harmonic bunch injection/extraction for the elic circulator ring
DESCRIPTION
Harmonic Bunch Injection/Extraction for the ELIC Circulator Ring. Andrew Hutton. Introduction. 2.4 Amps of polarized electrons are required to reach the ultimate luminosity in the ELIC proposal - PowerPoint PPT PresentationTRANSCRIPT
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Harmonic Bunch Injection/Extraction for the ELIC Circulator Ring
Andrew Hutton
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 2
Introduction
• 2.4 Amps of polarized electrons are required to reach the ultimate luminosity in the ELIC proposal
• It is generally felt that future electron guns may be able to produce up to around 100 mA of polarized electrons• Present record is about 300 µA
• Slava Derbenev proposed to get around this limitation by using a circulator ring in which the electrons would spend up to 100 turns before being energy recovered• However, no viable scheme has yet been proposed to
inject and extract electrons in the circulator ring• Harmonic injection/extraction provides a partial solution
to the problem based on existing hardware• Could be implemented today
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 3
Concept
Concept assumes single bunches accelerated at a uniform, low repetition rate• Repetition rate is 1497/h MHz • Example is the 31.2 MHz G0 beam (=1497/48 MHz)
• Several RF separator cavities at different frequencies are used to extract one bunch every h bunches and re-inject a replacement bunch • Harmonic number of circulator ring should have no
common factor with h• Every bunch in the ring will be replaced every h
turns• Design for no kick on adjacent bunches
• Kick not required to be zero between bunches
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 4
Injection/Extraction Layout
Harmonic RF Injection/Extraction
System
Injected Bunch
Extracted Bunch
InjectionSeptum
ExtractionSeptum
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 5
Example h = 6
Kick Kick Kick
X X X X X X X X X X X X
Ring
Linac
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 6
Inject/Extract One Bunch Every Six Bunches
Use three sub-harmonics of bunch frequency and DC kick
• Solution provides required values at bunch positions
Sub- Frequency Kick Bunch Bunch Bunch Bunch Bunch Bunch Bunchharmonic MHz µrad 0 1 2 3 4 5 6
0 DC Kick 50 50 50 50 50 50 50 50
2 749 50 50 -50 50 -50 50 -50 50
3 499 100 100 -50 -50 100 -50 -50 100
6 250 100 100 50 -50 -100 -50 50 100
Total Kick Strength µrad 300 0 0 0 0 0 300
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 7
Inject/Extract One Bunch Every Twelve Bunches
• Use six sub-harmonics of bunch frequency plus a DC kick
• Solution provides required values at bunch positions• Solution is not perfect between bunches
Sub- Frequency Kick Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunchharmonic MHz µrad 0 1 2 3 4 5 6 7 8 9 10 11 12
0 DC Kick 25 25 25 25 25 25 25 25 25 25 25 25 25 25
2 749 25 25 -25 25 -25 25 -25 25 -25 25 -25 25 -25 25
2.4 624 50 50 -43 25 0 -25 43 -50 43 -25 0 25 -43 50
3 499 50 50 -25 -25 50 -25 -25 50 -25 -25 50 -25 -25 50
4 374 50 50 0 -50 0 50 0 -50 0 50 0 -50 0 50
6 250 50 50 25 -25 -50 -25 25 50 25 -25 -50 -25 25 50
12 125 50 50 43 25 0 -25 -43 -50 -43 -25 0 25 43 50
Total Kick Strength µrad 300 0 0 0 0 0 0 0 0 0 0 0 300
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 8
Field Variation
Calculation by Reza Kazimi
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 9
Inject/Extract One Bunch Every Sixteen Bunches
• Use eight sub-harmonics of bunch frequency plus a DC kick
Eight sub-harmonics is about the maximum that is reasonable
Sub- Frequency Kick Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunch Bunchharmonic MHz µrad 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0.0 DC Kick 50 20 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50
2.0 749 50 20 -50 50 -50 50 -50 50 -50 50 -50 50 -50 50 -50 50 -50 50
2.3 655 100 40 -92 71 -38 0 38 -71 92 -100 92 -71 38 0 -38 71 -92 100
2.7 561 100 40 -71 0 71 -100 71 0 -71 100 -71 0 71 -100 71 0 -71 100
3.2 468 100 40 -38 -71 92 0 -92 71 38 -100 38 71 -92 0 92 -71 -38 100
4.0 374 100 40 0 -100 0 100 0 -100 0 100 0 -100 0 100 0 -100 0 100
5.3 281 100 40 38 -71 -92 0 92 71 -38 -100 -38 71 92 0 -92 -71 38 100
8.0 187 100 40 71 0 -71 -100 -71 0 71 100 71 0 -71 -100 -71 0 71 100
16.0 94 100 40 92 71 38 0 -38 -71 -92 -100 -92 -71 -38 0 38 71 92 100
