
the best possible arrangement that supplies the amount of power required by each
application. Isolated dividers and couplers can be used to avoid oscillations or other
phenomena which could lead to the destruction of the transistors. Circulators can also
be used to decouple each amplifier, making it unconditionally stable, and in this case
non-isolated splitter/combiners can be used. Splitter/combiners and circulators are
therefore extremely important elements of solid state RF amplifiers.
Once a great amount of power has been collected from smaller devices, proper
management of this power is very important, especially when it is reflected and has to
be redistributed to all the contributors. In principle power combiners become splitters
when used backward but, due to improper matching, the whole structure can become
significantly asymmetrical and each pallet has to handle reflected power higher than
the power generated.
230
In case of the failure of a few transistors, the solid-state architecture can still provide a
significant amount of power. In principle, in well-designed systems, it is even
possible to replace the broken module without interrupting the amplifier’s operation.
In practice this characteristic is strictly linked to the power supply architecture and
mechanical layout. Another important point of the amplifier reliability is the computer
control. A huge number of transistor current and interlock conditions must be
monitored and localized for fast troubleshooting.
7.2.4.3 Proposed system structure for ILSF solid-state amplifier
In the following the proposed system structure for a 200KW solid-state amplifier
based on the BLF578 transistor is presented. The amplifier layout follows the
topology of SOLEIL’s amplifier towers.
Unit amplifier: The unit amplifiers (UAs) constitute the heart of the solid-state
amplifier. High-power amplification can be achieved by the parallel combination of
the output power of several individual UAs. The unit amplifier is based on BLF578
NXP LDMOS transistor. As shown in Figure 7.16, the UA at its output port has a
circulator with a high-power termination that provides stability and isolation required
in the combining system. Each UA has its own DC power supply. The BLF578
requires 50V power supply with no more than 15A at its maximum output power
(simulations results). Each unit amplifier and its power supply are assembled at the
opposite sides of a water-cooled plate. The current consumed by BLF578 must be
continuously monitored for the safe operation of the amplifier.
Circulator: A high-power circulator with a high-power 50 Ω RF termination is
integrated in each UA module to protect the transistor from excessive reflected power.
Also this component could ensure stable operation of the amplifier.
DC Power Supply: Each UA module has its own power supply with 15A at its
maximum output power. Some control and status signals are processed by a micro-
controller in the supply board and transmitted to the central control unit via a reliable
bus. Because of thermal dissipations in DC/DC converters, power-supply boards are
assembled at opposite sides of water cooled plate (other side of UA box).
Cooling System: The main performance parameters (power, gain and efficiency) of
the transistor will be degraded in UAs because of high dissipation in a small area.
Thus, heat produced must be removed effectively for the reliable operation of
transistors. Water cooling is a good choice in this system because of compactness and
Figure 7.16 Unit amplifier layout.
231
better efficiency than air cooling. For lower thermal resistance and better transmission
of heat to the cooling system, an aluminum box (UA's box) with a copper slug at the
bottom of transistor is attached directly to the cooling system as indicated in
Figure 7.17.
Combining network:
(a) 200kW amplifier -- For the generation of a 200kW power, we combine four
towers of 50kW solid state amplifier in two steps. As shown in Figure 7.17, in the
first step two towers are combined separately to generate two 100kW power
amplifiers and then they are combined for the final 200kW power. Towers are
connected to each other with high-power combiners and transmission lines. At the
output of the 200kW combiner a coaxial to waveguide transition is used to transmit
RF energy to the cavity systems.
(b) 50 kW amplifier – Each tower generates 50kW of power from sixteen 4-kW
amplifiers added in two groups. Each group consists of eight, 4kW amplifiers which
generate 32 kWs of power. Two 32-kW outputs are added together and 50 kWs of
power is generated. We use a UA and 8:1 splitter to drive each 32-kW amplifier.
Combiners and amplifiers are connected via RF cables. Some of the power generated
is lost by the insertion loss of combiners and cables. So after prototyping some slight
Figure 7.17 UA cooling plate.
Figure 7.18 Configuration of 200kW power amplifier.
232
changes may be required in the chain of amplifier. The proposed configuration of
50kW tower is indicated in Figure 7.19.
(c) 4 kW amplifier – Combining eight unit amplifiers, 4kW output power is
generated. With the combination of 64 of these 4-kW amplifiers, the required power
of 200kW will be provided. A coupler is placed at the output of a 4kW combiner to
sample the power for control purposes (Figure 7.20).
Figure 7.19 50 kW tower configuration.
233
7.2.5 Low-level RF system
The main goal of synchrotron light source is producing a stable synchrotron radiation
by passing relativistic electron bunches through insertion devices. To accelerate the
electron bunches one or more cavities should be placed along the electron path. The
resonating field inside the cavities interacts with the electron bunches. One can
accelerate the electrons up to very high energies by maintaining precise phase,
amplitude, and frequency synchronization between the resonating field and the
electron bunches. Furthermore, user requirements for the synchrotron radiation (e.g.
time jitter) impose certain stability requirements on the phase, amplitude, and
frequency of the cavity resonating field. In practice, however, temperature changes in
cavities and feeding waveguides, fluctuation in the power amplifier gain and phase
shift, and beam loading could heavily change the phase, amplitude, or even frequency
of the resonating field inside the cavities. To stabilize the resonating field, each cavity
is controlled by its dedicated low-level RF (LLRF) system.
In the storage ring, the LLRF should stabilize the resonating field of cavities where
the amplitude of the field is constant. The requirement on the synchrotron radiation
can be translated to phase, amplitude, and frequency stability of cavity resonating
field. At this stage the precise requirements for the radiation is not determined yet.
However, one can use the typical requirements on the cavity field that are around ±0.5
degrees on phase, ±1% on amplitude, and ±1 ppm.
Figure 7.20 Configuration of 4kW amplifier.
234
7.2.5.1 Various approaches for realizing LLRF systems
The LLRF system consists of several controlling loops (amplitude, phase and
frequency) which take an RF signal as input and generate an RF signal as output. The
input RF signal is a sample of the resonating field inside the cavities and the output
RF signal is the driving signal for the main amplifier. As the frequency tuning loop is
separated from the phase and amplitude adjustment systems, it is explained separately
in the next section.
(a) First Approach11
-- Fully analogue LLRF system: A first approach to realize the
LLRF system is a fully analogue LLRF system, which can operate at the actual
frequency of the cavities. A schematic block diagram of fully analogue LLRF systems
is shown in Figure 7.21. The master oscillator drives the whole system with a
frequency-stable sinusoidal signal. This signal passes through the phase loop and
amplitude loop to get the proper phase and amplitude. Finally, the signal will be
amplified in order to gain enough energy to feed the cavity.
Although the analogue nature of first approach makes it very fast and relatively
simple, lack of flexibility makes a digital LLRF system more desirable. The first
approach is very difficult to be digitally implemented because of the speed limitation
of analogue to digital converters (ADCs). Therefore, a second approach has been
proposed to be implemented digitally for ILSF RF system.
(b) Second Approach – Digital LLRF system: In a digital LLRF system we want to
perform the same functions as a fully analogue system, digitally. Hence, the analogue
sample of cavity signal should be converted to its digital form by an analogue to
digital converter (ADC). Then a digital processor performs the required adjustments
on the phase and amplitude of the digital signal. Finally, the adjusted signal is
converted back to its analogue form using a digital to analogue converter (DAC), and
goes to the main amplifier and cavity.
11
First approach, historically
Figure 7.21 Schematic block diagram of fully analogue LLRF system which operates at the same RF frequency of cavities. (a) Inside of phase regulation loop. (b) Inside of amplitude regulation loop. The dashed line shows the controlling loop
235
(c) Semi-digital LLRF: The block diagram of a semi-digital LLRF system is shown
in Figure 7.22. In this architecture, the signal processing unit is digital, but the signal
conditioning unit is analogue. In the operation cycle of this LLRF system, a sample of
the cavity signal is converted from the cavity frequency to an IF frequency by the
quadrature down-converter. Then the ADC block digitizes the IF signal and delivers it
to the digital signal processing unit where the required adjustments are calculated (on
both amplitude and phase) for the IF signal. To perform these adjustments, a digital
command is sent to the signal conditioning unit through a DAC. After performing
proper signal conditioning on the IF signal, it is converted back to the cavity
frequency by a quadrature up-convertor and then passes through the main amplifier
and finally reaches the cavity.
(d) Fully-digital LLRF: In the semi-digital LLRF, only the signal conditioning unit
is analogue. This unit can be implemented digitally to obtain a fully-digital LLRF
system. In semi-digital LLRF the signal conditioning is realized by physical
components (analogue amplifiers and combiners), so they introduce negligible delay.
On the other hand, in fully-digital LLRF, the signal conditioning should be done by
digital processors that can introduce considerable delay. For this reason, dedicated
processors like FPGAs12
and/or DSPs13
are usually used to reach reasonable delays.
Nowadays fully-digital LLRF systems are popular, but in case the system delay is
critical, semi-analogue systems are favored. The conceptual block diagram of a fully-
digital LLRF system is shown in Figure 7.23. Note that quadrature up-down
converters are not displayed.
12
Field Program-able Arrays 13
Digital Signal Processors
Figure 7.22 Block diagram of semi-digital LLRF system: The signal processing algorithms are very flexible; they can be changed only by software.
236
7.2.5.2 Frequency tuning loop
The resonance frequency of a cavity is determined by its physical dimensions. In
high-power cavities, like those in a synchrotron, power dissipates as heat and causes
the expansion of cavity metal and changes in the dimensions of cavity. The cavity
cooling system is responsible for taking out the excess heat and maintaining cavity at
a constant temperature. However, in practice some fluctuations occur in the cavity
temperature and consequently in the cavity resonance frequency.
Deviation of the resonance frequency from its nominal value has two undesirable
effects. First, it causes mismatch between the cavity and its feeding waveguide.
Second, as the frequency of resonating field changes, the phase relationship between
the field and electron bunches will no longer be constant.
Figure 7.23 Fully-digital LLRF system. Note that quadrature up-down converters are not displayed.
Figure 7.24 Frequency tuning loop: Since the frequency of mixer output is relatively low (less than few MHz), the frequency to voltage converter can be eliminated, and the mixer output digitized directly by ADC.
237
To maintain a constant resonance frequency, each cavity has an actuator which can be
moved in order to tune the resonance frequency of the cavity. In practice, an electric
motor is attached to the actuator to move it in or out of the cavity. Electric motors,
like stepped motors, can be used to tune the cavity resonance frequency in coarse
steps (e.g. tens of kHz), and for fine tuning, piezoelectric actuators can be used to
reach a higher accuracy (e.g. tens of Hz). The schematic of this digital frequency
tuning loop is shown in Figure 7.24.
7.2.6 Waveguide system
The waveguide system is the path through which the power generated at the RF high
power generator is transferred to the cavity. As the transferred power to the storage
ring cavity is extremely high (about 200kW), the waveguide system should be based
on the transmission lines that can handle high power such as rectangular waveguides.
The appropriate one for RF frequency of 500MHz is WR1800 with a frequency range
of 430-620 MHz according to the EIA standard. The electric field distribution in a
straight piece of WR1800 and also the scattering parameters are shown in Figure 7.25.
The waveguide systems in synchrotron light sources can typically be divided into
three main parts of circulators, dummy loads, and transmission lines. The circulator,
which is a 3-port directional waveguide component, prevents the power reflected from
the cavity go back toward the amplifier and cause damage. Any reflection from the
cavity is absorbed by the dummy load installed in the third port of the circulator. The
maximum power that should be handled by the dummy load is the generated power
since all of this power could be reflected in case of problems with the cavity. Water
loads are appropriate for this purpose.
(a) (b)
Figure 7.25 Rectangular waveguide WR1800: (a) 500MHz Electric field distribution, (b) Scattering parameters versus frequency.
300.00 400.00 500.00 600.00 700.00 800.00Freq [MHz]
-80.00
-70.00
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
Y1
Ansoft Corporation HFSSDesign1WR1800
Curve Info
dB(S(WavePort1,WaveP
Setup1 : Sw eep1
dB(S(WavePort2,WaveP
Setup1 : Sw eep1
238
Transmission lines are comprised of all different waveguide parts that are required to
connect all the main parts:
Straight lines to transport the RF signal on a straight path.
Bends to turn the wave direction 90 degrees in E-plane or H-plane.
Bellows to give flexibility to the waveguide system in case of temperature changes.
Waveguide-coaxial transitions to match the RF power in the waveguide to the
coaxial line of the cavity coupler.
Bi-directional couplers to couple the forward and reflected power out for
measurement.
(a)
(b)
Figure 7.26 Waveguide systems: (a) Schematic layout of ILSF waveguide system connecting the solid state amplifier to the cavity, (b) Waveguide system in ALBA booster.
239
Different parts of the waveguide system are marked in the schematic layout of the
waveguide system in Figure 7.26(a). The output of the last combiner of a 4-tower
SSA travels through the waveguide system to feed the cavity. The waveguide system
is not lossless and that is why in RF power calculations in Table 7.7 it is necessary to
generate 10% more power than what is required for the cavity. Since the generated
power passes through all parts of the waveguide system, the maximum handled power
is one of their main specifications which should be about 170kW CW in ILSF.
Another important specification is VSWR14
which is not the same for different parts
of the waveguide system but it should be as low as possible in component designs. As
an instance of a real system, ALBA waveguide system is shown in Figure 7.26(b)
7.2.7 Storage ring RF plant configuration
As mentioned before, two EU, ELETTRA, or ASP cavities fit in one 2.8 m long short
straight section, therefore the RF system will occupy three short straight sections.
Each of these RF plants consists of two four-towered solid state amplifiers which feed
two cavities through their corresponding waveguide systems. For PEP-II cavity, there
will be 5 RF plants as only one cavity fits into a short straight section.
One possible configuration for ILSF RF plant is shown in Figure 7.27. The overall
space occupied by this proposed arrangement is approximately 13.5 m × 10 m. The
final configuration should be optimized after the detailed designs of components are
carried out.
14
Voltage Standing Wave Ratio
Figure 7.27 Proposed configuration for ILSF RF plant in the storage ring.
240
7.3 Booster RF System
The booster RF acceleration system must capture the bunch train injected from the 3
GHz linac, accelerate it from 150MeV to 3 GeV, and transfer the bunch train to the
storage ring RF buckets at 500 MHz. Table 7.10 shows the main RF parameters of
Iran FODO lattice, considered so far for ILSF booster.
Table 7.5: RF related lattice parameters of ILSF booster ring (Iran FODO lattice).
Parameters ILSF Booster
Injection Energy, Einj(MeV) 150
Beam current (mA), Ib 10
Extraction Energy, Eext (MeV) 3000
Circumference (m) 192
Energy loss per turn at extraction (keV) 787.6
Momentum compaction factor 5.90×10-3
Revolution frequency(MHz), frev 1.56
Repetition rate (Hz) 2
Harmonic number 320
RF voltage is selected in accordance with both the desired energy acceptance at
booster extraction and the ramping energy required in the booster. Lifetime is not a
matter of choice in the booster as opposed to the storage ring because the particles do
not stay for a long period in the booster. Thus, for determining the RF voltage at
extraction, energy acceptance is calculated by equation (7-15) and plotted versus RF
voltage as shown in Figure 7.28. In order to get the desired energy acceptance of 0.7%
at booster extraction, a 1.454 MV RF voltage will be required.
Figure 7.28 Energy acceptance as a function of RF voltage.
1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
0.4
0.5
0.6
0.7
0.8
0.9
1
X: 1.455
Y: 0.7005
RF Voltage (MV)
En
erg
y a
ccep
tan
ce (
%)
241
To obtain the booster phase space with this RF voltage (corresponding to φs = 147.2°),
the synchrotron equation of motion could be derived from a Hamiltonian for phase-
space coordinate ( ) as given by [7.20]
(7.26)
where h is the harmonic number, ωrev is the angular revolution frequency, VRF is the
RF voltage, Eext is the extraction energy and φs is the synchrotron phase. Calculating
the Hamiltonian for the above-mentioned lattice parameters and plotting it in phase-
space coordinates ( ), the booster phase space is plotted in Figure 7.29. As
expected, the RF bucket height is 0.7%, the value of calculated energy acceptance.
The separatrix is plotted in green and the stable area with the focal point of the
synchrotron phase (φs) between φ1 and φ2 is indicated in the figure.
7.3.2 Time structure
Booster time structure is designed so that the particle energy increases from 150 MeV
to 3 GeV during half of the repetition period. The electron energy ramping shown in
Figure 7.30, is sinusoidal as given by the following formula,
0 cos 2t rE E a f t (7.27)
where ext inj
ext inj
E Ea
E E
, and is the repetition rate which is 2 Hz.
The corresponding radiation loss per turn is very simply calculated from
4
88.4 ( )r
EV keV
R (7.28)
Note that E is the electron energy in GeV and R is the bending radius in meters [7.1].
Figure 7.29 Booster phase space diagram.
242
If the RF voltage provides only this radiation loss, the electron energy in the booster
will remain constant as in the storage ring. Therefore, the RF voltage should also
provide the energy increase required during ramping which can be calculated by
taking the derivative of the electron energy.
02 sin 2t r rE t f E f t D D
(7.29)
The sum of these energy changes plotted in Figure 7.31 is the minimum energy which
should be provided by the RF voltage so that the electron energy rises to 3 GeV.
Therefore, after RF voltage calculation, it should be checked that the RF voltage is
higher than the total energy to be compensated. It should be noted that the figure has
been achieved for tD of 10 µs.
Figure 7.31 Electron energy required to be compensated during the ramping in ILSF booster.
0 0.05 0.1 0.15 0.2 0.250
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
t (s)
En
erg
y (
MeV
)
Radiation Loss
DEt
Total energy to be compensated
Figure 7.30 Electron energy ramping in ILSF booster.
0 0.05 0.1 0.15 0.2 0.250
500
1000
1500
2000
2500
3000
3500
X: 0.05701
Y: 500.3
t (s)
En
erg
y (
MeV
)
150
Extraction: 250ms
half of repetition
rate period
500
243
The RF voltage calculated before is the required RF voltage at the end of the ramping
to achieve a 0.7% energy acceptance. To determine the required voltage at injection,
the pre-calculation is done in order to have a 3% energy acceptance at 500 MeV
electron energy. The RF voltage achieved is 1.336 MV that remains constant from the
beginning of the injection until the electron energy reaches 500 MeV. Then, the RF
voltage increases linearly up to 1.455 MV during half of the repetition period.
Comparing the RF voltage ramping shown in Figure 7.32 with the previous figure
verifies that the obtained RF voltage provides more than the total required energy
during ramping.
Having calculated the RF voltage and radiation loss during the ramping, the energy
acceptance in the booster is simply calculated by Equation 7.1 and plotted in
Figure 7.33. As can be noticed in this figure, the energy acceptance of 5.5% at
injection time drops to reach the desired 0.7% energy acceptance at extraction.
Figure 7.32 RF voltage ramping in ILSF booster.
0 0.05 0.1 0.15 0.2 0.251.32
1.34
1.36
1.38
1.4
1.42
1.44
1.46
t (s)
RF
Vo
ltag
e(M
V)
Figure 7.33 Energy acceptance during the ramping in ILSF booster.
0 0.05 0.1 0.15 0.2 0.250.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
t (s)
En
erg
y A
ccep
tan
ce (
%)
0.7
Extraction
244
7.3.3 Cavity Considerations
Contrary to the storage ring, there is no need to use HOM-free cavities in the booster
because of low beam current. Looking at Table 7.2, Petra cavity has been used in the
booster of many 500MHz light sources. It has two similar designs of 5 cells and 7
cells at 500MHz. The general specifications of these cavities are compared in
Table 7.11 while their schematics are shown in Figure 7.34.
Table 7.6: General specifications of 5 and 7 cell PETRA cavities [7.21]-[7.22].
5-cell Petra 7-cell Petra
π mode frequency (MHz) 499.67 499.67
Shunt impedance (MΩ) 15 23
Nominal accelerating voltage (MV) 1.34 1.67
Maximal accelerating voltage (MV) 1.94 3
Total length (mm) 1800 2200
Outside diameter (mm) 445 448
According to the specifications, 1.455 MV RF voltage is within the voltage interval of
both cavities therefore both cavities can be used in the ILSF booster. Three different
cavity options can be assumed by using:
(a)
(b)
Figure 7.34 (a) 5-cell PETRA cavity [7.21]. (b) 7-cell PETRA cavity [7.22].
245
One 5-cell PETRA cavity,
Two 5-cell cavities
One 7-cell PETRA cavity.
Also there is a fourth option of using the storage ring cavity in the booster. In this
case, only one surplus cavity will be adequate for both storage ring and the booster.
However, two storage ring cavities are required as their maximum tolerable voltage is
lower than the required voltage. In addition, they have very low shunt impedance in
comparison with the other options that means more required power. Thus this option
can be eliminated even without considering the higher price of these cavities. The
required powers of all four scenarios are calculated in the same way as done for the
storage ring and the results are summarized in Table 7.12.
Table 7.7: RF power considerations for different cavity options at extraction.
One
5-cell cavity
Two
5-cell cavities
One
7-cell cavity
Beam Current (mA) 10 10 10
Beam loss per turn (keV) 787.6 787.6 787.6
Beam power (kW) 7.876 7.876 7.876
Shunt Impedance(MΩ) 15 15 23
RF voltage per cavity (kV) 1454 727 1454
Total dissipation power (kW) 70.47 2×17.617 46
Total RF Power (kW) 78.35 43.11 54
Total RF Power + 10% transfer
losses (kW) 86.18 47.421 59.3
Required
equipment
Cavity 1 & 1 surplus 2 & 1 surplus 1 & 1 surplus
Amplifier 1 2 (24kW) 1
In general, an RF system with a minimum number of cavities would be preferable
according to cost and simplicity considerations. Possibility of generating the total
required power is another item that should be taken into account.
As the cost of 5-cell and 7-cell Petra cavities are not that much different, option 1
would be omitted in favor of option 3 due to its 27 kW additional required power.
Selection between the remaining two options should be done according to the cost
comparison of one extra cavity in option 2 with 12 kW more required power in option
3. Moreover, complexity and necessity of one more low-level electronics (LLRF)
system in option 2 should be taken into account for the final decision. Consequently,
one 7-cell Petra cavity would be the best choice among the proposed options for ILSF
booster RF system. The total RF power required to be provided at the RF generator
should increase from 43 kW to 60 kW during the ramping according to Figure 7.35 in
order to fulfill the ramping time structure presented in the previous section. Usually a
linear ramping above the required power (Figure 7.35) is applied for facilitating the
ramping process.
246
7.3.4 High-power RF generator
One of the solid-state amplifier towers in the storage ring should be modified to
provide the required power of 60kW. The main difference between the booster and
the storage ring amplifier is that in the booster the generated power should vary as
plotted in Figure 7.35, whereas, in the storage ring the generated power is constant
and does not change in time.
7.3.5 Low-level RF system
The concept and approach of the LLRF in ILSF booster is the same as in the storage
ring. Only, in the booster ring the resonating field should be stabilized in terms of
phase and frequency where the field amplitude is raised during the ramp operation.
7.3.6 Waveguide system
The components of the booster waveguide are similar to those of the storage ring.
Only due to the lower power that is being handled, the design and fabrication of some
parts might become simpler. For instance, for powers lower than 80kW, as is the case
of ILSF, some rectangular waveguides could be replaced by coaxial lines EIA 6 1/8".
Also dummy loads with very high power handling capacity are not required.
Figure 7.35 Generator RF power during the ramping in ILSF booster.
0 0.05 0.1 0.15 0.2 0.2542
44
46
48
50
52
54
56
58
60
t (s)
Tota
l RF
Pow
er
(kW
)
(10%
tra
snfe
r lo
ss is
inclu
ded)
Linear ramping of total RF power
Total required RF power
247
References:
[7.1] H. Winick, Synchrotron Radiation Sources (World scientific publishing,
1994).
[7.2] E. Weihreter, F. Marhauser, "HOM Damped Cavities For High Brilliance
Synchrotron Light Sources", Brilliant Light in Life and Material Sciences
(Springer 2007).
[7.3] M. Abo-Bakr, E. Weihreter, G. Wüstefeld, “On the Optimum RF Frequency
for a Low Energy Synchrotron Radiation Source”, EPAC 2000, p. 1456-8.
[7.4] Helmut Wiedemann, Particle Accelerator Physics, 3rd
ed., (Springer, 2007).
[7.5] L. O. Dallin, I. Blomqvist, M. de Jong, E. Hallin, D. S. Lowe, R. M. Silzer,
"The Canadian Light Source: Status Report", MEDSI02 (Argonne National
Laboratory, Argonne, Illinois U.S.A, September, 2002).
[7.6] P.J. Chou, J. Chen, K.T. Hsu, C.C. Kuo, Ch. Wang, M.H. Wang, "Collective
Effects In The TLS Storage Ring After The Installation Of Superconducting
RF Cavity", Proceedings of 2005 Particle Accelerator Conference, Knoxville,
Tennessee.
[7.7] M. R. F. Jensen, M. J. Maddock, P.J. Marten, S. A. Pande, A. Rankin, S.
Rains, D. Spink, A. Watkins, " First 18 Months Operation of The DIAMOND
Storage Ring RF System ", Proceedings of EPAC08, Genoa, Italy.
[7.8] Z. M. Dai, G. M. Liu, L.X. Yin, D.K. Liu, Z.T. Zhao, "Status Of the SSRF
Storage Ring", Proceedings of EPAC08, Genoa, Italy.
[7.9] NSRRC - , June 2008.
[7.10] SESAME Yellow Book, May 2003.
[7.11] Angel Olmos, Paco Sánchez, Michel Langlois, "ALBA RF System New
Developments", 14th ESLS, 19-20 October 2006.
[7.12] Jack Tanabe, Iron-Dominated Electromagnets Design, Fabrication, Assembly
and Measurements, SLAC-R-54 (June 2005).
[7.13] P. Sanchez, "RF High Power Projects at ALBA" 4th
MAC Meeting, March
2006.
[7.14] CANDLE design report, http://www.candle.am/TDA .
[7.15] R. M. Franks, R. A. Rimmer, H. Schwars, “FABRICATION PROCESSES
FOR THE PEP-II RF CAVITIES”, IEEE 1998.
[7.16] P. Marchand et. al., “OPERATION OF THE SOLEIL RF SYSTEMS”,
Proceedings of PAC07, Albuquerque, New Mexico, USA.
[7.17] P. Marchand, T. Ruan, F. Ribeiro, R. Lopez, “High power 352 MHz solid state
amplifiers developed at the Synchrotron SOLEIL”, Phys. Rev. ST Accel.
Beams 10 (2007) 112001.
[7.18] Grigori Doudorov, “Evaluation of Si-LDMOS transistor for RF power
amplifier in 2-6 GHz frequency range,” Master thesis, Linköping University,
Sweden, 2003.
[7.19] Marco Di Giacomo, Ganil-Spiral2, “Solid State RF Amplifiers for Accelerator
Applications”, PAC09, Canada, 2009.
[7.20] S. Y. Lee, Accelerator Physics (World scientific publishing, 2004).
[7.21] DESY/BalzersHochvakuum GmbH Data Sheet, “500 MHz 5-cell PETRA
cavity”, DESY-MHFe, Vers. 2.0 (July 2007).
[7.22] DESY/BalzersHochvakuum GmbH Data Sheet, “500 MHz 7-cell PETRA
cavity”, DESY-MHFe, Vers. 2.0 (October 2007).
[7.23] J. Watanabe, K. Nakayama, K. Sato, A. Jackson, G. S. LeBlanc, K. Zingre, N.
Nakamura, H. Sakai, H. Takaki, M. Izawa, T. Koseki, “DESIGN AND COLD
248
MODEL TEST OF 500 MHz DAMPED CAVITY FOR ASP STORAGE
RING OF RF SYSTEM’, Proceedings of 2003 Particle Accelerator
Conferencec, Knoxville, Tennessee.
[7.24] H. Ego, M. Hara, Y. Kawashima, Y. Ohashi, J. Suzuki, I. Akeshita, H.
Yonehara, “Higher-order modes in the bell-shaped single-cell cavity of the
Spring-8 storage ring”, Nuclear Instruments and Methods in Physics Research
A 383 (1996) 325-326.
[7.25] A. Fabris, P. Craievich, C. Passoti, M. Svandrlik, “RF system for the
ELETTRA booster synchrotron”, EPAC 2000, Sincrotron Trieste, Italy.
[7.26] A. Anderson, M. Bergqvist, M. Eriksonn, L. Malmgren, L. Thanell, “The 100
MHz RF system for Max II and Max III”.
[7.27] P. A. McIntosh, “Comparison of RF cavity designs for 3rd
generation light
sources”, Fifth European Particle Accelerator Conference 1996.
[7.28] R. A. Rimmer, J. M. Byrd, D. Li, “Comparison of calculated, measured, and
beam sampled impedances of a higher order mode-damped RF cavity”,
Physical Review Special Topics – Accelerators and Beams Vol. 3 (2000).
[7.29] F. Perez, B. Baricevic, H. Hassanzadegan, A. Salmon, P. Sanchez, D. Einfeld,
“NEW DEVELOPMENTS FOR THE RF SYSTEM OF THE ALBA
STORAGE RING”, Proceedings of EPAC 2006, Edinburgh, Scotland.
249
CHAPTER 8: Power Supplies
8.1 Introduction
Power supplies play a vital role in all particle accelerators especially in low-emittance
light sources. All of the magnets in the storage ring, booster and transfer lines are
energized by their highly stable and low-ripple power supplies that generate the
magnetic fields to steer or focus the electron beam.
The output current of the power supplies flows through power cables to the magnets.
Some magnets are fed with their own power supplies and some of them should be
connected in series and fed with one large power supply.
8.2 Power supply topologies
Power supplies are usually divided in three main categories with respect to their
topologies:
1. Linear power converters.
2. Line-commutated thyristor power converters.
3. Switched-mode power converters.
CERN started using the switched-mode power supply for synchrotron magnets in
1982 and since then the use of this type of power supply has increased day by day.
Nowadays instead of comparing three main topologies for power converters in
modern accelerators, the main objective is to choose the most suitable topology for
switching-mode power supplies (SMPS) or any possible combination of two or three
types of them.
