ILC Damping Ring Alternative Lattice Design （ Modified FODO ） ** Yi-Peng Sun *,1,2, Jie Gao 1, Zhi-Yu Guo 2 Wei-Shi Wan 3 1 Institute of High Energy Physics, CAS, Beijing 2 State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 3 LBNL, USA CCAST ILC Accelerator Workshop, IHEP, Beijing 6 November, 2007

2 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Layout of ILC

3 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Main timeline OCS2FODO2OCS6FODO3FODO-4 Completed time Quad’s number> <448 Number of wiggler S84(2)422 Alpha (10 -4 )4(2) 2～42～42～62～6

4 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Ilc dr alternative lattice design goals 1.Smaller number quadrupoles and sextupoles used (roughly two thirds), and lower cost. 2.Freely tunable momentum compaction factor in the range between 2×10 -4 and 6× Good dynamic aperture. 4.Simpler layout, with only two wiggler sections and cryogenics shaft.

5 ILC DR Alternative Lattice Design Yi-Peng Sun et al. layout 4 arc sections. 4 straight sections, one for injection, one for extraction, and the other two for RF/wiggler. Two shafts in all and no TL. Beam is counter-rotating.

6 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Considerations for the arc cell Scan some arc cell parameters.  Arc cell number: from 120 to 240.  Arc cell length: from 20 m to 40 m.  The short drift length: from 1 m to 3 m. To get proper dispersion and beta functions at the sextupole location in a cell, suitable maximum beta function (less than 55 m, constrained by vacuum chamber), and freely tunable alpha with different arc cell phase advance. At last, we select the arc cell length to be 29.4 m, and the arc cell number to be 184.

7 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Comparison with ocs8 OCS8 ( )FODO-4 Circumference [ m ] Arc cellTMEFODO Phase advance of arc cell90/9060/60~90/90 Momentum compaction [ ]42~6 Quadrupoles in all Dipoles in all 114 × 6 m ﹢ 12 × 3 m 368 × 2 m Sextupoles in all Number of wiggler straights42

8 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Arc cell design Left: 60/60 cell, corresponding to 6×10 -4 alpha Left: 90/90 cell, corresponding to 2×10 -4 alpha

9 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Dispersion suppressor design Add one arc cell after the last standard arc cell and modify the bending angle of these two cells according to the phase advance. The aim is to have undisturbed TWISS parameters in the dispersion suppressor.

10 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Injection/extraction design 2 septums and 21 stripline kickers (lumped kickers) Uses two periodic cells, with the total horizontal phase advance matched to be 180 degree

11 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Chicane Adjustment of one Chicane: adjustable 4 Chicane Emittance +9.2 ％

12 ILC DR Alternative Lattice Design Yi-Peng Sun et al. 6×10 -4 momentum compaction Dispersion suppressorTotal ring 60/60 cell, 6×10 -4 momentum compaction

13 ILC DR Alternative Lattice Design Yi-Peng Sun et al. 4×10 -4 momentum compaction Dispersion suppressorTotal ring 72/72 cell, 4×10 -4 momentum compaction

14 ILC DR Alternative Lattice Design Yi-Peng Sun et al. 2×10 -4 momentum compaction Dispersion suppressorTotal ring 90/90 cell, 2×10 -4 momentum compaction

15 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Total parameters of three critical modes Parameterα P =2×10 -4 α P =4×10 -4 α P =6×10 -4 Circumference [ m ] Harmonic number14042 Energy [ GeV ]555 Arc cellFODO Tune58.29 / / / Natural chromaticity-74 / / / -46 Momentum compaction [ ]246 Transverse damping time [ ms ]25 / 25 Norm. Natural emittance [ mm-mrad ] RF voltage [ MV ] Synchrotron tune Synchrotron phase [ o ] RF frequency [ MHz ]650 RF acceptance [ % ] Natural bunch length [ mm ]999 Natural energy spread [ ]1.28

16 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Chromaticity correction The chromaticity corrected to (0.3,0.31). The tune variation with momentum spread ±1% is ~1×10 -4

17 ILC DR Alternative Lattice Design Yi-Peng Sun et al. High order magnets errors Dipole (1×10 -4 )Quadrupole (1×10 -4 )Sextupole (1×10 -4 ) Radius30mm Error typeSysRanΦ (°)SysRanΦ (°)SysRanΦ (°) * Sys: system error; Ran: random error

18 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Dynamic aperture 6×10 -4 alpha case Left: no errors; Right: with high order magnets errors

19 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Dynamic aperture 4×10 -4 alpha case Left: no errors; Right: with high order magnets errors

20 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Dynamic aperture 2×10 -4 alpha case Left: no errors; Right: with high order magnets errors

21 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Comparison with ocs8 (PAC07) 4×10 -4 momentum compaction mode, on momentum particles, with errors; Left: OCS8 (PAC07), Right: FODO-4

22 ILC DR Alternative Lattice Design Yi-Peng Sun et al. FMA optimization results FMA is used to optimize the lattice and the DA. The optimized result for 2×10 -4 momentum compaction mode

23 ILC DR Alternative Lattice Design Yi-Peng Sun et al. With harmonic sextupoles 2×10 -4 momentum compaction mode, with 3 group harmonic sextupoles Left: no errors; Right: with high order magnets errors

24 ILC DR Alternative Lattice Design Yi-Peng Sun et al. SCAN FOR THE HARMONIC SEXTUPOLES AND TUNES The full scan is still on-going now.

25 ILC DR Alternative Lattice Design Yi-Peng Sun et al. others Touschek lifetime: 4×10 -4 momentum compaction mode. Energy acceptance 1.48%, bunch population 2×10 10, Touschek lifetime is 160 minutes ElementLength [m]Field or GradientAperture[m]Pole-tip field[T] Dipole T Quadrupole0.310 T/m Sextupole T/m

26 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Several slides from Andy Wolski on Fermi GDE Meetings.

27 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Possible “alternative” FODO lattice injection extraction Yi-Peng Sun (IHEP) Jie Gao (IHEP)

28 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Possible “alternative” FODO lattice Potential advantages of the FODO alternative include: improved flexibility, from the ability to vary the momentum compaction factor (can play off bunch length against instability thresholds); improved performance, from increased dynamic aperture; reduced cost, from reduced number of magnets. The OCS8 lattice is more mature, and the engineering design studies are more likely to proceed smoothly if based on this lattice. A systematic comparison is needed to decide whether the potential benefits of the FODO lattice could be realised in practice. Comparative studies of the OCS8 and FODO lattice are planned, and a decision on the lattice will be made by the end of 2007.

29 ILC DR Alternative Lattice Design Yi-Peng Sun et al. Acknowledgement Thanks to A. Xiao and L. Emery et al. in ANL who designed the RF/wiggler sections. Many thanks to Prof. M. Zisman for his kind suggestions and help. Also thanks Prof. Cai of SLAC for his help.

30 ILC DR Alternative Lattice Design Yi-Peng Sun et al.