EM background tests of IP feedback hardware

Christine Clarke

Oxford University

24th September 2007

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

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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

e+e- 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

Quad Pole face

Stripline BPM

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FONT at ESA: Requirements 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

All charges at the ILC

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

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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.

Energy spectra from Aluminium Radiators and ILC charges

Energy spectra of charges hitting BPM striplines for ILC and ESA proposal

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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.

28.5 GeV e- beam

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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 = (A+B)/(A-B)

z = C/(A-B)

A

B

CMean(d) error Mean(z) error

No foil 0.0364 4e-4 -0.0326 2e-4

5 % foil 0.0363 4e-4 -0.0325 2e-4

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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.