8.2.1 Switched-mode power converter
The switched-mode power supply may consist of a series and/or parallel connection
of a number of lower-power modules rated at 50 or 100 kilowatts each. This scheme
results in a good efficiency, but involves higher running costs and a higher load on the
thermal management system. By careful filtering the harmonics on the input supply
must be minimized, but the power factor is close to unity.
The SMPS technology offers several advantages over linear regulator technology
including higher efficiency, higher bandwidth (better regulation), smaller size, and
lower weight. The semiconductor switching device in an SMPS is operated either in
cut-off mode (blocking high voltages) or saturation mode (carrying high currents).
Since no current flows through the semiconductor switch in cut-off (off) state and the
voltage across the device is low in saturation (on) state, the conduction power loss is
low. Likewise, the very high-speed switching of the power semiconductors leads to
low switching losses. Thus, low conduction and switching losses result in a higher
250
efficiency of SMPSs compared to linear regulators. An SMPS regulates the output
voltage closely regardless of the changes in the input supply voltage and the load
current with almost no change in efficiency. Due to the high operating switching
frequencies of the semiconductor switching devices; transformers, inductors, and
capacitors utilized in an SMPS are smaller in size and lower in weight which results
in smaller, lighter, and more economical power supplies.
The power of an SMPS ranges from several watts to hundreds of kilowatts. So the
most suitable approach for ILSF dipoles is a high-frequency phase-shifted switched-
mode buck converter.
8.2.2 SMPS topologies
There are several topologies commonly used to implement SMPS. Each topology has
its own unique features, which make it best suited for a certain application:
(a) Buck converter.
(b) Boost converter.
(c) Forward converter.
(d) Two-switch forward converter.
(e) Flyback converter.
(f) Push-pull converter.
(g) Half-bridge converter.
(h) Half-bridge resonant converter.
(i) Full-bridge converter.
8.3 Subassembly of power supplies
8.3.1 Input section
Input section for each type of power supply is different: it could be a large 12 pulse
rectifier to convert 22 kV or 6.3 kV to 650 V nominal DC bus for a dipole or
sextupole power supply, or, a 4500 W power factor corrector for 220 V single-phase
input, or, 380 V three-phase input power distribution.
Figure 8.1 Switched-mode power supply diagram.
251
8.3.2 Control assembly
The control assembly for a power supply is a central control including local/remote
controls, indicators, monitors, meters, sensing, and protection circuits. Except for the
quadrupole power supplies in the storage ring, all power supplies will use full digital
control technology even for pulse-width modulation (PWM) pulse generation.
8.3.3 Converter assemblies and redundancies
Dipole, quadrupole, and sextupole power converters use an N+1-redundant power
module configuration. The 5 kW models use five 1.25 kW converters; 3.5 kW models
use four 1.25kW converters; and 2.5 kW models use three 1.25kW converters.
If a power module fails, the PWM drive to it is inhibited. A catastrophic failure, e.g.
an IGBT, MOSFET or freewheel diode short circuit, will blow either a module input
or output fuse, isolating the module. Operation can continue with the remaining
modules as the digital controller automatically re-synchronizes for minimum ripple
current.
A failed module can be replaced quickly by a new one, at a convenient time, and
repaired in the workshop rather than on-site. Corrector, quadrupole, and sextupole
modules may be hot-swapped but this is not practical for the dipole or sextupole
power converters.
8.3.4 Display assembly and remote control
This unit is mounted behind the front panel and contains the digital meters, operating
mode, over-voltage, and over-current indicators.
8.3.5 Power supply interlocks
All power supplies will have sufficient interlocks that will prevent the power supply
from being damaged due to changes in cooling conditions, AC power disturbances,
and nonstandard operation.
All power supplies will have an electrical safety interlock that will prevent the power
supply from turning on if the machine safety system requires it.
8.4 Storage ring power supplies
These power supplies should be designed to stay at a fixed current except for the fast
correctors. All the power supplies are rated for operation at 3 GeV plus a 15% safety
factor on both current and voltage, and an additional 5% safety factor on the voltage
to allow for cable voltage drop. All power supplies will have at least a 20% operating
current margin.
8.4.1 Dipole power supply
The ILSF storage ring will be equipped with 32 dipole magnets of two types. Series
connection of the same-type dipoles means that the current flow through every
magnet would be the same, thus the generated magnetic field by each dipole would be
252
the same too. To attain this operational condition, two single converters feed the two
series-connected strings of dipole magnets.
8.4.1.1 Specification of power supply for dipole magnets
The first circuit consists of a series connection of 24 dipole magnets and its power
converter has the following specifications:
Table 8.1: Specifications of the power supply for the 1st type of dipole magnet.
AC input power 3-phase 6.3kV VAC / 22kV
DC maximum output current – Imax 529 ADC
DC output voltage 588 VDC
Stability (1 h–8 h) (referred to Imax) ±10 ppm
Stability (30 h) (referred to Imax) ±10 ppm
Absolute accuracy (referred to Imax) 100 ppm
Current ripple + Noise (referred to Imax) 10 ppm
Measured current resolution 18 bit ±1 LSB at 50 μsec
The second circuit consists of a series connection of 8 dipole magnets and its power
converter has the following specifications:
Table 8.2: Specifications of the power supply for the 2nd type of dipole magnet
AC input power 3-phase 6.3kV VAC / 22kV
DC maximum output current (Imax) 529 ADC
DC output voltage 198 VDC
Stability (1 h – 8 h) (referred to Imax) ±10 ppm
Stability (30 h) (referred to Imax) ±10 ppm
Absolute accuracy (referred to Imax) 100 ppm
Current ripple + Noise (referred to Imax) 10 ppm
Measured current resolution 18 bit ±1 LSB at 50 μsec
8.4.1.2 Selection of topology for dipole power supply
Buck converters are non-isolated DC/DC converters, which include the basic DC/DC
converter topologies. They usually utilize a single controllable semiconductor
switching device and a diode.
Advantages: Few components, one switch, simple circuit, high reliability if not
overstressed
253
Disadvantages: Output is DC and unipolar, so there is no possibility of high-
frequency transformer or bipolar output, low-frequency transformer must be used in
front of the buck for isolation and to match the line voltage to the load voltage
Applications: Used widely in accelerator power systems, typically for large power
supplies (perhaps 350 kW and used in conjunction with a 12-pulse rectifier with 6-
phase transformer).
When the output current requirement is high, the excessive power loss inside the
freewheeling diode D1, limits the minimum output voltage that can be achieved. To
reduce the loss at high current and to achieve lower output voltage, the freewheeling
diode is replaced by a MOSFET/IGBT with a very low ON state resistance RDSON.
This MOSFET/IGBT is turned on and off synchronously with the buck
MOSFET/IGBT. Therefore, this topology is known as a synchronous buck converter.
A gate drive signal, which is the complement of the buck switch gate drive signal, is
required for this synchronous MOSFET/IGBT.
But it is almost impractical to design a single synchronous buck converter to deliver
very high load current at a low output voltage. If the load current requirement is high,
more than one converter is connected in parallel to deliver the load. To optimize the
input and output capacitors, all the parallel converters operate on the same time base
and each converter starts switching after a fixed time/phase from the previous one.
This type of converter is called a multiphase synchronous buck converter. Figure 8.3
Figure 8.2 Schematic for buck converter.
Figure 8.3 Three-phase synchronous buck converter diagram.
254
shows the multiphase synchronous buck converter with a gate pulse timing relation of
each leg and the input current drawn by the converter. The fixed time/phase is given
by Time period/n or 300/n, where “n” is the number of the converters connected in
parallel [8.1][8.1] .
So the most suitable approach for ILSF dipoles is a multiphase synchronous buck
converter. A schematic diagram of such a switch-mode circuit similar to power
converters of ALBA is shown in Figure 8.4 [8.2].
The power converter for powering 24 bending magnets is comprised of 4 paralleled-
series modules. The other one for powering 8 dipoles consists of 2 paralleled
modules. Each module is a non-isolated step down 4-phase synchronous buck
converter regulator operating at a fixed frequency. IGBT devices are used as the
switching element. The switching frequency of converter would be about 12 KHz.
Input power would be 22 KV or 6.3 KV 3-phase power, which is transformed down
and 12 pulses are rectified to form a 650 V nominal DC bus feeding the power
modules. Capacitance on this DC bus provides half-cycle line dropout immunity.
8.4.2 Quadrupole power supplies
A total number of 104 quadrupole magnets, split into 9 families, will be required for
the ISLF storage ring lattice. Each quadrupole magnet is fed with its own power
supply with highly stable and low-ripple current that generates a quadrupole magnetic
field to focus the electron beam in the vacuum chamber. In other words each
quadrupole magnet is connected with its own independent power supply, to provide
optimum versatility in adjusting the lattice functions in the insertion regions.
Figure 8.4 Schematic for dipole power supply.
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8.4.2.1 Specifications of power supply for quadrupole magnets
Typically each power supply for quadrupole magnets has the following specifications:
Table 8.4: Quadrupole power supply specifications
AC input power 3-phase 380 VAC / 1-phase 220 VAC
DC maximum output current (Imax) 190 ADC
DC output voltage 24 VDC
Stability (1 h–8 h) (referred to Imax) ±10 ppm
Stability (30 h) (referred to Imax) ±10 ppm
Absolute accuracy (referred to Imax) 100 ppm
Current ripple + Noise 10 ppm
Measured resolution of current 18 bit ±1 LSB at 50 μsec
8.4.2.2 Selection of topology for quadrupole power supplies
Each power supply will fit in a standard 19 inch electronics rack, will be air-cooled
and equipped with precision hybrid analog and digital regulators to control the
current. The power supplies will use DCCT as the current feedback device similar to
other magnet power supplies.
First Option: Power supplies will consist of three or four switch-mode
programmable power supplies with high-output bandwidth, followed by a precision
linear regulator (which consist of a power MOSFET bank and paralleled shunt), to
maximize overall stability and minimize current ripple.
The central control unit will control the output current by measuring the current and
sending slow commands to each inner programmable power supply to allow at least
100 ppm current regulation as a coarse control. Then current will flow to a series
connection of a linear regulator and the load. In order to minimize the power
dissipation on the linear regulator, a shunt resistor will be connected in parallel to the
MOSFET bank. So the control unit will be able to fine control the output current on
the order of 10 ppm by sending fast command signals to the linear regulator board. A
schematic diagram of such a circuit is shown in Figure 8.5
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Second Option: In case a commercially available programmable power supply
module is used, the central control unit as well as the precision linear regulator will be
developed in-house. The other option is developing a new type of synchronous push-
pull converter as shown in Figure 8.6 which is under development at the time of
writing this report at power supply group of ILSF. In this design the outputs of two
synchronized push-pull converters (one for coarse regulation and another for fine
current regulation) will be added together before rectification. In this manner, there
will be no need for extra high-current electronic parts. Another advantage of this
design is using a high-voltage inductor on the switching side rather than a high-
current inductor ion the high current side. The PWM signal to control of buck
converter (at the input stage of each unit) will be generated inside a DSP or dsPIC
with as high a resolution as possible.
8.4.3 Sextupole power supplies
A total number of 128 sextupole magnets, split into 9 families, will be required for the
ISLF storage ring lattice. All magnets from each family will be connected in series
and will use one power supply.
Figure 8.5 Schematic for hybrid quadrupole power supply (option 1).
Figure 8.6 Schematic for quadrupole power supply (option 2).
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8.4.3.1 Specification of power supply for sextupole magnets
Typically each power supply for sextupole magnets will have the following
specifications:
Table 8.5: Typical specifications for sextupole power supplies.
8.4.3.2 Selection of topology for sextupole power supplies
Each one of the 9 families of sextupole magnets is powered by a separate power
converter in the configuration of 3-phase synchronous buck converter. Using two
paralleled modules will provide N+1-redundancy.
8.5 Ramping power supplies for booster magnets
The booster of ILSF is designed to raise the energy of a 150 MeV electron beam up to
3 GeV in approximately 250 msec. So all magnet power supplies of the booster
should be able to ramp from a low current at injection to a higher current at
extraction, they are designed to work at 2 Hz repetition rate.
AC input power 3-phase 380 VAC / 1-phase 220 VAC
DC maximum output current (Imax) 127 ADC
DC output voltage 192 VDC
Stability (1 h–8 h) (referred to Imax) ±10 ppm
Stability (30 h) (referred to Imax) ±10 ppm
Absolute accuracy (referred to Imax) 100 ppm
Current ripple + Noise 10 ppm
Measured resolution of current 18 bit ±1 LSB at 50 μsec
Figure 8.7 Schematic for quadrupole and sextupole power supply.
258
The basic equation for determining the power supply properties is:
or
where V(t) is the output voltage of the power converter and consists of two parts: an
inductive part and a purely resistive part. During ramp-up both L (inductance of the
magnets) and RI(t) will have positive values, so V(t) should be high enough in the
positive direction to make . During ramp-down while L and RI(t) will be
positive, in order to guarantee that becomes negative with the specified value,
V(t) should be negative. As a result the power supply must be a bipolar power supply.
The most important point about power supplies of the booster is to minimize the
tracking error between the dipole current and the corresponding quadrupole magnets’
currents. It means that the current waveform of all the power supplies must be
synchronized with each other and also with the energy of the electron beam.
One approach has been to use a resonant power circuit and a sinusoidal acceleration
cycle, but this usually requires a large capacitor bank and fast cycle rates. The silicon-
controlled rectifier (SCR) technology is one of the first topologies used for booster
power supplies, but it involves low power factors and hence a big influence over line
power. On the other hand, switched-mode power supplies have high efficiencies, high
power factors, and fast response.
In addition to using switched-mode power supplies, the best solution would involve
providing a feed-forward voltage waveform to the power supply that would
correspond to the voltage needed to drive the desired current waveform through the
magnet load. By taking advantage of the cycle-to-cycle repeatability of the system, it
is possible to successively modify the feed-forward waveform based on the measured
current ramp from previous cycles to reduce systematic errors in the output current.
The general approach is shown in Figure 8.8 [8.3].
Initially a voltage feed-forward waveform is computed based on the desired current
output waveform and the known load characteristics. The resulting output current
waveform is compared with the desired output and the residual error is used to modify
the feed-forward waveform. The optimal feed-forward waveform is therefore
Figure 8.8 Ramping power supply block diagram.
259
“learned” over many ramp cycles. More recent systems integrate the feed-forward and
current feedback in a single digital system.
8.5.1 Dipole magnet power supply of booster
The ILSF booster will be equipped with 48 identical dipole magnets. Series
connection of the dipoles means that the current flow through every magnet would be
the same, thus the generated magnetic field by each dipole would be the same too. To
attain this operational condition, one single converter feeds the series-connected string
of dipole magnets.
8.5.1.1 Specifications of the power supplies for booster dipole magnets
The circuit consists of a series connection of 48 dipole magnets and its power
converter has the following specifications:
Table 8.6: Specifications of dipole magnets’ power supply.
AC input power 3-phase 6.3kV VAC / 22kV
Peak current (Imax) 602 ADC
Peak voltage 542 VDC
Stability (100S – 8 h) (referred to Imax) ±10 ppm
Current resolution (referred to Imax) 10 ppm
Reproducibility (referred to Imax) 100 ppm
Measured current resolution 18 bit ±1 LSB at 50 μsec
8.5.1.2 Topology of the dipole magnets’ power supply
The proposed power supply is composed of 8 stations connected as shown in
Figure 8.9. Every station is composed of a 6 pulse full-wave bridge rectifier and an
input filter that charges a capacitor bank. In addition, a four quadrant dc to dc
converter is used to convert the capacitor bank voltage into a pulsed dc voltage across
the magnets. This topology makes it possible to store the energy from the inductive
load during ramp-down in the capacitor bank to minimize power consumption.
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8.5.2 Quadrupole power supplies
A total number of 92 quadrupole magnets, split into 6 families, will be required for
the ISLF booster. Each family of quadrupoles will be connected in series and share
one power supply.
8.5.2.1 Specifications of the power supply for quadrupole magnets
Typically each power supply for quadrupole magnets has the following specification:
Table 8.7: Typical quadrupole Power Supplies Specifications
AC input power 3-phase 6.3kV VAC / 22kV
Peak current (Imax) 140 ADC
Peak voltage 537 VDC
Stability (100S – 8 h) (referred to Imax) ±10 ppm
Current resolution (referred to Imax) 10 ppm
Reproducibility (referred to Imax) 100 ppm
Measured current resolution 18 bit ±1 LSB at 50 μsec
8.5.2.2 Selection of topology for the quadrupole magnets’ power supply
This design consists of a twelve-pulse rectifier fed from a 50 Hz transformer, a filter,
a capacitor bank and a 4-quadrant converter.
Figure 8.9 Schematic for dipole power supply of booster.
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References:
[8.1] Microchip application note AN01114, Switched-mode power supply
topologies part1
[8.2] M. Pont et al., Power converters for ALBA storage ring (Proceeding of IPAC
2010, Kyoto, Japan).
[8.3] J. Carwardine et al., Trends in the use of digital technology for control and
regulation of power supplies (International conference on accelerator and
large experimental physics control systems 1999, Trieste, Italy).
Figure 8.10 Schematic for quadrupole power supply of booster.
262
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CHAPTER 9: Diagnostics
9.1 Introduction
A synchrotron light source requires a diagnostic system to carry out its
commissioning and maintain its design performance during normal conditions of
operation. Diagnostic devices must measure both machine and beam parameters under
all modes of standard operation and, also, under abnormal conditions. The goal is to
guarantee a stable photon beam within the nominal specifications to the users. To this
end various devices will be distributed around the accelerator. These devices, together
with their signal processing electronics make up the diagnostic system. The diagnostic
system, in summary, is needed to monitor the stored beam, to reach the desired
performance and to keep the storage ring running efficiently. The diagnostic tools for
the facility will provide:
Measurement of the injected and stored beam currents
Beam lifetime monitoring and control
Beam’s transverse and longitudinal profile measurements
Aperture measurement
Beam loss measurement
Longitudinal and transverse instability measurements
Energy and energy spread measurement
Tune monitoring
The diagnostics instruments and their functionality are summarized in Table 9.1.
As a basic policy, whenever possible, we will pursue the utilization of commercial
off-the-shelf devices in order to reduce cost as well to achieve better reliability.
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Table 9.1: List of diagnostic instruments
Instrument Acronym Measured
parameter
Beam position monitor BPM Position
Stripline BPM Stripline
Faraday cup FCUP
Charge
Fast current transformer FCT
Beam charge monitor BCM
DC current transformer DCCT
Annular electrode AE
Fluorescent screen/OTR FS/OTR
Size Synch. rad. monitor
Visible synch. rad. monitor
X-Ray synch. rad. monitor
SRM
V-SRM
X-SRM
Beam loss monitors BLM Others
Scrapers SCR
9.2 Description of the diagnostics elements
9.2.1 Fast current transformer (FCT)
Fast Current Transformer (FCT) is used to measure the bunch charge and its
longitudinal profile. It is also used for filling pattern measurements. To maintain
uniform fill and to mitigate dependence of the BPM receivers on the filling pattern, a
FCT will provide electrical signal proportional to the charge of individual bunches.
Figure 9.1 shows a typical FCT that can be directly mounted on the beam chamber
with a ceramic break. FCT-WB-082-20:1 model by Bergoz has 1.75 GHz bandwidth
with a 200 psec rise time [9.1]. Its specifications are shown in Table 9.2.
Figure 9.1 Bergoz fast current transformer [9.1].
265
Table 9.2 Typical specifications for the fast current transformer by Bergoz
Nominal Sensitivity [V/A] 1.25
Rise Time (typ.) [ps] 200
Droop [%/μs] <6
Upper cutoff frequency [MHz] 1750
Lower cutoff frequency [KHz] <9.5
Position sensitivity [%/mm] <0.2
Minimal L/R time constant [μs] 17
Maximum charge per pulse (pulses<1ns) [μC] 0.4
The FCT will be placed over a ceramic break and provided with RF-shielded housing
(Figure 9.2). Fast ADC sampling of the voltage with 500 MHz on the top of each
pulse will make the charge distribution available to the control system. Summing the
amounts of the charges found for all bunches will provide an alternative means for
measuring the total beam current.
9.2.2 DC current transformer (DCCT)
A DC current transformer will monitor the DC-component of the beam. The Bergoz
New Parametric Current Transformer (NPCT) [9.1], is the latest evolution of
commonly known DCCT. It is shown in Figure 9.3. NPCT has large dynamic range
and high bandwidth, making it a versatile device for measuring lifetime and injection
efficiency. It is insensitive to the synchrotron revolution frequency and bunch fill
pattern, thus enabling full bandwidth operation down to a very low current.
The NPCT-115-C30-HR-H model (Figure 9.3) has a radiation-hardened sensor and
four ranges (±20 mA, ±200 mA, ±2 A, ±20 A) with remote control by TTL signals. Its
specifications are shown in Table 9.3. Wide operational range allows utilization of
Figure 9.2 FCT in the vacuum chamber [9.2].
266
NPCT starting at commissioning and during regular operations without compromising
the requirements for accuracy. Its resolution is better than 1 μA/ Hz . The high
bandwidth of the DCCT will allow measurements of the steps in the current after
injection, and therefore provide a means of continuously monitoring injection
efficiency.
The instrument needs a gap to avoid measuring stray currents in the vacuum pipe.
Electric shielding will prevent the strong electromagnetic field developed across the
gap from propagating outside. More details about DCCT can be found in [9.3].
Table 9.3 Typical specifications for the DC current transformer by Bergoz
Full scale ranges ±20mA, ±200mA, ±2A, ±20A
Range control 2 TTL lines
Output [V] ±10
Output bandwidth 8KHz in 20mA range, 10 KHz other ranges
Response time (at 90%) [μs] <50
Resolution [μA/ ] <5
Output accuracy [%] ±0.1
Linearity error [%] <0.1
Output impedance [Ω] 100
9.2.3 Annular electrode (AE)
Annular Electrode (AE) is used for qualitative measurement of the bunch length. AE
consists of an electrode which completely covers the inner whole beam pipe (Figure
9.4). This ensures that all the beam image charge is captured by it (regardless of beam
displacement). The output is simply read by a scope. The electrode is isolated (and
supported) from the vacuum chamber with a small ceramic. The advantage of this
non-destructive method is that is has up to 8 GHz bandwidth [9.4]. In Figure 9.5, a
typical implementation of AE in the storage ring in combination with FCT and DCCT
can be seen [9.2].
Figure 9.3 Bergoz NPCT (New Parametric Current Transformer) [9.1].
267
9.2.4 Scrapers (SCR)
In injection, straight scrapers are needed to get rid of the undesired beam halo
particles and protect the insertion devices from possible damages produced by mis-
steered or off-energy particles. One scraper is installed in horizontal plane (SCRH)
and another should be installed in the vertical plane (SCRV). The scrapers are moved
inside the vacuum chamber by a stepper motor in order to intercept the beam. The
mechanical support of the scraper has to be very stable in order to guarantee sub-
micrometer resolution of the blade position. The motor-actuated scraper beam blades
should be operated from the control panel in the control room. The control panel
displays the scraper position as detected by linear potentiometers on the instruments.
Devices incorporate micro-switch interlocks, preventing excessive travel.
Figure 9.6 shows the schematic diagram of a scraper. Horizontal and vertical scrapers
are shown in Figure 9.7.
Figure 9.4 Annular electrode (AE) [9.5]
Figure 9.5 A typical implementation of AE, FCT and DCCT [9.2]
Figure 9.6 Schematic diagram of scraper [9.2]
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9.2.5 Beam position monitors (BPM)
The position information of the electron beam is obtained by a set of BPMs, which in
addition to determining the position, are used to derive information concerning lattice
functions and beam dynamics. Furthermore, the operation of the feedback system,
with which the beam orbit is corrected if and when needed, also relies on the
information provided by the BPMs. The cross section of the vacuum chamber with the
position of the BPMs and the distribution of the electrical field from the bunch charge
is presented in Figure 9.8.
The electron beam-position monitor (BPM) is a small vacuum chamber equipped with
four button electrodes shown in Figure 9.8. The principle of the operation of BPM is
that the electric field of the electron beam induces a voltage on the electrodes. By
collecting the data from all 4 buttons with an electronic processor, taking account of
the shape and geometry of the buttons, the horizontal and vertical position of the
electron beam can be calculated. When the electron beam is centered in the vacuum
chamber, the electric field of the beam induces the same voltage on all four buttons.
However, an off-center beam induces different voltages on different buttons. The
closer the beam to the button, the higher the induced voltage on that button
(Figure 9.8).
The mechanical dimension of buttons and their locations should be selected carefully
with the aid of numerical modeling and with mechanical considerations. Modeling
will help the design of BPM block to optimize the positions, angles and extraction
impedance match of the BPM structure. Offset and linearity of the BPM block can be
measured by the BPM calibration bench before installation. Calibrated data as well as
data from numerical calculations can be stored at the control database for further use
to compensate BPM offset and nonlinearity errors.
Figure 9.7 Horizontal and vertical scrapers [9.2]
(a) (b)
Figure 9.8 Button-type beam position monitor (a) centered beam (b) off-center beam (distribution of electric field)
269
9.2.5 Stripine
For tune measurement, one stripline is used to excite the transverse oscillations of the
beam. Horizontal and vertical betatron oscillations are excited by one stripline. The
stripline which is composed of 4 strip electrodes (two for horizontal plane and 2 for
vertical plane) is shown in Figure 9.9. Any BPM in the storage ring can be used to
obtain the transverse oscillations of the beam after being excited, and tune is
calculated from the acquired response.
To use the stripline for beam excitation in each plane, voltages of different polarities
are applied to the electrodes of each plane as shown in Figure 9.10. As a result an
electric field is produced between two electrodes which excites transverse oscillations
of the electron beam.
Tune measurement in the booster is carried out using two 50Ω matched striplines: the
first one excites the beam with an electric kick (SEXC); the second one is used to
obtain the transverse oscillations (SMES) and thus infer the tune frequency. The
required setup for tune measurement which consists of exciting stripline (kicker),
measuring stripline (pick-up) and network analyzer is shown in Figure 9.11.
It is better to choose the location of the striplines where the phase advance is as close
as possible to 90º in each plane. After the commissioning of the booster, and provided
the beam in the booster provides a large enough signal in the button BPMs, any of the
BPMs can be used to measure the betatron oscillations.
Figure 9.9 Stripline BPM for storage ring: view from outside (left) and from inside (right) [9.2]
Figure 9.10 Schematic diagram of a stripline BPM [9.2]
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9.2.7 Fluorescent screens (FS)/ Optical transition radiation (OTR)
Fluorescent screens are used to have a qualitative image of the beam, its size and
position. Fluorescent screen is typically comprised of the screen, an insertion
mechanism, an illumination system, and a video camera for the detection as can be
seen in Figure 9.12.
The principle of fluorescent screens is that charged particles traversing a material
ionize and excite the atoms or molecules inside. Part of the energy deposited in the
material in this process is then returned as light. On the screen, at each location, the
amount of light emitted is proportional to the number of particles that have crossed it.
For a monitor to work properly the linearity between particle density and light
emission is of utmost importance. This means that not only the fluorescent screen
itself must have a linear curve of emission, but the detector must also have a linear
response and that no saturation should occur.
Fluorescent screens are usually rather thick, of the order of one or more millimeters.
The multiple scattering occurring inside the material increases the divergence of the
beam and induces beam losses. That is why the screens are inserted only when
required and otherwise retracted. Often the screen is installed at 45˚ to the beam and
the camera at 90˚ as depicted in Figure 9.12.
Figure 9.11 Setup for tune measurement [9.7].
271
The advantage of the fluorescent screen is that it produces a lot of light, however FS
saturation for large beam densities and the saturation of the CCD camera by such
large amount of light, are the two main disadvantages of these screens. To avoid the
saturation, optical transition radiation (OTR) screens can be used. In OTR which has a
thin layer of AL-foil, light is emitted because of the different permittivity as the
electron beam goes through the screen (Figure 9.13).
The advantage of the OTR screen is that no saturation occurs since it is an
instantaneous effect. However the disadvantage is that little visible light is produced
for low beam currents. To make use of the advantage of the both screens, the
combination of FS and OTR (abbreviated as FS/OTR) can be used for beam size
measurement in the booster. At low currents, the FS provides sufficient photon flux,
while for high currents and small beam sizes, saturation of the screen can be avoided
by using the combination of FS/OTR can be seen (Figure 9.14).
Figure 9.12 Fluorescent screen setup [9.2].
Figure 9.13 OTR [9.2].
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9.2.8 Synchrotron Radiation Monitor (SRM)
Synchrotron radiation monitors use the radiation from bending magnet to determine
the profile of the electron beam. They are of two types; visible SRM (VSR) and X-ray
SRM (XSR). The VSR is used for quantitative bunch length and bunch purity
measurements and the XSR is used to monitor the beam emittance by measuring
beam size and the well-known method of quadrupole scan.
9.2.9 Visible synchrotron radiation front-end
The optical setup for the VSR is shown in Figure 9.15. As can be seen, the set-up
consists of an in-air mirror which reflects the visible part of radiation toward the slit.
Then this radiation is focused on a CCD camera by means of lenses. The CCD camera
analyzes the profile of the emitted radiation from which the profile of the electron
beam can be deduced.
Figure 9.14 FS/OTR for the booster [9.2].
Figure 9.15 Optical setup for VSR, schematic and typical implementation in ALBA [9.2].
273
9.2.10 X-ray synchrotron radiation front-end (pinhole)
In the storage ring, because of its low-emittance and high-energy beam, the beam
transverse size is typically in the same range as the resolution of the cameras (around
10 μm). The simple principle of a pinhole system is widely used in synchrotron light
sources to overcome this limitation. Since imaging using the visible range is
diffraction-limited, the pinhole system has to use the X-ray part of the spectrum of the
synchrotron radiation. In a pinhole system, the image of a beam with general
transverse size (sub-index u denotes either the horizontal or vertical direction) is
amplified in a pinhole system by:
where is the distance from the object (beam inside the dipole) to the pinhole
position, and is the distance from the pinhole (sheet) to the screen where the image
is formed. The screen resolution limitation is avoided if the magnification, i.e. the
ratio is large enough. A typical XSR setup is shown in Figure 9.16.
The X-ray beam traverses a vertical slit in the beam-port absorber before traversing an
Al window. The window has to be thin enough to transmit a sufficient radiation flux,
and thick enough to be able to sustain the mechanical stress due to the pressure
difference and the temperature variation. In addition, the elevation of temperature due
to the absorption of the radiation should be much less than 500C [9.7].
