CEPC booster and damping ring system Dou Wang
CEPC booster and damping ring system Dou Wang on behalf of CEPC AP group Many Thanks to: K. Oide, M. Koratzinos, N. Iida CEPC international workshop, 18 -20 November, 2019. IHEP, Beijing, China.
Outline Ø Booster progress • Refine of CDR design • Lower emittance booster study • Feedback system design status Ø Damping ring progress • Damping ring • EC / BC 2
CEPC injector chain 100 km Injection energy: 10 Ge. V • 10 Ge. V linac provides electron and positron beams for booster. • Top up injection for collider ring ~ 3% current decay • Booster is in the same tunnel as collider ring, above the collider ring. • Booster has the same geometry as collider ring except for the two IRs. • Booster bypasses the collider ring from the outer side at two IPs. 3
Booster parameters (CDR) 4
Booster optics (CDR) • • • 90 / 90 FODO cell 2 cells @ booster = 3 cells @ collider Noninterleave sextupole scheme • RF FODO cell • IR: booster bypasses the collider. • 25 m separation: Low average beta to reduce the multibunch instability IR - civil engineering - radiation protection - Synchroneity w collider 5
Booster error studies • Gaussian distribution and cut-off at 3σ D. Ji • Relax misalignment error: 50 um 100 um • Relax field error for dipole: 3 10 -4 1 10 -3 Errors Setting Parameters Dipole Quadrupole Sextupole Transverse shift x/y (μm) 100 100 Longitudinal shift z (μm) 100 150 100 Tilt about x/y (mrad) 0. 2 Tilt about z (mrad) 0. 1 0. 2 1 10 -3 2 10 -4 3 10 -4 Tilt (mrad) 10 Gain 5% Nominal field BPM Accuracy (m) 1 10 -7 Offset after BBA(mm) 30 10 -3 6
Dynamic aperture with errors • • With only COD corrections, DA is nearly two thirds of bare lattice At 120 Ge. V, radiative damping and sawtooth was considered. DA requirement @ 10 Ge. V determined by the beam stay clear region DA requirement @ 120 Ge. V: 1) H- quantum lifetime, 2) V- re-injection process from the collider in the on-axis injection scheme DA requirement 10 Ge. V ( x= y =40 nm) 120 Ge. V ( x=3. 57 nm, y= x*0. 005) • DA results H 4 x +5 mm V 4 y +5 mm H 12 x +5 mm V 21 y +5 mm 6 x +3 mm 49 y +3 mm 11. 5 x +3 mm 173 y +3 mm RMS Orbit ~ 180 um, RMS betabeat ~15%, RMS disp. ~29 mm, RMS coupling: <0. 5% 7
Multipole errors @ booster -1 • Reference radius: 27. 5 mm dipole quadrupole • 10 Ge. V sextupole B 2/B 0 2 10 -4 B 2/B 1 5 10 -4 B 3/B 0 2 10 -5 B 3/B 1 1 10 -4 B 3/B 2 2 10 -3 B 4/B 0 8 10 -5 B 4/B 1 1 10 -4 B 4/B 2 3 10 -4 B 5/B 0 2 10 -5 B 5/B 1 1 10 -4 B 5/B 2 2 10 -3 B 6/B 0 8 10 -5 B 6/B 1 5 10 -5 B 6/B 2 3 10 -4 B 7/B 0 2 10 -5 B 7/B 1 5 10 -5 B 7/B 2 2 10 -3 B 8/B 0 8 10 -5 B 8/B 1 5 10 -5 B 8/B 2 3 10 -4 B 9/B 0 2 10 -5 B 9/B 1 5 10 -5 B 9/B 2 2 10 -3 B 10/B 0 8 10 -5 B 10/B 1 5 10 -5 B 10/B 2 3 10 -4 8
Multipole errors @ booster -2 • 10 Ge. V • Reference radius: 27. 5 mm dipole quadrupole sextupole B 2/B 0 5 10 -4 B 2/B 1 5 10 -4 B 3/B 0 2 10 -5 B 3/B 1 1 10 -4 B 3/B 2 2 10 -3 B 4/B 0 1 10 -4 B 4/B 1 1 10 -4 B 4/B 2 3 10 -4 B 5/B 0 2 10 -5 B 5/B 1 1 10 -4 B 5/B 2 2 10 -3 B 6/B 0 1 10 -4 B 6/B 1 5 10 -5 B 6/B 2 3 10 -4 B 7/B 0 2 10 -5 B 7/B 1 5 10 -5 B 7/B 2 2 10 -3 B 8/B 0 1 10 -4 B 8/B 1 5 10 -5 B 8/B 2 3 10 -4 B 9/B 0 2 10 -5 B 9/B 1 5 10 -5 B 9/B 2 2 10 -3 B 10/B 0 1 10 -4 B 10/B 1 5 10 -5 B 10/B 2 3 10 -4 • requirement of field uniformity for low field dipoles :<1 10 -3 9