Total Kick Strength µrad 320 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 800
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 10
General Solution
• The exact solution is clear from these examples• Requires h/2 harmonically related RF frequencies
• Amplitude is equal for all except for 799.5 MHz which is half the amplitude
• Also requires a DC kick of half the amplitude
• The number of RF systems required goes up linearly with h• At some point, system becomes unmanageable• Also, total length of cavities must be small
compared to beta function at the cavities to maintain proper cancellation
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 11
Basis for Hardware Design
• Existing CEBAF RF separators• Five–pass separators work up to 6 GeV • They are designed to work up to 12 GeV
• Fifth-pass system uses three 499 MHz RF Cavities powered by a single IOT
• There are a total of four IOTs which are powered by a single power supply
Hardware solution for example of h = 6• 3 CEBAF RF separator-style cavities
• Each powered by a separate IOT• Frequencies are: 749,5 MHz, 499 MHz, 249.5 MHz
• One DC corrector
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 12
CEBAF RF Separator
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 13
RF Separator Cavities in CEBAF Tunnel
Three RF separator cavities are used to split 6 GeV beams in CEBAF
Separation is completed by downstream Lambertson septum magnet
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 14
Driver for CEBAF RF Separators
IOT with drive electronics
Power supply for 4 IOTs
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 15
Choice of h
• If h is small • Kickers are easier, fewer elements• Bunches stay only a few turns in ELIC
• Better for emittance degradation
• If h is large• Need many frequencies
• Many different RF systems• May also need matched sets of RF separators Π apart in
betatron phase to compensate residual kicks on adjacent bunches
• Easier for Injector• Gun current required = 2.4/h Amps
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 16
Optimum Value of h
• Maximum current in circulator ring 2.4 A• Maximum gun current (majority opinion) 100
mA
• Minimum value of h 24
• Maximum number of turns a bunch stays in circulator ring (emittance growth) 100
• Optimum value of h = 24-100
This proposal seems OK for h up to about 16
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 17
Harmonic Number of Circulator Ring
• If the harmonic number of the circulator ring Hc has no common factors with h, all bunches will be replaced in h turns
• This condition will be maintained if the number of bunches is a sub-harmonic of Hc
• Easiest choice h = 16, and Hc is odd (not divisible by 2)
• Circumference of circulator ring is about 1200 m• Wavelength at 1497 MHz is about 0.2 m
Harmonic number of ring Hc should be about 6000
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 18
Harmonic Number of Circulator Ring (cont)
• Harmonic number Hc should be divisible by many factors
• At a minimum 3, 5, 7 • Hc should be divisible by 105
• Good options are: Hc Circumference(3x5x7)x7x7 = 5145 1031 m• (3x5x7)x3x17 = 5355 1073 m• (3x5x7)x53 = 5565 1115 m(3x5x7)x5x11 = 5775 1157 m• (3x5x7)x3x19 = 5985 1199 m• (3x5x7)x59 = 6195 1241 m• (3x5x7)x61 = 6405 1284 m(3x5x7)x3x3x7 = 6615 1326 m
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 19
Example
• Assume h = 16, Hc = 5775
• Possible bunch spacings• 1, 3, 5, 7, 11, 15, 21, 25, 33, 35, etc
• Linac bunch frequency (MHz)• 1497, 499, 299, 214, 136, 100, 71.3, 59.9, 45.4, 42.8,
etc• Number of bunches in circulator ring
• 5775, 1925, 1155, 825, 525, 385, 275, 231, 175, 165, etc
• All bunches in the ring are replaced every 16 turns
• This layout preserves flexibility for commissioning and operating options
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 20
Summary
• Harmonic RF injection/extraction is a reasonable option up to about h = 16
• To first order, circulating bunches see no net kick• Second order effects come from total cavity length
• If the ring circumference is chosen wisely, there are many options for commissioning using same (or simpler e.g. h = 8) injection/extraction scheme
• Designed around existing CEBAF extraction system with cavities and power sources scaled to different frequencies• Another option might be a single (or a few) non-
resonant structure(s) fed by multiple frequencies simultaneously from a wideband amplifier
• Good topic for engineering design effort