The role of the imaging system (fluorescent screen, lens assembly, CCD camera) is to
take a measurable picture of the X-ray beam profile, in order to find the electron beam
size and calculate the emittance and energy spread of the stored electrons. The
fluorescent screen has to convert X-rays into visible light. The lens assembly focuses
the image of the X-ray beam profile onto the CCD camera. The conversion efficiency
of the screen, the resolution of the screen, of the lens and the camera has to be taken
into account [9.7].
Figure 9.16 Optical setup for XSR [9.7].
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9.2.11 Beam loss monitors (BLM)
The required BLMs are based on p-I-n diodes, which are commercially available from
Bergoz [9.1] (Figure 9.17). The loss monitors have a pulse output (one pulse per lost
particle) and are insensitive to the synchrotron radiation photons. The monitors are
small and can be easily relocated to regions of interest.
CosyLab has developed signal conditioner and interfaces for easy integration of
BLMs with the control system [9.8] shown in Figure 9.18. They will probably be
installed in the storage ring with an average distribution of one or two units per
straight section, with clusters around loss elements such as collimators and
quadrupoles.
9.3 BPM design for the ILSF synchrotron
The beam position monitors (BPMs) have to be designed to provide reliable and
accurate beam position readings. Simulation and computational codes have been used
to optimize the design of BPMs for given vacuum chamber dimensions.
Figure 9.17 BLM from Bergoz [9.1].
Figure 9.18 Signal conditioner for BLM and interface for control system from Cosylab [9.1].
275
The optimization takes into account the usual sensitivity and intrinsic resolution
parameters as well as the wake field loss factor of the buttons. Due to the storage ring
small vertical vacuum chamber dimension and the high design current, the beam
power deposited in the buttons and HOM power is a concern since uneven
temperature distribution at surface can result in thermal deformation effects and can
introduce errors at the submicron level. To arrive at the appropriate dimensions for the
button, a compromise has to be reached between the need for a higher intrinsic
resolution and a lower power deposited from the beam in the buttons (decreased
HOM power effect).
As a whole, the button geometry, gap between the button and the vacuum chamber
and the geometry of vacuum feed-through that connects the button to the BPM
coaxial connector and related materials, determine the performance of the BPM.
Figure 9.19 shows the detailed structure of three buttons used in there different
accelerators and the types of material used in them.
9.3.1 Storage ring BPMs
BPM blocks are planned to be directly welded on the vacuum chamber section, with
no flanges or bellows. Four button-type capacitive pickups will be mounted in each
block. Figure 9.20 shows a SR BPM block and the button pickup.
Figure 9.19 BPM structure and the materials used in three different accelerators [9.9][9.10].
276
The SR vacuum chamber, where BPMs are located, has a vertical aperture of 24mm
and a width of 70mm. Theoretical calculations based on Matlab code were performed
to determine the ideal button electrode features according to these dimensions.
Chosen features and sizes must satisfy the reduced HOM effect and intrinsic
resolution, by finding the highest capacitance that will yield the required sensitivity in
both the vertical and horizontal directions.
Figure 9.21 shows the schematic of the software used for comparison and analysis of
different structural sizes of BPM.
To obtain the horizontal and vertical sensitivity, a widely used method known as
Delta over Sum is used. Sensitivity mainly relies on the diameter of the electrodes and
their distance to the electron beam. The vertical position of the buttons is fixed due to
the chamber height and the horizontal separation which is mainly defined by the
available space.
In the ILSF storage ring, the available separation is about 21.23mm. According to the
optimized values given in Table 9.4, the horizontal separation was chosen to be
19mm.
Figure 9.20 SR BPM block and button pickup [9.11]
Figure 9.21 The GUI for analyzing different BPM's parameters.
277
Table 9.4: Deduced capacitance and sensitivities for different separations
Sy Sx Cb Distance between
two buttons
0.0698 0.1062 1.22 21.23 mm
0.0780 0.0997 1.22 19 mm
0.0821 0.0960 1.22 18 mm
0.0924 0.0849 1.22 15 mm
The thickness of the buttons at other light sources varies between 2 to 4mm. Table 9.5
shows features of each one. By choosing 4mm as the thickness of the BPMs we will
have more capacitance, less beam power deposition, with same sensitivities.
Table 9.5: Deduced capacitance and sensitivities for different thicknesses
Sy Sx Cb Thickness
0.0780 0.0997 1.22 4mm
0.0780 0.0997 0.9149 3mm
0.0780 0.0997 0.6099 2mm
Another structural feature that should be designed is the annular cut or air gap
between the block and BPM's plane. A smaller annular cut will result in a smaller
HOM effect. However one has to consider the limits of fabrication for such small
gaps. According to Table 9.6 an air gap of 0.5 or 0.3mm is preferable.
Table 9.6: Deduced capacitance and sensitivities for different air gaps
Sy Sx Cb Annular cut gap
0.07804 0.09979 1.22 1 mm
0.07804 0.09979 2.3337 0.5 mm
0.07804 0.09979 3.8172 0.3 mm
The value of the diameter is subject to conflicting requirements. A smaller value
reduces power losses, but also the signal transmission; losses are reduced due to the
higher frequency of the electromagnetic mode trapped at the button, but the coverage
of the impedance spectrum by the bunch spectrum is also reduced. The signal
transmission is reduced due to the lower induced signal but priority should be given to
the reduction of the power losses as long as the transmission would not be reduced
below an acceptable level. Table 9.7 shows different diameters used at other
accelerators and their features. As can be seen a radius of 5mm results in a larger
capacitance, but thermal effects at 5mm is severe, therefore a radius of 3.5mm (a 7
mm diameter) is the preferred value for ILSF. Figure 9.22 shows related parameters
compared with each other.
278
Table 9.7: Deduced capacitance and sensitivities for different air gaps
Sy Sx Cb Radius of button
0.0780 0.09979 2.3337 5 mm
0.07416 0.1043 1.6657 3.5 mm
0.07318 0.1057 1.22 2.5 mm
Thus the optimal and final values for ILSF storage ring BPMs are:
Radius of button: 3.5mm
Annular cut: 0.5-0.3mm
Thickness: 4mm
Distance between buttons: 19mm
9.3.1 Booster BPMs
The buttons of the BPM blocks will have electrodes with a diameter of 15.18 mm
which will be placed symmetrically at 45 º from the axes (Figure 9.23).
Figure 9.22 Comparison of different characteristics corresponding to different radii at 4KHz bandwidth [9.11].
Figure 9.23 Booster BPMs and their placement [9.11].
279
Similar to the storage ring, the main parameters of the booster BPMs such as annular
cut, thickness and radius must be designed so as to have less HOM and thermal
effects and more capacitance and sensitivity. Figure 9.24 shows the results the
evaluations performed for this purpose. Based on these values a thickness of 4 mm
and a 0.3-0.5mm annular cut offer the best compromise again.
9.4 Fast positional global feedback for the storage ring
Stability of the closed orbit of the electron beam in the storage ring is limited by the
stability of the components defining this orbit i.e. magnet positions and the field
values. Measurements of the variation of the stored beam orbit with respect to a
nominal orbit and application of orbit corrections derived from these measurements
can reduce these distortions.
The reduction of the orbit distortions in the rest of the machine is also mandatory in
order to achieve good emittance and lifetime, and to protect the vacuum chamber
against synchrotron radiation.
Below 0.1 Hz we ground motion due to seasonal variations or tidal motions and
thermal effects create such orbit distortions. They will be dealt with by machine
realignments (seasonal effects) and beam position measurements followed by closed
orbit corrections using corrector dipole magnets. Between 0.1 Hz and 100 Hz,
perturbations come from the ground vibrations transmitted by magnet girders, water
circulation and AC power distribution system. These additional fast sources of
perturbation should be minimized at their source, but residual orbit perturbations can
persist up to a level of above 1 µm, even on well-designed machines.
Variation in the positions of quadrupoles or sextupoles, tilts in the orientation of the
dipoles, and field fluctuations, will result in additional angular kicks to those of the
nominal dipole fields of the ring. These kicks are compensated by closed orbit
corrections, where the effect of perturbations is corrected by kicks produced by the
Figure 9.24 Evaluation of the main design parameters of booster BPMs.
280
offset of the perturbed beam’s closed orbit with respect to the quadrupole center. To
perform a closed orbit correction an orbit measurement should be performed using a
set of electron (or photon) BPMs in order to apply a set of correction kicks using
corrector dipole magnets [9.12].
9.4.1 Global corrections
With this scheme, M BPMs, spread all over the machine are used to measure the orbit
distortion. The vector of the M beam position offsets is used to calculate a
correction vector containing the values of N correction kicks using an
correction matrix . The number and location of the BPMs and correctors are
functions of the lattice design, the space available on the machine, and the quality of
the correction needed. The number of BPMs and correctors used can be very large.
However, due to the quasi-periodic pattern of beam distortion due to random kicks, a
significant reduction of distortion can be obtained using a much smaller number of
BPMs and correctors. A rule of thumb is that using a number of BPMs and correctors
equal to the tune number of the planes considered, one can achieve a reduction by a
factor of 3 to 5 of the most random orbit distortions [9.12].
9.4.2 Local corrections
Since the orbit stability is particularly important at some special locations like at
insertion devices or interaction points, the correction can be aimed at suppressing the
orbit distortion only at these locations using a closed bump, leaving the rest of the
machine uncorrected. Such a scheme requires two BPMs for the orbit distortion
measurements in a straight section and four correctors for the local cancellation of
both position and angle and the bump closing [9.12].
9.4.3 Local and global scheme comparison for fast corrections
For a good performance of a machine in terms of emittance, lifetime, and resonance
limitation a slow orbit correction system based on a large number of BPMs and
Figure 9.25 Block diagram of a feedback loop orbit [9.12].
281
correctors is needed. The rate of the possible corrections with such a large number of
components will be limited (especially by the corrector's bandwidth).
Additional corrections at a higher rate can be needed in a limited number n of discrete
locations, for instance at the emission points of a light source. If n is small, the
implementation of N additional local correction systems (using BPMs and
correctors) can be the solution. However if n becomes large a fast global
scheme using a limited number of dedicated wideband BPMs and correctors is a
better solution [9.12].
9.4.4 General guidelines
The number of components (BPMs, correctors, control interfaces) needed for fast
corrections is only a fraction of the number needed for slow corrections. If the
performance required for fast correction components cannot be achieved by the slow
correction components without extra cost or compromise on the performance level
(principally speed and BPMs noise spectral density), it will be more efficient to
implement specific components for this purpose. If adopted, this separation will
require a de-coupling of the two systems. Different decoupling schemes are possible.
The choice of a frequency separation of the slow and fast system can ease the design
of the BPMs and correctors [9.12].
9.4.4.1 Electron BPMs
To achieve a good resolution for slow corrections, the wideband spectral noise density
of the BPMs output signal is not a major concern since it is possible to filter this noise
with a low-pass filter. For a fast BPM, this filtering cannot be applied and the noise
density must be kept as low as possible [9.12].
9.4.4.2 Photon BPMs
Due to the smaller space between their electrodes, and high synchrotron radiation
power available, the photon BPMs can achieve a lower noise spectral density for
wideband position measurements than electron BPMs. Dipole emission can only be
used for vertical position measurements; insertion device emission can be used in both
planes; but their use in electron beam orbit local correction systems in straight
sections is impaired by the pollution of the photon signal of the insertion device by
adjacent dipoles’ emissions. However, for a global vertical orbit correction system,
photon vertical BPMs using the dipoles emission would be very good candidates
compared to electron BPMs; the high vertical value at the dipole source point is an
advantage, and the resolution of electron BPMs in the vertical plane can be at the limit
of what is required for some recent storage rings [9.12].
9.4.4.3 Corrector magnets and power supplies
Given the low delay and high bandwidth required, air-core magnets must be used for
high-resistivity vacuum chamber walls (thin stainless steel wall for instance). Air-core
magnets are bulkier than iron-core magnets, so their number should be limited to what
is required for fast corrections. If these magnets are used only for the corrections of
vibrations without delivering DC currents, this will also relax the power requirements
for their power supplies. Driving an inductive load, with a flat frequency response and
282
a low delay is not easy. To damp the inductance with a low value resistor two
solutions are possible: use an over-dimensioned voltage power supply, or use a PWM
switched current power supply with a current control loop optimized for the magnet
load [9.12].
9.5 Tune measurement
Tune (Q) is the number of betatron oscillations per turn. The tune value can be split
into two parts as with the integer part and q the fractional part.
Most measurement methods can only determine the fractional part q which is usually
measured by observing the signal from a single BPM that at each revolution, records
the position of the beam, excited so as to perform a coherent betatron oscillation
(Figure 9.26). Coherent betatron oscillations are excited by a fast kick which has to be
much shorter than the revolution time 1/f0. It is preferable to place the BPM at lattice
point with a large value of the betatron function. The beam position is monitored turn-
by-turn (broadband processing only) and it is stored as a function of time or frequency
[9.13] [9.14].
As an example, Figure 9.27 shows the positions of an oscillating bunch on six
subsequent turns. Intuitively, one would draw a sine-curve through the data points and
obtain the one labeled 0.23 or 0.77. To find the corresponding frequency (fm) that fits
these dots, one can use fm = (m ± Q) frev, where m is the mode and frev is the revolution
frequency.
Using this method, not only the integral part, , remains unknown, one can also not
distinguish between and its complement (0.23 and 0.77 in Figure 9.27). In
order to determine whether is above or below 0.5, one may change the focusing
Figure 9.26 A single BPM records the position of an oscillating beam at every revolution [9.13].
Figure 9.27 Beam position on six subsequent turns and the three lowest-frequency fits [9.13].
283
properties of the machine (e.g. the current in the F and D quadrupoles) and observe in
which direction this shifts the frequencies fm.
Historically, the first method was to excite a beam by applying an RF voltage to a
transverse kicker (Figure 9.28a). Scanning with the RF generator, one found the
frequencies fm at which beam loss occurred [9.14].
Often the beam is excited by a single kick lasting for a fraction of a revolution,
(Figure 9.28 b). A filter selects a suitable fm for measurement with a counter, after a
delay to allow the filter transients to die away. In selecting the band in which fm is to
be measured, one must consider the length and shape of the kick, since the "response
function" depends on them [9.14].
9.6 LIBERA beam position processors
Figure 9.29 shows different products from Instrumentation Technologies known as
Libera beam position processors for light sources. There are three types of products
for beam position monitoring at a storage ring or a booster, each with some
advantages and shortcomings. Among them Brilliance is better due to more
satisfactory specifications and cost.
(a) (b)
Figure 9.28 (a) RF excitation; a feedback loop may provide lock-on;. (b) Application of a single short kick [9.14].
Figure 9.29 Different Libera products for beam diagnostics [9.14].
284
In Figure 9.30, three electrical processing setups for BPMs at storage ring or booster
are compared. For measuring position at the Linac, LTB, or BTS Brilliance Single
Pass is preferred. For local and global corrections especially fast orbit corrections we
need to detect the position of photon or synchrotron radiation at the front-end so
photon beam position processing is required for this purpose. For studying betatron
phase advance, chromaticity, and some nonlinear quantities we need to detect each
bunch via the so-called bunch-by-bunch processing. By this account we would need 2
units of Bunch-by-Bunch and Bunch-by-Bunch Front End processors and one unit of
a low-jitter clock distribution system such as the Sync synchrotron for synchronizing
between processors.
For fast orbit feedback integration Libera Brilliance provides fast acquisition data
concentration and fast acquisition output stream. These are essential for fast global
orbit feedback. The data gathered from the Libera Brilliance units are sent through
fast ports (SFP) at a rate of approximately 10 kHz. There are two principal methods
for fast acquisition data concentration: Libera Grouping and Communication
Controller (developed by Diamond Light Source)
The main difference between them is the topology which is used for connecting the
Liberas and collecting the data. The fast acquisition output stream is transmitted in the
form of UDP/IP packets over the Libera Gigabit Ethernet Interface (1000Base-T/LX).
Figure 9.30 Comparison of Libera electron, Brilliance and Brilliance+ for processing of BPM at storage ring or booster [9.15].
Figure 9.31 Schematic drawing of linking between Brilliance and other devices [9.15].
285
Data from Libera Gigabit Ethernet Interface or Libera Grouping can be easily
acquired using simple receiver software with Linux or Windows with a Gigabit
Ethernet port (Figure 9.31). Data from Communication Controller can be collected
using external hardware receiver commercially available FPGA board (Figure 9.32).
Libera Bunch-by-Bunch and Libera Bunch-by-Bunch Front End make the closure of
transverse and longitudinal feedback loops possible. The system successfully damps
coupled bunch instabilities. Libera Bunch-by-Bunch Front End demodulates phase or
amplitude of the wideband signal received from hybrid. It provides processing of two
signals for transverse and one for longitudinal feedback. Its outputs can be connected
directly to the Libera Bunch-by-Bunch processing unit.
Libera Bunch-by-Bunch samples data at a sampling rate equal to the RF frequency of
the machine by using fast 12 bit ADC. Samples are divided per bunch. Each bunch is
filtered with 16 tap FIR filter. Additional processing, like gain, delay or phase
Figure 9.32 Schematic drawing of Communication Controller scheme for data gathering [9.15].
Figure 9.33 The interior logical operations of Bunch-by-Bunch block [9.15].
286
shifting, can be applied. Due to restrictions on the speed of FPGA devices, processing
is divided into 4 chains, where each chain processes one quarter of all bunches.
Processed samples are converted to analogue signals using 14-bit 500 MHz digital to
analogue converter (DAC). Figure 9.34 shows the relation between these 2 blocks
with BPM processors and related feedbacks for orbit correction.
9.7 Distribution of the diagnostic instruments in the storage ring
All required instruments for the diagnostics in the storage ring are listed in Table 9.8
and their distribution is shown in Figure 9.35.
Figure 9.35 Distribution of diagnostic instruments in the storage ring.
Figure 9.34 Block diagram for feedback and orbit-correction system [9.15].
287
Table 9.8: List of required diagnostic instruments in the storage ring
Instrument Measured parameter
1 Beam Position Monitor (BPM)
button pick-up Position of the electron beam
2 DC Current Transformer
(DCCT)
Total beam current circulating in the Booster over
one revolution (DC beam current)
3 Fast Current Transformer
(FCT)
bunch charge in a bandwidth between 1 kHz and
1GHz
(measurement of the filling pattern)
4 Fluorescent Screens (FS) Qualitative measure of beam's size and position
5 Synchrotron Radiation
Monitor Emittance of the electron beam
6 Stripline Excitation of transverse oscillations for tune
measurement
7 Horizontal Scrapers (SCRH) ,
Vertical Scrapers (SCRV) Bunch scraping and collimation
8 Annular Electrode (AE)
Provides a large bandwidth (up to 10 GHz) and is
used to qualitatively monitor the bunch length and
charge
9 PIN Diode Beam Loss
Monitor Beam loss pattern
10 Streak Camera Bunch length measurement
The BPMs will be distributed according to Figure 9.36.
Figure 9.36 Distribution of BPMs in the storage ring for one matching cell (left) + one unit cell (right).
288
9.8 Distribution of the diagnostic instruments in the booster
All required instruments for the diagnostics in the booster are listed in Table 9.9 and
their distribution is shown in Figure 9.37.
Table 9.9: List of required diagnostic instruments in the booster
Instrument Measured parameter
1 Beam position monitor (BPM)
button pick-up Position of the electron beam
2 DC current transformer (DCCT) Total beam current circulating in the booster over
one revolution (DC beam current)
3 Fast current transformer (FCT) Bunch charge in a bandwidth between 1 kHz and
1GHz
4 Fluorescent screens/optical
transition radiation (FS/OTR) Beam's transverse size
5 Stripline Excitation and measurement of the transverse
oscillation for tune measurement
6 Annular electrode (AE)
Provides a large bandwidth (up to 10 GHz) and is
used to qualitatively monitor the bunch length and
charge
7 Synchrotron radiation monitor Emittance of the electron beam
Figure 9.37 Distribution of diagnostic instruments in the booster.
289
Figure 9.38 shows the probable distribution of the BPMs around the booster.
9.9 Distribution of diagnostic instruments in the booster to storage ring (BTS) transfer line
The required instruments for the diagnostics in the BTS are summarized in Table 9.10
and their distribution is shown in Figure 9.39.
Table 9.10: List of required Instruments for booster to storage ring (BTS) transfer line
Instrument Measured parameter
1 Fast current transformer (FCT) bunch charge and filling
pattern
2 Beam position monitor (BPM) button pick-up Position of the electron beam
3 Fluorescent screens/optical transition radiation
(FS/OTR) beam's size
4 Synchrotron radiation monitor (VSR) transverse bunch size
The parameters which have to be measured during commissioning and routine
operation in BTS are:
BTS transmission efficiency: the transmission efficiency along the transfer line is
given by the ratio of the charge measured at FCT positioned at the end of the line to
that of the one positioned at the beginning of the transfer line.
Figure 9.38 BPMs in the booster.
290
Beam emittance: the beam emittance at the BTS must be the same as the one
measured in the booster. If needed, this measurement can be done using the SRMs
and/or FS/OTRs along the BTS.
Beam orbit: the beam orbit is measured using the BPMs in the BTS.
9.10 Conclusion
According to the distribution of BPMs for lattice parameter measurements, correction
and tune measurement purposes as mentioned above, the number of BPMs needed for
the ILSF synchrotron include:
1 at the end of linac
3 in the linac to booster transfer line (LTB)
36 in the booster
3 in the booster to storage ring transfer line (BTS)
128 in the storage ring
To perform tune measurement, diagnostics and multi-bunch instabilities, 2 extra
BPMs should be placed in the booster and 3 in the storage ring. Total number of
BPMs beam position measurement units (booster + storage Ring) can be reduced by
using some of the same units used for the commissioning of the booster for the ring
and during regular operation.
Assuming the availability of Libera units which can support 4 BPMs simultaneously,
20 will be required for the ring and 5 for the booster.
Figure 9.39 Distribution of diagnostic instruments in BTS [9.16].
291
References:
[9.1] http://www.bergoz.com.
[9.2] Ubaldo Iriso, Beam Diagnostics (September 2010).
[9.3] Beam Diagnostics, CERN Accelerator School, Dourdan, France, 28 May – 6
June 2008
[9.4] Z. Greenwald, D. L. Hartill, R. M. Littauer, S. B. Peck, D. H. Rice, “Bunch
Length Measurement using Beam Spectrum” , IEEE 1991,
http://accelconf.web.cern.ch/accelconf/p91/PDF/PAC1991_1246.PDF .
[9.5] www.Hamamatsu.com
[9.6] Conceptual Design Report of NSLS II,
http://www.bnl.gov/nsls2/project/CDR/NSLS-
II_Conceptual_Design_Report.pdf.
[9.7] C. A. Thomas, G. Rehm “AN X-RAY PINHOLE CAMERA SYSTEM FOR
DIAMOND”, Proceedings of DIPAC 2005, Lyon, France.
[9.8] http://www.CosyLab.com
[9.9] Peter Forck, Piotr Kowina, Dmitry Liakin,
Beam position Monitors", CERN Accelerator School 2010,
http://www-bd.gsi.de/uploads/paper/cas_bpm_main.pdf.
[9.10] N. Kurita, D. Martin, S. Smith, C. Ng, M. Nordby, C. Perkins,
"DESIGN OF THE BUTTON BPM FOR PEPII",
http://epaper.kek.jp/p95/ARTICLES/MPQ/MPQ25.PDF .
[9.11] A. Olmos,T. Günzel, F. Pérez, "BPM DESIGN FOR THE ALBA
SYNCHROTRON", Proceedings of EPAC 2006, Edinburgh, Scotland,
http://accelconf.web.cern.ch/accelconf/e06/PAPERS/TUPCH078.PDF .
[9.12] E.Plouviez, "FAST POSITIONAL GLOBAL FEEDBACK FOR STORAGE
RING", Proceedings of DIPAC99, Chester, UK,
http://www.esrf.eu/Accelerators/Groups/Diagnostics/fast-orbit-feedback-
1999/feedback1999.pdf .
[9.13] P. Forck, "Lecture notes on Beam Instrumentation and Diagnostics", JUAS
2011
[9.14] H. Koziol, "Beam Diagnostic Lecture Note" CERN, Geneva
[9.15] www.i-tech.si .
[9.16] http://www.cells.es/Divisions/Accelerators/RF_Diagnostics/Diagnostics/Diagn
ostics_Scheme
292
293
CHAPTER 10: Pre-Injector
10.1 Introduction
The pre-injector system, which contains the electron gun, linac, and other focusing
and compression systems, is a part of most light sources. It should provide a beam
with high quality and sufficient energy for the booster ring. Since the design and
manufacture of the injector system takes a lot of effort and it should be completely
and flawlessly operational in order to commission the booster and storage ring, this
system will probably be bought from foreign research companies such as RI15
,
THALES, and IHEP. These companies are quite famous for their products around the
globe. For instance, the linear accelerators in the Swiss Light Source (SLS), Diamond
Light Source (DLS), and Taiwan Photon Source (TPS) are products of RI. ALBA (the
light source of Spain), and BESSY II, the accelerator at Helmholtz Zentrum Berlin,
use the linacs made by THALES. And PLS, (Pohang Light Source of South Korea)
uses an IHEP linac.
10.2 Definitions and specifications
10.2.1 Structure, RF frequency, and resonant mode
Operation in the S band frequency is much easier, especially when there is not much
previous experience in driving RF structures. Every problem in the injector system,
from generating, amplifying, and circulating RF wave, to undesired modes inside the
gun and linac, will become more serious when the frequency increases. Once a system
is supposed to operate in S band, 2.9979 GHz is usually chosen in order to have
rounded cavity lengths.
The preferable resonant mode in standing wave structures is usually π mode due to the
ease of fabrication. Although π/2 mode has the advantage of smaller cavity length and
therefore, smaller linac length, 2π/3 mode is usually more desirable in travelling wave
structures because of more radial focusing RF force [10.1]. Thus, when the structure
type is selected, the best resonant mode would be more straightforward to pick.
Almost all commercially available linacs are constant-gradient travelling wave
structures operating in 2.9979 GHz, 2π/3 mode. This structure has the advantages of
rounded cavity lengths, more RF focusing power, and constant accelerating gradient
which will result in better emittance control. The purchased linac for ILSF will
probably have the same structure, frequency and resonant mode. Although the pre-
buncher unit will operate in 500 MHz, since the bunch spacing needs to be matched
with the operating frequency of the booster ring.
15
Research Instruments: former ACCEL.
294
10.2.2 Pulse length and charge per bunch
Pulse length together with charge per bunch specifies the beam current. Particles
moving through accelerating cavities induce some charges in the walls of the cavities.
These induced charges absorb some energy from particles reducing the particles’
energy and increasing the energy spread. This phenomenon is called the wake-field
effect. As the beam current increases, the wake-field effect should be taken into
account. Emittance control will also become more of an issue for high beam currents
since the space charge effect will become considerable in such cases.
The total charge inside the storage ring is
The booster ring's circumference is 192 m and its harmonic number is 320, with a 2
Hz repetition rate. For filling up the storage ring (multi-bunch mode), assuming the
booster ring's filling factor is 80%, 256 bunches must be injected into the ring. The
pulse length of such injection would be
Usually, there is a 30% pulse loss during injection from linac into the booster ring. So
the required linac pulse length should be about 800 ns. A reasonable current for long-
term operation of the linac is about 2 mA. Therefore, the total linac pulse charge is 1.6
nC. Assuming the 30% pulse loss and another 33% charge loss (this loss will be
explained later) during the injection, the booster charge will be about 800 pC and
therefore, each bunch in the booster ring would have a charge of 3 pC. This way it
will take less than 15 min to fill the storage ring.
In the single-bunch operation mode, it may be required to fill one bunch in the storage
ring within at most 5 shots, so up to 200 pC should be injected into one bucket of the
storage ring. Assuming we have 25% loss in the booster-to-storage-ring transfer line,
we need 250 pC per bunch in the booster ring.
The linac bunch charge in both single-bunch and multi-bunch mode is dependent on
the pre-injector lattice and will be discussed later in this report.
10.2.3 Beam energy
A higher beam energy is equivalent to a larger linac length. In some cases, due to RF
power limits, focusing, or vacuum difficulties, a few independent linac sections are
required. The beam injected into the ILSF booster ring is required to have the energy
of 150 MeV.
10.2.4 Energy spread
Variation of the energy distribution of the particles in a bunch can cause a positive
feedback procedure. More energy spread will lead to larger bunch width and therefore
higher phase disparity between head and tail of the bunch. Since the accelerating
gradient on each electron depends strongly on its injection phase, the phase difference
produced by the initial energy spread will result in more energy spread.
295
If the energy spread is kept low enough in the acceleration process, there would be no
need for bunch compression systems, such as chicane magnets. A reasonable value for
rms energy spread is less than 0.5%, which is achievable in all commercial linacs.
The definition used in this report for the RMS energy spread is given by
(10.1)
10.2.5 Pulse to pulse energy variation
The bunch energy coherency is not only dependant on the energy spread within the
bunch, but also more importantly on the energy variation of different bunches. As a
result, the relative pulse to pulse energy variation, also known as pulse to pulse energy
jitter, is desired to be less than the relative energy spread.
In order to have a stable beam, the energy variation between different pulses should
be even less than the energy spread in each bunch. This parameter is assumed to be
controlled to less than 0.25% in ILSF pre-injector.
10.2.6 Beam emittance
The beam emittance is the phase space occupied by the distribution of the electrons. It
determines particle distribution as a function of displacement and angular divergence.
The beam transverse position and divergence phase space contours in a linac often
have the approximate shape of an ellipse, usually called the trajectory ellipse [10.2].
One reason for this shape is the predominance in most accelerators of linear focusing
forces.
The beam transverse normalized emittance at the output of pre-injector at ILSF is
needed to be less than 25 π mm.mrad. As a result, the un-normalized emittance of the
beam injected into the booster ring will be
while β is assumed to be unity and γ is calculated for 150MeV.
10.2.7 Repetition Rate
A higher repetition rate means less top-up time for the booster ring, but many
technological issues have to be taken into account in order to increase the repetition
rate. Since these problems become more serious inside the booster, repetition rate is
usually determined by the specifications of the booster.
The best choice for the pre-injector repetition rate is the same as that of the booster
ring. This way, the booster ring will never be full at the time of injection but no beam
slot will be left empty. The repetition rate of the booster ring at ILSF is 2 Hz.
