1. Accelerator Design of CEPC PDR and APDR Scheme Dou Wang, Jie Gao, Feng Su, Yuan Zhang, Ming Xiao, Yiwei Wang, Bai Sha, Huiping Geng, Tianjian Bian, Na Wang, Zhenchao Liu, Jiyuan Zhai, Xiaohao Cui, Yuanyuan Wei, Qing Qin 所创新项目 CEPC 预研中期进展报告会, June 21, 2016, IHEP

2. Difficulties of CEPC single ring scheme H Z Pre-CDRLow-HOM Number of IPs2 2 2 Energy (GeV) 120 45.5 Circumference (km) 54 SR loss/turn (GeV) 3.1 0.062 N e /bunch (10 11 ) 3.79 1.0 0.13 Bunch number 50 187 4800100 Beam current (mA) 16.6 55.51.1 SR power /beam (MW) 51.7 50 3.450.072 Bending radius (km) 6.1 Momentum compaction (10 -5 ) 3.4  IP x/y (m) 0.8/0.0012 0.06/0.0010.4/0.0012 Emittance x/y (nm) 6.12/0.018 6.13/0.0180.9/0.018 Transverse  IP (um) 69.97/0.1519.2/0.1318.9/0.15  x /IP 0.118 0.031 0.072  y /IP 0.083 0.074 0.028 V RF (GV) 6.87 0.68 f RF (MHz) 650 Nature  z (mm) 2.14 2.13 1.5 Total  z (mm) 2.652.4 1.5 HOM power/cavity (kw) 3.61.0 0.550.01 Energy spread (%) 0.13 0.05 Energy acceptance (%) 2 1.5 Energy acceptance by RF (%) 66.1 4.5 nn 0.23 0.21 0.028 Life time due to beamstrahlung_cal (minute) 47 46 F (hour glass) 0.68 0.66 0.82 L max /IP (10 34 cm -2 s -1 ) 2.04 2.1 1.040.022 2

3. Machine constraints / given parameters Energy E 0 Circumference C 0 N IP Beam power P 0  y * Emittance coupling factor   Bending radius  Piwinski angle   y enhancement by crab waist F l ~1.5 (2.6) Energy acceptance (DA) Phase advance per cell (FODO) 3

4. Constraints for parameter choice  Limit of Beam-beam tune shift  Beam lifetime due to beamstrahlung  Beamstrahlung energy spread  HOM power per cavity F l :  y enhancement by crab waist *J. Gao, emittance growth and beam lifetime limitations due to beam-beam effects in e+e- storage rings, Nucl. Instr. and methods A533 （ 2004 ） p. 270-274. BS life time: 30 min A=  0 /  BS (A  3) V.I. Telnov 4

5. parameter for CEPC partial double ring （ wangdou20160325 ） Pre-CDRH-high lumi.H-low powerWZ Number of IPs22222 Energy (GeV) 120 8045.5 Circumference (km) 54 SR loss/turn (GeV) 3.12.96 0.590.062 Half crossing angle (mrad) 0 15 Piwinski angle 0 2.52.658.5/7.6 N e /bunch (10 11 ) 3.792.852.670.740.46 Bunch number 5067444001100 Beam current (mA) 16.616.910.526.245.4 SR power /beam (MW) 51.75031.215.62.8 Bending radius (km) 6.16.2 6.1 Momentum compaction (10 -5 ) 3.42.52.22.43.5  IP x/y (m) 0.8/0.0012 0.25/0.001360.268 /0.001240.1/0.001 Emittance x/y (nm) 6.12/0.018 2.45/0.00742.06 /0.00621.02/0.0030.62/0.0028 Transverse  IP (um) 69.97/0.1524.8/0.123.5/0.08810.1/0.0567.9/0.053  x /IP 0.1180.030.0320.0080.005/0.006  y /IP 0.0830.11 0.0740.084/0.073 V RF (GV) 6.873.623.530.810.12 f RF (MHz) 650 Nature  z (mm) 2.143.13.03.253.9 Total  z (mm) 2.65 4.14.03.354.0 HOM power/cavity (kw) 3.6 2.21.30.99 Energy spread (%) 0.13 0.090.05 Energy acceptance (%) 222 Energy acceptance by RF (%) 6 2.22.11.71.1 nn 0.230.47 0.30.27/0.24 Life time due to beamstrahlung_cal (minute) 473632 F (hour glass) 0.680.820.810.920.95 L max /IP (10 34 cm -2 s -1 ) 2.042.962.013.093.61/3.09 5

6. Beam-beam simulation Case: H-low power Case Z IBB: Strong-Strong Beam-Beam Code with Beamstrahlung effect Developed by Y. Zhang@IHEP Case: Pre-CDR Case: H-high lum

