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Collimation Simulations and Optimisation

Collimation Simulations and Optimisation. Frank Jackson ASTeC, Daresbury Laboratory. Contents. Collimation design (like BDS) lead by SLAC/FERMILAB Areas of input – collimation depths and collimation optimisation. Collimation Depths For recent and current BDS designs.

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Collimation Simulations and Optimisation

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  1. Collimation Simulations and Optimisation Frank Jackson ASTeC, Daresbury Laboratory

  2. Contents • Collimation design (like BDS) lead by SLAC/FERMILAB • Areas of input – collimation depths and collimation optimisation. • Collimation Depths • For recent and current BDS designs. • BDSIM cross check (off energy calculation) • Collimation Optimisation and Halo Tracking • Method and History • Latest results 2006e

  3. Collimation Depths Overview LDC small xing angle • Criteria, clean passage of halo SR through IR apertures • Beamcal and extraction quads are limiting apertures • Many complicating factors • Multiple crossing angle 20,14,2,0 mrad • Multiple detector designs, L* • IP Parameter Sets (Nominal only here, as in BDS design)

  4. BCD (2005) Collimation Depths • Used original NAPOLY DBLT SR fan tracing code • Linear, on-energy optics, head-on • Play tricks for crossing angle situations. • 20 and 2 mrad was baseline, similar depths

  5. New BDS for RDR • 14 mrad approved after Vancouver, now likely to become single IR • Identical FD to 20 mrad but different IR design 14 mrad 20 mrad 2006”c”

  6. BDSIM cross check for 2006c • DBLT is linear on-energy envelope tracking • BDSIM can track off-energy halo through FD SR profile at 1st Extraction Quad (r=18mm) p=1%, Gaussian On-energy, p=1% Gaussian

  7. Alternative BDS • Head-on re-emerged as small-angle alternative

  8. Other Parameter Sets? • Rough estimation possible • Smaller IP beam size  larger IP angles • Wider SR fan  tighter collimation • Example: high lumi parameters • Beamsize ~2 smaller than nominal • Collimation ~2 tighter

  9. Collimation depths ideas for further work/collaborations • The real RDR deck, 2006”e” incorporates reoptimisation of extraction quad apertures, need to check collimation depth • All collimation depths assume ideal criteria clean SR passage • Tolerances never really studied • BDSIM/detector interface for effects of non-clean SR passage.

  10. Collimation Optimisation • Some history from pre-ILC days • NLC and TESLA collimation efficiency compared in TRC report. • NLC rather good collimation efficiency • ILC evolved from NLC • Survivable betatron spoiler optics • Collimation performance poorer. Tighter apertures in y. SPEX as secondary betatron spoiler. • Can we tweak ILC lattice to restore NLC performance?

  11. More History and Basic Design • ILC BDS gone through multiple revisions since 2005 • But none have specifically addressed collimation optimisation • Latest 2006e deck is for minimised length/cost • PHASE ADVANCES not perfect for any design • BANDWIDTH through final doublet not well controlled for any design

  12. 2006e Collimation Features • 2 spoilers /2 apart, energy spoiler • Phase advances not exact • Does not deliver nominal performance, even on-energy • Mitigate by aperture tightening (SPEX as betatron spoiler!) SP2 SPEX SP4 x= 0.38 y=0.59 x= 2.76 y=2.34 1.00 2

  13. 2006e Bandwidth • Bandwidth figure of merit: Twiss  vs. E at IP 2006e NLC

  14. Optimisation Strategy • Work done in 2006 • Advice and tools from A. Seryi and M. Woodley • Restore phase advances between SP4,SPEX,IP • Optimise Bandwidth • MAD fitting driven by optimisation routine

  15. EPAC 2006 Results • Starting with ‘FF9’ BDS • Used explicit matching section 7 quads and 1 drift length • Constrain Twiss at SP4 and phase advances SP4-IP • No constraint on bandwidth • Multiple solutions obtained, best bandwidth chosen x,y=n/2

  16. EPAC 2006 Results Halo (p=1%) Tracking to FD entrance • Collimation performance checked by halo tracking in MERLIN • ‘Black spoilers’ no secondaries • Some improvement clear from phase restoration and bandwidth optimisation • Design performance only delivered by spoiler tightening Original FF9 Performance New Performance

  17. 2006e Latest Work SPEX optimisation • Use 4 quads + 2 drift lengths at end of betatron section match phase SP4/SPEX • Then repeat IP-SP4 matching as before, optimising bandwidth • Able to achieve matched solution with promising bandwidth

  18. 2006e Optimised Performance Tracking Results • Several simulation parameters here different to EPAC06 • Halo distribution and population • Improved performance, suggest no longer need vertical SPEX collimator Original 2006e Performance New Performance Same population in both halos at FD

  19. NLC 2006e Optimised Features • Bandwidth • Phase advances 2006e optimised

  20. 2006e Optics Original Optimised Optimised 26m longer (single BDS)

  21. Conclusions • Optimised lattice performance seems much improved for primary halo tracking • Full simulation (secondaries) and losses along line needed • BDSIM/STRUCT • Lattice longer/costlier so ultimately this optimisation may not be feasible. • Additional quads rather than longer length?

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