296
10.2.8 Pulse to pulse time jitter, beam position stability and single bunch purity
In order to be sure that each bunch will be captured in the desired bucket at the
desired phase, one should be certain about the exact time interval between two
consecutive bunches. Correspondingly, it is important to have a low pulse to pulse
time jitter.
In the single-bunch mode, only a few of the available stable RF buckets are populated
with electrons, the others being kept empty. User experiments in synchrotron
radiation sources typically require the pattern to be as exact as possible, ideally with
no electrons in unwanted bucket/bunch positions. The ratio of these unwanted/wanted
populations is called bunch purity.
The stability of beam transverse position is really important when the beam is passing
through quadrupole or bending magnets. Poor beam position stability at those points
will result in an increase in beam radius and transverse emittance.
The arrival time jitter of the bunches should be kept small in order to have better
control on beam injection and single bunch purity. The time jitter for the pre-injector
at ILSF is chosen to be less than 100 ps (rms). The single bunch purity is chosen to be
better than 1%. Beam position stability is also chosen to be at the maximum 10% of
the beam size.
Table 10.1 shows the required specifications of the ILSF pre-injector system as
discussed above. In Table 10.2 the specifications of the pre-injectors of different
synchrotron radiation facilities have been listed for comparison. It should be noted
that measurement methods may vary from one facility to another.
Table 10.1 Required specifications of the ILSF pre-injector system
Structure type Constant gradient
Resonant mode 2π/3
RF frequency 2.9979 GHz
Beam energy > 150 MeV
M.B. Pulse length 1 μs
M.B. beam charge 5 Nc
Energy spread < 0.5% (rms)
Beam emittance < 25 π mm-mrad
Repetition rate 3 Hz
P2P energy variation < 0.25%
P2P time jitter < 100 ps (rms)
Single bunch purity < 1%
Beam position stability 10% of beam size
297
Table 10.2 Specifications for the preinjectors of different light sources [10.1], [10.4], [10.5], [10.6] , [10.8][10.8], [10.9], [10.11]
Facility ALBA BESSY II TPS DLS SLS PLS
Manufacturer THALES THALES RI RI RI IHEP
Linac structure
type
TW
Constant
gradient
TW
Constant
gradient
N.A.
TW
Constant
gradient
TW
Constant
gradient
TW
Constant
gradient
Linac RF
frequency
2.997
GHz
2.997
GHz
2.997
GHz
2.997
GHz
2.997
GHz
2.856
GHz
Linac resonant
mode 2π/3 2π/3 N.A. 2π/3 2π/3 2π/3
Linac length 2×3.7 m 3.47 m N.A. 2×5.2 m 2×5.2 m 160 m
Final energy > 100
MeV > 50 MeV
> 150
MeV
> 100
MeV
> 100
MeV 3 GeV
S.B. pulse length < 1 ns
(FWHM)
< 1 ns
(FWHM)
< 1 ns
(FWHM)
< 1 ns
(FWHM)
< 1 ns
(FWHM)
< 1 ns
(FWHM)
M.B. pulse length 112~102
4 ns
40~300
ns
200~100
0 ns
max 1000
ns
100~100
0 ns N.A
S.B. charge ≥ 1.5 nC ≥ 0.35 nC ≥ 1.5 Nc ≥ 1.5 nC ≥ 1.5 nC N.A.
M.B. charge 3 ≤ Q ≤ 4
nC 3 nC ≥ 5 Nc < 3 nC ≥ 1.5 nC N.A.
Energy spread ≤ 0.5 %
(rms)
≤ 0.4 %
(rms)
≤ 0.5 %
(rms)
≤ 0.25 %
(rms)
≤ 0.5 %
(rms)
≤ 0.2 %
(rms)
Normalized
emittance
≤ 30 π
mm-mrad
≤ 50 π
mm-mrad
≤ 50 π
mm-mrad
≤ 50 π
mm-mrad
≤ 50 π
mm-mrad
≤ 25
nm.rad
Repetition rate 3~5 Hz 1~10 Hz 1~5 Hz 1~5 Hz 1~10 Hz N.A.
Time jitter P2P ≤ 100 ps
(rms) N.A.
≤ 100 ps
(rms) N.A. N.A. N.A.
Single bunch
purity ≤ 1% N.A. ≤ 1% ≤ 1% ≤ 1% N.A.
Beam position
stability P2P
< 10% of
beam
size
N.A. N.A. N.A. N.A. N.A.
Energy variation
P2P ≤ 0.25% N.A. ≤ 0.25% ≤ 0.25% ≤ 0.25% ≤ 0.2%
Linac filling time 880 ns N.A. N.A. 740 ns 740 ns N.A.
Linac shunt
impedance
63~69
MΩ/m N.A. N.A. 51 MΩ/m
52-62
MΩ/m N.A.
298
10.3 Pre-injector structure
10.3.1 Lattice layout
There are three possible layouts for the pre-injector system. The first layout which is
widely used in light sources around the world is the pre-injector with DC thermionic
cathode electron gun. Figure 10.1 shows the lattice layout of the pre-injector at
ALBA, manufactured by THALES. Figure 10.2 shows the lattice layout of pre-
injector at TPS, manufactured by RI. Both of them consist of two pre-buncher units
(one operating at 500 MHz and the other at 3 GHz), one buncher unit and the
accelerating sections. Since each one of these linac sections can increase the beam
energy by about 50 MeV, two of them are used in ALBA to reach a final beam energy
of 100 MeV and three of them are used in TPS to reach a final energy of 150 MeV.
Since we want our pre-injector at ILSF to accelerate electrons to 150 MeV as well,
three linac sections will be utilized.
Figure 10.1. Pre-injector structure at ALBA [10.3].
Figure 10.2. Pre-injector structure at TPS [10.12].
299
Figure 10.3 shows the cross-sectional view and Figure 10.4 shows the schematic
diagram of a thermionic electron gun. A thermionic gun consists of a DC diode or
triode and a thermionic cathode. The main limitation of this type of injector is cathode
emissivity A/cm2 [10.10]. As a result, to have a reasonable bunch charge
within a bunch width of a few picoseconds, the cathode radius has to be considerably
large i.e. the bunch width time scale for normal cathodes is in the μs~ns range. The
other limitation of thermionic electron gun is the limited electric field due to diode
saturation (Child-Langmuir law) [10.10].
The electron beam generated in the electron gun will enter a 500 MHz sub-harmonic
pre-buncher unit. This unit will set a 2 ns time interval between the bunches. After
this the beam will enter the 2.9979 GHz pre-buncher unit and then into the final
2.9979 GHz buncher unit. In order to control the emittance growth, focusing
Figure 10.3 Cross-sectional view of a triode electron gun with control grid [10.11].
Figure 10.4 SLC Polarized Thermionic Electron Gun [10.10].
300
solenoids are required between these units and also around the final buncher unit
since the latter has a relatively long length.
When the bunch has attained its proper width, the beam will be injected into a
sequence of accelerating linacs. Hopefully, at this point the beam has gained enough
energy so that the space charge effects on the beam emittance have become
negligible. Therefore, there would be no focusing solenoids required around the first
accelerating linac. However, an arrangement of focusing quadrupoles is still required
at the end of each accelerating linac in order to control the beam radius.
Some diagnostic devices should be installed in the pre-injector lattice. In addition a
diagnostics line has to be built to see the beam parameters. A bending magnet will be
used at this point to select the beam path, one path going to the booster ring and the
other to the diagnostics line.
The second layout is the pre-injector with the photo-cathode RF gun, also known as
photo-injector. Figure 10.5 shows the lattice layout of the photo-injector at NSRRC.
Since this type of injector has high beam parameters it is commonly utilized for FEL
experiments, but the complexity and instability of the laser system used to drive the
photo-cathode makes it undesirable for synchrotron pre-injector system.
Figure 10.6 shows a schematic diagram of an RF electron gun and the RF electric
fields inside it. The RF photo-injector consists of a full and a half (or 0.6) RF cavities
and a laser driven photo cathode. The major improvements of this type of electron
Figure 10.5 Block diagram of the photo-injector at NSRRC [10.12].
Figure 10.6 UCLA/SLAC/BNL S-band next gen. RF photo-cathode gun [10.10].
301
gun over the old thermionic gun are higher beam brightness and ps bunch-width time
scale. The need for an RF buncher after the electron gun is also eliminated since the
bunching can be done by a pulsed laser. This type of gun also has higher accelerating
gradient and correspondingly, the output electron beam has a lot more energy
compared with the old thermionic guns.
A comparison between different specifications of thermionic cathode DC guns and
RF photo-cathode RF guns is shown in Table 10.3.
Table 10.3 Different specifications of thermionic injectors and RF photo-
injectors [10.5], [10.11], and [10.14]
The third layout is the thermionic cathode RF electron gun, which is a combination of
the two types of guns mentioned above. Figure 10.7 shows the block diagram of the
thermionic cathode RF injector used at the SPEAR3 (SLAC) and APS (Argonne)
facilities. This type of pre-injector has the advantages of less required RF power and
more stability than the laser driven photo-cathode RF gun, but requires the bulky and
heavy alpha and chopper magnets and also has less beam quality than the photo-
cathode RF gun, which is not needed for injection into the booster anyway.
Electron Gun
Type
Thermionic
Injector
Laser driven
RF Photo-injector
Structure DC diode or triode with
thermionic cathode
RF Cavity with
photo-cathode
Bunch Charge 1~100 nC 0.1~10 nC
Bunch Width Time Scale μs~ns* Ps
Beam Current 1~10 A 10~100 A
Average Accelerating Gradient ~ 10 MV/m 50 ~ 150 MV/m
Final Beam Energy 80~150 keV 2~6 MeV
Minimum Achievable Normalized Beam Emittance after Solenoid
< 20 π mm.mrad < 1 π mm.mrad
Normalized Beam Brightness ~ 1010
A/(m.rad)2
~ 1015
A/(m.rad)2
*ps time scale is achievable by utilizing RF bunchers
302
In this type of gun, the output bunch length is larger than that required for injection
into the accelerating linac. Therefore, an alpha magnet is used after the gun to
compress the bunch longitudinally by making the particles with higher energies (and
therefore higher velocities) turn in higher radius circles and reach the linac at the same
time as the low energy particles.
For utilizing this pre-injector in single bunch mode, only one to three bunches should
be produced by the gun. Since it is not possible to operate the cathode for a short
pulse, a chopper magnet will be used to pick three bunches out of the bunch train
generated by the gun and omit the rest. The chopper magnet consists of a bending
magnet which deflects the beam into a beam dump. There is a coil supplied with a fast
current pulse in front of the magnet that cancels the bending magnet effect on the
beam for a very short time (~1 ns), letting only one to three bunches pass through to
the linac sections.
The three injecting bunches will then combine and form one bunch in the booster
ring, with about 33% charge loss. So if required bunch charge in the booster ring is a,
the linac bunch charges needs to be a/2. Therefore, as calculated in Section 10.2.2.the
linac bunch charge is 1.25 pC in the multi-bunch mode and 125 pC in the single-
bunch mode.
Figure 10.7 Block diagram of the thermionic cathode RF injector of
SPEAR3 facility at SLAC [10.15].
303
10.3.2 Main components
Since the pre-injector with thermionic cathode RF gun has better beam quality than
the thermionic DC guns and more stability and less complexity than the photo-
cathode RF guns, it was chosen for as the ILSF pre-injector system. Figure 10.8
shows the general layout of the ILSF pre-injector's lattice. This lattice will be
explained in more detail in the next section.
10.3.2.1 Electron gun
Since we have no experience in manufacturing and operating an RF electron gun, we
have decided to design our first RF gun as a simple 1.5 cell, disk-loaded structure
without any nose cones. This design has the benefits of easier manufacturing and a
lower probability of RF breakdown inside the structure at the cost of less uniform on-
axis electrical field. Figure 10.9 shows the geometric layout of ILSF thermionic
cathode RF gun.
This structure is designed to resonate in π mode at a frequency of 2997.9 MHz.
Eigenmode calculations were done using the code SUPERFISH in order to tune and
evaluate the RF fields and other properties of the structure. To have an output beam
with less energy spread, the electrical field in the first cell has to be more uniform. For
this to happen, a wing was designed around the cathode. The amplitude of the
electrical field in the first cell was also set lower than the second cell (about 60%).
This lower field will result in less beam transverse divergence in the gun's output and
also more energy spread in the high energy head of one bunch. This energy spread
increases the effectiveness of the alpha magnet in longitudinal bunch compression.
Figure 10.10 shows the electrical field contours inside the structure and Figure 10.11
shows the on-axis electrical field, normalized to 1 MV/m average accelerating
gradient.
Figure 10.8 General layout of the ILSF pre-injector's lattice.
304
Table 10.4 shows the RF specifications of the structure. Figure 10.12 shows the
energy and time spread (phase spread) of a bunch at the gun output for the RF input
energy of 4 MW. It should be noted that 50% low energy particles are neglected in
this figure. These particles will be eliminated by the focusing channel before the alpha
magnet or in the alpha magnet energy filter itself.
Figure 10.9 ILSF thermionic cathode RF gun geometric layout (dimensions in cm).
Figure 10.10 Electrical field contours inside the ILSF thermionic cathode RF gun.
305
Table 10.4 RF specifications of the ILSF thermionic cathode RF gun
Resonant frequency 2997.42 MHz
Transit time factor 0.6593521
Unloaded Q value 13410.9
Shunt impedance 46.372 MΩ/m
ZT2
21.464 MΩ/m
Emax/E0 2.3933
Figure 10.11 On-axis electrical field in the gun, normalized to 1 MV/m average accelerating gradient.
Figure 10.12 Energy vs. time for a bunch at the gun output (60%
low energy particles are neglected).
306
10.3.2.2 Linac structure
The linac sections we have chosen for the ILSF pre-injector system are 2997.9 MHz,
2π/3 mode, 3 m long, constant-gradient with ~17 MV/m accelerating gradient
manufactured by IHEP, China. Each one of these linac structures has to be injected
with 25 MW of RF input power with a filling time of approximately 800 ns.
10.3.2.3 Alpha magnet
Figure 10.13 shows a simplified cross-sectional view of the alpha magnet designed
for the SSRL project. The alpha-magnet is essentially one half of a quadrupole
magnet, with a symmetry plane in the middle and a vertical mirror plane along the
longitudinal axis. This mirror plane provides the symmetry necessary to obtain
quadrupole-like fields in the interior of the magnet. Rather than inject the beam along
the quadrupole axis, the beam is injected through the front plane (through the iron
piece that functions as the magnetic mirror plane). The longitudinal bunch
compression occurs as a result of energy differences between the particles in the head
and tail of the bunch. Particles with different energies travel along different alpha-like
trajectories inside the magnet. At the correct strength of the alpha magnet the particles
will reach the first linac section at almost the same time within about one picosecond.
The alpha magnet of the ILSF pre-injector system has been chosen to have a gradient
of 324 G/cm, based on the average energy of the particles leaving the RF gun and the
required drift spaces before and after the alpha magnet. The central particle, which
has a momentum of βγ = 5.75, travels a path of 25.54 cm inside this magnet.
Figure 10.13 Simplified cross sectional view of SSRL alpha magnet [10.16]
307
10.3.2.4 Quadrupole magnets
The quadrupole magnets of the ILSF pre-injector system are designed based on the
GTL quadrupoles of the 3 GeV injector system at the Stanford Synchrotron Radiation
Laboratory (SSRL). These quadrupoles have an effective length of 7.845 cm and can
have gradients up to 6 T/m. Figure 10.18 shows the geometric layout of these
quadrupole magnets.
10.3.2.5 Steering magnets
To make small corrections to electron beam trajectories it is common to use steering
magnets, which typically perform the function of steering the beam along both
transverse axes.
10.4 Beam dynamics calculations
The codes used for these calculations are SPIFFE (SPace charge and Integration of
Forces For Electrons) and ELEGANT (ELEctron Generation ANd Tracking), both
developed by Advanced Photon Source, APS [10.17][10.18]. SPIFFE was used to
calculate the beam parameters inside the thermionic RF gun and ELEGANT was used
for the GTL (Gun To Linac) transfer line and the linac sections. Figure 10.14 shows
the layout of GTL and Figure 10.15 shows the layout of linac sections of the ILSF
pre-injector.
Figure 10.14 Layout of GTL of the ILSF pre-injector.
308
For ease of demonstration, ten different points were selected through the lattice as
longitudinal positions and beam parameters were calculated at these points. These
points are as follows:
1. after electron gun,
2. after filtering 50% of low energy particles which will be lost anyway by the alpha
magnet scraper,
3. before the alpha magnet,
4. after the alpha magnet,
5. before the first linac,
6. after the first linac,
7. after the quadrupole lattice between the first and second linacs,
8. after the second linac,
9. after the quadrupole lattice between the second and third linacs,
10. after the third linac.
Table 10.5 shows the gradient of quadrupole magnets. Since the final quadrupole
lattice after the third linac section is part of the LTB (Linac To Booster) transfer line,
the results after that lattice is not included here.
The calculations were done for 100 pC of bunch charge. Since the beam energy after
the RF gun is more than 2 MeV for most of the particles, the space charge forces have
been lowered by a factor of 25. Therefore, the results will be almost the same for
higher beam charges.
Figure 10.16 shows that the beam gains an average energy of 2.5 MeV in the RF gun,
it then enters into the linac sections and gains 50 MeV of energy in each section,
reaching the final energy of more than 150 MeV.
Figure 10.15 Layout of linac sections of the ILSF pre-injector.
309
Table 10.5 Gradient of quadrupole magnets
Quadrupole magnet Gradient [T/m]*
After the RF gun
Q1 0.434
Q2 -0.632
Q3 0.395
After the alpha magnet Q4 0.513
Q5 -0.316
Between the 1st and 2nd
linac sections
Q6 0.142
Q7 -0.207
Q8 0.103
Between the 2nd and 3rd
linac sections
Q9 0.237
Q10 -0.356
Q11 0.395
*Positive sign refers to focusing and negative sign corresponds to
defocusing quadrupoles.
Figure 10.17 shows the beam RMS energy spread. Although this parameter is
considerably high after the RF gun, it starts to decrease by adiabatic damping in linac
sections, especially in the first one, decreasing to 0.06% at the end tail of the pre-
injector. This decrease happens as a result of longitudinal bunch compression in the
alpha magnet, which is shown in the Figure 10.18. As seen in this figure, the bunch
length starts to decrease dramatically after the alpha magnet, although it rises a little
in the first linac section. This rise happens as a result of uneven accelerating gradient
Figure 10.16 Average beam energy at different longitudinal positions.
310
on head and tail of the bunch, the same phenomenon that causes the beam energy
spread.
Figure 10.19 shows the RMS beam envelope in x and y directions. It is evident from
the figure that the RMS beam size is kept by quadrupole lattices under 2.5 mm
throughout the pre-injector, resulting in almost no particle loss due to beam transverse
spread.
Figure 10.17 RMS beam energy spread for different longitudinal positions.
Figure 10.18 Absolute bunch length for different longitudinal positions.
311
Figure 10.20 shows the normalized beam transverse emittance in both x and y
directions. The reason for the growth of emittance in the GTL is the dependence of
the quadrupoles focal force to the particles energy and large energy spread (~10%) of
the particles. The phase space distribution at the end of the GTL and at the end of the
pre-injector system are shown in Figure 10.21 and Figure 10.22 and Table 10.6 shows
the final beam parameters of the pre-injector system.
Figure 10.19 RMS beam envelope for different longitudinal positions.
Figure 10.20 Normalized transverse emittance for different longitudinal positions.
312
Table 10.6 Beam parameters at the end of the pre-injector system
Bunch charge 100 pC
Average beam energy 154.8 MeV
RMS bunch energy spread 0.06%
RMS beam envelope in x direction 1.1 mm
RMS beam envelope in y direction 1.3 mm
Normalized emittance in x direction 4.9 mm-mrad
Normalized emittance in y direction 20.4 mm-mrad
Absolute bunch length 2.64 ps
Figure 10.21 Transverse phase space at the end of GTL.
Figure 10.22 Transverse phase space at the end of the pre-injector.
313
10.5 Space required for the pre-injector system
The pre-injector bunker is chosen to be placed in the service area, between booster
ring and storage ring. The bunker is a 26 m×3.25 m rectangle with more space in the
upper corners, encircled with 1 m thick concrete walls. Figure 10.23 shows the layout
of this bunker. The lengths of the sections are somewhat overestimated to make sure
that they will fit inside the bunker.
References
[10.1] M. Ferrario et al., “HOMDYN Study for the LCLS RF Photo-injector”,
SLAC-PUB- 8400, March 2000
[10.2] Thomas P. Wangler, “Principles of RF linear accelerators”, John Wiley and
Sons, USA 1998
[10.3] U. Iriso, “Measurements of ALBA linac specifications”, 9th
MAC Meeting,
October 9, 2008.
[10.4] A.P. Lee et al., “Technical Considerations of the TPS Linac”, Proceedings of
EPAC08, Genoa, Italy, 2008
[10.5] S.J. Park et al., “Upgrade of Pohang Light Source (PLS) Linac for PLS II”
[10.6] A. Setty et al., “Beam Dynamics of the 50 MeV Preinjector for the Berlin
Synchrotron BESSY II”, Proceedings of IPAC’10 (Kyoto, Japan, 2010).
[10.7] C. Christou et al., “The Pre-injector Linac for the Diamond Light Source”,
Proceedings of LINAC 2004 (Lübeck, Germany, 2004).
Figure 10.23 Layout of the pre-injector bunker in the service area.
314
[10.8] M. Peiniger et al., “A 100 MeV Injector Linac for the Swiss Light Source
Supplied by Industry”, Proceedings of the 1999 Particle Accelerator
Conference (New York, USA, 1999).
[10.9] M. Pedrozzi et al., “Commissioning of the SLS-Linac”, Proceedings of EPAC
2000 (Vienna, Austria, 2000).
[10.10] L. Serafini, Advanced Electron Sources, (US-CERN-Japan-Russia Joint
Accelerator School, Long Beach, CA, Nov. 8th 2002).
[10.11] C. J. Karzmark et al., Medical Electron Accelerators (McGraw-Hill, USA,
1993).
[10.12] A. P. Lee et al., “Design of a high brightness electron linac for FEL
experiments at NSRRC”, to be published in proceedings of 32nd
International
FEL conference, Malmo, Sweden, 2010
[10.13] P. M. Lapostolle, A. L. Septier, Linear Accelerators, (North Holland
Publishing Co., Netherlands 1970).
[10.14] S. H. Wang, RF Electron Linac, (Institute of High Energy Physics, Beijing,
China).
[10.15] David Bocek, “Generation and Characteristic of Superradiant Undulator
Radiation”, SLAC-Report-512, June 1997, USA
[10.16] Michael Borland, “A High Brightness Thermionic Microwave Electron Gun”,
SLAC-Report-402, February 1991, USA.
[10.17] Michael Borland, “Summary of Equations and Methods Used in SPIFFE”,
APS/IN/LINAC/92-2, June 1992, USA.
[10.18] Michael Borland, “ELEGANT: A Flexible SDDS-Compliant Code for
Acceleration Simulation”, Advanced Photon Source LS-287, September
2000, USA.
315
CHAPTER 11: Insertion devices
316
317
CHAPTER 12: Front ends
12.1 Front-end design
The front ends (FEs) are essential parts of a synchrotron light source facility. They
connect the vacuum system of the storage ring with that of the beamlines. The front
ends should serve the following objectives:
Ensure radiation safety beyond the shielding wall during beam operation.
Maintain the vacuum in the storage ring and protect it from any accident occurring
during the operation of the experimental beamlines.
Protect optics and experimental stations from the synchrotron radiation power
emitted from the bending magnet and insertion devices which are not used for the
experiments.
Monitor the photon beam position as well as the characteristics of the photon
beam.
To understand the specifications of different components in front ends, the
characteristics of different insertion devices are summarized in Table 12.1. P(tot) is
the overall emitted radiation power and P(dens) is the power density in the normal
direction. These powers are needed for the layout of the 2nd
absorber and the photon
shutter.
Table 12.1: Characteristics of the insertion devices that could be used for phase-1 beamlines at ILSF.
Table 12.2 summarizes the opening angle of the radiation cones coming from the
insertion devices (Xˊ and Yˊ) and the opening requirements from the users (Δθ and
Δψ) for the photon beams in the beamlines. In all cases Xˊ and Yˊ are larger than Δθ
and Δψ. The radiation cone not needed for the users has to be absorbed in the 2nd
absorber of the front end.
Source B(max) Period Length K Gap P(dens) P(tot)
(T) (mm) (m) (kW/mrad^2) kW
Bend 1.42 0.249
MPW 1.782 80 1.07 13.32 12.5 7.61 6.87
IVU 0.805 21.3 2 1.6 5.5 26.57 2.95
EU (hor) 0.92 71.36 1.655 6.14 15.5 7.63 3.28
EU (vert) 0.73 71.36 1.655 4.69 15.5 5.8 1.92
EU (circ) 0.56 71.36 1.655 3.75 15.5 3.32 2.44
318
Table 12.2: Opening angle of the radiation cones (Xˊ and Yˊ) from different ID’s and required opening angles (Δθ and Δψ).
12.1.1 General layout of a front end
The general layout of a front end with the arrangement of its different elements is
given in Figure 12.1 and Figure 12.2. In the following the different components and
their functions are described, of course at different light sources one or more
components could be missing:
(1) Gate valve at the end of the vacuum system (beam pipe) of the storage ring: This
is a manual valve only used for maintenance.
(2) First fixed absorber at the end of the beam pipe: This absorber must be
introduced to protect the beam pipe against synchrotron radiation from the bending
magnet, but it must have an opening to pass all the radiation coming from the
insertion devices. This absorber is usually called the “crotch absorber”.
(3) Vacuum tube with a length of up to 2.0 m and a diameter of 40 mm: This tube is
needed to get enough space between the front end and the storage ring for the
installation of front-end components. Also a pumping unit has to be installed in this
section in order to control the vacuum. The vacuum gauge of this unit controls the
gate valve to the storage ring and is connected to the interlock system.
(4) A fluorescent screen to monitor the radiation pattern from the IDs: this screen has
to be inside the vacuum tube described in (3). The use of the fluorescent screen is
only possible for small stored currents (roughly 5 to 10 mA) within the storage ring
.The fluorescent screen will only be used for the commissioning of the beamline.
(5) First XBPM to monitor the position of the radiation beam coming from the
insertion device: this XBPM is at the end of the vacuum tube described in (3). In
order to have a precise measurement of the position of the ID radiation, the whole
radiation fan from the insertion devices has to reach the 1st XBPM. This means again,
that no ID radiation has to be stopped at the crotch absorber. During the
commissioning of the beam line, the XBPM can be cross-checked with the fluorescent
screen.
(6) Second fixed absorber and bellows which determine the aperture within the front
end: the 2nd fixed absorber more or less absorbs the main part of the radiation coming
from the insertion device which is not needed for the experiments. The design of the
2nd fixed absorber has to be made to absorb all the radiation coming from the
insertion devices.
Source X(max) X'(max) Y(max) Y'(max) Δθ Δψ(μm) (μrad) (μm) (μrad) (μrad) (μrad)
Bend ±0.25 ±0.25
MPW 28.1 2.26 0.01 0.5 ±0.75 ±0.13
IVU 0.9 0.4 0.01 0.4 ±0.1 ±0.03
EU (hor) 11.9 1.13 0.01 0.45 ±0.15 ±0.15
EU (vert) 0.01 0.45 9.11 0.86 ±0.15 ±0.15
EU (circ) 7.3 0.9 7.28 0.9 ±0.15 ±0.15
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(7) Photon shutter, which absorbs all the radiation coming from the insertion
devices: the photon shutter completely intercepts the x-ray beam via a fast- acting
mechanism in order to isolate the downstream components (beamline) from the
source (storage ring). The photon shutter also acts as a safety device to protect the
bremsstrahlung-shutter from direct x-ray beam impingement. The photon shutter
should be combined with the 2nd fixed absorber and both components should be
combined with a pumping unit. The photon shutter is needed in order to protect the
following valves from being irradiated with synchrotron radiation from the bending
magnet and insertion devices. The time for closing the photon shutter is roughly
between 0.3 and 1 second.
Figure 12.1 Different elements used in front ends.
1.) Gate valve at the end of the storage ring vacuum system (beam pipe)
2.) 1st absorber at the end of the beam pipe
3.) Vacuum tube with a length of 1.5 m and a diameter of 40 mm.
4.) A flourescence within the vacuum tube under 3.)
5.) 1st XBPM.
6.) 2nd fixed absorber ( combined with the photon shutter)
7.) Photon shutter (combined with the 2nd fixed absorber)
8.) 2nd gate and fast valve (combined with 6. and 7.)
9.) Delay line (if needed)
10.) If needed a 2nd XBPM (the distance to the 1st XBPM should be 4 m)
11.) Collimator for Bremsstrahlung absorption
12.) Moveable absorber ( aperture for the experiment)
13.) Diaphraghma, filter, etc
14.) Bremsstrahlung shutter
15.) Gate valve (at the end of the shielding wall)
General Layout of a Front End
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(8) The second gate valve in combination with a fast valve is the next unit. A
pumping unit also has to be used for both components, because the fast valve can be
opened only if the pressure is roughly the same at both its sides. This combination of
gate and fast valve has to protect the storage ring against vacuum failures in the front
end and beamline. The 2nd gate valve should be as near as possible to the storage
ring. The time for closing is roughly 8 to 10 milliseconds the fast valve and 1 to 2
seconds for the gate valve.
(9) Delay line if needed. The above-mentioned conductance pipe could be used as a
delay line.
(10) A second XBPM (if needed) to monitor the position of the radiation beam
coming from the insertion device: the distance between the 1st and 2nd XBPMs
should be at least 4 m .
(11) Collimator for absorbing some parts of the bremsstrahlung coming from the
long straight sections. The transverse dimensions of the collimators are determined
from ray tracing calculations.
(12) Moveable aperture to determine the aperture needed for special experiments.
Figure 12.2 Arrangements of elements in a front end.
1.) 2.) 3.) 4.) 5.) 6.) 7.) 8.) 9.) 10.) 11.) 12.) 13.) 14.) 15.)
Gate valve
1st absorber
Beam pipe
Flour.-sreen
1st XBPM
2nd absorber
Photon shutter
G&F-valve
Delay line
2nd XBPM
Collimator
Mov.-abs.
