EM background tests of IP feedback hardware Christine Clarke Oxford University 24 th 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

24/09/07 C.I.Clarke 2 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

24/09/07 C.I.Clarke 3 FONT at ESA: Hits on striplines GEANT3 Simulations by Tony Hartin (Oxford) show up to 10 5 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.

24/09/07 C.I.Clarke 4 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

24/09/07 C.I.Clarke 5 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

24/09/07 C.I.Clarke 6 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 10 6 electrons. Ran at 28.5 GeV, ~10 7 electrons beam charge. Produced ~15000 times more hits per stripline than worst case ILC.

24/09/07 C.I.Clarke 7 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.

24/09/07 C.I.Clarke 8 FONT at ESA: Method 1 Simulations Simulating these results in GEANT has had some success (Tony Hartin).  Normal stripline response + Secondary emission Real Data from ESA Simulation (T. Hartin)

24/09/07 C.I.Clarke 9 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

24/09/07 C.I.Clarke 10 FONT at ESA: Method 2 3 aluminium foils used, 1%, 3%, 5% X 0. Recorded 1000 stripline signals without foils. Recorded 1000 stripline signals with foils. With 5% X 0 foil in, Produced ~5000 times more hits per stripline than worst case ILC GeV e- beam

24/09/07 C.I.Clarke 11 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 C Mean(d)errorMean(z)error No foil e e-4 5 % foil e e-4

24/09/07 C.I.Clarke 12 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.

24/09/07 C.I.Clarke 13

24/09/07 C.I.Clarke 14 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.