Overview of SuperKEKB

M. Tawada (KEK)

Super B Factory Workshop in Hawaii

April 20, 2005

Contents

• Strategy• Machine Parameters• Beam-beam simulations• Lattice design• Interaction region• Magnet system• Impedance and collective effects• RF system • Vacuum system• Beam instrumentation• Injector & damping ring• Construction scenario• Summary

€

L =γ e±

2ere1+σ y

*

σ x*

⎛

⎝ ⎜

⎞

⎠ ⎟Ie±ξ y

e±

β y*

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟RLRξ y

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

Beam size ratio@IP1 ~ 2 % (flat beam)

Beam currentBeam-beam parameter

Vertical beta function@IP

Ratio of luminosity &tune shift reductionfactors: 0.8 ~ 1(short bunch)

Lorentzfactor

Classical electronradius

Strategy

Increase beam currents•1.7 A (LER) / 1.3 A (HER) → 9.4 A (LER) / 4.1 A (HER)

Smaller y*/ Shorter z

•6 mm→3 mm / 5mm →3 mm

Increase y

•0.05→0.187

Lattice Parameters and Beam-Beam Effectbare lattice with beam-beam unit

Beam current (LER/HER) I 9.4/4.1 9.4/4.1 A

Beam energy (LER/HER) E 3.5/8.0 3.5/8.0 GeV

Emittance x 24 128 nm

Horizontal beta at IP x* 20 2.3 cm

Vertical beta at IP y* 3 2.4 mm

Horizontal beam size x* 69 54 m

Vertical beam size y* 0.73 1.23 m

Beam size ratio r = y*/x

* 1.1 2.3 %

Crossing angle (30 mrad crab crossing)

x 0 0 mrad

Luminosity reduction RL 0.86 0.82

x reduction Rx 0.99 0.97

y reduction Ry 1.11 1.16

Reduction ratio RL/Ry 0.78 0.72

Horizontal beam-beam

(estimated with S-S simulation)x 0.152 0.041

Vertical beam-beam

(estimated with S-S simulation)y 0.215 0.187

Luminosity L 4.0 x 1035 cm-2s-1

8GeVPositron beam4.1 A

3.5GeVElectron beam9.6 A

0.15

0.10

0.05

0.002.01.51.00.50.0

I+ (mA)

(b)0 mrad

11 mrad

Beam-beam limit

• Beam-beam parameter of 0.05 has been already achieved with a finite crossing angle at KEKB.

• Beam-beam simulation say: – Head-on collision improve the bea

m-beam parameter.

Crab crossing scheme

Head-onCrab-crossing

Crab crossing scheme restores the full luminosity of head-on collision.

Crab cavity will be tested at the current KEKB machine in 2006.

Beam-beam simulation

Tune Survey in SuperKEKBwithout parasitic collision effect.

Lpeak=4.0x1035cm-2s-1 (L/bunch=8.0X1031, Nb=5000)

0.60

0.58

0.56

0.54

0.52

0.5200.5150.5100.5050.500νx

5e+31

1.5e+31

1.5e+31 1e+31

1e+31

5e+30

Talk by Ohmi

Lattice Design: the arc section

The beam-optical parameters can be adjusted to SuperKEKB without changing the lattice in the arc section.

KEKB lattice: 2.5pi cell and non-interleaved chromaticity correction scheme.Wide tunability of horizontal emittance, momentum compaction factor. Principle nonlinearities in sextupole pairs cancelled out to give large dynamic aperture

Talk by Koiso

Dynamic aperture issue

• Dynamic aperture of SuperLER with beam-beam effects.

• Tracking simulation is "Weak-Strong".

• Small difference between no beam-beam and y=0.07.

• Case y=0.14, dynamic aperture slightly shrinks.

• Touschek lifetime:

– 50 min (no beam-beam)

– 45 min (y= 0.14)

p/p0 (%)

2J x

(m

)

2Jy/2Jx=1%

νx/νy=45.51/43.545 No beam-beam

y=0.07

y=0.14

* no damping / 1000 turns* no machine error

IR design layout

QCSRQCSLQC2RP

QC2LP

QC2LE

QC2RE

QC1RE

QC1LELERbeam

HERbeam

• Move QCSs, QC1s, QC2s closer to IP.• QCS and compensation solenoid magnets overlap in SuperKEKB.• Full crossing angle 30 mrad.• Rotate LER beam 8 mrad.