Diaph. /Filt.
Bremsstr.-shutter
Shielding wall
Gate valve
1.) 2.) 3.) 4.) 5.) 6.) 7.) 8.) 9.) 10.) 11.) 12.) 13.) 14.) 15.)
Gate valve
1st absorber
Beam pipe
Flour.-sreen
1st XBPM
2nd absorber
Photon shutter
G&F-valve
Delay line
2nd XBPM
Collimator
Mov.-abs.
Diaph. /Filt.
Bremsstr.-shutter
Shielding wall
Gate valve
321
(13) Space for a diaphragm or filter holder.
(14) Bremsstrahlung shutter in front of the shielding wall: the bremsstrahlung
shutter is not cooled. The transverse dimensions of the bremsstrahlung shutter are not
cooled. The transverse dimensions of the bremsstrahlung shutter are determined from
ray tracing calculations.
(15) Gate valve with pumping unit behind the shielding wall (inside the experimental
hall): This unit must incorporate a fast pressure sensor for triggering the fast and gate
valves as well as the photon and bremsstrahlung shutters.
(16) Beryllium window.
Figure 12.3 shows the layout of a front end used at ALBA. In Figure 12.4 and
Figure 12.5 the layouts of the front ends used respectively for an elliptical undulator
and a superconducting wiggler are shown.
Figure 12.3 Front-end components used in ALBA.
trigger unit
lead wall unit Bremsstrahlung unit
pneumatic valve
unit
moveable mask
unit
pumping unit
photon shutter
unit
XBPM unit
1st mask unit
Trigger Unit
Lead Wall Unit Bremsstrahlungs
Unit
Moveable
Mask Unit
Pumping UnitPhoton
Shutter Unit
XBPM
Unit
1st Mask Unit
Pneumatic Valve
Unit
trigger
unitvacuum tube
through
shielding wall
double
Bremsstrahlung
shutter
moveable
masks XBPM unit1st fixed
mask
2nd fixed
mask
photon
shutterfast
closing
shutterprotection
shutter: gate valve
: ion pump
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Figures 12.6 to 12.8 depict another front end used in Diamond and the details of its
modules.
Figure 12.4 Layout of a front end used for an elliptical undulator beamline: the overall space from the gate valve downstream the bending magnet to the shielding wall is roughly 9 m.
Double
Bremsstrahlungs-
ShutterMoveable
MaskGate and
Fast Valve
Photon-
ShutterXBPM &
Screen
Gate
Valve
Trigger
Unit
Fig.12.5 Layout of a front end used for a superconducting wiggler beam line: the overall space from the gate valve downstream the bending magnet to the shielding wall is roughly 8 m.
Trigger
Unit
Double
Bremsstrahlungs-
ShutterMoveable
Mask
Gate and
Fast Valve
Photon-
Shutter
XBPM &
Screen
Gate
Valve
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Figure 12.6 Front-end components and elements used at DIAMOND .
J.Strachan
Front-end Components
NSLS Presentation 21/05/2004
Valve
1st Aperture
1st PBPM
1st AbsorberValve
Fast closing valve
2nd PBPM
Custom Apertures
2nd Absorber
Twin port shutter
Valve
Pipe through Shield Wall
First Module
Second Module
Figure12.7 Components and elements of the first module of the front end at the synchrotron light source DIAMOND.
J.Strachan NSLS Presentation 21/05/2004
Fast closing valve
Valve
1st Aperture
1st PBPM
1st Absorber
Valve
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12.1.2 A particular front-end layout
The layout of each individual FE has to be adapted in order to take into account the
geometrical constraints defined by the available distance from the SR isolation valve
to the front wall of the tunnel and by interference with adjacent elements (SR girders,
RF cavities, cooling water pipes, etc). Besides, radiation absorbing elements have to
be designed to meet the aperture and power load requirements posed by both the
characteristics of the photon source and the needs of the users of the beamline. At the
same time, an effort should be made to keep a suitable degree of standardization
among the components of different FEs. With this aim a modular design approach has
been adopted.
The distance from the SR isolation valve to the front wall for Phase I FEs ranges from
7 m to 9 m, but due to the proximity of the storage ring the space effectively available
for the installation of FE components inside the tunnel is within 5 m to 7 m. The
typical layout of Phase I FEs is illustrated in Figure 12.3, with the following sequence
of components going from the SR isolation valve to the beamline: (1) first fixed mask,
(2) X-ray position monitor (XBPM), (3) second fixed mask, (4) photon shutter,
(5) protection shutter, (6) fast-closing shutter (FCS), (7) movable masks, (8) double
bremsstrahlung shutter, (9) vacuum pipe through the front wall, and (10) trigger unit.
These elements are described below:
Figure 12.8 Components and elements within the second module of the front end at the synchrotron light source DIAMOND.
2nd PBPM
Custom Apertures
2nd Absorber
Twin port shutter
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(1) First fixed mask: A first fixed mask is installed in all FEs with an ID as a source
in order to protect downstream FE components from dipole radiation. This element
consists of a 39 mm-thick copper block with internal water cooling, which is
integrated into the first vacuum pipe connecting the SR isolation valve and the first
pumping chamber of the FE. The copper block has an aperture which allows the
passage of the full ID radiation fan taking into account the maximum allowed mis-
steering of the e-beam.
(2) XBPM : Each FE is equipped with one XBPM in order to monitor the position of
the photon beam at a distance of 7-10 m from the source point. Monitors have been
produced according to the designs developed by K. Holldack from BESSY in
collaboration with FMB. Each XBPM makes use of four narrow negatively-biased
blades which intercept the edges of the photon beam distribution. The photoelectrical
currents generated at each blade are measured using a low current monitor, and after
being combined they allow an on-line determination of the horizontal and vertical
position of the centre of the beam. Two different blade configurations have been
employed depending on the characteristics of the source. In the case of BM sources,
four copper blades in the so-called staggered pair monitor (SPM) configuration have
been used. This configuration allows only the determination of the vertical position of
the beam, but as a counterpart it provides an internal calibration standard. In the case
of ID sources, four tungsten blades arranged in an X-shape have been used, providing
information for both horizontal and vertical planes. This configuration requires a
proper calibration for each setting of the ID source. The size and geometry (distances
and angles) of the tungsten blades have been adapted to the beam characteristics of
each ID in order to optimize the sensitivity of the system.
(3) Second fixed mask : In all cases, 2nd
fixed masks consist of an out-of-vacuum
copper body (either OHFC or Glidcop , depending on the case) with an internal
rectangular aperture defined by four inclined surfaces. Depending on the amount of
power to be absorbed, different cooling schemes have been implemented. For small
heat loads (<0.5kW, BM source and IVU sources), a single cooling loop drilled
around the aperture has been used. For medium heat loads (within 0.5 and 4 kW such
as EU and conventional wiggler sources) a “spiral cooling” configuration has been
used (see Figure 12.9), with a stainless steel cover (water box) brazed to the
cylindrical body of the absorber, where a cooling channel in spiral has been
machined. For higher heat loads (> 4kW, SCW source) a “side cooling” configuration
has been used (Figure 12.9), with grooves machined next to each surface defining the
aperture, and a cover with the appropriate dimensions closing the machined cavity.
(4) Photon shutter: The photon shutter is responsible for interrupting the photon
beam when required, protecting all downstream components from synchrotron
radiation. In the case of bending magnet sources with associated powers of less than
100W, an in-vacuum pneumatically-actuated absorber has been used. The absorber
consists of a water-cooled plate of OFHC copper forming an acute angle (30º) with
respect to the incident beam. In the case of FEs with an ID as a source (between 1.5
and 13.5kW), an out-of-vacuum design based on the high-power absorber from ESRF
has been used. In this design two brazed Glidcop blocks define an internal aperture
whose profile depends on its vertical position. When in open position, the aperture
consists of two lateral straight surfaces that allow the passage of the full radiation fan
as defined by the 2nd
Fixed Mask. When in closed position, the two lateral surfaces
are tapered and water-cooled according to the “side-cooling” scheme (Figure 12.9),
and stop completely the photon beam. The vertical stroke required in order to go from
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one position to the other is 16mm, and the pneumatic actuator which drives the
system takes ~200 milliseconds to close the shutter.
(5) Protection shutter: This element consists of a pneumatic cylinder and an in-
vacuum 10 mm-thick copper plate. It does not have any water cooling and completely
blocks the photon beam when in closed position. It is triggered together with the fast
closing shutter (FCS) and has a closing time of ~50 msec, thus protecting the FCS
from synchrotron radiation during the time lapse required by the photon shutter to
close.
(6) Fast closing shutter (FCS): It is a Series 77 DN40 all-metal fast shutter from
VAT which closes in less than 10 msec when triggered. The vacuum gauges
providing the trigger signal for the FCS are located in the trigger Unit, which is
installed in the optics hutch of the beamline, thus protect the SR against a vacuum
failure in the beamline.
(7) Movable masks: Movable masks allow users to define the photon beam delivered
to the beamline. They consist of a pair of Glidcop blocks, each one having a
rectangular aperture with two tapered surfaces (left-top surfaces for mask#1 and right-
bottom surfaces for mask#2) that intercept part of the photon beam. All inclined
surfaces are water-cooled using the “side cooling” scheme. Each mask is mounted on
a motorized X-Y stage, and when combined the two masks delimit a rectangular
cross-section aperture with customisable size and position within the maximum
aperture defined by the 2nd
Fixed Mask.
(8) Double bremsstrahlung shutter: This radiation safety element comprises two
pneumatically-actuated UHV-compatible tungsten-alloy blocks with a cross section of
120 mm×120 mm and a thickness of 200 mm. The two blocks are driven
simultaneous but independently due to redundancy reasons, and in combination with
the photon shutter they provide a safe access for the users to the optics hutch of the
beamline during operation.
Figure 12.9 Second fixed masks for (left) conventional wiggler sources and (right) superconducting wigglers, illustrating “spiral” and “side” cooling schemes.
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(9) Vacuum pipe through front wall: This rectangular cross-section pipe, providing
the connection between the accelerator tunnel and the optics hutch, has a standard
length of 1.9 m and an internal opening of 41 mm×20 mm for all FEs which have a
larger vertical aperture requirement.
(10) Trigger unit : The so-called trigger unit consists of a vacuum chamber where the
two dedicated vacuum sensors that trigger the FCS are installed.
12.1.3 Cooling of front-end components
The design and validation of all power absorbing elements have to be carried out in-
house by means of finite-element analysis (FEA, ANSYS) . As a rule of thumb, the
incidence angle of the radiation on the cooled surfaces of the absorbers has to be
decreased, reducing the maximum power density down to 10-15 W/mm2.
A cooling water velocity of 3 m/s has been considered in most of the cases, and it has
been increased up to 4 m/s if required. The upper limits for the peak values of the
different magnitudes considered within the FEA thermal analysis have been:
(a) 100 ºC for the cooling water temperature; (b) 150ºC for the temperature on the
walls of the cooling channels; (c) 65-70 MPa stress and 0.1% strain in the case of
OFHC copper absorber bodies; and (d) 250 MPa stress and 0.2%s train in the case of
Glidcop absorber bodies.
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CHAPTER 13: Control systems
13.1 Introduction
This chapter is essentially ALBA’s CCD-GDCT-ER-XXXX document entitled “A
Control System for a Synchrotron”. In this document both hardware and software
architectures are covered. The components and their distribution as well as their
relations are described. The pros and cons of the adopted standards will also be
analyzed from the viewpoint of installation and commissioning.
At present s separate support group has been envisioned, but the possibility remains
open of having separate groups in charge of various tasks as is customary in the
installation and commissioning of hardware and software for the control system in
other synchrotron light sources, as well as the intervention of other software groups.
13.2 Architecture
The control system hardware is distributed with accordingly designed software. At a
first level there is a separation between the controls for the beamlines and those for
the machine since the former has many moving parts and need to be flexible as it is
Figure 13.1 ALBA’s data acquisition in a slide for the Machine Advisory Committee.
330
necessary to control each part separately while the latter is much larger and has some
custom-made elements. This implies two main systems:
The Main Control System the covers the linac, booster, storage ring, front-ends, RF
system, magnets, power supply, diagnostics, vacuum, etc. The system has networks
operating independently and dedicated servers in the control room.
Another autonomous system for each beamline that controls the motions, optics,
diffractometers, sample holders, beamline vacuum, etc. These systems have
different databases, and are independently linked to the storage ring for the purpose
of data acquisition. However for some purposes such as control of the insertion
devices and front-end diagnostics these systems have to be highly interconnected
with the Main Control System.
As in Alba, ILSF has adopted Tango as the standard control system toolkit which is
an object-oriented framework for the purpose of building distributed control systems.
Tango operates on the basis of the device server model. The server being a program
managing one or several devices, entails the encapsulation of devices in a single piece
of software (a class). The Tango collaboration webpage hosted at Alba
http://www.tango-controls.org
Computers distributed around the technical areas of the accelerators and beamline
control racks, know as Input/Output Controllers (IOCs) run the distributed control
system. Industrial PCs (containing disk drives) are widely used however the IOCs are
typically Compact PCI crates (cPCI) which are diskless.
13.3 Network
The architecture of the control system is designed on the basis of Ethernet which will
be used at the supervisory level and for most fieldbuses. Fieldbus is the network
system used in industry for real-time distributed control systems. The main reasons
for this choice are cost and maintenance.
Figure 13.2 Software’s architecture.
DevicePool, MacroServer. Tango Servers
Hardware
Data Display and Archiver
Configuration Editor. Save And restore tools
GUI. TAURUS
Tango
Client
Server
SPOCK macros
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An Ethernet connection is required for all devices. Many devices do have Ethernet
connection however some devices are not available on the market with Ethernet links
and have other links.
13.3.1 Ethernet-connected devices
All power supplies are controlled by Ethernet links.
The oscilloscopes, spectrum analyzers and signal generators used in the diagnostics
system have an Ethernet links.
Libera boxes for BPM controls.
Motor controllers.
CCD cameras (Gigabit Ethernet GigE) for the Fluorescence screens and OTRs.
Management of the IOCs (for remote control, booting, and monitoring of the
control computers)
Radiation Monitors. The PLCs for the Personnel Safety System are also linked
through Ethernet for user interface and diagnostics.
Some vacuum devices, like RGAs are linked with Ethernet.
Figure 13.3 Networks’ layout.
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13.3.2 Devices not connected by Ethernet
OCEM correctors for storage ring:. These have a PSI interface. The performance
of an Ethernet link does not meet the requirement of the Fast Orbit Feedback,
which has a closed loop in the 10 kHz range.
PLCs: Due to performance considerations and cost, the CPUs and remote
periphery are connected through separate links. The fieldbus is X2S (B&R) and the
communication between CPUs is PowerLink. Due to high traffic and unintended
this has been separated from general network hardware. For design reasons the
PLCs for the Personnel Safety System use a dedicated SafetyBus (Pilz). The PLC
chosen for the Circulator uses RS485.
Vacuum devices: The question of the type of link to be used for pump controllers
and gauge controllers depends on the availability of respective devices on the
market. At some installations (e.g. Alba) these devices have serial links since no
such devices with Ethernet links were available on the market at the time. The
solution of having serial to Ethernet connections was not satisfactory since it would
have the problems inherent to the Ethernet connection and an extra failure point
(the Ethernet-to-serial converters) was added to the network. This problem could
possibly be overcome today since a much wider selection of vacuum controllers
are on offer in the market.
Beam Loss Monitors: An independent RS 485 network will be used as it is the
most cost-effective option.
Particular devices and detectors for the beamlines with particular hardware needs,
use GPIB, serial line, dedicated fiber optics, etc. to interface with other devices.
A firewall separates the controls networks from the offices network. Many VLANs
that are for machine controls are configured in the service and have private IPs. The
beamlines, many of the computing services and office networks have public IPs.
Dynamic Host Configuration Protocol (DHCP) will be extensively used. The IPs and
MAC addresses are assigned when possible during the preinstallation and kept in the
cabling database to preserve consistency. Network configuration files like radius,
DHCP and DNS are generated from this cabling database.
Several VLANS will be used for machine controls including one general network and
one generic controls network per sector, one for diagnostics, one for monitoring and
one for safety.
In order to avoid unwanted interactions with the switches, the network dedicated to
the PLCs (Ethernet PowerLink) has been removed from the general switches. It is
implemented in dedicated hardware.
13.3.3 Other points
A short document will be provided with the necessary specifications and
distributed to different groups to avoid purchase of hardware that do not follow the
specifications which would require specific software to be written.
However specifications may not be forced in all cases, e.g. it has proven in other
cases very difficult to match the power supplies for the correctors with an Ethernet
link.
In cases where Ethernet cannot be used more complicated specifications may be
required, e.g. for serial connections it must be clearly specified whether RS422 or
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RS485 (or RS232 if noise levels and cable lengths allow it) will be used, if possible
only one should be used for all devices; the cable type, and even connector type
and pinout should also be specified.
The network for the PLCs needs to be deterministic i.e. latencies bigger than the
cycle time will result in a FAULT, as Ethernet installation is not possible and an
independent network out of VLANs and with dedicated hardware needs to be
created.
13.4 Controls Administration
Packages, software and other operations are performed from a control account created
for administration with packages, scripts, configuration files already installed in a
predefined structure. This directory controls databases, deals with servers and clients,
as well as graphical interfaces, scripts, remote booting, and backups.
13.4.1 Development environment
For version control SVN (and to some extent git to) are used. In addition,
the Tango collaboration has a repository in sourceforge (http://tango-
ds.cvs.sourceforge.net/tango-ds/). Tango runs on both Windows and Linux. The main
operating system will be Linux, although Windows may be used in some particular
cases. Tango supports C++, Java and Python for both client and server sides. Eclipse,
kdevelop, QT designer are tools commonly used by developers. Most developments
shall be on Linux, in particular Python and Qt, but other languages like C++ and Java
may be used. Some devices run on Windows XP, like the control for DLLRF, or
interferometer for metrology measurements etc.
13.4.2 Standard tool for maintaining versions of software packages installed
A central storage for version control (SVN), while mandatory, is not sufficient for
keeping an inventory of all versions installed on every machine. In addition, a tool for
packaging and deploying software is needed. At ILSF the tool developed at the ESRF
(blissinstaller) will be used. This tool keeps a central database which includes the
software packages as well as different versions of the packages installed on every
machine (beamline, accelerators, etc). However it is essential to have a standard way
for installing the control system from scratch. Of the various utilities available for bug
tracking, such as Bugzilla, TRAC, RT, and Redmine, one or two should be chosen
from the start and used exclusively (RT or Redmine perhaps).
13.4.3 Remote booting
More than 160 industrial computers will be used for the control of the machine
including 120 compact PCIs for interfaces with timing, 16 industrial computers for
vacuum control, 10 industrial PCs for front-ends and 6 for insertion devices. This
number excludes the computers needed for Tango and archiving databases. They are
diskless and an external server loads their operating system. Beamlines have
independent controls.
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13.5 Operator interfaces: TAURUS
TAURUS is the graphical layer that ALBA synchrotron uses for its
control systems. ALBA has worked extensively on TAURUS (http://www.tango-
controls.org/static/taurus/latest/doc/html/index.html). It manages the connections
between the Graphical User Interfaces and/or any other client and device server.
TAURUS provides a complete set of reusable widgets for developing control
applications. We propose to use this interface for ILSF too.
13.5.1 TAURUS’s look and feel
Setpoints, digital values, color codes etc. shall follow the same criteria as other
subsystems of the control system and general controls policies. As a general rule three
fields will be associated with every value (in the first level display) namely Name,
CurrentValue, and SetPoint. Clicking on it one can display alarm and warning
thresholds as well as other particular information like the tango name, where the
signal comes from, etc. TAURUS ensures having a common look-and-feel for the
Graphical interfaces.
13.6 The control system central managing point: the Sardana “device pool”.
The Sardana device pool is designed to provide the capability of easily adding and
removing new hardware in the middle experiment as well as the possibility of
configuration of scans. Such capability is needed in the control system of the
beamlines. But in many cases this capability is also useful for the machine as for
cycling magnets or for scanning power supplies during commissioning.
Figure 13.4 Taurus’s graphic user interface (GUI).
335
So the Sardana device pool provides an abstraction of the hardware, with a simple and
easy-to-use configuration tool, and with a complete interface for configuring and
executing scans and managing different User Interfaces (Graphical User Interfaces or
Command Line Interfaces) at the same time. The link to the documentation is
http://www.tango-controls.org/static/sardana/latest/doc/html/
13.7 Backups, storage, databases, central management information system and system administration.
Almost all the disciplines referred to in this document are critical for the control
system and hence require backup. These require systems and network administration,
network design and maintenance, central disk storage, server hosting, and web
interfaces. Financial applications and project management tools are excluded from
these considerations.
13.8 Naming conventions
Compatible naming conventions for engineering drawings and control system should
be developed at an early stage in the project. At Alba, and Equipment and Cabling
Database (CCDB) was created at an early stage which has served as the central
repository for cables, equipments, and controls.
Figure 13.5 A Sardana GUI based on Taurus.
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13.8.1 Coupling software naming conventions to hardware conventions
It is essential to keep a consistent, intuitive, and easy-to-remember nomenclature for
software and hardware, since people other than the original developer will have to
access and maintain the projects.
At Alba lowercase names without underscore were used unless required otherwise.
Naming was also carried out in such a way as to keep related things together since
Jive sorts them alphabetically e.g. VelocityHigh, VelocityLow, VelocityScan,
VelocityCurrent as opposed to HighVelocity, LowVelocity, ScanVelocity.
Tango devices names are formed out of three parts DOMAIN/FAMILY/ MEMBER.
The domain/family part of the name reflects the physical organization of the
synchrotron. It can be useful having all related devices in the same family so that one
does not have to jump around in database.
The last part of a device name, MEMBER, is up to the developer of the subsystem;
ideally it should be the word that people use to identify the device with.
Conventions for the software should maintain a close relation with those for the
hardware. Cables, equipments and racks also have a naming convention. For example
Racks are named on the following way:
RK+position+sector/cell+row+position_in_row
For example:
A rack in the service area (position code A), in sector 10, row B, position 3, will be
RKA10B03
A rack in the experimental area (position code X) beam line 03, only 1 row of
racks (A), position 5, shall be RKX03A05
In some cases the purpose of the rack is also specified
(System.Subsystem.RackName). i.e. SR.CT.RKA10B03 is a computing rack in the
storage ring.
Figure 13.6 Snapshot of the user interface of cabling database.
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13.9 Equipment, controls and archiving databases
Databases at Alba have 3 main categories, and all of them run mysql which has so far
proven adequate for Alba’s needs after few other databases were considered.
The cabling database (CCDB mentioned in the previous paragraph) at Alba has been
developed at an early stage and has been essential for the definition of cabling. It has
been intensively used during the specification, contracting and installation of the
cabling system. It has also proven to be an excellent tool for keeping the equipment
up-to-date, making reports for cabling installation, status and validation, and later for
the development, installation and commissioning of the control system. This database
is used for preinstalling software in the IOCs, defining network configuration (such
as, DNS, DHCP files and Radius, PLC variable definition, etc.) and generating code
automatically. The Equipment Protection System relies on this database for defining
PLC variables, Tango dynamic attributes, and GUI configuration files.
The Tango database is also mysql. It is used among other things as a name service by
Tango. This is the central point of the control system.
The archiving DB is a mysql database running on a separate hardware. It saves and
makes available up to 9000 values archived in few seconds; these include
temperatures, setpoints, pressures and many other process variables all of which are
archived by the archiving DB.
Signals can be seen online in trending graphs and can also be recovered from the
history database. Data will be kept during few months and then stored on tapes. At
CELLS database is provided and run on dedicated servers based on mysql to store
data. Different triggering modes for the archiver are available:
Regular intervals (user defined)
On change (interval defined by user)
Thresholds (greater/lower than a certain value)
Statistics: computation of minimum, maximum, average, RMS, FWHM, of the last
X (user-defined) samples.
13.9.1 Fast data logger.
Fast data logger although performs a job somewhat similar to the archiver, is very
different: the archiver is part of Tango and works on device servers; so it collects data
from device servers and puts them into a database. The archiver also has tools to
configure data for archiving (signals, frequency, etc.). It also provides a tool to make
trending graphs with online data and history data from the database.
Fast data logger is an independent application, with independent hardware. It reads a
reduced set of signals, which have to be stored in the range of a few microseconds.
The goal is to have a record of the last few milliseconds to be used for diagnosis.
Studying an event means having a track of some important signals before and after the
event. This is accomplished by means of one or more ring buffers, which could have
specific sampling rates for different signals, comprised of fast ADC cards
(ADLINK2005; 4 ADC channels 16 bits simultaneous), running on a cPCI crate. In
some cases other equipment are used (like Lyrtech and digital low-level RF).
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13.10 Equipment Protection System
The beamlines are expected to deal with very high powers and power densities. It is
therefore necessary to monitor any component which is required to handle these high
levels of power. The Equipment Protection System (EPS) performs this monitoring
and will act on alarm conditions by mitigating the situation that has caused the alarms.
The Equipment Protection System (EPS) concerns the so-called interlocks and other
components like fluorescence screens, shutters, etc. It is comprised of Vacuum,
Magnets, Radio Frequency, Insertion Devices, Front Ends and Beamlines. It is
implemented using B&R PLCs having the CPUs in the service area and the Remote
periphery inside the Tunnel. The communication between them is provided by a X2S
Bus. Intercommunication between PLC CPUs is provided by a deterministic network
(Ethernet Power-Link).
The next figure shows the hardware layout of the vacuum system and their equipment
protection. Racks with PLC CPUs are represented in red. Those have also an
industrial PC (IOC) with a rocket port Serial card for data acquisition from gages,
pumps and splitters
Figure 13.7 Distribution of the Equipment Protection System for an RF plant.
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Figure 13.8 Expert graphical interface for the Equipment Protection System of an RF plant.
Figure 13.9 Main GUI for the Equipment Protection System.
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13.11 Machine controls
A distributed software architecture will be used for machine control. On input-output
controllers (IOCs such as linux machines and PCI/CPCI computers) Tango servers
run, and Tango human interfaces run on so-called workstations in the control rooms.
IOCs and PLCs access field devices. Links between workstations and IOCs and PLCs
are based on Ethernet TCP/IP.
All software for the operation, user interfaces, device servers, archiving/restoring
utilities etc. communicate through Tango. User interfaces include monitoring, settings
and also archive/restore tools, trend graphs, etc. Two levels are defined
1. The server level, which manages the hardware, runs on an industrial PC. It
interfaces AI/AO, DI/DO cards and has also a connection to PLCs.
2. The client level includes user interfaces for monitoring/settings and also the
archiver.
13.11.1 Subsystems
Functionally the control system can be divided into five parts:
Timing and Fast Interlock System used for synchronization of the machine and
propagation of fast interlocks along the accelerator.
Equipment Protection System (EPS) responsible for the protection of all the
machine equipment. It has been treated in Section 13.10.
Personnel Safety System (PSS) guarantees that any operation is done under safe
conditions and in case of failure sends the corresponding systems to a safe state.
Supervisory Control system (Tango) including:
Device servers, which control and get data from hardware and devices.
Servers grouping low-level devices and implementing sequences (Sardana
device pool, macroserver, …).
Figure 13.10 Diagram of the conceptual design of the control system.
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Generic Graphical Interfaces for monitoring, configuring and operating the
machine, which are used by operators, machine physicists and beamline
scientists. These interfaces are provided by Tango
Archiving Tools to configure archive and restore signals stored for long terms
on the central databases.
Alarm Handling to manage the configuration and operation of alarms, provide
tools for acknowledging and archiving alarms, sorted by category, severity,
etc.
Save/Restore Utilities: The accelerators and beamlines are complex machines
having a huge number of distributed parameters and setpoints which need to
be stored and saved resulting in a sort of catalogue of recipes available for
restoring, consulting comparing, etc. at a later time.
Fast data logger: It will be used to trace interlocks and problems in case of trips. It
will run in the µs range.
13.11.2 Vacuum system requirements
The vacuum control system is highly distributed. It involves controls, interlocks and
data acquisition. At Alba the vacuum subsystem contains around 170 ion pumps, 70
cold cathode gauges, 35 Pirani gauges, 45 gate valves, and more than 500
Figure 13.11 Main GUI used for the booster control system which concentrates the state of all elements in a single view.
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thermocouples. Other devices, like RGA, NEG, etc. need also be considered (typically
16, one per sector).
Figure 13.12 Vacuum rack for the straight section (one per sector).
Figure 13.13 Synoptic view of the vacuum control.
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13.11.3 Power supplies
At Alba all power supplies are interfaced by an Ethernet link with the exception of the
ones for the storage ring correctors whose interface is implemented using PSI,
because no company was able to comply with the requirements with an Ethernet
interface. For Alba Bruker manufactured the power supplies for the booster and
transfer lines, Hazemeyer manufactured power supplies for the storage ring dipoles,
quadrupoles and sextupoles, and PPT Power Supplies constructed the ones for the
pulsed elements. The development of the digital control boards for Bruker power
supplies was problematic at Alba requiring twice as much time and effort from both
sides. Local control is performed using a “local link” (an RS232 serial line) from a
laptop.
13.11.4 Radiofrequency system (RF)
At Alba the control system of the RF has two levels: PLC (Programmable Logic
Controller) and IOC (Input Output Controller). The IOC is an industrial PC running
Suse Linux 11.1. Both levels are linked via Ethernet using the TCP/IP protocol.
Fast control loops are performed on a digital LLRF subsystem. Slow-loop archiving
and control servers run on cPCI crates. The plungers are controlled by an Icepap (2
axes per plunger), configured in slave mode and getting pulse and direction from the
Lyrtech card.
A Digital Low Level RF subsystem is implemented on Lyrtech cards, programmed by
the RF section in the Accelerators division. Two loops for the regulation of phase and
amplitude are needed. The process involves a fast sampling ADC, IQ modulation and
down-conversion, regulation, and DAC.
Figure 13.14 Graphical interface for the power supplies
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Figure 13.15 GUI for the DLLRF.
Figure 13.16 Main synoptic for a RF plant.
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13.11.5 Diagnostics
Beam position monitors and beam loss monitors are distributed along the ring. Other
diagnostic devices are concentrated in some sectors. Remote desktop connected to
oscilloscopes are widely used, for Fast Current Transformers, DCCTs, etc.
