ILC Damping Ring Alternative Lattice Design (Modified FODO)

Transcription

1 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, China 2 State Key Laboratory of Nuclear Physics and Technology, Peking University, China 3 LBNL, USA KEK Damping ring Workshop, KEK December, 2007

2 2 Most important update after Fermi GDE meeting (October 2007) Re-matched the dispersion suppressor and the matching sections between dispersion suppressor and wiggler (injection) sections. Now newest FODO DR lattice can truly be tuned with momentum compaction between 2e-4 and 6e-4, by only tuning the quadrupole s strength, not change any geometry of the ring (dipole strength in the dispersion suppressor do not change).

3 3 THE ADVANTAGE OF FODO LATTICE 1. Smaller number quadrupoles and sextupoles used (roughly two thirds), and lower cost. 2. Freely tunable momentum compaction factor in the range between and Good dynamic aperture. 4. Simpler layout, with only two wiggler sections and cryogenics shaft, no long Transport Line for cryogenics needed.

4 4 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.

5 5 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.

6 6 COMPARISON WITH OCS8 OCS8 ( ) FODO-4 Circumference [ m ] Arc cell TME FODO Phase advance of arc cell 90/90 60/60~90/90 Momentum compaction [ 10-4 ] 4 2~6 Quadrupoles in all Dipoles in all m m Sextupoles in all Number of wiggler straights m

7 ARC CELL DESIGN β ± = L P μ ( 1± sin ) 2 sin μ Yi-Peng Sun et al. φ (1 ± 4sin 1 μ sin ) 2 2 Left: 60/60 cell, corresponding to alpha Left: 90/90 cell, corresponding to alpha D ± = L P 2 μ 2 7

8 DISPERSION SUPPRESSOR DESIGN (90 DEGREE CASE) Select the 90 degree case as the baseline, the bending angle in the dispersion suppressor is set to be half of the bending angle in the normal arc cell, so that zero dispersion at exit is got naturally for 90 degree case. Yi-Peng Sun et al. 8

9 WIGGLER SECTION TOGETHER WITH DISPERSION SUPPRESSOR (72 DEGREE CASE) Tune the quadrupole s strength in the dispersion suppressor for the 72 degree case, to make sure dispersion is free at exit, and dipole strength not changed (Geometry is the same). Yi-Peng Sun et al. 9

10 WIGGLER SECTION TOGETHER WITH DISPERSION SUPPRESSOR (60 DEGREE CASE) Tune the quadrupole s strength in the dispersion suppressor for the 60 degree case, to make sure dispersion is free at exit, and dipole strength not changed (Geometry is the same). Yi-Peng Sun et al. 10

11 11 INJECTION/EXTRACTION DESIGN (90 DEGREE) 2 septums and 21 stripline kickers (lumped kickers) Uses two periodic cells, with the total horizontal phase advance matched to be 180 degree

12 12 CHICANE (90 DEGREE CASE) Adjustment of one Chicane: ± 2θ 2 ( l ) c l B 10-6 adjustable 4 Chicane Emittance +9.2%

13 MOMENTUM COMPACTION 90/90 cell, momentum compaction

14 MOMENTUM COMPACTION 72/72 cell, momentum compaction

15 MOMENTUM COMPACTION 60/60 cell, momentum compaction

16 TOTAL PARAMETERS OF THREE CRITICAL MODES Parameter α P = α P = α P = Circumference [ m ] Harmonic number Energy [ GeV ] Arc cell FODO FODO FODO Tune / / / Natural chromaticity -74 / / / -49 Momentum compaction [ 10-4 ] Transverse damping time [ ms ] 25 / / / 25 Norm. Natural emittance [ mm-mrad ] RF voltage [ MV ] Synchrotron tune Synchrotron phase [ o ] RF frequency [ MHz ] RF acceptance [ % ] Natural bunch length [ mm ] Natural energy spread [ 10-3 ] Yi-Peng Sun et al. 16

17 17 DYNAMIC APERTURE ALPHA CASE The blue line is three times injected positron bunch size. Tracking for 1000 turns, no errors, using MAD.

18 18 FMA ALPHA CASE 50 ILC DR FODO4 lattice, calculated frequency map (NAFF), y position [mm] x position [mm] (injection straight) 10

19 19 DYNAMIC APERTURE ALPHA CASE The blue line is three times injected positron bunch size. Tracking for 1000 turns, no errors, using MAD.

20 20 FMA ALPHA CASE 30 ILC DR FODO4 lattice, calculated frequency map (NAFF), y position [mm] x position [mm] (injection straight) 10

21 21 DYNAMIC APERTURE ALPHA CASE (AT RESULTS) 25 Dynamic Aperture dp/p=0% dp/p=+1% dp/p= 1% 25 Dynamic Aperture dp/p=0% dp/p=+1% dp/p= 1% y[mm] y[mm] x[mm] x[mm] Left: no errors; Right: with high order magnets errors. The blue line is three times injected positron bunch size.

22 22 FMA OPTIMIZATION RESULTS y (mm) Vertical tune x (mm) Horizantal tune FMA is used to optimize the lattice and the DA. The optimized result for momentum compaction mode

23 23 WITH HARMONIC SEXTUPOLES Dynamic Aperture dp/p=0% dp/p=+1% dp/p= 1% Dynamic Aperture dp/p=0% dp/p=+1% dp/p= 1% y[mm] 15 y[mm] x[mm] x[mm] momentum compaction mode, with 3 group harmonic sextupoles Left: no errors; Right: with high order magnets errors

24 24 COMPARISON WITH OCS8 (MAD RESULTS) momentum compaction mode, on momentum particles, without errors; Left: OCS8, Right: FODO-4b The blue line is three times injected positron bunch size.

25 25 OTHERS Element Length [m] Field or Gradient Aperture[m] Pole-tip field[t] Dipole T Quadrupole T/m Sextupole T/m τ e 0 Touschek lifetime: = D( ε) 8πγ 2 r δ 2 3 max cn momentum compaction mode. Energy acceptance 1.48%, bunch population , Touschek lifetime is 160 minutes σ x σ y σ z

26 26 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.

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