7. CEPC Higgs luminosity vs. crossing angle

8. CEPC Higgs Luminosity vs beam power 8

9. CEPC PDR Luminosity vs circumference * Fabiola Gianotti, Future Circular ColliderDesign Study, ICFA meeting, J-PARC, 25-2-2016. 9

10. 100km CEPC PDR vs Fcc-ee P HOM,CEPC =11.3 kw The large difference of Z is due to the constraint for RF HOM power. * Fabiola Gianotti, Future Circular ColliderDesign Study, ICFA meeting, J-PARC, 25-2-2016. 10

11. bypass (pp) Advantage: Avoid pretzel orbit Accommodate more bunches at Z/W energy Increase luminosity and reduce beam power with crab waist collision Advantage: Avoid pretzel orbit Accommodate more bunches at Z/W energy Increase luminosity and reduce beam power with crab waist collision 11

12. ARC lattice FODO cell Dispersion Suppressor Sextupole configuration

13. CEPC Partial Double Ring Lattice 13

14. Crab sextupole Critical energy: Ec=190 keV Dipole strength: B=0.019 T Critical energy: Ec=190 keV Dipole strength: B=0.019 T Partial double ring FFS design with crab sextupoles Betax=0.25m Betay=0.00136m K2hs=26.8 m -3 K2vs=32.2 m -3 IP  The second FFS sextupoles of the CCS-Y section work as the crab sextupoles. 14

15. Combine with partial double ring lattice 30 mrad 10 m 15

16. CEPC IR sextupole strength Ec=190keV Ec=100keV

17. DA of the whole ring (arc+PDR+bypass+FFS) Arc sextupole: 2 groups DA (on-momentum): 27  x  57  y DA (  0.5%): 2  x  2  y Crab sextupoles - off 17

18. Magnet field error on DA in CEPC PDR With bend B*L error (whole ring including FFS) μx= 0 μy= 0 Orbit in X With bend B*L error (whole ring including FFS) Orbit in Y With bend B*L error (whole ring including FFS) With bending magnet field errors, horizontal orbit has changed a lot, but vertical has no change Tune has changed to be an integer resonance, beam is not stable. Orbit correction is needed in horizontal Tracking in 240 turns, coupling factor κ=0.003 for ε y Could be cured by adjusting the current during commissioning  Main effect coming from the bending magnet no error

19. Multipole errors effect on DA in CEPC PDR Multipole errors of all magnets Multipole errors of bend Multipole errors of quadurpoles Multipole errors of sextupoles Multipole errors reduce DA a little bit, but not much. It seems to have not much effect on DA, especially of off-momentum DA. Orbit has no change due to multipole errors.

20. CEPC Advanced Partial Double Ring Layout I SU Feng 2016.5.23 IP1_ee IP3_ee IP2_pp IP4_pp 3Km RF 1/2RF RF 1/2RF IP1_ee/IP3_ee, 2.968Km IP2_pp/IP4_pp, 1132.8m APDR, 1052.87m 4 Short Straights, 141.6m 4 Medium Straights, 566.4m 4 Long Straights, 1132.8m 4 ARC1, 124*FODO, 5852.8m 4 ARC2, 24*FODO, 1132.8m 4 ARC3, 79*FODO, 3728.8m 2 ARC4, 24*FODO, 1132.8m C=62967.86m 1/2RF Bypass about 42m ARC1 ARC3 ARC2 ARC3 ARC2 ARC4 ARC1 APDR

21. ARC CEPC Advanced Partial Double Ring Layout II SU Feng 2016.6.2 IP1_ee IP3_ee 3Km 1/2RF IP1_ee/IP3_ee, 2.968Km IP2_pp/IP4_pp, 1132.8m APDR, 1052.87m 4 Short Straights, 94.4m 12 Long Straights, 566.4m 4 Long ARC, 124*FODO, 5852.8m 4 Medium ARC, 104*FODO, 4908.8m 4 Short ARC, 14*FODO, 660.8m C=65640.2m 1/2RF APDR

22. CEPC Advanced Partial Double Ring Optics PDR1 APDR Bypass APDR PDR3 Bypass APDR

23. CEPC APDR SRF considerations The 8-double ring and 6-double ring seem available when using the same parameter as PDR(V RF =3.62GV) for HL. The 8-double ring has a lower phase variation than the 6- double ring. The phase region is from 35.2-33 degree for bunches in a bunch train for the 8-double ring HL mode. The phase region is from 35.2-32.3 degree for the 6-double ring HL mode. The bunch energy gain in each cavity is constant. The RF to beam efficiency is ~100%. The 8-double ring and 6-double ring seem available when using the same parameter as PDR(V RF =3.62GV) for HL. The 8-double ring has a lower phase variation than the 6- double ring. The phase region is from 35.2-33 degree for bunches in a bunch train for the 8-double ring HL mode. The phase region is from 35.2-32.3 degree for the 6-double ring HL mode. The bunch energy gain in each cavity is constant. The RF to beam efficiency is ~100%.