13.11.5.1 Beam position monitors
The beam position monitors are managed by the Libera electron processor. This
device has an ARM processor embedded and it has an Ethernet port for
communication and integration with the accelerator control system. Alba has used the
device server developed by Soleil.
The Libera electron needs several timing signals: system clock (10 MHz), machine
clock which is the revolution clock (1.1 MHz for the storage ring, or 1.2 MHz for the
booster), trigger, which is the injection trigger (3 Hz), post-mortem, a trigger signal
generated by the interlock system.
13.11.5.2 Beam loss monitors (BLMs)
At Alba 80 Beam loss monitors will be installed in the tunnel. Beam loss monitors are
Bergoz detectors with a V2F converter. Signal conditioners by Cosylab are daisy-
chained by RS485 links. Four modules (reading eight BLMs) are chained and read by
an IOC.
Figure 13.17 Snapshot of the GUI of a Libera box for a beam position monitor.
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13.11.5.3 Fluorescent screen
The fluorescent screen and OTR are acquired with Basler SCA1000 30GM. They are
triggered by the Timing and connected by an Ethernet GigE link. The screens are put
in place and removed by the EPS-PLC.
13.11.5.4 Scrappers and other motions in the machine
It is important to reuse as much hardware and software. The scrappers of the machine
are very similar to slits in the beamlines and movable masks in the front-ends. All
these are movable elements comprised of motors, pseudo-motors (gap and offset), and
graphical components. The hardware and software is the same for all, with the
consequent gain in development and maintenance cost and time.
13.11.5.5 Oscilloscopes
There are many signals for which the best interface is still an oscilloscope or a
spectrum analyzer. Providing an Ethernet connection to these devices (remote desktop
to Windows-based devices) is cost effective and solves problems and keeps the
cabling in the control room simple.
13.11.6 Insertion Devices
Two phase stepper motors have been specified for being used with a standard Icepap
motor controller. They all have encoders configured in closed loop, getting a precision
better than a micron. Encoders have typically a precision of 0.1 microns and the
stepper motors move in closed loop with the encoders. The max speed obtained at
Alba is reported as 1mm/sec. Alba has interlocks for the deviation of the tapper (max
2 mm in 1 meter length). Synchronization with the beamline monochromator is
Figure 13.18 Snapshot of the GUI of a synchrotron radiation monitor.
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foreseen, although the first commissioning will be made with standard scans (step
scans on software).
13.11.7 Orbit correction
The closed orbit correction involves two feedback loops sharing most of the
hardware. The slow loop running at speeds around one Hz stabilizes the static orbit.
This static loop takes care of the master orbit, and includes energy drifts and RF
frequencies. The fast loop (known as Fast Orbit FeedBack or FOFB) corrects for
small deviations, and stabilizes the orbit at frequencies higher than 100 Hz.
At Alba a global orbit feedback has been chosen which shares the same corrector
magnets and beam position monitors for both fast and slow loops. 120 beam position
monitors controlled by Libera boxes (instrumentation technologies) and a number of
corrector magnets integrated. Counting on the fast orbit feedback and foreseeing a
communication controller in the first contract turned out very crucial for the Liberas.
13.12 Motor controllers
Alba uses icePAP motor control developed at ESRF. Through a contract with ESRF,
Alba developed high-level software and also took part in hardware and firmware
development and in return got its units at a good price. The collaboration has proved
to be a success and Alba is happy with the choice of icePAP. Similar motor
controllers can be used at ILSF.
13.13 Calls for tenders and outsourcing.
Whenever a system is outsourced and bought “turn-key”, technical specifications for
call for tenders should follow a common structure. Whenever possible, an API
(application programming interface) for a shared library (at Alba Linux) shall be
required. Example programs linking with those libraries shall also be useful. At Alba,
interface over fieldbuses has been required in some cases e.g. power supplies.
Figure 13.19 Synoptic for an Apple II undulator (left), the architecture defined for the tenders (right).
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Systems should be designed so that they can be controlled both locally (manually) and
remotely with only one type of control (local or remote) active at a given time. It
should be easy to change between the local and remote control. All Read or
Read/Write parameters should be accessible from the IOC and archivable. It should
be noted the most outsourced equipment at Alba are operated remotely.
13.13.1 Structure
The system shall be divided into subsystems, each of which will have different types
of parameters. These parameters include commands which specify an action,
attributes which are readable and writable, properties which are constants, and errors
which act as alarm flags.
Figure 13.20 indicates the procedures followed at Alba. Alba is responsible for the
part painted in white, and the supplier is responsible for the part in blue. Note that the
application programs are the ones used for the acceptance tests and commissioning
and should be built on top of the API. Alba suppliers were not forced to use a PLC,
but this nevertheless has been the preferred solution at Alba.
13.14 Timing system
The timing system will provide all trigger signals of initiation of the operation with an
injection of current into the main ring. These operations include firing the Linac (gun)
and triggering the booster injection kicker and injection septum, as well as all
diagnostics events and all events concerning power supplies. After the booster has
ramped up, the booster extraction kicker and the extraction septum should be
triggered, as well as the main ring injection septum and injection kickers.
The timing system of Alba is based on the events and utilities provided with the
hardware sold by MicroResearch, Finland.
Synchronization signals are distributed by events. Those events (132 user-defined) +
8-bit distributed bus signals are generated by internal counters, triggers or software.
Events are distributed by fiber optics (multimode 850 nm). Jitter is very small (25 ps
Figure 13.20 Control architecture specified for calls for tenders at ALBA.
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rms). Both transmitter and receivers are flexible to do the final fine tuning. Receivers
have a timestamp to use with each event.
The event stream is a frame consisting of (for example) of two bytes that is sent out at
a fixed rate (system event clock) and constitutes one event code. These event codes
are either user-defined or system-defined. The event receivers understand and decode
the event stream and extract the transmitted code. The event receive will generate a
trigger signal in the form of a predefined output with a predefined width and delay,
according to the received code. This trigger signal (normally electrical) goes to the
injection and diagnostic devices. All events are received by all the event receivers.
The injection system allows filling the storage ring according to a predefined pattern
(uniform, 1/3, etc). The injection is divided into several cycles. During one cycle, one
or several consecutive buckets in the storage ring are filled. An injection cycle lasts
320 ms, so it is repeated at a rate of 3.125 Hz until the desired filling pattern is
reached.
The radio frequency and the machine circumference determine the maximum number
of bunches which can be stored in the synchrotron. At Alba, these parameters are:
FRF = 499.654 MHz.
Booster circumference = 249.6 m, which means 416 (32*13) buckets.
Storage ring circumference = 268.8 m, which means 448 (32*14) buckets.
As 32 is the common maximum divisor, the booster can be considered divided into 13
sections containing 32 buckets, and the storage ring divided into 14 sections
containing 32 buckets. With this division of the booster and storage ring in 32
sections, any booster section can be injected into any storage ring section (n booster
sections in coincidence with m storage ring sections), waiting less than 14 booster
turns in the worst case. Other scenarios could be found, but they will have a higher
number of turns.
Figure 13.21 Hardware layout of the timing system at ALBA.
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13.15 Personnel Safety System (PSS)
The Personnel Safety System (PSS) monitors radiation levels and controls the access
to all accelerators (linac, booster synchrotron, and storage ring). It prevents anyone
from getting a radiation dose higher than the limits set by law. It shall be reliable and
fail-safe.
It is subjected to Ionizing Radiation Regulations and it has to be independent from
any other system.
Radiation hazards prevention involves technical aspects strictly regulated by different
laws.
The system has a number of inputs and produces an output. The output shall be
redundant and diverse.
Redundancy will be achieved by having two independent lines for every signal (as
specified by SIL3 in the norm IEC 61508).
Diversity means that any action will be applied to two different parts of the system,
for example disabling the RF means dumping the RF driver and dumping the HV
power supplies. In other words, each action results in two redundant outputs (four
signals in total).
Light panels will be placed in the main cabinet and inside the bunker and tunnel. They
will display the status in the corresponding area.
OPEN – The bunker is open and may be accessed by authorized personnel.
RESTRICTED – The bunker is being secured. (In the case doors are closed then
they are only accessible by authorized personnel in “restricted mode” using the
personnel keys) – no general access.
INTERLOCKED – The patrol has been done. The tunnel is clear of personnel.
Once the permits are given (and no restricted access is granted, it goes to secured).
SECURED – The bunker / tunnel is secure and the LINAC_PERMIT /
BEAM_PERMIT is enabled for this zone. NO access.
BEAM ON – Beam is present.
Alba has chosen to build the Personnel Safety System with Safety PLCs. This has
proven to be a good choice. It is very flexible and cost-effective. Installation of the
Personnel Safety System was outsourced to Pilz/Procon. It has proven to be a good
choice. Pilz has provided reliable components and Procon has given a very good
quality. Extra effort should be made to define the logic and components at the earliest
possible time. The interactions between electrical and radiological safety concerns
should be specified as early as possible to avoid later refinements of the contracts.
13.16 Beamlines
Seven experimental stations, one diagnostics beamline and one test beamline have
been built at Alba. The hardware architecture for controls is distributed. Operator
interfaces (OPIs) are in the control hutches and Input-Output Crates (IOCs) in the
racks. Most components of the control system are shared with the machine. This is the
case for motor controls, vacuum equipments, PLCs (Equipment protection and
Personnel Safety), etc. The experience at Alba indicates that it is crucial to specify
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precisely how the Factory Acceptance Tests and Site Acceptance Tests should be
performed.
13.16.1 Control interfaces between the machine and the beamlines
There are several cases where the machine control system needs to be accessed from
the beamlines. That is the case of read-only experimental channels, like Energy, Live-
time, Electron-beam intensity, etc. Those values are useful for being included in both
graphical interfaces and experimental channels. Tango allows such communications,
but network access restrictions complicate matters. The machine is protected by a
private firewall and private subset of VLANs, whereas the beamlines are on
independent public VLANs.
Other interactions between the machine and the beamlines are needed for the regular
operation. Those are the control of the Insertion devices and the control of the front-
end elements.
13.16.1.1 Front-end
The front-end needs to be opened and closed from the beamline. The front-end
shutters are given general permits from the Personnel Safety System and second-level
permits and operations managed by the Equipment Protection System.
13.16.1.2 EPS Front End – Beamline communications
Eight hardwired signals provide front-end managing capabilities from the Beamline,
while keeping the beamline independent from the rest of the machine:
Figure 13.22 First specifications for the controls layout of a beamline at ALBA.
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IO
number Front End to Beamline Beamline to Front End
1 STATUS - FRONT END OPEN COMMAND - OPEN FE VALVES
AND SHUTTERS
2 STATUS - FRONT END
INTERLOCK
COMMAND - CLOSE FE
SHUTTERS
3 COMMAND - CLOSE TRIGGER
UNIT VACUUM VALVE
STATUS - BL VALVES OPEN / BL
READY
4
STATUS - FRONT END
CONTROL STAUS: control form
BL DISABLED
COMMAND - RESET FRONT END
INTERLOCKS
This could be done by the deterministic network of the PLC, by the high-level
communication of the control system, or by dedicated hardwired connections between
machine PLCs and beamline PLCs.
13.17 Organization and economical aspects
The control system is a critical issue for accelerators and beamlines. It has to be
considered from the beginning and it shall be present in all phases of the
development. The initial design and strategy for the installation has to be ready at
early stages. Call for tenders for the different components should include the
specification for the interface with the control system. This includes for example
defining specifications for the control of components such as, linac, power supplies,
diagnostics, motors, mechanical components, radiofrequency elements, insertion
devices, monochromators, benders, mirrors, etc.
Also, a project management system need be set up from the beginning, sharing data
between different subsystems and integrating the schedules for deliveries of the
components and their installation. The outcome is a common Gant chart for the
delivery, installation and commissioning of the different components.
A model for project management could be Prince2, for example, which is the
methodology followed at Alba for computing projects.
In the mean time, the services will grow, and some of them will be in operation during
the installation, such as vacuum bakeouts, archivers, and other parts of the control
system and microcomputing. A system for tracking user requests and a central point
of contact for the helpdesk would also be very convenient. The use of ITIL best
practices could also be an interesting guideline for implementing service support.
From the economical point of view, a good approach is reserving a budget of 10% of
the total cost of the project for the control system and computing services. This might
vary depending on the strategy used in terms of software development and COTS
(Commercial Off-The-Shelf) products. Writing all the software from scratch is
money- and time-consuming. The right balance of in-house development and re-use
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of existing software (preferably imported from existing institutes) is the key to
success. There is inevitably some software to be written (either for new hardware,
new features or new requirements), whereas there are parts, where existing (and in
some cases industrial) solutions are the best choice. The use of industrial solutions
(PLCs), and regular computers (industrial PCs) has worked very well at Alba. It is
cost-efficient and reliable. The next table shows an estimation of the cost of a generic
synchrotron. These are only guidelines and depend a lot on the choices made. Also
manpower is very much dependent of the institute itself.
Figure 13.23 Simulation of the cost of a control system for a synchrotron.
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CHAPTER 14: Conventional Facilities
14.1 Introduction
The conventional facilities required for a synchrotron light source have to provide
housing for very sensitive instruments as well as spaces for research and development
and the required maintenance work. The successful implementation of these spaces
requires coordination among various engineering teams working on various aspects of
designing the synchrotron as well as the potential users.
14.2 Goals
The design goals of the conventional facilities are not different from those of the
whole ILSF project. In designing the facilities intended for special purposes such as a
synchrotron laboratory, it is of crucial importance to have the viewpoints of the
researchers and the users of the facilities taken into account. In particular, attention to
the following details is indispensable:
Creation of a world-class scientific complex.
Choice of an appropriate site.
Appropriate workspaces.
Following sustainable development goals and utilization of sustainable
architecture principles.
Optimum consumption of energy.
Reduction of construction and maintenance costs.
Flexibility of design.
Completion of all the designs in pace with overall project schedule.
14.3 Buildings and installations
The complex required for a synchrotron facility generally includes:
Buildings to accommodate the synchrotron equipment.
Temperature control systems.
Power, water, and air control systems.
Lifts, cranes and other transport equipment.
Communication systems.
Shielding walls and equipment.
Special-purpose infrastructures such as clean rooms.
Central control infrastructures.
Emergency equipment and buildings.
Security control systems.
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Laboratory facilities.
Various workshops (mechanical, vacuum, electrical, etc.).
Storage facilities and loading docks.
General-purpose laboratories (chemistry, dark room, etc.).
Special-purpose laboratories (molecular biology, wet labs, pharmacology, clean
rooms, etc.).
Office buildings.
Lecture rooms and conference halls.
Library.
Restaurant and coffee shops.
Lodgings for users and guests
Some of these could be considered less important than others. Figure 14-1 shows
various spaces considered for ILSF.
Figure 14.1 The basic layout of Iranian Light Source Facility (the first option with a storage ring circumference of 300 m).
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14.4 Site selection
Seismological study is an important task for modern synchrotrons. Any sort of
vibrations should be taken into account and strategies should be developed to deal
with the effects of soil layers on synchrotron structures, the stability requirements of
the structure and optimization of the essential function of various facilities. The site at
Qazvin was selected based on the following considerations.
14.4.1 Technical requirements
In choosing a location for a synchrotron certain technical, environmental, and
economical requirements need to be taken into account:
14.4.1.1 Geological and vibrational requirements
Vibrational requirements:
(a) Appropriate distance from seismic faults and other sources of vibration.
(b) Proper distance from railways and transit roads.
Geological requirements:
(a) Avoidance of deep layers of loose soil.
(b).Appropriately low slope.
(c) Small seasonal changes of groundwater levels.
14.4.1.2 Environmental requirements:
Closeness to academic, research, and industrial centers.
Room for future development.
Adequate access to roads, train stations, airports.
Availability of infrastructural technical facilities such as workshops and factories.
Availability of adequate lodgings for users.
Attractive environment for work and living.
Availability of shopping centers.
Being away from archaeological sites.
Being away from protected environmental zones.
14.4.1.3 Economic requirements:
Proper legal support from local officials
Proper support for the required infrastructures including utilities and
communication from the local government officials
Economical local construction costs during the building and commissioning
phases
Affordable cost of living in the area
14.4.2 Analysis of the proposed sites
Several sites in Tehran, suburbs of Qazvin and Isfahan were studied from among
which the Qazvin site was selected finally. The locations of proposed sites across the
country are shown in Figure 14-2. Figure 14-3 shows the aerial picture of the Qazvin
site. At present the relevant information for the proposed site including reports on the
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geotechnical studies performed for other projects are being gathered and the need for
any further tests will be determined soon.
Figure 14.2 Location of proposed sites (Tehran, Ghazvin, Isfahan).
Figure 14.3 Aerial view of the Qazvin site.
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Qazvin site lies almost 1 km to the north of Qazvin – Zanjan highway. Its distance
from Tehran is about 150km. Qazvin Azad University lies on the south of the selected
site between the site and the highway. Imam Khomeini Science and Technology Park
is on the south-east of the site. The city of Qazvin is located to the south of the
aforementioned highway.
14.5 Ground vibrations
14.5.1 The measurements
Vibrations from the environment can be divided by frequency range as follows:
Low frequencies (less than 1 Hz): sea waves, microseismic waves from
microseismic activities
Medium frequencies (1 Hz < f < 100 Hz): traffic, machinery, wind, water,
resonant mechanical frequencies
High frequencies (f > 100 Hz): electromechanical waves, vibro-acoustic waves
The goals of the measurements are the detection of vibration sources, distinguishing
between the vibrations on the basis of their sources and finally obtaining the power
spectral density. The first step is inspection of the site and gathering the necessary and
useful information. It is important at this point to detect the sources of vibration such
as roads, factories, faults, and to check the possibility of utilizing topographic and
geological data if available. During site inspection the primary geometric, geological,
and geotechnical estimations are performed, and the locations for making the
measurements are determined. The resonator factors and site places with maximum
vibrations should be distinguished regarding geology specifications.
In the next step, the different stages required for performing the measurements as well
as the time schedule for doing it are delineated and the required technical points for
performing the work efficiently and correctly will be stated.
IIEES (International Institute of Earthquake Engineering and Seismology) was
selected as the contractor for performing the vibration measurements which is an
experienced institute at this field.
All measurements were done under the supervision of an experienced geophysicist.
Measurement instruments are able to measure vibrations in the frequency bandwidth
between 0.01 HZ and 100 HZ. So far measurements have been performed at two
locations. These are shown in Figure 14.4. The selected points were arranged to be at
the same coordinates as the main building ring foundation. Sensors should be installed
in dense soil not in loose medium or bulk volume of concrete.
Measurements were performed on the three week-days when there is maximum
traffic. The effect of heavy moving machinery was also examined by a loaded truck
travelling along a specified road (Barajin) at the edge of the site. Figure 14.5 shows
some of the activities on those days including the digging of ground, leveling of
instruments, placement of the sensors, power supply, digitizer and solar batteries.
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Figure 14.4 Location of two vibration measurements performed in Qazvin.
Figure 14.5 Environmental vibration measurement operations.
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14.5.2 Analysis of results
Figures 14.6 and 14.7 show plots of measured environmental vibrations at points 1
and 2 in the north-south (horizontal) and vertical directions respectively. Data
sampling was performed at a rate of 200 samples per second. To ensure no effect from
the sampling rate on the results, data sampling was also performed at 100 samples per
second. No difference was observed. Measurement at the frequency band of 20-50 Hz
shows vibrations probably originating from a thin soil layer resonance or from
turbulences of an industrial zone. These can also be seen in Figure 14.8 which shows
the ratio of horizontal to vertical amplitudes. To identify the source of these vibrations
more measurements are required, yet these vibrations are within the range of
vibrations measured at some established light source sites. High-amplitude vibrations
are also observed at frequencies lower than 0.05Hz. These are most probably related
to natural sources i.e. sea waves (Caspian Sea) and climate effects.
Figure 14.6 Amplitude of earth’s vibration in north-south direction (point 1).
10-3
10-2
10-1
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101
102
10-10
10-8
10-6
10-4
10-2
100
102
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Freq (Hz)
Dis
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en
t P
ow
er
Sp
ectr
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Den
sit
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SD
/ (
m
)2/H
z
db13N.mat
Figure 14.7 Amplitude of earth’s vibration in vertical direction (point 2).
10-3
10-2
10-1
100
101
102
10-10
10-8
10-6
10-4
10-2
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Freq (Hz)
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14.6 Geotechnical survey
14.6.1 Site's geology
Some geotechnical investigations have been conducted in the area surrounding the
selected site in Qazvin. Since the geology of the site and the regions surrounding it are
the same, it is possible to evaluate the geological properties of the selected site and
make the necessary estimates.
Alborz mountain range lies to the north of the region. Alborz mountains were formed
from Jurassic and Tertiary volcanic rocks and sediments seemingly uplifted by
volcanoes and given their present shape. Previous geophysical tests show that the
bedrock is 300 m below the ground surface. The sediments on the southern slopes of
Alborz Mountains were mainly formed by seasonal flood waters. Figure 14.9 shows
general ground characteristics and soil types of the project site in Qazvin.
Some geotechnical tests have been carried out for Qazvin Azad University buildings
that give a clear picture of the general properties and types of the underlying soils.
Figure 14.8 Spectral ratio of horizontal to vertical amplitudes during a 1 hour period.
Figure 14.9 Geological survey of the selected site in Qazvin (Geological
Survey Organization of Iran (GSI)).
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There is a 0.5-1.0 m thick topsoil that has no mechanical resistance. According to this
study the frozen soil depth, which determines the minimum foundation depth from the
ground surface, is 1.0 m. Boreholes at Azad university site indicate that the soil types
at depths more than 4 m are mainly clay, and silty gravel mixed with sand; and at
depths between 4 m to 20 m the soil types are mainly clay mixed with gravel and sand
with varying percentages of gravel and sand.
In order to obtain a better evaluation of the geological and geotechnical properties of
the soil further laboratory and field tests have to be carried out including general soil
physical and chemical tests, direct shear and consolidation tests in laboratory, field
tests such as SPT and down-hole tests necessary for the evaluation of soil resistance
and type of layers. These data are necessary for static and dynamic analysis and the
design of foundation and ensuring its vibrational stability.
14.6.2 Geotechnical characterization tests
Geotechnical study is one of the most important tasks for the ILSF project. This task
is comprised of two stages: site & laboratory geotechnical characterization;
geotechnical analysis. Site & laboratory characterization includes some field and
laboratory tests that determine the physical and mechanical properties of the soil.
However a complete assessment of the properties of the soil layers underlying the
ILSF site is necessary and other tests should be done. Thus some laboratory tests are
required including:
Sieve test
Water content, relative density and unit weight determination tests.
Direct shear test.
Triaxial soil test.
Consolidation test.
Resonant column test.
Tests that determine the chemical properties of the soil and water.
The tests above, allow the evaluation of the precise mechanical properties of the soil
in the laboratory that will be useful for settlement and resistance analysis of the
ground under the weight of the foundation. Shear modulus (G), bulk modulus (K),
internal friction angle (φ) and cohesion (C) are the essential soil parameters that will
be extracted from these tests. The chemical properties help decide the type of material
to be used for the foundation and assess its long-term durability.
But the laboratory soil data are insufficient since laboratory samples are disturbed
samples that constitute a very small portion of the ground where the light source is
going to be built. Some of the most important field tests that should be carried out are
the following:
Standard penetration test (SPT)
Plate load test (PLT)
Pressure meter test (PMT)
Down-hole test
SPT is a field test that distinguishes soil type and allowable soil bearing (qa) and shear
wave velocity via correlations and approximations. PLT is a field test for the
determination of soil stiffness, settlement and allowable soil bearing that is very
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useful for the structural design of the foundation. The pressure meter test is an in-situ
testing method used to achieve a quick measure of the in-situ stress-strain relationship
of the soil. In principle, the pressure meter test is performed by applying pressure to
the sidewalls of a borehole and observing the corresponding deformation. Down-hole
test is also a useful test for determination of soil stiffness at very low strains. These
parameters are useful for ground dynamic analysis.
14.6.3 Geotechnical analysis
Geotechnical analysis includes two parts: static simulation and dynamic simulation. In
static simulation, non-homogenous settlement of the main building should be
determined and if the relative settlement is more than the allowable value, necessary
measures should be considered such as heavier concrete slab, trenches, isolators, etc.
Static settlement analysis of the ground will be done by finite element method (FEM)
or finite difference methods (FDM) where a three-dimensional model will be used.
Dynamic simulation also known as random response analysis should be done to
estimate the effect of the environmental vibrations on the main building ground. The
dynamic parameters of the ground soil should be known precisely. This dynamic
simulation is done for low strains. In this simulation the soil behaves elastically.
Further dynamic simulation should be done in order to take into account the effects of
an earthquake. For this purpose dynamic parameters are measured at low and high
strains. Shear strain and Poisson ratio are the elastic parameters that are measured.
Also depending on the behavior of the constituent soil, knowledge of other parameters
such as plastic ones is necessary. This modeling tells us how much the vibrations of
an earthquake are amplified at the site. The properties of earth layers will show
whether earthquake waves or environmental vibrations are damped or amplified.
14.7 Foundation stability requirements
The annual relative displacement of two points on the base of the synchrotron should
be no more than 0.25 millimeters per each 10 m and no more than 2.5 millimeters
over the whole length of synchrotron. The allowable ranges of displacements are
listed in Table 14.1.
Table 14 1: Magnitudes of allowable concrete slab relative settlements
< 0.25 mm/10 m/ year
< 0.05 mm/10 m/month
< 10 μm/10 m/ day
< 1 μm/10 m/ hour
The above requirements and those mentioned in previous sections should be achieved
by good and satisfactory foundation stability design. Sufficient static and dynamic
stability is possible through one or more of the following primary methods:
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Appropriately thick concrete slab (foundation).
Excavation to reach stiff soil layers.
Separation of the foundation of the critical sections (the floor of the storage ring
and the experimental area) from the foundations of the other structures to reduce
vibrations transfer.
Deep foundations.
Adequate approaches should be adopted to prevent the transfer of vibrations from
neighboring sections as well as the damping of any possible vibrations. This aim
could be achieved e.g. by appropriate selection of the dimensions of the main
building's foundation since the mass of the foundation influences vibration damping.
Good geotechnical survey is essential for a proper determination of how the
settlements and deflections are to be controlled. One of the solutions that affects the
stability is excavation deep enough to reach a resistant soil layer such as a layer of
gravel. Gravel provides lower static settlement and good vibration damping. Soil
compaction and improvement is another solution. Compaction or improvement is
done when it is not possible to lower the foundation. When the ground contains soft
soil or clay and removing the soft medium entails high excavation cost, using piles is
a reliable option.
Additional operations which enhance the stability of concrete slab against the
vibrations and other loads are:
Isolation of the critical floor from internal vibration sources such as mechanical
installations, access roads, etc.
Adequate drainage of the ground beneath the foundations.
Separation of the foundations of the accelerator and the beam-lines from the
surrounding buildings.
Mounting vibration sources such as compressors, chillers, etc. on such foundations
and holders as massive concrete blocks and using vibration-absorbing material and
joints such as elastomeric supports, vibration isolators, vibration dampers, etc.
Isolation of the pipes and installation racks connected to the accelerator through the
use of isolating devices and flexible supports.
Adequate distance between the mechanical installations and support facilities from
the critical area.
14.8 Architecture
14.8.1 Sustainable architecture
For the buildings required for a light source the question of temperature and vibration
control is very significant. Global experiment shows that around 25~30 % of the total
cost of such projects is due to the construction and maintenance of the buildings and
other conventional facilities. So sustainable architecture, i.e. using potential sources of
energy within the environment can significantly reduce these costs as well as reducing
the amount of waste energy produced in these facilities which is generally high. The
constraints on temperature variation within the main building circumvent prolific use
of transparent material, yet for other buildings it is important to follow the principles
of sustainable architecture and energy conservation.
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The principles of sustainable architecture that have been considered in the design of
ILSF in order to optimize the per capita energy consumption include:
Reducing the consumption of non-renewable energy sources by the proper choice
of building material.
User-friendliness: flexible spaces, control of lighting, temperature, and noise.
Environment-friendliness: the least amount of damage to natural resources at the
site.
Energy waste avoidance.
Cogeneration, as well as use of environmental energy (wind and solar energy).
Choosing the materials in a way that saves environmental energy (energy of the
sun).
Flexibility of the spaces.
Economical and intelligent design offering special solutions for this particular
building
Shielding inhabitants of the buildings from undesirable radiation.
Using natural light and ventilation to enhance the quality of working spaces.
Control of light, vibrations and noise.
14.8.2 Buildings
14.8.2.1 Types of buildings
The types of buildings required in this project are of the following major types:
The main building.
Laboratory building.
Administrative office building.
Utility and infrastructure buildings.
Residential and recreational areas.
Service and storage buildings.
Access roads and campus.
14.8.2.2 Duration of use
The main building is occupied 24 hours a day and requires continuous care for the
equipment installed in it. But the other buildings are used on average 8 hours a day by
a limited number of occupants.
14.8.2.3 Occupancy and projected surface area
Table 14.2 summarizes the buildings considered for ILSF. For the campus area, a
plant cover is required for environmental purposes and for providing shade and
physical protection for the complex.
14.8.2.4 Main building
The main building houses the storage ring, the booster (located in separate tunnels)
and the service area, around which various experimental and basic science
laboratories will be located. The total area of this building is large (about 13000 m2)
due to the separate tunnels for the booster and the storage ring. The main parts of this
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building are the storage ring tunnel, the booster tunnel, the service area, the
experimental hall, access stairs and corridors
Table 14.2 Functional program of ILSF
Space Area (m2) Footprint* (m
2)
Main building 12870 13000
Laboratories 1550 1550
Utility & infrastructure buildings 3500 2500
Administrative office building 3500 1500
Guest House & recreational facility 6000 3500
Parking lot 6500 6500
Total 33920 28550
* The ground surface area occupied by the building
(a) Storage ring tunnel: The storage ring comprises the main part of the machine,
whose performance determines the overall performance of the machine. The storage
ring does not accelerate the electrons but maintains the energy of the electrons at
3 GeV. The storage ring is comprised of dipole, quadrupole, sextupole magnets, RF
cavities, diagnostic equipment, control and feedback instruments, leveling systems,
insertion devices, and the vacuum chamber containing the beam. The circumference
of the storage ring of ILSF (option 1) is 297.6 m.
