Collimation Studies for the Linear Collider

1
Collimation Studies for the Linear Collider

• Frank Jackson
• ASTeC Daresbury Laboratory (CCLRC)

2
Introduction

• The design and performance of linear collider
  collimation
• Introduction to beam delivery collimation in
  linear colliders
• Purpose of collimation
• Collimation requirements
• Description of collimation system with comparison
  of TESLA and NLC
• Collimation studies at ASTeC
• Future direction

3
Purpose of Collimation

• Future particle physics experiments need beam
  collimation
• The halo of electron beams is a source of
  experimental background
• Has been seen to limit experimental performance
  at Stanford Linear Accelerator
• Collimation system also should provide energy
  collimation and machine protection

1 Beam Halo
Tracking Chamber Wires Hit ()
No Beam Halo
Collimator Aperture
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Reason for Collimation

• A very large halo will directly hit parts of the
  detector
• Even a relatively small halo (10 times the beam
  size) can produce a fan of synchrotron radiation
  which may hit the detector
• Synchrotron radiation fan is the main constraint
  on collimation depth sequence of spoiler
  apertures in BDS
• Determining a realistic collimation depth is a
  complex, non-linear problem

5
NLC and TESLA Collimation Similarities

• Both use betatron collimation section as the
  primary collimation instrument
• Additional secondary collimators downstream
• Betatron collimation
• Dedicated section of beamline with optics purely
  designed for collimation
• Illustration (TESLA)

Collimation depth
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NLC and TESLA Collimation System Differences

• Machine protection philosophy (dedicated optics
  vs consumable spoilers)
• Energy collimation placement (upstream or
  downstream of betatron collimation)
• Spoiler apertures and collimation depths
• NLC betatron spoilers narrower than required
  collimation depth (apertures possibly determined
  by tracking)
• TESLA spoilers set at collimation depth (linear
  semi-analytic design)

7
ASTeC Collimation Studies

• Repeat existing international results on
  collimation
• Set up tracking simulations MERLIN (N. Walker, A
  Wolski) and STRUCT (A. Drozhdin)
• Measure and understand existing collimation
  designs
• Previous studies were co-ordinated in a PAC2003
  contribution (A. Drozhdin et al)
• NLC primary collimation efficiency 100
• TESLA - fraction (0.01) of bunch (core halo)
  population escapes collimation depth
• Qualitative behaviour of TESLA collimation
  confirmed with MERLIN and BDSIM

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ASTeC Collimation Studies

• NLC and TESLA halos at final doublet (Uniform
  phase space, 1 energy spread, MERLIN 2nd order
  transport)

NLC
TESLA
9
ASTeC Collimation Studies

• NLC design apparently more efficient collimation
  system
• Tighter collimation apertures (although less
  complete phase coverage)
• Energy collimation scheme more effective
• STRUCT provides more complete simulation (GEANT
  -based)
• Secondary e/e- and ? production at
  spoilers/absorbers
• Installed and running preliminary tracking
  simulations
• Would benefit from benchmarking/comparison with
  other codes

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Future Plans

• Final collimation design will link closely to
  evolution of ILC BDS
• Strawman BDS plan exists so far but no
  internationally agreed optics design
• First attempts at ILC BDS put forward by SLAC for
  non-zero horizontal crossing angle, based on NLC
  design
• First scheme may be to adopt NLC-type collimation
  system but this very dependent on many other BDS
  factors
• Confirm NLC and new ILC design performance with
  detailed simulations like STRUCT, BDSIM, MERLIN
• Investigate potential improvements
• Muon and other secondary production should be
  included