IR magnet design issue -> Talk by Ohuchi

Issues for IR design• QC1 magnet - Normal or Superconducting• Strong synchrotron light from QCS• Dynamic aperture with high beam-beam parameter• Background to Belle

Since we change working point near the half integer tune, IR need to be re-designed.

IR Vacuum design issues

• Strong SR from QCS magnets.– SR power: 194 kW in HER & 78 kW in LER– Large aperture is needed at QC2 magnets in order to avoid SR s

ince two beams and the SR don’t lie in the same plane.– Should provide sufficient cooling to every SR irradiation.

• Intense HOM power– Extrapolation from KEKB gives a heat by HOM about 100kW*(bu

nch length factor).– The cooling of HOM will be a big problem.– Compact HOM absorber will be needed.

• Denser Distribution of vacuum pumps to need to reduce the beam background.– The space for the pump must be reserved in the magnet.

Beam duct layout Left hand side (1)

SR:65kW

•Flange connection in the bore of QCS-L (magic flange).•The ducts of LER from QCSL to QC2LP escape SR.•LER downstream ducts avoid SR down to 5m from IP.

BM:Beam Position Monitor, BL:Bellows

Beam ductsSeparatez=1.5m from IP.

LERLER ducts avoid SR.

Magicflange

IP

Beam duct layout Right hand side (1)

SR:179 kW

•In HER , all ducts are expected to avoid SR.•The BPM at the end of the QCS chamber is possible only if the electrodes clear the inner bore of QCSR.•HER downstream ducts avoid SR down to 8m from IP(?).

HER

LER

BM:Beam Position Monitor, BL:Bellows

Beam ductsSeparatez=1.5m from IP.

Manageablein installation ?

HER ducts avoid SR

IP

Magnet　 System

• Outside of the IR, most of the present KEKB magnets will be reused.

• Some magnets for Nikko RF section and ante-chamber section will have to be newly designed and fabricated.

• Half of the wiggler magnets will be removed due to add RF cavities to Oho straight section. Damping time in LER will be 1.5 times larger.

Magnet Number Location

Big bore radius HER Quad

20 Nikko

LER-Quad 2 Oho

Sextupole 49 Arc

Wide gap steering 450 Arc & Tsukuba

Impedance and Collective Effects

• Resistive Wall Instability– Growth rates (800-1000 s-1) <damping rate of feedback system (5000 s-1).

• Closed Orbit Instability due to long-range resistive wake (Danilov)– Thresholds (12.3/12.2 A for LER/HER) > design currents

• Electron Cloud Instability (Positron Ring)– With ante-chambers and positrons in the HER, simulations show that 60G

solenoid field should clear the electrons. Uncertainties:

• Distribution on walls and amounts of electrons.• Behavior of electrons inside lattice magnets.

• Ion Instability (Electron Ring)– Currently suppressed by feedback.– With electrons in LER, simulated initial growth rate faster than feedback da

mping rate, leading to dipole oscillation with amplitude of order of vertical beam size →possible loss of luminosity.

• Coherent Synchrotron Radiation– Investigations under way.

Coherent synchrotron radiation• CSR cause the energy spread and instability because of (1) sh

orter bunch length, (2) higher bunch current and (3) small bending radius.

• Dr. Agoh has developed new method to estimate CSR with shielding effect by vacuum chamber.

• Simulation shows – CSR affects SuperLER seriously.

– CSR can be suppressed by smaller vacuum chamber.

• Investigation with the other impedances is in progress.

Talk by Agoh

Vacuum system

• High beam current and shorter bunch length causes:– Heating due to intense synchrotron radiation.

• 28 kW/m in LER, twice as high as in KEKB• 22 kW/m in HER, 4 times as high as in KEKB

– High gas load• Need higher pumping speed.

– High photoelectron yield• -> Ante-chamber• -> Surface coating with low SEY materials• -> Solenoid field

– Heating due to intense HOM power• Minimize loss factor for each vacuum components• HOM absorbers to be installed near large impedance sources.