Dipole reproducibility requirement@10 Gev • Increase/decrease the strength of all the dipoles by the same amount. • Decrease/increase the strength of quadrupoles & sextupoles energy mismatch • Evaluate the influence: working point, closed orbit, DA, energy acceptance • Working point should not pass through the lower order resonance (<4) • No shrink for dynamic aperture • Reproducibility requirement for dipoles: ~0. 02% • Stability requirement for power supply: ~0. 01% original +0. 01% -0. 01% +0. 05% -0. 05% nux 263. 20376 263. 1367 263. 271 262. 868 263. 5397 nuy 261. 21034 261. 1437 261. 277 260. 877 261. 5437 x (um) 0 -54 54 -270 DA (%) 100 100 90 90 10
Power supply stability@120 Gev • Increase/decrease the strength of all the dipoles by the same amount. • Decrease/increase the strength of quadrupoles & sextupoles energy mismatch • Evaluate the influence: working point, closed orbit, DA, energy acceptance • Working point should not pass through the lower order resonance (<4) • No shrink for dynamic aperture • Including SR damping, excitation and sawtooth effect • Stability requirement: ~0. 02% original +0. 01% -0. 01% nux 263. 2038 263. 1366 263. 2710 263. 3381 263. 0695 262. 8680 263. 5397 nuy 261. 2103 261. 1437 261. 2770 261. 3437 261. 0770 260. 8770 261. 5437 x (um) 0 0 0 0 100 100 DA (%) +0. 02% +0. 05% -0. 05% 11
Effect of earthfield @10 Ge. V • ~20% vacuum pipe (drift) is exposed in earthfield directly. • treat drifts as week dipole to simulate the effect of earthfield • Assume earthfield: ~0. 6 gauss, no solution for the close orbit, optics unstable (263. 204, 261. 210) (262. 717, 260. 727) • Without shielding to the bare pipe, the earthfield effect is intolerable. • Global COD correction will be tested. 0. 6 gauss 0. 06 gauss 12
Ramping dynamic simulation • Energy: 10 Ge. V ~ 120 Ge. V by 2. 6 s • Tracking by elegant, w/o error • 360 particles • Linear ramping for magnets • RF ramping curve: s=0. 13 • including SR damping & excitation 13
Reduction the size of beam pipe • use smaller beam pipe thanks to smaller Linac emittance with DR - Emittance of Linac: 120 nm 40 nm - BSC: 4 +5 mm d= 34 mm - Size of beam pipe: 55 mm 44 mm • 44 mm inner diameter is enough for future high lum. Z - Max bunch current potential: 2. 2 u. A - Max beam current potential: 16. 2 m. A - Instability was checked at both 10 Ge. V & 120 Ge. V • Power for magnets and power supply is reduced by ~50% • Cost of power supply is reduced by ~30% 14
eddy current effect • Dedicated ramping curve to control the maximum K 2. • Analytical study was done – deeper understanding about eddy current - New formula created agree with simu. - Dipole w core multipole field - Dipole w/o core No multipole field * • K 2 is one order smaller than before Maximum K 2=0. 000064 (m-3) • Chromaticity distortion is corrected by 2 sext. families during ramping. • Small DA reduction with dynamic chromaticity correction (~10%) * Yuan Chen, et al. , https: //arxiv. org/abs/1910. 09781 15
Lower emittance booster study • off-axis injection for collider (Higgs mode in CDR) can work • on-axis injection for collider (Higgs high lumi. mode) can work • Emittance: 3. 57 nm 1. 29 nm • Coupling requirement: 0. 5% 1. 4% 16
New lattice design based on TME • emittance=1. 29 nm @120 Ge. V • TME lattice dis. supressor • Cell length: 110 m • Interleave sextupole scheme arc cell Straight sec. 17
DA of booster new lattice CDR new • Same DA for on-momentum particles • Two times of off-momentum DA 18
Sawtooth effect @120 Ge. V • • • 2 RF stations Maximum sawtooth orbit: 1. 1 mm Maximum optics distortion: ~1. 5%, Maximum dispersion distortion: ~20 mm Emittance growth: ~1. 7% (1. 288 nm 1. 310 nm) No DA reduction due to sawtooth effect Magnets energy tapering is unnecessary 19
Dynamic aperture w/o errors 120 Ge. V 10 Ge. V ( x= y =40 nm) 120 Ge. V ( x=1. 29 nm, y= x*0. 014) 120 Ge. V DA requirement H V 4 x +5 mm 4 y +5 mm 6 x +3 mm 13 y +3 mm DA results H 14 x +5 mm 9. 4 x +3 mm V 18 y +5 mm 22 y +3 mm 20
