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Collimation Depths and Performance for 2mrad and 20mrad

Collimation Depths and Performance for 2mrad and 20mrad. Frank Jackson ASTeC Daresbury Laboratory. Contents. A method of estimating collimation depths for current ILC-BDS designs Semi-analytical procedure Evaluated collimation depth for different BDS designs 20 mrad crossing angle

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Collimation Depths and Performance for 2mrad and 20mrad

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  1. Collimation Depths and Performance for 2mrad and 20mrad Frank Jackson ASTeC Daresbury Laboratory

  2. Contents • A method of estimating collimation depths for current ILC-BDS designs • Semi-analytical procedure • Evaluated collimation depth for different BDS designs • 20 mrad crossing angle • ‘2 mrad’ crossing angle, long and short final doublet • Evaluated collimation performance for 20 mrad BDS • Use tracking simulation • Thoughts about important issues and future studies ILC-BDIR, Royal Holloway University

  3. Collimation Depth Evaluation • ‘First-Order’ method of estimating collimation depths for a given final doublet • To achieve SR fan clearance through IR apertures • Coded in ‘DBLT’ by Olivier Napoly (Saclay) • Used for TESLA BDS • Analytical calculation • Evaluates SR fan profile as function of collimation depth • Constrain SR profile  solve for collimation depth • Assumes on-energy halo, omits effect of local chromaticity correction • Benefit of simplicity • Requires further tuning, simulations ILC-BDIR, Royal Holloway University

  4. Collimation Depth Calculation Issues • Recent studies have highlighted some general issues • Beam parameters • WG1 have published parameters table. • Not all FD designs use same parameters. • Crucial apertures • Vtx, masks, and extraction quads • Mask issues • Detector masks still to be determined • Some background studies suggest masks may be tightest apertures • Crossing angle issues • SR fan may ‘see’ non-symmetric apertures ILC-BDIR, Royal Holloway University

  5. 20 mrad collimation depth IR layout • Used ‘FF9’ final doublet on web • http://www.slac.stanford.edu/~mdw/ILC/Beam_Delivery/20050316/ • Designed for x* = 15mm, y* = 0.4mm (TESLA/US-COLD) • No detector mask • Most crucial aperture is first extraction quadrupole (r = 12 mm) • Mask would not be tightest constraint • No symmetry problems • Collimation depth 8.8 x 68.9 y • Spoiler gaps ax = 1mm, ay = 0.5 mm http://www.slac.stanford.edu/xorg/lcd/ipbi/lcws05/maruyama_backgrounds.ppt Solution ILC-BDIR, Royal Holloway University

  6. 2mrad designs • Short and long doublet designs initially based on different beam parameters • Difficult to make fair comparison • Doublets may be independent of IP beta-functions • Optics upstream FD control IP • Coll. depth can be calculated for different IP beta-functions for a given doublet • 2mrad extraction means difficult situation • Symmetry – SR fan does not ‘see’ circular apertures • Masks would be crucial apertures (assume circular mask aperture = vtx aperture) ILC-BDIR, Royal Holloway University

  7. 2mrad Results (L*=3.51 all cases) • In each case can trade Nx for Ny and vice-versa • Short doublet seems more relaxed coll. depths • QF aperture may limit halo as well as SR fan ILC-BDIR, Royal Holloway University

  8. 20 mrad Collimation Performance • Studied collimation performance up to FD using simulation • Not tried to re-evaluate collimation depth • Collimation system • 2-phase betatron spoilers + absorbers • Energy spoiler (x-plane) + absorber • Performance studied by A. Drozhdin with STRUCT • http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-04-05/pap_ILCFF9.pdf • Collimation depth scaled from NLC (8x  57y) • Energy spoiler used as secondary betatron collimator (10x  63y) • Change betatron spoiler gaps to 8.8x  68.9y, energy spoiler to 10 x  68.9y, andrepeat analysis ILC-BDIR, Royal Holloway University

  9. 20 mrad Collimation Performance • 100 K particles, 1/r halo extending to 13x, 93y • Halo intercepted by SP2, SP4, SPEX and secondaries are absorbed before FD • 0.1% of initial halo population escapes 8.8x, 68.9y depth p = 1% p = 0% ILC-BDIR, Royal Holloway University

  10. 20 mrad Collimation Performance • Horizontal, non-symmetrical halo leakage • Not due to off-energy particles • Non-linear effects of slit-transport • Just tighten x-apertures? • NLC collimation depth was 15x, set spoilers to 10x • Same tightening here would give ~6x! • Additional spoilers? ILC-BDIR, Royal Holloway University

  11. Conclusions • Simple method of coll. depth determination • Not perfect but very useful • First estimation 20mrad collimation depth • Compare 2mrad designs • Feel for impact of mask geometry, IP parameters • Final depth estimation needs simulation fine-tuning • 20mrad collimation design performance • Good but not perfect (some halo leakage) • How can we improve performance? ILC-BDIR, Royal Holloway University

  12. Notes • Collimation depth solution is given by a curve not two fixed numbers. • Use of DBLT for TESLA l*=5m. Detailed post-tuning resulted in 30% smaller x collimation depth (PAC 2003, http://accelconf.web.cern.ch/AccelConf/p03/PAPERS/RPAB001.PDF) ILC-BDIR, Royal Holloway University

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