Slight variations of temperature can be very disruptive to this lattice, in fact this
lattice constitutes the most important and sensitive part of the whole complex and
requires:
Stability of temperature to within 0.1 oC.
Space for moving equipment in and out of the tunnel.
Shielding tunnel made from composite-material (high density material with
different ratios of concrete, lead, etc.) for protection against harmful photon and
neutron radiation.
Access space from experimental area.
Space for mechanical and electrical installations.
Access to the ceiling from the experimental hall.
(b) Booster tunnel: The booster's circumference is 192m. Its spatial characteristics
and requirements are like those of the storage ring with the only difference being the
requirement for access from the service area, namely:
Stability of temperature to within 0.1 oC.
Space for moving equipment in and out of the tunnel.
Shielding tunnel made from composite-materials (high density material with
different ratios of concrete, lead, etc.) for protection against harmful photon and
neutron radiation.
Space for access from the service area.
Space for mechanical and electrical installations.
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(c) Experimental hall: The experimental hall will have a height of about 12 meters
and a width of about 15 meters, so that the laboratories containing the beamlines can
be easily accommodated. At a height of 4 meters various bridges will provide access
to the computer and control rooms, and the space above the storage ring.
The requirements of experimental hall include stability of temperature to within
0.5 oC and space forinstallation of beamlines.
(d) Service area: The service area with an average width of 9m is located between
the booster and the storage ring and occupied by power supply, RF, electrical and
mechanical equipments. It should have the same conditions as that of the
experimental hall.
14.8.2.5 Laboratories
The laboratories themselves are comprised of two types: those requiring heavy
machinery which should be located far from the main building (to avoid the
vibrations), and basic science labs such as those for chemistry and physics which
should be as close to the main building as possible. The laboratories surround the
experimental hall and have the following requirements:
Closeness to beamlines.
Separate entrance and parking space.
Access from experimental hall.
Separate access route between the laboratories themselves.
Possibility for future expansion.
Appropriate air conditioning.
The laboratories that have been established so far are:
Beamline supplementary laboratories: 7 labs, 100 square meters for each lab.
Measurement lab: 1 lab, 100 square meters.
Detector lab: 1 lab, 100 square meters.
Vacuum lab: 1 lab, 100 square meters.
Electronic lab: 1 lab, 100 square meters.
RF lab: 1 lab, 100 square meters.
RF lab for service area: 1 lab, 50 square meters.
Electromagnetic lab for service area: 1 lab, 150 square meters.
Vacuum lab for service area, 1 lab, 50 square meters.
General workshop, 100 square meters.
10% additional space required for walking area.
In total the area proposed for the laboratories (adjacent to the experimental halls) is
about 1550 square meters with the possibility of further expansion
14.8.2.6 Utility building
This building is for the maintenance of the electrical and mechanical equipment, so
the dimensions of this space should be proper for this equipment. It can be 2 or 3
stories and requires a surface area of 4000 to 5000 m2. The required space for this
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sector includes the area needed for the pumping station, water storage tanks for the
cooling tower and fire protection systems, ionized water lab, cooling system,
pressurized air, steam boiler room, static and dynamic UPS, technical room, public
mechanical workshop, electrical workshop, generator room, technical gallery, offices,
etc.
14.8.2.7 Administrative Office building
It is preferable to have this building as close as possible to the main building and the
laboratories, with direct access to the main building. It is predicted to provide work
space for about 100 personnel and to include 60 office room and some service area
and mechanical room. This building has several departments, such as administration,
computing, engineering, safety, directorate, accelerator, experiment, and service, each
department having its own offices. A 10% additional space has been considered for
walking area. Overall the administrative building will occupy an area about 3500 m2.
14.8.2.8 Guest house and recreational facilities
The guest house provides temporary residence for guests predicted to number about
100; this area should also contain lobby and reception areas, director’s office
complex, guest rooms, restaurants, stores, toilets, parking space, recreational areas
and sports gymnasium plus an additional 10% area providing walking space. A
minimum of 20 m2 per person would amount to a total area of 4500 m
2.
14.8.2.9 Parking
The number of parking spaces required for the whole complex is estimated to be 400
with a surface area of 6500 m2.
14.8.3 Architectural design
Figures 14.10 to 14.13 show the floor plan, its cross section, and the 3D view of the
main building. In this design it is assumed that the booster and the storage ring are
housed in separate tunnels. In the present design the laboratories form one half of a
complete ring around the main building and the administrative building is connected
to the main building through a bridge.
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Figure 14.11 First floor plan of the main building.
Figure 14.10 Ground floor plan of the main building.
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Figure 14.12 Cross-sectional view of the ILSF building.
Figure 14.13 Three-dimensional view of the ILSF complex.
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14.8.4 Site Plan
The location of buildings is generally determined by the slope, size, natural features
of the site (trees, shrubbery, etc.), relation between buildings, proximity to the main
entrances etc. In any case it is better to have buildings which can be viewed from the
highway and the city. Figure 14.14 shows a preliminary site plan of the ILSF.
14.9 Structural system
14.9.1 Building Design Codes
The structural designs are based on the Iranian building codes and standards as listed
below:
Iranian code of practice for seismic resistant design of buildings, Standard No.
2800-05
Iranian National Building Regulations, No. 6: "Loads on the Building."
Iranian National Building Regulations, No. 9: "Design and Construction of
Concrete Structures"
Iranian National Building Regulations, No. 10: "Design and Construction of Steel
Structures".
Figure 14.14 The site plan of ILSF complex.
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American Institute of Steel Construction’s, ANSI/AISC 360-10: "Specifications for
Structural Steel Buildings".
American Concrete Institute, ACI 315-99: “Details and Detailing of Concrete
Reinforcement”.
American Concrete Institute, ACI 318-05: “Building Code Requirements for
Structural Concrete and Commentary”.
14.9.2 Building Design Loads
Building design loads are listed in the following tables (Tables 14.3, 14.4, 14.5):
Table 14.3 Live Loads
Location Load (kg/m2)
Main building roof 150 (snow load)
Experimental hall 1200
Laboratories 600
Offices 500
Corridors 500
Table 14.4 Building Wind Load factors
Factor Value
Basic wind speed 100 mps
Wind reference pressure (q) 50 kg/m2
Wind speed variation impact factor (Ce) 2
Table 14.5 Building Earthquake Load factors
Factor Value
Peck Ground Acceleration(PGA) 0.35g
Seismic important factor (I) 1.4
Site Class II
The ILSF site ground at Qazvin is located at a windy region; therefore, a special study
on wind effects on buildings seems to be necessary. Wind effects on the main
building can be estimated by software simulations and wind tunnel testing.
Iran is located on the earthquake belt stretching from the Alps to the Himalayas.
Qazvin region in particular is an area with a high seismic activity and has suffered
several major earthquakes. Therefore, complimentary studies must be performed to
assess earthquake hazards.
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14.9.3 Main building structural design
In the layout of ILSF synchrotron, the storage ring and the booster form two
concentric rings. The circumference of the SR and the booster are respectively 297.6
meters and 192 meters. The layout of the ILSF is shown in Figure 14.15. Thus the
main building is an annular structure with a height of 13 meters, an inner diameter of
44 meters, and an outer diameter of 136 meters. The external circumference of the
main building will be about 430m and the circumference of central open portion is
equal to 136 meters. Using the same numbers of columns in both the outer and inner
surface of the main building would result in uncommon spans due to the large
difference between the external and inner circumferences of the main building, so the
outer circumference will have 63 columns and the inner circumference will have 21
columns. There will be two access corridors around the service area and the
experimental hall. The arrangement of columns for the main building is shown in
Figure 14.16.
The structural system of the main building could be a combination of reinforced
concrete frames and steel roof frames or a combination of steel frames and steel roof
frames. The reinforced concrete frames have a lower cost and better performance for
vibration suppression. On the other hand construction of steel frames is easier and
faster. Lateral loads in radial direction will be supported by reinforced concrete
moment frames, whereas, braced frames will be used for tangential loads.
The roof structure will be supported by steel or concrete columns spaced along the
inner and outer perimeters of the experimental hall with a maximum spacing of 40 m.
In order to cover the radial span of the main building, curved steel trusses will be used
as the main beams. Trusses as the main beams are preferrable because of economic
reasons, especially for long spans. Their other advantage is the possibility of using
their openings for utility channels. Figures 14.17 to 14.19 show the typical structural
system considered for the main building and e adjacent laboratories.
Figure 14.15 The layout of the ILSF synchrotron lattice.
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Figure 14.16 Arrangement of columns in the main building.
Figure 14.17 Structural system for the main building and adjacent laboratories.
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Figure14.18 Structural system of the main building.
Figure 14.19 Cross section of the main building.
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14.10 Mechanical systems
14.10.1 Codes and standards
The design and construction of the mechanical systems should meet the requirements
of the following codes and standards:
American National Standards Institute.
American Society of Mechanical Engineers.
American Society for Testing Materials Standards.
American Society of Heating, Refrigeration, and Air Conditioning Engineers
(ASHRAE) Design Guidelines.
ASHRAE Standard 90.1-2001 Energy Standards for Buildings except for Low-
Rise Residential Buildings.
American Welding Society.
ANSI/ASHRAE Standard 62-2001 Ventilation for Acceptable Indoor Air Quality.
ANSI/AIHAZ 9.5-1992 Standards for Laboratory Ventilation.
ANSI/ASHRAAE 110-1985 Method of Testing Performance of Laboratory Fume
Hoods.
Industrial Control Standards (NEMA).
Institute for Electrical and Electronic Engineers (IEEE).
Illuminating Engineers Society (IES).
National Fire Protection Standards (NFPA) standards.
Energy Conservation Code of New York State (2002 Edition).
Leadership in Energy and Environmental Desigan (LEED) 2.2.
LEED for Labs.
14.10.2 Design constraints
HVAC design should be with consideration given to indoor and outdoor conditions.
14.10.2.1 Outdoor design
Appropriate methodology for outdoor design depends on the meteorological data of
Qazvin. It should include:
Information on location: latitude, longitude, and elevation.
Outdoors temperature including dry bulb temperature (DBT) and wet bulb
temperature (WBT).
Data on diurnal and seasonal variations of temperatures such as daily ranges,
yearly ranges and extreme values.
Wind data such as prevailing wind directions and speeds.
Data on humidity and moisture content.
Solar radiation and cloud data.
Other data such as the average number of cold and warm days.
14.10.2.2 Indoor design
Different spaces pose different conditions for indoor design. Table 14.6 lists
requirements for various spaces inside the main building.
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Table 14.6 Indoor design conditions for various spaces
Design RH(%) Design Temperature (°C) Design Zone
Accuracy Heating Cooling Accuracy Heating Cooling
±10% 30 50 ±0.1 25 25 Storage ring
±10% 30 50 ±0.1 25 25 Booster ring
±10% 30 50 ±0.5 25 25 Linac
±10% 30 50 ±0.5 25 25 Experimental hall
±10% 30 50 ±2.5 25 25 Laboratories
±10% 30 50 ±2.5 25 25 Offices
14.10.2.3 Pressure
The ILSF main building will be maintained at a positive pressure to minimize
infiltration of outside air into the facility. The other spaces will have positive or
negative pressure with respect to the main building base pressure. Table 14.7
summarizes (gauge) pressure of each zone relative to the pressure of the main
building.
Table 14.7 Relative pressure of each zone regarding to the main building
Zone Names Relative Pressure with respect to the main
building pressure
Positive Negative
Storage ring
Booster
Linac
Laboratories
Experimental hall
Toilets and locker rooms
14.10.3 Mechanical utilities
The following mechanical utilities are required for the main building:
Cooling system
Processor of the water cooling tower
Steam generator
Compressed air
Liquid nitrogen
De-ionized water system
Fire extinguisher system
Exhaust
Potable water
Sanitary sewer
Storm drain
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14.10.3.1 Cooling System
The cooling system consists of two main parts:
Heating, Ventilation and Air Conditioning (HVAC) system for the storage ring and
booster tunnels, experimental hall, laboratories and offices. These systems will
provide the required air quality and control the air temperature and humidity within
the allowable range.
Water cooling system for machine components (magnets, RF cavities, absorbers,
front ends, power supplies)
Chilled water from the chillers flow through the pipeline and serves the air handling
units (AHUs) and other devices that need cooling. The pumping station is in the
central utility building located outside the main building.
(a) HVAC for the storage ring and booster tunnels: A great amount of heat is
generated in magnet coils and power cables connected to them that needs to be
dissipated, to maintain the alignment of magnets. The magnet coils are cooled with
water circulation and of course some of the heat is dissipated into the surrounding air.
Air is supplied through nozzles to keep the air temperature in the tunnels within the
allowable range of ±0.1 °C. AHUs will provide cool air. The supply and return fans of
the AHUs should be equipped with adjustable frequency drives to control the air flow
through the ring. The air entering the AHU passes across the cooling coil and its water
content condenses to keep the humidity at the desirable level. It is then warmed by the
heating coil. The final discharge temperature will be controlled by the electrical
reheating coils that respond to duct sensors in the main supply duct. Sensors inside the
tunnels well reset the discharge temperature to maintain the tunnel temperature at the
preset level.
There will be 5, 3, and one air handling units for the storage ring, booster, and linac
respectively. Figure 14.20 shows the air supply ducts for the storage ring, booster, and
the linac. Figure 14.21 shows air supply and return ducts for the experimental hall and
the service area.
(b) HVAC for the experimental hall: Twelve AHUs will be located around the main
building, each supplying air for one part of the experimental hall. Each AHU consists
of an inlet fresh air section, return air, cooling coil, heating coil, humidifier, pre- and
final filters, supply fan, return fan, motor damper, and adjustable frequency drive.
Variable air volume (VAV) systems will be used to regulate the amount of supply air
delivered to the experimental hall based on its thermal needs. VAV boxes may work
independently or be connected to a central control system.
(c) Machine cooling: The cooling water system involves a water-cooling tower,
chilled water, hot water, and de-ionized water (DIW) system. Figure 14.22 shows the
flow diagram of the chilled water production system which contains cooling towers,
chillers and heat exchangers. All of the water circulates in a closed loop with the
required control system that provides a cooling source at a stable temperature and
pressure. The return DIW system includes three subsystems: Cu DIW for magnets and
powers devices; Al DIW for vacuum chambers, RF DIW for the RF system.
Figure 14.23 shows the flow diagram of the DIW system for Al, Cu, and RF circuits.
Table 14.8 lists the specifications of the cooling water system.
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Figure 14.20 Air supply ducts for storage ring, booster, and linac. THIS DRAWING IS A PRIVATE AND CONFIDENTIAL COMMUNICATION AND PROPERTY OF ILSF. IT MAY NOT BE LENT OR COPIED WITHOUT OUR WRITTEN PERMISSION.
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Figure 14.21 Air supply and return ducts for the experimental hall and the service area.
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Figure 14.22 Flow diagram for the chilled-water production system.
THIS DRAWING IS A PRIVATE AND CONFIDENTIAL COMMUNICATION AND PROPERTY OF ILSF. IT MAY NOT BE LENT OR COPIED WITHOUT OUR WRITTEN PERMISSION.
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Figure 14.23 Flow diagram for Al, Cu, and RF circuits in the DIW system.
THIS DRAWING IS A PRIVATE AND CONFIDENTIAL COMMUNICATION AND PROPERTY OF ILSF. IT MAY NOT BE LENT OR COPIED WITHOUT OUR WRITTEN PERMISSION.
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Figure 14.24 Flow diagram for hot-water production system.
THIS DRAWING IS A PRIVATE AND CONFIDENTIAL COMMUNICATION AND PROPERTY OF ILSF. IT MAY NOT BE LENT OR COPIED WITHOUT OUR WRITTEN PERMISSION.
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SC
AL
E:
AP
PR
OV
ED
DE
SIG
NE
D
DR
AW
ND
RA
WIN
G N
O.:
DR
AW
ING
TIT
LE
:
DE
SC
RIP
TIO
N:
CD
B. K
AM
KA
RI
B. K
AM
KA
RI
385
Table 14.8: Specifications of the water cooling system.
Temperature (°C)
Cu DIW 25± 0.1
AL DIW 25± 0.1
RF DIW 25± 0.1
Chilled Water 7± 0.2
Hot Water 60± 0.3
Water supply temperature is maintained at 25.5±0.1 °C. Cooling water system
includes de-ionized water (DIW) which should be treated and monitored with filters,
reverse osmosis, conductivity meters, pH monitors, flow meters and various resins.
The resistivity of DIW will be kept higher than 10MΩ. The dissolved oxygen will be
maintained at a level less than 10 ppb and the pH value will be maintained at 7±0.2.
Hot water can be used for both the regulation of cooled water temperature and AHU
during cold seasons. Figure 14.24 shows the flow diagram for the hot water
production system.
14.11 Electrical Installations
14.11.1 Required electrical installations
The required electrical installations include:
General distribution system
Emergency power for: (i) internal and external lighting, (ii) fire alarm system, (iii)
fire protection system, (iv) HVAC control system, (v) mechanical control systems.
Uninterruptable power for: (i) control systems, (ii) communication systems, (iii)
security systems, (iv) special-purpose equipment
It should be noted that the utilization of the electricity from the generators should be
limited as much as possible so that laboratory equipment can use this power when the
need arises (some experiments require electricity for several days uninterruptedly).
14.11.2 Estimation of electrical power requirement
Table 14.9 lists an initial estimate for the power requirements of various parts of
ILSF. These numbers can be made more accurate in the future.
386
Table 14.9 Power requirement of various parts of ILSF
Location of power consuming equipment Power demand (kW)
Magnet power supplies Storage ring 870
Booster ring 300
Vacuum Vacuum pumps 40
Radio frequency Storage ring 1700
Booster ring 130
Laboratories 400
Experimental hall 500
Lighting 800
Cooling utilities 3500
Other 1000
Total 9250
References:
[14.1] ILSF CDR-Nov 2010, pp 34-38
[14.2] NSLS II Conceptual Design Report, December 2006.
[14.3] Diamond Synchrotron Light Source, Report on Design Specifications,
December 2006.
[14.4] National Synchrotron Radiation Research Center, Report of Geology
Exploration and Tests, December 2005.
[14.5] Herman Winnick, Synchrotron Radiation Sources (2005).
[14.6] TPS Conceptual Design Report: Civil Engineering.
[14.7] TPS Conceptual Design Report: Safety Systems.
[14.8] Alexander Wu Chao, Maury Tigner, Handbook of Accelerator Physics
and Engineering.
[14.9] Neufert, (2011) pp 101-103.
[14.10] Building and Housing Research Center, Iranian code of practice for
seismic resistant design of buildings (Standard No. 2800-05).
[14.11] ANSI, “Radiation Safety for the Design and Operation of Particle
Accelerators”, ANSI N.43. 1. Standard (American National Standard
Institute, 2007).
[14.12] NCRP, “Radiation Protection for Particle Accelerator Facilities”, NCRP
Report No. 144, (National Council on Radiation Protection and
Measurements, 2003).
387
CHAPTER 15: Radiation safety and shielding
The goal of accelerator shielding design is to protect the workers, general public, and
the environment against unnecessary prompt radiation from accelerator operations.
Additionally, shielding at accelerators may also be used to reduce the unwanted
background radiation in the vicinity of detectors, to protect equipment against
radiation damage, and to protect workers from potential exposure to radiation from
machine components.
The aim of this report is to document the assumptions, tools and techniques for
synchrotron radiation shielding planned for the ILSF project. The shielding design
criteria are based on the ALARA (As Low As Reasonably Achievable) principle.
Therefore the considerations of ILSF shielding are such that the measured annual
equivalent dose at any point in the facility even immediately outside the shield is
below 1 mSv.
Radiation safety system as a combination of active and passive systems designed to
protect personnel from prompt radiation includes such features as quality control,
configuration control, protections against adventitious production of radiation and
induced radioactivity, as well as a control system which includes barriers, beam
inhibiting devices, and interlocks.
15.1 Ionizing radiation hazards
Several phases of accelerator operation give rise to sources of radiation: electron
beam loss during different stages of acceleration, electron beam loss in the storage
ring and synchrotron radiation from bending magnets and insertion devices located
around the storage ring.
The radiation field from high energy electron loss depends strongly on the target
material, its thickness and the energy of the electrons. A brief description of the
mechanisms involved in the production of radiation follows.
15.1.1 Bremsstrahlung
Bremsstrahlung (braking radiation) is produced by the interaction of high energy
electrons with accelerator components or residual gas molecules in the vacuum
chamber. Under the influence of the nuclear field, bremsstrahlung photons may go on
to produce electron-positron pairs and lead to the propagation of the electromagnetic
shower. The angular distribution of the photons is forward peaked relative to the
initial electron trajectory, but the transverse component must be considered in
shielding design as well. The full width at half-maximum of the bremsstrahlung is less
than 1° for incident electron energies over 100 MeV [15.1].
388
Another source of bremsstrahlung is the interaction of stored electrons with residual
gas within the storage ring, called gas bremsstrahlung. [15.1].
15.1.2 Neutron production
Because photons have substantially larger nuclear cross-sections than electrons,
neutrons and other particles resulting from scattering are produced mainly by the
photon component of the EM shower [15.1].
15.1.2.1 Giant resonance neutrons (GRNs)
Above the threshold of ~4 MeV for heavy nuclei and ~ 12 MeV for light nuclei, a
photon interacts with nucleus producing an excited compound which de-excites
through the loss of neutron. The spectral peak of these neutrons is at ~ 1MeV with an
average energy of ~ 2MeV and has an isotropic distribution [15.1].
15.1.2.2 High energy neutrons (HENs)
When the photon energy exceeds 25 MeV, high energy neutrons are produced. These
are neutrons with energies in excess of 100 MeV that are an integral part of the
hadronic cascade initiated by high energy photons in an electromagnetic cascade. This
is the radiation component that dominates for thick shields. Again, this group is
forward peaked but not as strongly as BRM photons. [15.1]
The production of giant resonance neutrons increases with the atomic number of the
material (Z), but the production of high-energy neutrons decreases with Z. Thus, the
wall thickness for adequate neutron shielding depends on both the beam power and
the nature of the material struck by the beam. [15.1]
15.1.3 Induced Radioactivity
Induced activity results primarily from bremsstrahlung photons that produce
radionuclides by reactions such as (γ,n) or (γ,p). The amount of activity depends on
the electron energy, beam power, bremsstrahlung production efficiency, and the type
of material [15.1].
15.1.4 Synchrotron radiation
Synchrotron radiation is generated when the electrons are bent in the magnetic fields
of the storage ring.
15.2 Shielding objectives
The shielding design criteria are based on the ALARA principle which states that
exposure to any person should be kept as low as reasonably achievable. This requires
that the radiation shielding design be optimized in a way that the measured annual
equivalent dose at any point in the facility even immediately outside the shield is
below 1 mSv (corresponding to 0.5 μSv/h for 2000 working hours per year). Dose
limits are expressed in terms of dose equivalent to compare the risk from different
389
kinds of radiation where the relative biological effectiveness of these radiations is
taken into account.
15.2.1 Analytical methods
There are some empirical formulas for calculation of dose from different components
of radiation and also shielding assessment in synchrotron accelerators for simple
geometries. Here we have explored the analytical methods which are common for
shielding design in high-energy synchrotron facilities. These formulas will be
introduced in Section 15.5 in detail.
15.2.2 Simulation methods
Monte Carlo methods are accurate, widely applicable, consistent, and flexible. In
shielding calculations Monte Carlo methods can especially be used to deal with
complicated geometries. FLUKA and MCNPX are two of the most widely used
Monte Carlo codes in this kind of calculations.
FLUKA is a general-purpose tool for the calculation of particle transport and
interactions with matter, covering an extended range of applications ranging from
proton and electron accelerator shielding to target design, calorimetry, activation,
dosimetry, detector design, accelerator driven systems, cosmic rays, neutrino physics,
radiotherapy, etc. [15.2].
MCNPX is also a general-purpose Monte Carlo radiation transport code for modeling
the interaction of radiation with matter. MCNPX stands for Monte Carlo N-Particle
extended. It extends the capabilities of MCNP4C to nearly all particles, nearly all
energies, and to nearly all applications without an additional computational time
penalty. MCNPX is fully three-dimensional and time-dependent. It utilizes the latest
nuclear cross sections libraries and uses physics models for particle types and energies
where tabular data are not available [15.3].
In some particular cases it is not possible to use analytical formulae and because of
their complexity the dose calculation should be done by Monte Carlo methods.
Among Monte Carlo codes, FLUKA has the highest applicability in synchrotron
radiation shielding simulations.
The shielding estimations are based on conservative assumptions. To calculate the
accurate dimensions and thicknesses of shielding walls some essential parameters
should be known, such as beam energy, beam current, geometry of the machine and
especially beam loss points and percentage of loss in these points. Since the ILSF
project is in the planning phase now, this report contains approximate values based on
the characteristics of similar facilities.
15.3 Beam loss calculations
The first step in shielding calculations is to determine the loss points and loss
percentages in all parts of the machine. The electrons are generated in an electron gun,
then accelerated in the linac and booster and are finally fully injected into the storage
ring. Two transfer lines (LTB and BTS) transfer electrons from the linac to the
booster and from the booster to the storage ring respectively. To estimate the amount
390
of loss, in some parts of the accelerator the electron trajectory has to be divided into
separate sections. These points are listed in Table 15.1.
Table 15.1: Electron loss points
Loss points
Linac
1st accelerating section
2nd
accelerating section
3rd
accelerating section
LTB Bending magnets
Booster
Injection septum
Extraction septum
Point sources (48 points)
BTS Bending magnets
Storage ring Injection septum
Point sources (32 points)
Electron loss calculations in all parts of ILSF accelerator as well as the main
parameters to be used for designing the shielding walls are presented in the following.
15.3.1 Linac
The linac consists of three different sections. Since each one of these linac sections
can increase the beam energy by about 50 MeV, the final energy will reach to 150
MeV. The main parameters of the linac are as follows:
Beam energy 150 MeV
Beam charge 5 nC
Tunnel length 18 m
Repetition rate 3 Hz
Beam current 15 nA
Thus, the number of electrons per second that pass through the linac is 9.4 × 1010
. The
end of each accelerating section is where the electrons have the highest energy. Thus
the electron loss points of ILSF linac are at the end of the first, second and third
accelerating sections.
15.3.2 Booster
ILSF booster is designed to boost a 150 MeV electron beam, extracted from the linac,
to the final energy of 3 GeV. The main features of the booster synchrotron are given
below: Beam energy 3 GeV
Maximum current 10mA
Ring circumference 192 m
Repetition rate 2 Hz
Radiation loss per turn 788 keV
391
For booster, the loss points consist of injection and extraction septum and bending
magnets (ILSF booster has 48 magnets). Also, two different loss points has been
considered for the storage ring: the injection septum and 32 points related to bending
magnets in ILSF storage ring.
The transfer lines (linac-to-booster and booster-to-storage ring) transport the electron
bunches from one section to another. The electrons are partially lost in transfer lines
and bending magnets.
15.3.3 Storage ring
The ILSF storage ring stores a 400 mA current of 3.0 GeV electrons injected by the
booster synchrotron. The main parameters of ILSF storage ring are given below:
Beam energy 3 GeV
Beam current 400 mA
Beam lifetime 10 hr
Circumference 298.5 m
Radiation loss per turn 1 MeV
The injection septum is an important loss point. Electrons are lost during injection
(booster and storage ring) and during ramping (booster). The extraction septum (only
in the booster) is also an important electron loss point because the electrons are lost
during ramping along the booster and extraction [15.4].
The stored charge in the storage ring (q [C]) can be calculated as:
(15.1)
where I is the storage ring current in Amperes; and, c is the speed of light [m/s], so:
and the number of stored electrons in the storage ring will be:
Taking the beam lifetime to be 10 hr, one gets a loss rate of
Table 15.2 shows the loss percentages, number of electron losses and number of
extracted electrons in each section of accelerator.
Percentages of loss points in all sections of ILSF accelerator is presented in
Figure 15.1. Taking into account 2,000 work hours per year, the total electron loss per
year at each loss point can be calculated.
392
Table 15.2: Electron loss per second and number of lost electrons per second in different parts of the machine
No. Loss (%) Eloss/s E out /s
Linac
Gun 1 20 6.45×1010
First accelerating section 2 20 1.29×1010
5.16×1010
Second accelerating section 3 5 1.03×1010
4.13×1010
Third accelerating section 4 5 2.06×109 3.92×10
10
Linac to
booster Linac tunnel 5 20 1.96×10
9 3.73×10
10
Booster
Injection septum 6 5 7.45×109 2.98×10
10
Point sources 7 5 1.49×109 2.83×10
10
Extraction septum 8 5 1.42×109 2.69×10
10
Booster to
storage
ring
Before bending magnet 9 5 1.34×109 2.56×10
10
After bending magnet 10 5 1.28×109 2.43×10
10
Storage
ring
Injection septum 11 5 1.21×109 2.31×10
10
Point sources 12 5 1.15×109 2.19×10
10
Figure 15.1 Beam loss in a schematic layout of ILSF.
393
15.4 Shielding wall thicknesses
Shielding wall thickness is determined on the basis of the beam energy, beam current,
beam position, and distance between loss points and points of observation. Also
depending on electron trajectory, some directions for the loss points in all parts of
accelerator are considered: forward, forward side, backward, inward, and outward
(Figure 15.2 and Figure 15.3).
The values for shielding wall thicknesses and distances between loss points and points
of dose calculation in different parts of the machine are listed in Tables 15.3 to 15.13.
It should be noted that the thickness values have been calculated for ordinary concrete
(ρ = 2.4 g/cm3). In some cases high density concrete can be used or a second layer
(such as lead and polyethylene) can be added to save space by reducing the walls’
thicknesses. In calculating the values listed in the tables the effective thickness as
shown in Figure 15.2 has been used.
15.4.1 Linac
Based on the electron beam trajectory and the point of calculating the dose, four
different directions have been defined as shown in Figure 15.3.
Figure15.2 Effective shield thickness.
Figure 15.3 Dose point directions with respect to the electrons trajectory in the
linac.
