EM background tests of IP feedback hardware

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EM background tests of IP feedback hardware
Oxford (P. Burrows, C. Perry, G. Christian, T.
Hartin, H. Dabiri Khah, C. Clarke, C. Swinson, B.
Constance) Daresbury (A. Kalinin) SLAC (Mike
Woods, Ray Arnold, Steve Smith) KEK

• Christine Clarke
• Oxford University
• 24th September 2007

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FONT at ESA The ILC Environment

• The IP feedback BPM sits between the Beam
  Calorimeter and the first extraction line quad.
• This area has lots of low energy particles due to
  interaction of ee- pairs and photons (from
  beam-beam interaction) with IR material.

Low-Z mask
Beam Cal
IP Feedback BPM
Extraction Quad
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FONT at ESA Hits on striplines

• GEANT3 Simulations by Tony Hartin (Oxford) show
  up to 105 particle hits per stripline
• Are simulations correct down to low energies?
• Charges being added or removed from the BPM
  causes errors (1pm per charge Steve Smith).
• FONT requires resolution on the micron level.

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FONT at ESA Module

• Recreate the environment around the BPM
• (Match the particles entering the region)
• Match the materials in the region
• Constructed at Daresbury.

Low Z Mask
Beam Cal
Stripline BPM
Quad Pole face
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FONT at ESA Requirements
All charges at the ILC

• ILC conditions impossible to replicate but we can
  identify the parts that matter- energies and
  fluxes of particles that cause hits on BPM
  striplines.
• We require electrons and positrons of average 4
  GeV impacting front face of module as well as the
  original electron beam.

Low Z Mask
Charges that go on to cause hits on striplines
The charges that cause hits on the striplines
peak around 4 GeV
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FONT at ESA Method 1

• Ran tests at End Station A (ESA) at SLAC.
• Scanned the electron beam across the front face
  of the module.
• CCD camera to aid positioning beam spot on the
  front face of the module.
• A Low Flux Toroid monitored beam charge down to
  106 electrons.
• Ran at 28.5 GeV, 107 electrons beam charge.
  Produced 15000 times more hits per stripline
  than worst case ILC.

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FONT at ESA Method 1 Results

• Signals with the beam on the Low Z mask were
  different from BPM stripline signal- suggestive
  of secondary emission.
• The signals caused by secondary emission were not
  large enough to cause problems for the operation
  of the IP BPM.

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FONT at ESA Method 1 Simulations

• Simulating these results in GEANT has had some
  success (Tony Hartin).
• Normal stripline response Secondary emission

Simulation (T. Hartin)
Real Data from ESA
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FONT at ESA Method 2

• Second method delivers both electrons and
  positrons as a halo around the main electron beam
  using thin radiators just upstream of module.
• The energies of charges hitting the module do not
  match.
• GEANT simulations show this does not affect the
  energy distribution of what hits the striplines.
• Can make numbers match.

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FONT at ESA Method 2

• 3 aluminium foils used, 1, 3, 5 X0.
• Recorded 1000 stripline signals without foils.
• Recorded 1000 stripline signals with foils.
• With 5 X0 foil in, Produced 5000 times more
  hits per stripline than worst case ILC.

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FONT at ESA Method 2 Results

• No change with foil in and foil out.
• Statistical errors on parameters (d and z)
  greater than the difference between the foils in
  and out.
• Statistical error is 700 times smaller than the
  value that constitutes a 1 micron error in
  position measurement at the ILC.

d (AB)/(A-B)
A
z C/(A-B)
C
B
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FONT Summary

• IP Feedback BPM sits in a region where
  backgrounds are present.
• Created backgrounds and recorded stripline
  behaviour.
• Stripline signal shows secondary emission.
• Some success in understanding the exact form just
  using GEANT3.
• Signal is not large enough to cause problems with
  micron-level position measurement at the ILC.
• General
• Ability to simulate IR backgrounds.
• Other beamline elements can be tested there.

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FONT at ESA Method 3 (no plans to use this
method)

• To match energies and fluxes, we propose Be
  target in BSY.
• We can select only 4 GeV electrons.
• We can fill the entire beampipe with electrons so
  illuminating the whole front face of the module.
  Collimators and optics control the shape.
• We can change fluxes to match ILC backgrounds or
  to make them a factor of ten worse.
• We only have spray- no primary beam to measure.