Multipole errors for new lattice CDR new • requirement of field uniformity for low field dipoles is harder than CDR lattice • Analyze multipole error effect order by order • DA optimization with errors 21
Booster new parameters Diameter of beam pipe: 44 mm Extraction Injection 22
Geometry design of new lattice • Exact match for three rings -- error= 0. 17 m 23
Multi-bunch instability • Feedback system is essential @10 Ge. V. - Damping time: 90 s - Growth time (T): 3. 1 ms - Growth time (L): 6. 3 ms 24 • tap number always more than 2. • Quick feedback + large ring low order filter
Transverse feedback status J. H. Yue et al. E=10 Ge. V,βm=βk=120 m,Δx=0. 3 mm, τFB =1. 45 ms,so ΔVFB⊥= 9. 27 k. V, P=344 w. • 4 -tap filter was considered • One BPM and One kicker, 90 degree phase shift and DC rejection both are got in FPGA. • 2 amplifiers, 300 W for each 25
Longitudinal feedback status J. H. Yue et al. E=10 Ge. V,α=0. 0000244, νs=0. 1, τFB =50 ms,so ΔVFB|| = 2144 V,P=884 W. 65 • 20 -tap filter was considered • One BPM and One kicker • 90 degree phase shift and DC rejection both are got in FPGA. • 4 amplifiers, 250 W for each 26
Layout of damping ring system RF system (650 MHz) C=75 m E=1. 1 Ge. V RF system (2860 MHZ) RF system (2860/1300 MHz) BC EC 27
DR parameters • Linac repetition: 100 Hz • two-bunch storage scheme • Storage time: 20 ms • Emittance (norm. ): 2500 530 mm. mrad • Large trans. acceptance inj. efficiency 28
DR optics • 60 /60 FODO • interleave sextupole scheme • 2 sextupole families • DA > 5 injection beam size Dis. suppressor Arc FODO RF & Inj. /ext. 29
Impedance threshold Y. D. Liu • BSC: 4 +5 mm d= 33 mm (including dispersion effect) • Size of beam pipe: 44 mm, Al, 2 mm thickness • Circular beam pipe (SR power density=5 W/m) CEPC Super. KEKB 30
CSR threshold • The beam is assumed to be moving in a circle of radius ρ between two parallel plates at locations y=±h • The threshold of bunch population for CSR is given by • For CEPC DR, σzρ1/2/h 3/2=4. 4 (=> CSR shielded) - Inner diameter of beam pipe: 44 mm • The CSR threshold in CEPC DR is Nb, Th = 1. 46× 1011 >> Nb = 9. 36× 109. 31
IBS effect S. K. Tian • • Equilibrium emittance (H/V): 359/18 mm mrad No emittance growth at design bunch current (1. 5 n. C/bunch) IBS threshold: ~100 n. C/bunch IBS is not a concern in CEPC DR. 32
EC/BC parameters EC BC E 0 (Gev) 1. 1 0 (%) 0. 6 0 (%) 0. 05 z 0 (mm) 1. 5 z 0 (mm) 7. 5 f. RF (MHz) 2860/1300 VRF (MV) Length of acc. Structure (m) RF (degree) 22. 0 VRF (MV) Length of acc. Structure (m) RF (degree) 0. 82 89. 7 13. 1/29 0. 48/2. 5 89. 6 R 56 (m) -0. 833 R 56 (m) -1. 4 Ef (Gev) 1. 1 f (%) 0. 18 f (%) 0. 54 zf (mm) 0. 7 zf (mm) 5 33
Beam simulation on transport lines Linac DR (2. 86 GHz) DR Linac (1. 3 GHz) 34
Emittance evolution on transport lines • Dipole strength for the chicane: 0. 49 T • No error included • No emittance growth due to radiation effect Linac DR DR Linac 35
Summary • Booster design in CDR was refined. Become more solid. • A lot of effort to find a new design for booster with lower emittance - Higgs off-axis injection in CDR - Higgs on-axis injection in high lumi. mode • No principle difficulties to use the new booster. Still comprehensive assessment of error effect is necessary. • Both transverse and longitudinal feedback system has substantive progress. • DR system was specified. Key beam parameters can be realized. Error studies on the way.
Thanks for your attention!
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Off-momentum DA of booster (CDR) SAD AT 39
- Slides: 39