24. 8 double ring APDR(HL V RF =3.62) APDR (H-low power V RF =3.53) APDR (Z) Number of IPs222 Energy (GeV) 120 45.5 Circumference (km) 54 SR loss/turn (GeV) 2.96 0.062 Half crossing angle (mrad) 15 Piwinski angle 2.52.68.5 N e /bunch (10 11 ) 2.852.670.46 Bunch number 17x411x4275x4 Beam current (mA) 1710.545.4 SR power /beam (MW) 5031.22.8 Bending radius (km) 6.2 6.1 V RF (GV) 3.623.530.357/0.12/0.12 f RF (MHz) 650 Cavity No. 384384/768/19248/16/16 Cavity gradient 20.620/20/2016.2/16.3/32.6 Accelerating phase 35.2-3333-31.6/33- 31.6/33-31.6 80.1-79.9/58.9- 56.9/58.9-58 CW power/cavity （ kW ） 260163.3/81.6/326.6117/350/350 Peak power/train (kW) 1389843884 Total Power （ MW ） 100.462.75.6 Cell/cavity 22/1/42/2/1 Cavity/module 66/12/36/2/2 Module/station 88/8/81/1/1 Total module 6464/64/648/8/8 R/Q ( Ω) 206206/103/412206/206/103 G 268 HOM loss factor/cavity (V/pC) 0.540.54/0.27/1.080.54/0.54/0.27 HOM power/cavity (kW) 0.8380.485/0.24/0.970.36/0.36/0.18 Working Temperature （ K ） 222 Q0 2E10 τ （ ms ） 0.8111.2422.243/0.76/0.76 QL 1.656e62.53e64.58e6/1.55e6/1.55e6 Bandwidth(kHz) 0.1960.1280.071/0.209/0.209 Detuning F (kHz) -0.138-0.083-0.234/-0.347/-0.347 Stored energy/cavity(J) 107.410065.3/65.3/133 Frev(kHz) 5.484 Gap length TB (us) 20 η(RF to beam efficiency)(%) ~100 Vc decrease(%) 2.51.61.7/5.3/2.5 TB/τ 0.0250.00980.0089/0.0263/0.0263 8 DR Z mode 8 DR H-Low power mode

25. CEPC full double ring scheme is also under look… (In Feng Su’s talk)

26. MDI layout and issues : single  partial double ring Beam background Shielding design Collimator design SC magnet design Beam pipe Solenoid compensation Lumical & fast lumi measurement & feedback …….. Partial double ring MDI Single ring MDI (In Sha Bai’s talk)

27. CEPC booster design  Wiggling Bend Scheme  Normal Bend Scheme Both design fulfil the requirement toward CDR  For injection, emit of booster@120Gev should be about 3.5E-9 m*rad.  1 percent energy acceptance for enough quantum lifetime.  DA_x and DA_y should bigger than 5~6 sigma for injection. Both design fulfil the requirement toward CDR  For injection, emit of booster@120Gev should be about 3.5E-9 m*rad.  1 percent energy acceptance for enough quantum lifetime.  DA_x and DA_y should bigger than 5~6 sigma for injection.

28. CEPC Injector Emittance.RMS@6GeV= 0.21 mm-mrad 左边为电子枪 + 聚束系统 + 加速段（ 200 MeV ） 右上为电子打靶，能量沉积 右下为正电子收集及加速系统结果

29. International collaboration 1 ）王毅伟 2015 年 10 月 4 日 -11 月 2 日 （ KEK Super-KEK B, Japan) 2 ）边天剑 2016 年 1 月 23 日 ~2016 年 4 月 22 日 (SLAC, USA)) 3 ）苏峰 2016 年 3 月 15 日 -4 月 15 日 (BNL, USA) 4 ）白莎 2016 年 3 月 15 日 -4 月 15 日 (LAL, France) 5 ）赵同宪 2016 年 2 月 22 日 -2016 年 4 月 30 日 (KEK, Japan)

30. summary A consistent calculation method for CEPC parameter choice with carb waist scheme has been created. Larger ring has the potential to reach higher luminosity. Based on partial double ring scheme, we can get higher luminosity (  50% ) keeping Pre-CDR beam power or to reduce the beam power (30 MW) keeping same luminosity. FFS with crab sextupoles and lower emittance arc has been designed. On-momentum DA of whole ring is good enough and the optimization of DA bandwidth is ongoing. Advanced partial double ring scheme has been proposed in order to improve the RF efficiency. 100% efficiency can be achieved. CEPC full double ring scheme is also under look…