CEPC partial double ring scheme and crabwaist parameters
CEPC partial double ring scheme and crab-waist parameters Dou Wang, Jie Gao, Feng Su, Ming Xiao, Yuan Zhang, Jiyuan Zhai, Yiwei Wang, Bai Sha, Huiping Geng, Tianjian Bian, Xiaohao Cui, Yuanyuan Guo 1 st IHEP-BINP CEPC Accelerator Collaboration Workshop, Jan 12 -13, 2016. IHEP
Advantage: bypass (pp) • Avoid pretzel orbit • Accommodate more bunches at Z/W energy • Reduce AC power with crab waist collision bypass (pp)
Machine constraints / given parameters • • • Energy E 0 Circumference C 0 NIP Beam power P 0 y* Emittance coupling factor Bending radius Piwinski angle y enhancement by crab waist Fl ~1. 5 Energy acceptance (DA) Phase advance per cell (FODO)
Constraints for parameter choice Ø Limit of Beam-beam tune shift Fl: y enhancement by crab waist Ø Beam lifetime due to beamstrahlung BS life time: 30 min V. I. Telnov Ø Beamstrahlung energy spread A= 0/ BS (A 3) Ø HOM power per cavity *J. Gao, emittance growth and beam lifetime limitations due to beam-beam effects in e+e- storage rings, Nucl. Instr. and methods A 533(2004)p. 270 -274.
Parameter choice – step 1 Beam-beam limit: Fl: y enhancement by crab waist, ~ 1. 5.
Parameter choice – step 2
Parameter choice – step 3 BS life time: 30 min y: -- phase advance/cell, -- bending angle/cell. Estimate :
Parameter choice – step 4
Parameter choice – step 5 Effective bunch length: overlap area of colliding bunches Hour glass effect:
Parameter choice – step 6 Vrf , s Energy acceptance from RF:
Parameter choice – step 7 Ø Beam lifetime due to radiative Bhabha scattering Ø Beam lifetime due to Beamstrahlung Ø HOM power per cavity HOM loss factor: *V. I. Telnov, "Issues with current designs for e+e- and gamma colliders“, Po. S Photon 2013 (2013) 070. https: //inspirehep. net/record/1298149/files/Photon%202013_070. pdf
Primary parameter for CEPC double ring Number of IPs Energy (Ge. V) Circumference (km) SR loss/turn (Ge. V) Half crossing angle (mrad) Piwinski angle Ne/bunch (1011) Bunch number Beam current (m. A) SR power /beam (MW) Bending radius (km) Momentum compaction (10 -5) IP x/y (m) Emittance x/y (nm) Transverse IP (um) x/IP y/IP VRF (GV) f RF (MHz) Nature z (mm) Total z (mm) HOM power/cavity (kw) Energy spread (%) Energy acceptance by RF (%) n Life time due to beamstrahlung_cal (minute) F (hour glass) Lmax/IP (1034 cm-2 s-1) Pre-CDR H-high lumi. H-low power Z 2 120 54 3. 1 0 0 3. 79 50 16. 6 51. 7 6. 1 3. 4 0. 8/0. 0012 6. 12/0. 018 69. 97/0. 15 0. 118 0. 083 6. 87 650 2. 14 2. 65 3. 6 0. 13 2 6 0. 23 47 2 120 54 2. 96 14. 5 2 3. 79 50 16. 9 50 6. 2 3. 0 0. 306/0. 0012 3. 34/0. 01 32/0. 11 0. 04 0. 11 3. 7 650 3. 3 4. 4 3. 3 0. 13 2 2. 2 0. 49 53 8. 9 3. 1 1. 32 144 16. 9 50 6. 2 2. 3 0. 058/0. 0016 2. 32/0. 0058 11. 6/0. 097 0. 01 0. 11 3. 6 650 3. 0 4. 0 1. 0 0. 13 2 2. 2 0. 46 32 11. 5 2 2. 81 40 10. 1 30 6. 2 2. 6 0. 22/0. 001 2. 67/0. 008 24. 3/0. 09 0. 04 0. 11 3. 6 650 3. 2 4. 2 1. 5 0. 13 2 2. 2 0. 47 41 8. 7 2 2. 0 57 10. 1 30 6. 2 2. 5 0. 115/0. 001 2. 56/0. 0078 17. 6/0. 088 0. 028 0. 11 3. 7 650 3. 0 4. 0 0. 95 0. 13 2 2. 4 0. 46 32 2 45. 5 54 0. 062 16. 5 2. 6 0. 37 1100 36. 2 2. 2 6. 1 5. 4 0. 3/0. 001 1. 18/0. 0069 18. 8/0. 083 0. 02 0. 042 0. 28 650 3. 0 0. 73 0. 05 0. 68 2. 04 0. 73 2. 97 0. 89 2. 75 0. 69 2. 03 0. 7 2. 0 0. 08 0. 83 1. 25
