Collimation Baseline Configuration and Collimation Studies Frank Jackson ASTeC Daresbury Laboratory
Contents Baseline Configuration Document Collimation Studies
Collimation Baseline Configuration Document
What Happened at Snowmass Collimation and Background Session of WG4 (Beam Delivery System) 1 Summaries by N. Mokhov (FERMILAB), F. Jackson (Daresbury), and A. Sugiyama (Saga) Additional talks by K. Buesser (DESY) and J. Carter (RHUL) Baseline Configuration Document (BCD) outline plan 2 N. Mokhov and F. Jackson nominated as ‘authors’ of collimation section BCD to be completed end 2005 First draft 3 was provided for Global Design Effort (GDE) meeting on Sep
BCD Collimation Content States baseline design, alternatives to baseline, answers to GDE Snowmass questions, existing and future R&D, Baseline Adopt NLC BDS scheme (2-phase betatron upstream of energy collimation) Survivable spoilers/absorbers and protection collimators Octupole tail folding Alternatives Consumable spoilers GDE question: Order of energy and betatron collimation? Betatron, then energy, as in NLC. TESLA design had opposite order but lower collimation efficiency
BCD Collimation Content – Existing R&D Collimator survivability Spoilers can survive 2 bunches at 250 GeV, 1 bunch at 500 GeV Collimation Depths Evaluated with linear calculations and simulations Spoiler gaps < 1mm in both planes, but larger than NLC Dynamic Heat Load Need to thicken protection collimators (x3) to increase quad lifetimes for 0.1% beam halo Collimation Efficiency Halo tracking simulations show reasonable efficiency, poorer than NLC Muon Attenuation at Detector Muon spoiler simulations demonstrate effective design ~ 2.2 muons per 150 bunches
BCD Collimation Content. Future R&D Design of fast extraction system to match spoiler survival limit Wakefield effects yet to be studied in detail for current designs Wakefield measurements planned at SLAC. Optics optimisation for best halo removal efficiency Reduction of radiation loads on beamline components. Octupole tail-folding principle to be (re-)studied. Muon background tolerances in detector to be evaluated. Simulation benchmarking, code repositories
Collimation Studies: - Preliminary Optimisation - Wakefield Effects
Collimation Optics Optimisation A BCD future R&D topic Current efficiency of collimation system could be improved in 20 mrad and 2 mrad decks 20 mrad deck is the most ‘optimised’ Last couple of weeks started to look at optics optimisation of 20 mrad deck
Measuring Collimation Efficiency Halo-tracking with STRUCT been used in past Chose MERLIN tracking code for recent studies Can examine ‘primary’ beam halo just like STRUCT (secondaries not included) ‘Primary’ beam halo is sufficient for ‘first-order’ optimisation of collimation system Easiest and quickest for me to use!
MERLIN and STRUCT Benchmark For 20 mrad BDS, collimation depth = 9.6 x, 74.0 y Use identical end-of-linac halo 10K particles, dp = 1% Halo population at FD is 4% lower in MERLIN than in STRUCT Good enough agreement to use MERLIN for these studies Snowmass Results Merlin Results
Real Optics Performance ‘Snowmass performance’ used tight energy spoiler (10 sigx, 74 sigy) effectively as additional beta spoiler BETACOL FD optics more realistically studied by halo tracking with open energy spoiler (dE = 1.5 % in x, fully open in y) Y-collimation not perfect even with dp=0% Y-spoilers not at perfect phase w.r.t. FD. SP4-IP phase advance is 2.34 (units of 2 ). Phase advance should be 0 or /2 (modulo ). dp=1%dp=0%
MAD Optimisation Used Mark Woodley’s decks and optimisation routines. Vary matching section quadrupole strengths and drift space Adjust x and y phase advances SP4-IP to 2.75 (effectively /2) Need to optimise optics bandwidth at same time as varying phases Difficult problem to solve by MAD tweaking dp=1%dp=0%
ILC Technical Review Committee studied NLC wakefield effects of collimators Calculated jitter amplification factors at FD phase position jitter at IP A y = 1.20 considered too large, equivalent to y / y ~ 20% for 1. y of incoming jitter What is situation for ILC BDS design? Wakefield Effects (nb1) n. y of incoming jitter at collimators additional A y.n. y jitter at IP (nb2) Dispersion at collimators also converted to addtional IP jitter by A
Jitter Amplification for 20 mrad deck Used MATLAB code provided by P. Tenenbaum ILC-FF9 deck with apertures from A. Drozhdin’s halo tracking study (BDIR, RHUL June 2005) SP2,4,SPEX = Ti Opened SPEX (dp = 0.3% aperture), assuming we can optimise optics to allow this NLC had five betatron spoilers-absorber pairs and small spoiler apertures (0.2mm-0.3mm) ILC has two sp-ab pairs and larger apertures (0.5mm-1.0mm) But what about protection collimators and SR masks as sources of jitter? ILC 20 mrad BDS AxAx AyAy AA 0.14 (0.15 in NLC) 0.59 (1.20 in NLC) 0.09 (0.07 in NLC) y / y ~ 5.5%
Protection Collimators Good secondary absorption achieved for ILC deck by tightening PCs (nominal aperture 5mm) Some PC apertures < 1mm ! A. Drozhdin, BDIR meeting, RHUL 2005
Jitter Amplification for 20 mrad deck, incl. PCs ILC 20 mrad BDS, with PCs AxAx AyAy AA 0.28 (0.14 no PC) 1.28 (0.59 no PC) 0.88 (0.09 no PC) PC8,9 and SR masks contribute significantly to A y. They are at non-zero dispersion points, so also contribute to A SR masks have large apertures, but are at large beta-function location (A ), and are exactly in phase with FD
Conclusions Can we achieve NLC-like collimation efficiency, even with wider PCs and SPEX? If so, wakefield situation much improved Octupole tail folding should be (re)studied Effect of SR masks should not be ignored in wakefield calculations.