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.