CEPC single ring parameter H Number of IPs Energy (Ge. V) Circumference (km) SR loss/turn (Ge. V) Ne/bunch (1011) Bunch number Beam current (m. A) SR power /beam (MW) Bending radius (km) Momentum compaction (10 -5) IP x/y (m) Emittance x/y (nm) Transverse IP (um) x/IP y/IP VRF (GV) f RF (MHz) Nature z (mm) Total z (mm) HOM power/cavity (kw) Energy spread (%) Energy acceptance by RF (%) n Life time due to beamstrahlung_cal (minute) F (hour glass) Lmax/IP (1034 cm-2 s-1) Z Pre-CDR Low-HOM 2 120 54 3. 1 3. 79 50 16. 6 51. 7 6. 1 3. 4 0. 8/0. 0012 6. 12/0. 018 69. 97/0. 15 0. 118 0. 083 6. 87 650 2. 14 2. 65 3. 6 0. 13 2 6 0. 23 47 2 120 54 3. 1 1. 0 187 16. 6 50 6. 1 3. 4 0. 06/0. 001 6. 13/0. 018 19. 2/0. 13 0. 031 0. 074 6. 87 650 2. 13 2. 4 1. 0 0. 13 1. 5 6. 1 0. 21 46 2 45. 5 54 0. 062 0. 13 4800 55. 5 3. 45 6. 1 3. 4 0. 4/0. 0012 0. 9/0. 018 18. 9/0. 15 0. 072 0. 028 0. 68 650 1. 5 0. 55 0. 05 0. 68 2. 04 0. 66 2. 1 0. 82 1. 04 4. 5 0. 028
CEPC Partial Double Ring Lattice
Double ring FFS design with crab sextupoles Betax=0. 8 m Betay=0. 003 m IP Crab sextupole Critical energy: Ec=100 ke. V Dipole strength: B=0. 01 T L*=1. 5 m L(QD 0)=0. 91 m, G(QD 0)=-300 T/m L(QF 1)=0. 74 m, G(QF 1)=106 T/m L 0=4 m Ø As Oide said, the second FFS sextupoles of the CCS-Y section can work as the crab sextupoles, if their strengths and phases to the IP are properly chosen.
Crab sextupole strength x=2 , y=2. 5 Ø The crab sextupole should be placed on both sides of the IP in phase with the IP in the horizontal plane and at π/2 in the vertical one.
Combine with partial double ring lattice FFS orbit
Arc redesign-lower emittance Ø Length of FODO cell: 47. 2 m Ø Phase advance of FODO cells: 60/60 degrees Ø Emittance: 7. 9 nm, p=5. 38 E-5 Ø Bunch length: 2. 3 mm Ø Length of FODO cell: 37. 5 m Ø Phase advance of FODO cells: 60/60 degrees Ø Emittance: 4. 3 nm , p=2. 25 E-5 Ø Bunch length: 3. 3 mm
Arc redesign-ultra low emittance Ø Length of FODO cell: 37. 5 m Ø Phase advance of FODO cells: 90/60 degrees Ø Emittance: 2. 3 nm, p=1. 07 E-5 Ø Bunch length: 3. 3 mm B 0 Ø Dispersion supressor: Angle(BDIS 1)=3. 583724 E-03 Angle(BDIS 2)=-8. 598108 E-04 Angle(B 0)=2. 723923 E-03 BDIS 1 BDIS 2
summary • A consistent calculation method for CEPC parameter choice with carb waist scheme has been created. • 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. • Based on partial double ring scheme, we get a set of Z parameter with 1. 25*1034 cm-2 s-1 luminosity using 1100 bunches. • CEPC single ring scheme is neither easy to reduce cavity HOM power for Higgs nor to accommodate more bunches for Z. • FFS with crab sextupoles and lower emittance arc has been designed. DA optimization is undergoing.
THANKS!
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