394
Table 15.3: Distances from loss points and shielding thicknesses for linac’s first accelerating section
Direction Distance (m) Concrete thickness (m)
outward 3.76 1.61
inward 1.75 2.00
forward 18.62 2.97
upward 3.00 0.95
Table 15.4: Distances from loss points and shielding thicknesses for linac’s second accelerating section
Direction Distance (m) Concrete thickness (m)
outward 3.25 1.24
inward 1.75 1.48
forward 13.92 2.39
upward 3.00 0.95
Table 15.5: Distances from loss points and shielding thicknesses for linac’s third accelerating section
Direction Distance (m) Concrete thickness (m)
outward 3.58 1.14
inward 1.75 1.48
forward 9.22 2.57
upward 3.00 0.95
15.4.2 Linac-to-booster transfer line
Table 15.6: Distances from loss points and shielding thicknesses for linac bunker of LTB
Direction Distance (m) Concrete thickness (m)
outward 3.97 1.65
inward 1.75 1.78
forward 4.43 2.98
upward 3.00 0.95
395
15.4.3 Booster
Table 15.7: Distances from loss points and shielding thicknesses for booster’s injection septum
Direction Distance (m) Concrete thickness (m)
outward 3.01 1.28
inward 2.89 1.16
forward 12.11 2.08
upward 3.00 0.95
Table 15.8: Distances from loss points and shielding thicknesses for loss points in the booster
Direction Distance (m) Concrete thickness (m)
outward 1.46 1.97
inward 3.04 0.68
forward 7.00 5.12
upward 3.00 0.85
Table 15.9: Distances from loss points and shielding thicknesses for booster’s extraction septum
Direction Distance (m) Concrete thickness (m)
outward 1.55 2.24
inward 3.42 1.60
forward 10.84 4.87
upward 3.00 1.15
15.4.4 Booster-to-storage ring transfer line
Table 15.10: Distances from loss points and shielding thicknesses for the first part of BTS before the bending magnet
Direction Distance (m) Concrete thickness (m)
outward 1.45 2.57
inward 3.20 2.46
forward 6.62 2.79
upward 3.00 1.40
396
Table 15.11: Distances from loss points and shielding thicknesses for the first part of BTS after the bending magnet
Direction Distance (m) Concrete thickness (m)
outward 7.34 1.25
inward 2.49 3.11
forward 18.8 5.70
upward 3.00 1.40
15.4.5 Storage ring
The loss points in the storage ring and directions used for shielding calculations are
shown in Figure 15.4.
Table 15.12: Distances from and shielding thicknesses for injection septum loss points in the storage ring.
Direction Distance(m) Concrete Thickness(m)
outward 5.95 0.87
inward 1.84 2.08
forward 13.98 2.54
upward 3.00 1.10
Figure 15.4 Loss points in the storage ring and the directions used for
shielding calculations.
397
Table 15.13: Distances from and shielding thicknesses for loss points in the storage ring.
Direction Distance (m) Concrete thickness (m)
outward 3.79 0.58
inward 2.95 1.48
forward 13.86 1.84
upward 3.00 1.10
15.5 Shielding Calculations for ILSF
The expressions used for shielding calculations depend on the angle between electron
beam trajectory and the point of dose calculation [15.5].
15.5.1 Forward side direction
The dose behind the shielding material can be calculated in the following way:
where is the dose per primary electron (Sv/e); the dose before shielding wall
(Sv/e), the electron energy (GeV); an exponent that can be found in
Table 15.14 as a function of the angle θ; is the attenuation
coefficient ; the thickness measured in the direction of (cm),
therefore, for a pure lateral shielding of thickness (i.e. surface parallel to the beam
axis) x has to be replaced by ; and is the shield material density (g·cm-3
).
Values of can be found in Table 15.15 for iron [15.5].
Table 15.14: Energy exponents α [15.5]
w(cm) d(cm) ϕ(deg) α
θ = 7.5° θ = 25° θ = 90°
1.0 1.0 90 0.050 0.045
5.73 0.2 -2.0 0.61 0.52 0.51
5.76 1.0 -10 0.64 0.41 0.51
22.9 0.2 -0.5 1.01 1.00
28.7 1.0 -2.0 1.05 0.97 0.95
114 0.2 -0.1 1.10 1.15 1.37
398
Table 15.15: Parameters used in calculations as a function of the target thickness and observation angle [15.5].
d [cm] θ [deg] Ha [Sv] α
0.2
7.5º 2.3×1013
0.61
25º 3.5×1015
0.52
90º 1.3×1017
0.51
1.0
7.5º 1.5×1013
1.05
25º 3.5×1014
0.97
90º 4.4×1016
0.95
15.5.2 Forward direction
Dose behind shielding wall can be estimated using the following expression [15.6]:
where x is the shielding thickness in cm; r is the distance from the target to the front
surface of the shield in meters; is the attenuation coefficient ( );
is the effective path to the target in the direction of beam (cm). H0 can
take different values depending on the geometry; for d=1 cm and =900,
H0 = 1×10-12
(Sv/e) and for d = 0.2cm and =20, H0 =4.5×10
-13(Sv/e)
Figure 15.5 Target and shielding wall geometry used for calculations in forward and
forward side directions.
399
15.5.3 Upward and downward directions
Dose equivalent rate beyond shielding walls due to local beam loss of a given power,
perpendicular to beam trajectory, has been calculated using the following
expression [15.7]:
where is dose equivalent rate ( Sv/h); the conversion factor for the rth
radiation
component (Svh-1
kW -1
m 2); P the electron power loss (kW); R the distance between
the loss point and the point of observation (m); the thickness of the ith
wall (shield
thickness) (cm); and λ i,r the attenuation length of the material of the ith
wall for the
radiation of type r (cm).
This expression is useful for neutron shielding calculations as well as perpendicular
shielding walls for photons [15.7][15.8].The radiation attenuation factors used for the
materials in the current shielding calculations are given in Table 15.16 [15.7][15.8].
Table 15.17 lists the values of energy and power loss for ILSF shielding calculations.
Table 15.16: Radiation attenuation factors for common shielding materials [15.7]
Radiation component Shielding Material Density (g/cm
3)
Attenuation length (g/cm
3)
Bremsstrahlung
Concrete
Lead
Polyethylene
2.35
11.34
1.01
49
25
70
Giant Resonance Neutron
(E< 25MeV)
Concrete
Lead
Polyethylene
2.35
11.34
1.01
40
161
6.3
High-Energy Neutron
Concrete
Lead
Polyethylene
2.35
11.34
1.01
65 (<100MeV)
115 (>100MeV)
191
62
400
Table 15.17: Energy and lost power of the electron beam at the loss points.
Loss (%) Eloss/s E(GeV)
Power loss (W)
Power loss (j/h)
Linac
First accelerating section
10 1.29×1010
0.05 1.03×10-1
3.72×102
Second accelerating section
10 1.16×1010
0.10 1.86×10-1
6.68×102
Third accelerating section
10 1.04×1010
0.15 2.50×10-1
8.99×102
Linac to booster
Linac tunnel 5 4.70×109 0.15 1.13×10
-1 4.06×10
2
Booster tunnel
5 4.46×109 0.15 1.07×10
-1 3.85×10
2
Booster
Injection septum
20 1.70×1010
0.15 4.08×10-1
1.47×103
Point sources
15 1.02×1010
3 4.90 1.76×104
Extraction septum
15 8.65×109 3 4.15 1.49×10
4
Booster to storage ring
Before bending magnet
5 2.45×109 3 1.18 4.23×10
3
After bending magnet
5 2.33×109 3 1.12 4.03×10
3
Storage ring
Injection septum
25 1.11×1010
3 5.33 1.92×104
Point sources
25 8.29×109 3 3.98 1.43×10
4
15.6 Shielding calculation of ILSF beam stop
The design and shielding of the beam stop is one of the most important issues in
radiation protection considerations in light source facilities. For the beam stop
shielding calculations, it is assumed that all electrons are lost at one point. Thus this is
the worst case of a beam loss scenario. When a 3 GeV electron beam interacts with
the material of the beam stop, an electromagnetic shower will be generated due to
successive bremsstrahlung and pair-production interactions. A shower is developed in
the material when the primary electron energy is much greater than the critical energy
of the material. The critical energy, Ec, is the electron energy at which the average
energy loss due to radiation equals to that due to ionization and is given by:
where Z is the atomic number of the target material.
401
The lateral and longitudinal shower dimensions within the material are determined by
the Moliere radius (XM) and the radiation length (X0) of the material given
below [15.8]:
where A is the atomic mass.
The theory of electromagnetic showers stipulates that material of dimensions of
approximately 20 radiation lengths in longitudinal and 3 Moliere radii in transverse
direction will contain 99.99% of the electromagnetic shower [15.9].
Table 15.18 compares some materials that are used for beam stop. The material of
choice for ILSF’s beam stop is iron, for various qualities such as sturdiness, thermal
stability, good conductivity, and relative compactness of shower dimensions.
Moreover, iron is a low Z material and photo-neutron yield and the resulting
activation will also be minimal. Thus, an iron cylinder with a length of 35.4 cm and a
diameter of 7.68 cm will be sufficient to contain effectively the electromagnetic
shower in the beam stop.
Table 15.18: Radiation length and Moliere radius for various materials
Material Density (g/cm
-3)
Zeff A Critical Energy (MeV)
Radiation length (cm)
Moliere length (cm)
Aluminum 2.702 13 26 56.33 8.68 3.267
Copper 8.96 29 63 26.49 1.88 1.50
Iron 7.874 26 56 29.41 1.77 1.28
Air 0.001 6.83 29 99.56 84888.64 18075.92
Figure 15.6 shows the geometry which has been simulated by FLUKA and MCNPX.
In this arrangement an iron target has been located in the center of a concrete cylinder
with 1 m thickness. The distance from the target to inner surface of shield is 1 m in
forward and lateral direction. Neutron and photon dose equivalent have been scored in
0 and 90 degree outside the shielding wall. The results are shown in Table 15.19.
Figure 15.6 Geometry of simulated beam stop (all units in cm).
402
Table 15.19: Comparison of FLUKA and MCNPX results for gamma and neutron dose equivalent beyond 1 m of concrete
Type of radiation (Angle) FLUKA (pSv/e) MCNPX (pSv/e)
Gamma (0º) 4.03×10-5
2.62×10-5
Gamma (90º) 5.44×10-7
5.64×10-7
Neutron (0º) 7.06×10-6
5.41×10-6
Neutron (90º) 1.79×10-6
2.01×10-6
Total (0º) 4.08×10-5
3.16×10-5
Total (90º) 2.33×10-6
2.57×10-6
The table confirms that despite different library, algorithm, and physical models, the
results of two Monte Carlo codes have acceptable consistency
Figure 15.7 shows the spectrum of photons before and beyond shield calculated with
FLUKA. Most of the energy is concentrated in range of 0.1 to 10 MeV before and 0.1
to around 0.5 MeV beyond the shield. Both spectra have a clear peak around 0.5 MeV
resulting from the annihilation of positrons and electrons which is one of the
characteristics of the radiation field in high energy electron accelerators.
Figure 15.8 indicates the angular distribution of the photons produced in different
energy ranges as calculated by FLUKA. The number of photons decreases
significantly with photon energy above 1 MeV. Also there is an obvious peak at 0
degrees indicating that most of photons are forward directed. This is the reason that
dose equivalent in lateral direction is smaller than in the forward direction. By
increasing the angle with respect to beam trajectory the fluence (flux integrated over
time) of photons decreases dramatically.
Figure 15.7 Photon spectrum before and beyond the beam stop shield.
0
200
400
600
800
1000
1200
1400
1600
1800
1.E-6 1.E-5 1.E-4 1.E-3 1.E-2 1.E-1 1.E+0 1.E+1
Nu
mb
er
of
Ph
oto
n/p
rim
ary
E (GeV)
beyond shield
before shield
0.5Me
V
403
Figure 15.9 shows photon and neutron dose equivalent distributions in the beam stop.
These show that photon dose distribution is more intense around the beam direction
whereas neutron dose distribution is almost isotropic.
Total electron loss rate during storage period has been estimated to be about 6.8×107
electrons per second for ILSF. By considering this estimation the thickness of the
shielding wall in the lateral direction is enough to achieve the goal of a dose limit of
1 mSv/y for staff and users working 2000 hours in ILSF’s experimental area. But in
the forward direction 100 cm of concrete does not satisfy the design goal. Therefore
we need to add concrete thickness in this direction or use heavy concrete or add a thin
layer of local shielding such as lead and polyethylene.
Figure 15.8 Angular distribution of photons in three different ranges of energy.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 20 40 60 80 100 120 140 160 180
Ph
oto
n
Flu
en
ce(#
/Ge
V.c
m2
/pri
mar
y)
Angle(Degree)
Photon Flunce(E=10keV-1MeV)
Photon Fluence*100(E=1MeV-100MeV)
Figure 15.9 Dose equivalent distribution in the beam stop for photons (left) and neutrons (right).
404
15.7 Investigation of radiation streaming and shielding calculations for ILSF maze
Any practical accelerator shielding needs to have passageways for personnel access
and for passage of control and power cables, cooling-water pipes, heating, ventilation,
air-conditioning ducts. etc. Such openings compromise the integrity of the shield and
must be designed with great care.
There is no completely satisfactory theoretical basis for calculating the amount of
radiation that penetrates through such openings, and it is necessary to fall back on
experimental data, empirical methods, and computer simulations. Computer
simulations involve the use of complex Monte-Carlo codes which can be used for
both curved and rectilinear labyrinths.
ILSF bulk shielding consists of five five-legged labyrinths in the inner shielding wall
of the storage ring for both personnel access and passage of some utility pipelines.
The cross section of the passageway has been determined to be 1.5 m wide and 2 m
high.
For the purpose of calculation we have considered the worst-case scenario for beam
loss. In this model, a 3 GeV electron beam hits the so-called standard target of an iron
cylinder with a length of 30.48 cm and radius of 5.08 cm [15.10], which is located 1.0
m from the maze mouth. Under the worst-case scenario, the design goal is to reduce
the radiation streaming through the maze to an acceptable dose level similar to that
right behind the lateral shielding wall without any opening.
15.7.1 Monte Carlo simulations
FLUKA Monte Carlo code was used to simulate the problem. The calculation
geometry consisting of the target, the bulk concrete shielding, and the five-legged
maze is shown in Figure 15.10.
Figure 15.10 Calculation geometry simulated by FLUKA.
405
Eight scoring detectors have been placed along the centerline of the access-way to
evaluate the dose attenuation and spectrum change along the maze. An additional
detector has been located outside the lateral shielding wall as a reference detector for
comparison with others.
The result of simulation is shown in Figure 15.11. As this figure shows, at the mouth
of the labyrinth the contribution of photon dose is almost twice that of neutrons but it
attenuates more rapidly than the neutron dose along the maze, in particular, after
turning the first corner. After the second leg the contribution of neutron to the total
dose dominates and at the maze exit the neutron dose is about four times the photon
dose. This figure also indicates the photon and neutron doses increase in detectors 6
and 7 that are placed in fourth leg next to the concrete wall. It implies that 50 cm of
concrete is not thick enough to prevent high energy neutrons.
Figure 15.12 displays the distribution of total dose equivalent along the labyrinth. As
this figure shows the passageway is not safe enough near the first, second, and fifth
legs.
Figure 15.11 Neutron, photon and total dose equivalent along the centerline of the passageway.
1.E-7
1.E-6
1.E-5
1.E-4
1.E-3
1.E-2
0 500 1000 1500
Do
seE
qu
ivale
nt
(pS
v/e
letr
on
)
Centerline distance from maze mouth (cm)
H(total)
H(neutron)
H(photon)
Figure 15.12 Total dose equivalent distribution in the simulated geometry.
406
In Table 15.20 the photon, neutron and total dose equivalent that would be recorded
by the eight defined detectors in different locations along the passageway have been
given. It is clear that dose equivalent in detectors 1 to 4 and also 7 and 8 is higher than
reference detector. So these locations are not safe enough for personnel access.
Table 15.20: Photon, neutron and total dose equivalent at different locations in the labyrinth
As a solution we added a 10 cm layer of polyethylene to the second leg and a 10 cm
layer of lead to the fourth leg. Table 15.21 gives the results after this modification.
The dose equivalent scored by all detectors has become lower than the reference
detector and the passageway along the labyrinth and in particular, the maze exit has
become safe enough.
Table 15.21: The Comparison between dose equivalent before and after adding local shield
Det.
Total dose
equivalent (before)
(pSv/e)
Total dose
equivalent (after)
(pSv/e)
Det.
Total dose
equivalent
(before)
(pSv/e)
Total dose
equivalent (after)
(pSv/e)
1 8.67×10-3
8.70×10-3
6 3.52×10-6
2.6×10-6
2 1.25×10-3
1.25×10-3
7 8.09×10-6
4.2×10-6
3 3.57×10-5
2.4×10-5
8 5.76×10-6
3.8×10-6
4 7.25×10-6
5.9×10-6
5 3.09×10-6
1.9×10-6
Ref. 4.48×10-6
4.48×10-6
Location Photon (pSv/e) Neutron (pSv/e) Total (pSv/e)
Det. 1 2.53×10-3
1.06×10-3
3.99×10-3
Det. 2 7.72×10-4
4.02×10-4
1.29×10-3
Det. 3 5.26×10-6
2.86×10-5
3.49×10-5
Det. 4 8.71×10-7
7.83×10-6
8.80×10-6
Det. 5 7.70×10-8
2.84×10-6
2.29×10-6
Det. 6 2.75×10-7
2.47×10-6
2.81×10-6
Det. 7 2.54×10-6
4.33×10-6
7.25×10-6
Det. 8 1.60×10-6
4.04×10-6
5.97×10-6
Det. Ref 1.69×10-6
3.80×10-6
5.14×10-6
407
15.7.2 Comparison of the results from different methods
For estimating the radiation transmission through labyrinths, there are several
empirical solutions in the literature based on calculation or measurement results. They
usually describe the dose attenuation in labyrinths relative to the dose at the mouth of
the maze. To verify our simulation results we have used an empirical method that is
common for maze design in high-energy accelerator facilities for neutron attenuation
in labyrinths
Cossairt [15.11] has given a factorized approximation formula for neutron attenuation
in a labyrinth. For the first leg neutron dose equivalent is
where ro is simply a fitting parameter and d1 is the distance measured from the mouth
of the passageway in "units" of the square root of the cross-sectional area of the first
leg and is the dose at the mouth.
For the second and successive legs, the attenuation is estimated by employing the sum
of three exponentials as follows:
where di is the distance from the entrance of ith
leg to the point where the dose
equivalent is desired with similar definitions for d1, r1, r2, r3. K and J are given fitting
parameters.
Figure 15.13 confirms that FLUKA results are comparable with the empirical formula
up to a distance of 700 cm from the mouth of the maze. This distance is
corresponding to the end of the third leg. After that, the dose calculated from the
above formulas decreases more rapidly with distance than the results obtained from
FLUKA.
In Cossairt formulas the dose changes in proportion to the distance from the mouth of
the maze and is independent of the shield type and thickness, whereas these factors
can affect the final result. This is the main reason for the difference between results
obtained from FLUKA and the analytical method.
Figure 15.13 Comparison of FLUKA results with calculations using Cossairt formulas.
1.00E-08
1.00E-06
1.00E-04
1.00E-02
1.00E+00
0 500 1000 1500
Ne
utr
on
Do
se
Equ
ival
en
t (p
Sv/e
)
Centerline Distance From Maze Mouth(cm)
Cossairt Results
408
15.8 Gas bremsstrahlung in ILSF insertion devices
Gas bremsstrahlung is a source of high energy radiation which is produced by
electron beam interaction with residual gas (H2, CO, CO2, CH4 etc) or ions in the
vacuum chamber of electron storage ring. Because of its extremely high intensity and
high energy, and since it is collimated in the forward direction, gas bremsstrahlung is
one of the important issues of radiation protection and safety in any synchrotron
facility, especially for the third generation synchrotron radiation facilities in which
many insertion devices are installed.
The intensity of bremsstrahlung depends on the residual gas composition, the storage
ring pressure, the stored electron current and the length of the path of electron in
vacuum chamber
According to Ferrari et al [[15.11]] the maximum gas bremsstrahlung dose rate (Gy/h) in the forward direction is given by:
where E0 is the primary beam energy (MeV); m0c2 is the rest-mass energy of the
electron (MeV); L is the length of the straight section (m); d is the distance from the
end of the straight section to the point of interest (m); I is the stored beam current
(2.5×1018
electrons/s for 400 mA); P is the pressure in the straight section (Pa); and P0
= 1.33 x 10–7
Pa (10-9
Torr).
According to another analysis developed by Rindi and Tromba [15.13][15.14], the
dose rate at 10 meters from the straight path is:
where l is the effective length of the straight path (16 meters), I is the beam current in
e/s, E is electron beam energy in MeV, P is the operating pressure in the vacuum
chamber, and Patm is the atmospheric pressure. The expression that gives the dose rate
at a distance r from the center of the straight section is [15.14]:
Comparison of these analytic formulas and Monte Carlo technique will be described
in this section.
Figure 15.14 shows the geometry used in Monte Carlo simulations performed by
FLUKA and MCNPX codes for a 3GeV pencil-like electron beam interacting with
gas in a cylindrical air target of 15m length at a pressure of 1 atm. The results have
been scored in a 20cm×20cm rectangular parallelepiped human tissue phantom with
30 cm depth in the direction of the beam and 20 cm lead as a beam stop.
Table 15.22 gives the bremsstrahlung dose rates in ILSF beamline computed by the
expressions above and the results from Monte Carlo simulations. The Monte Carlo
results are in better agreement with Ferrari's formula.
409
Table 15.22: Bremsstrahlung dose rates in ILSF beamline -- comparison of
Ferrari and Rindi formulas with results of Monte Carlo methods
Figure 15.15 shows the photon and neutron dose equivalent in tissue phantom plotted
by FLUKA. Figure 15.16 shows the spectrum of the gas bremsstrahlung in a straight
section obtained by FLUKA. This curve shows a sharp dip for photon energies below
18 keV, which is due to the strong photoelectric absorption by residual gas atoms in
the vacuum chamber.
Method Dose rate
(pSv/e)
Assumptions:
E = 3GeV
I = 400 mA
Straight-section path length = 16 m
Distance to the dose point = 20 m
Straight-section pressure = 10-9
Torr
P=760 Torr
Ferrari 1.31×102
Rindi 4.98×102
FLUKA 1.62×102 ± 4%
MCNPX 1.74 ×102 ± 7%
Figure15.14 Geometry of the gas bremsstrahlung in a straight section.
Figure 15.15 Neutron (left) and photon (right) dose equivalent in tissue phantom.
410
Figure 15.17 shows the angular distribution of the gas bremsstrahlung scoring at the
end of straight section. The photon intensity peaks at 00 and falls off very rapidly for
angles larger than the characteristic angle.
Figure 15.16 The energy distribution for gas bremsstrahlung at the end of electron beam path in a straight section, due to interaction of 3 GeV electrons with a target of residual gas at the atmospheric pressure.
Figure 15.17 Angular distribution of gas bremsstrahlung at the end of a straight section, resulting from interaction of 3 GeV primary electrons with residual gas.
411
15.9 Radiation safety
Radiation safety systems (RSS) protect the personnel from prompt and hazardous
radiation generated as a result of the operation of the accelerator. The primary
components of RSS include:
Shielding, which attenuates radiation.
A personnel protection system comprised of an access control system that prevents
personnel from entering areas in which dangerous levels of radiation may be
present
Radiation control system to ensure that radiation in different places of accelerator
does not exceed design limit.
15.9.1 Personnel protection system
To protect personnel from prompt and hazardous radiation, personnel access should
be controlled for radiation and controlled areas. The entrance of persons is allowed by
health physics officer. Those persons must enter with radiation monitors and must
wear a pocket dosimeter or TLD badge. The radiation levels for other areas around
the accelerator to which access is free, should be checked periodically.
This part of protection may include an interlock system and warning signs and various
control devices.
15.9.2 Radiation monitoring system
Any accelerator facility should have a radiation monitoring system to check that
radiation level in different areas does not exceed the design limits under normal and
abnormal operating conditions. Special beam instrumentation along with radiation
monitors outside the shielding walls in different parts of accelerator and around the
boundaries of the facility should be used. Also some detectors should be used for
monitoring radioactive isotopes produced in water, air and soil.
The data from all these instruments and monitoring devices will be input to a central
computer in the main control room for periodical checking and processing.
References:
[15.1] James C. Liu, Vaclav Vylet, “Radiation protection at synchrotron radiation
facilities”, SLAC-PUB-9006, September 27, 2001.
[15.2] A. Ferrari, P.R. Sala, A. Fassò, J. Ranft, “FLUKA: a multi-particle
transport code”, CERN-2005-10 (2005), INFN/TC_05/11, SLAC-R-773,
http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-r-773.pdf.
[15.3] Denise B. Pelowitz, MCNPX USER'S MANUAL, Version 2.6.0, Los
Alamos National Laboratory, report- LA-CP-07-1473,
http://mcnpx.lanl.gov/opendocs/versions/v260/v260.pdf.
[15.4] F. Fernández, “Electron losses estimation at the ALBA accelerator” ALBA
Internal report H&S-HSRS-SR-0001 (2007).
[15.5] H. Dinter, J. Pang, K. Tesch, “Calculations of doses due to electron-photon
stray radiation from a high energy electron beam behind lateral shielding”,
Rad. Prot. Dos., Vol. 25, No. 2. (1988) 107-116.
412
[15.6] K. Tesch, “Shielding against high energy neutrons from electron
accelerators – a review”, Rad. Prot. Dos., Vol. 22, No. 1 (1988) 27-32.
[15.7] H. J. Moe, “Advanced Photon Source”: Radiological Design
Considerations, Argonne National Laboratory, APS-LS-141 ( July 1991)
http://www.aps.anl.gov/Science/Publications/lsnotes/content/files/APS_141
7734.pdf.
[15.8] William P. Swanson, “Radiological Safety Aspects of the Operation of
Electron Linear Accelerators" IAEA, Tech. Rept. Series No. 188, Vienna
(1979), www-pub.iaea.org/MTCD/publications/PDF/trs188_web.pdf, and
references therein.
[15.9] National Council on Radiation Protection and Protection, Radiation
Protection For Particle Accelerator Facilities, NCRP Report No. 144
(National Council on Radiation Protection and Measurements, Maryland,
2005).
[15.10] W. R. Nelson, T. M. Jenkins, “The SHIELD11 Computer Code”, SLAC-R-
737 (US Department of Commerce, Springfield, 2005)
www.slac.stanford.edu/cgi-wrap/getdoc/slac-r-737.pdf.
[15.11] J. Donald Cossairt, “Approximate technique for estimating labyrinth
attenuation of accelerator-produced neutrons”, Radiation Physics Note No.
118 (Fermi National Accelerator Laboratory, Batavia, 1995).
[15.12] Ferrari, M. Pelliccioni, P.R. Sala, Nucl. Instr. and Meth. B83 (1993) 518-
524.
[15.13] G. Tromba, A. Rindi, Nucl. Instr. and Meth. A292 (1990) 700.
[15.14] Rindi, Health Phys. 42 (1982) 187.
413
CHAPTER 16: Time schedule/Budget
16.1 Introduction
The Iranian Light Source Facility (ILSF) will be the first synchrotron ever built in
Iran. ILSF will constitute a great step in increasing the national scientific capabilities
by enabling the study of material properties and functions at a level of detail and
precision which had not been possible before in Iran. To achieve this, ILSF will
provide photon beams having ultra-high brightness and flux and exceptional stability.
ILSF will also provide advanced insertion devices, optics, detectors, robotics, and a
suite of scientific instruments. These tools should support around 2,000 scientists
from more than 200 academic, industrial, and government institutions every year.
Their myriad research programs will produce about 300 publications per year.
The unique characteristics of ILSF will enable exploration of the scientific challenges
faced in developing new materials with advanced properties, including: the
correlation between nanoscale structure and function, the profound effects of
confinement, finite size and proximity; the mechanisms of molecular self-assembly
which produces exquisite organic and inorganic molecular structures, and the science
of emergent behavior.
16.2 Scope of the project
The project scope includes the design, construction, installation, and commissioning
of the accelerator hardware, civil construction, and central facilities required to
produce a synchrotron light source. It includes a highly optimized electron storage
ring, full-energy injector, experimental beamlines and optics, and appropriate support
equipment.
16.3 Work breakdown structure
The realization of a project of this magnitude involves a series of phases along which
increasing commitment and involvement is required from both the funding agencies
and the user community. In particular, a variety of technical solutions and the
corresponding engineering considerations and cost benefit compromises must be
analyzed according to the present and future needs of the scientific community, as
expressed by the scientific cases to be detailed in close collaboration with the user
community. Once the critical components/subsystems are identified, prototypes
should be developed to validate the proposed solutions before a detailed engineering
design can be put together and precise cost estimates and a detailed construction
schedule can be prepared.
The work breakdown structure (WBS) for the ILSF contains a complete definition of
the project’s scope, and forms the basis for planning, executing, and controlling the
project activities (Figure 16.1). Elements are defined as specific systems/deliverables,
414
project management, research and development or pre-operations consistent with
discrete increments of project work and the planned method of accomplishment.
16.4 Cost and schedule
The total estimated cost (TEC) of ILSF project is $350M. The schedule for
construction will lead to the start of operations in fiscal year 2019. A preliminary
high-level summary of the costs of the ILSF project, at the second level of the work
breakdown structure, is given in Table 16.1
Table 16.1: Estimated costs for the ILSF Project.
No. Element Cost (US$)
1 Project management and support 20
2 Accelerators (linac, booster & storage ring) 138
3 Beamlines 91
4 R & D 10
5 Conventional facilities 85
6 Commissioning & pre-operation 8
Total estimated cost 350
A preliminary milestone schedule is given in Table 16.2.
Figure 16.1 Work breakdown structure of the ILSF project
415
Table 16.2: Preliminary level-0 milestone schedule.
PHASE
Milestones Design Construction
CDR Apr 2010 - May 2012
Building Jun 2012 - Nov 2013 Dec 2013 - May 2017
Linac Jun 2012 - Feb 2013 Mar 2013 - Feb 2017
LTB Jun 2012 - Aug 2013 Sep 2013 - Feb 2017
Booster Sep 2012 - Nov 2013 Dec 2013 - Aug 2017
BTS Sep 2012 - Mar 2014 Apr 2014 - Jul 2018
Storage Ring Sep 2012 - Sep 2014 Oct 2014 - Sep 2018
Insertion Devices Sep 2012 - Oct 2014 Nov 2014 - Dec 2018
Installation & Commissioning March 2017- Sep 2019
Operation Oct 2019