– High wall current• peak: 250A (z=3mm)

Talk by Suetsugu

Ante-chamber R&D

Electrons in the beam channelPhotoelectrons decreased by factors at high current

(Ib >1 000 mA).The reduction was by orders at low current (Ib <100

mA).Multipactoring seems to become important at highe

r current.Combination with solenoid field, and an inner surf

ace with a low SEY will be required at higher current.

Prototype ducts were installed in the LER (Jan.2004)

[Electron Monitor]

Smaller SR Power DensityLower ImpedanceLower photoelectron production

Bellows chamber with comb type RF-shield

Two circular bellows chamber was installed in LER two years ago.

Good results were obtained.Temperature decreased to <1/6Temperature of comb ~ 50 C at 1.6 ANo damage after 1.5 year operation

High thermal strength Low impedance No sliding contact on the surface facing the beam

Vacuum parameters (HOM related) for SuperKEKB

Loss factor (V/C)

Length or# of components

Total (V/C)

HOM power(kW)

Resistive wall 4.1109 2200 m 8.91012 1780

Pumping holes 8.8105 2200 m 1.9109 0.38

Flanges 1108 800 81010 16

Bellows 4109 800 3.21012 640

Photon mask 1104 800 8106 0.0016

Gate Valve 3109 16 4.81010 9.6

Movable mask 11012 16 1.61013 3200

Taper 3109 72 2.21011 44

HOM dampers to be installed.

RF system upgrade• To handle a much higher current and shorter bunch length, upgr

ade of RF system will be needed.

• Adopt the same RF frequency of 508MHz as KEKB.– Save the construction cost and time.– Technical uncertainties would be relatively small.

• Use ARES+SCC for HER and ARES for LER.

• The number of RF unit will be doubled.– ARES(LER) : 10 → 28

– ARES(HER) : 6 → 16

– SCC(HER) : 8 → 12

ARES upgrade

• Increase stored energy– By enlarging the coupling hole between the A-C cavities, incr

ease energy ratio Us/Ua = 9 → 15.– One klystron feed RF power to one ARES cavity.

• HOM load issues– Upgrade of HOM damper:26 → 80 kW/cavity.

• Input coupler– 400 kW/cavity → 800 kW/cavity. – TiN coated coupler have been completed and being tested i

n the new test-stand up to 800 kW (CW).• Longitudinal coupled bunch instability due to the ARES cavities

must be cured by bunch-by-bunch feedback system.

Talk by Kageyama

Superconducting Cavity

• Add 4 cavities for HER• In SuperKEKB, HOM power of 60kW/cavity at 4.1 A has to be absorbed.

– c.f. In KEKB, the current HOM power is only 15 kW/cavity at 1.2A.

• HOM damper upgrade is needed.

Talk by Mitsunobu

Two different types based on different methods to damp the accelerating mode (Lower Frequency Mode).

(1) Coaxial couplers Type (2) Waveguide damper Type

Waveguide damper for the LFM

Additional waveguide damperNotch filter

Coaxial coupler

Notch filter

Additional waveguide damper

Crab Cavity for SuperKEKB•A new type crab cavity will be needed, which can be used at 10 A.

Beam Position Monitors

• Front-end electronics– Use same 1GHz detector for normal c

hamber.– Need to develop the 508MHz detector

and up-converter for ante-chamber to avoid HOM contamination of pick-up signals.

• New button electrodes– Developing the new button electrodes.– 12 mm -> 6 mm diameter

• Signal power same as at present, at higher beam currents, to match dynamic range of existing front-end electronics.

– Use low permittivity ceramic to reduce HOM.

SMA connector with male contact pin

Flange mounted

Small diameter electrode

Talk by Flanagan

Synchrotron radiation monitors

• Current extraction chamber (copper) may need increased cooling.

• HOM leakage power will be 500 W.• May need HOM absorbers

• Direct mirror heating from SR irradiation should be minimized.• Increase bend radius of weak bends

• Lowers total incident power.• Also increases visible light flux – desirable to help see eff

ect of single crab cavity

Talk by Flanagan

Bunch-by-Bunch Feedback

• Transverse feedback similar to the present design– Detection frequency 2.0 -> 2.5 GHz.– Transverse kicker needs work to handle higher currents– Improved cooling, supports for kicker plates.

• Longitudinal feedback to cure ARES HOM and 0/Pi mode instability– Use DAfNE-type (low-Q cavity) kicker.

