collimation baseline configuration and collimation studies frank jackson astec daresbury laboratory
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Collimation Baseline Configuration and Collimation
Studies
Frank JacksonASTeC 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 plan2
N. Mokhov and F. Jackson nominated as ‘authors’ of collimation section
BCD to be completed end 2005 First draft3 was provided for Global Design Effort (GDE) meeting
on Sep 22
1. http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/2. http://alcpg2005.colorado.edu:8080/alcpg2005/program/accelerator/WG4/modified_BDS_BCD_ACD_sept8.doc3. http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/bds_bcd_acd.htm#collimation
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 = 9.6x, 74.0y 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
BETACOLFD 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
Ay = 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 Ay.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 BDSAx Ay A
0.14 (0.15 in NLC) 0.59 (1.20 in NLC) 0.09 (0.07 in NLC)
y/y ~ 5.5%
Protection Collimators
ILC collimators aperture, length and material. CP - spoiler, AB - absorber, MSK - photon mask, PC – protection collimators. Version ILCFF9.
June 21, 2005 A.Drozhdin,
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 PCsAx Ay A
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 Ay.
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.
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