• Digital FIR and memory board to be replaced by new GBoard under development at/with SLAC.– Low noise, high speed (1.5 GHz), with custom filtering functions po

ssible.– Extensive beam diagnostics.

Talk by Flanagan

Injector upgrade

Intensity upgrade e-: increase bunch current. e+: improve capture efficiency by improving pulse coil.

Energy upgrade for e+ • Boosted by the C-band accelerator modules.• Field gradient 21 42 MV/m

Smaller e+ emittance for IR & C-band module aperture.• e+ damping ring

Faster e+ / e- switching for continuous injection• switched by the kicker before the target.• e+ and e- go through independent beam lines.

Talk by Furukawa

C-band

1.8 ｍ

Inverter DC PS

C-band sectionS-band section

RF compressor - SLED type (TE038). - 200 MW output power is achieved at Test Stand. - Multiplication factor: 4.7 times at peak.

C-band modulator & klystron - Some problems of DC PS were fixed. - No trouble since Sep. 2004.

Mix-mode RF window - TE11 +TM11 - 300MW transmission power is achieved.

Prototype of C-band - Field gradient 42MV/m with RF compressor.

Damping ring

• Positron emittance needs to be damped to pass reduced aperture of C-band section and to meet IR dynamic aperture restrictions.– Electron DR may be considered later to reduce injection backgroun

ds in physics, but for now only DR considered.

• To reduce beam background to Belle– Injected beam charge is doubled– Needed damped beam for smaller energy-tail and emittance tail.

• Damping ring located downstream of positron target, before C-band accelerating section.

0 50 m

Positron targetSector-2 Sector-3

LTR-line(ECS)

RTL-line(BCS)

1-GeV Damping Ring

C-band acc. section

Damping ring parameters

RF: Use KEKB ARES cavity (509 MHZ)

Damping Ring Lattice

• FODO cell has large dynamic aperture, but large momentum compaction factor increases required accelerating voltage.

• Reversing one of the bends reduces the momentum compaction factor.

• Adopt reverse/forward ratio of ~1/3

Dynamic apertureGreen = injected beam, red = 4000 turns max deviation (thick = ideal machine, thin = machine errors included)

FODO cell w/alternating bends

Large dynamic apertureWide operational tune space

Facility

KEKB(design) SuperKEKB Unit

Magnet PS 3.84 3.84 MW

Magnet 6.35 6.35 MW

SR 8 26 MW

HOM 0.43 9 MW

RF system 16 38 MW

Total 34.6 83.2 MW

Total site consumption power : 120MW

Construction schedule

2004 05 06 07 08 09 10 11 12

KEKB S-KEKBshutdown

constructionJ-PARC 1 construction ILC construction

1000fb-1

Calendar year

Crab cavity

“Minor” upgrade “Major” upgradeBelle

KEKB

Budget

Budget

Summary

• SuperKEKB is a quite challenging.• Target luminosity is 4.0x1035cm-2s-1, a new lu

minosity frontier.• There are many issues due to the very high b

eam current and short bunch length.• Further simulation and hardware R&D work to

ward SuperKEKB are on-going.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Beam-beam simulationParasitic collision effect for KEKB

s

x

electronspositrons

Crossing angle22mrad

w/o parasitic(KEKB)

w/ parasitic(KEKB) 4 backet spacing

Parasitic collision - Long range beam-beam force - Beam-beam separation: 6.6 mm(KEKB, 22mrad) 9.0 mm (SuperKEKB, 30mrad) - Luminosity degradation is negligible if good working point are chosen .

simulation study is in progress

Parasitic collision

Crab cavity

s

x

electronspositrons

Crossing angle30mrad

w/o Crab cavity

w/ Crab cavity

Crab cavity effectively creates head-on collision.

It can improve the luminosity.

Crab cavity for KEKB will be installed in Nikko straight section in Jan. 2006.

Because of high HOM power to dampers, another type of crab cavity in Super KEKB will be necessarily.

0.15

0.10

0.05

0.002.01.51.00.50.0

I+ (mA)

(b)0 mrad

11 mrad

IR Vacuum design issues

50 100 150 200

20

40

-20

-40

250 300 350 400 450 500 550 600-50-100

330 530

300

QC2RE

QC2 design should be checked against the fact that the two beams and the SR don’t lie in the same plane.

SR fans from QCSR