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Simulation of Low Energy Backgrounds in the ILC IR: Impact on Feedback BPMs

This talk outlines a model for feedback BPMs in the ILC Interaction Region, focusing on low-energy backgrounds and their impact. Key aspects covered include Geant3 modeling, BPM noise from backgrounds, and future plans for transitioning to Geant4. Detailed comparisons of Monte Carlo packages and energy transport models are discussed.

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Simulation of Low Energy Backgrounds in the ILC IR: Impact on Feedback BPMs

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  1. Simulation of Low Energy backgrounds in the ILC IR Impact on feedback BPMs Tony Hartin - QMUL • FONT collaboration • QMUL: P Burrows, G Christian, C Clarke, G White, S Molloy

  2. Talk Outline • Model feedback BPMs in Geant description of 2x10 mrad and 2mrad IR • Geant mods for low Energy transport • Compare Monte Carlo packages (Geant3,Geant4, EGS) at low energies

  3. Geant 3 model • 2x10mrad & 2mrad IR models • Strips placed on the wall of the beampipe • Guinea-Pig pair particles and photons tracked with different kinetic energy cuts • Solenoid field -T. Maruyama, Quad fields – latest MAD optics Stripline BPM

  4. BPM noise from backgrounds • Copper strips with 1 mm gap to wall • Noise from secondary charges crossing strip-wall gap • ~1pm error for each charge absorbed or emitted. 1e6 hits per b.c. would be a problem! • Noise form factor sinc(π.f.T) • Secondary emission down to 100 eV needs to be considered • Geant3 minimum transport is 10 keV!

  5. BPM hits • Single 12 Gev e+ • Multiple hits through showering • Origin of hits: • Inner beampipe • Cylindrical mask • Calorimeter • 20% direct hits from IP

  6. Energy spectrum of BPM hits • Geant3 energy cuts for particle transport – default 1 MeV - minimum 10 keV • BUT.. at least half the BPM hits have k.e between 10 keV and 1 MeV • AND.. Eg e-/+ hits of just a few eV ionize BPM strips

  7. Transport Code Low E cuts • Geant3 • 1 MeV default, 10 keV min • Low E recode to 100eV • Computing time – 1 day per b.c. on Dual Opteron • . • 1 keV minimum • LowE package available -> 250eV • EGS • EGSnrc - 1 keV minimum • KEK (low-energy)Extensions to EGS4 100 eV

  8. Geant3/4 mod for Low Energy Transport • Geant3 X-section parametrization wrong below 10kev cut • Recode Geant3 to parametrize real data from NEA site • Similar schemes • Apostolakis 1999, Geant4 LowE • Kippen, New Astr Rev (2004) • Y. Namito and H. Hirayama, KEK Internal 2000-4

  9. Road test lowE mods – Copper disc model • Fire 100 identical Incident electrons at Cu strip • Emergent flux for different E cuts • LowE mods reveal more secondaries

  10. Geant3 total BPM hits – headon IR model • lowE mods reveal significant increase in BPM hits at 100eV cut • 6000 hits per strip per b.c NOT in the danger zone • Neutron impacts can be considered in Geant4 lowE – number of secondaries will increase

  11. Geant3 – 2x10 mrad IR model • Angular asymmetry in BPM hits • 7000 hits per strip per b.c but only 15% are charges

  12. G3 to G4 code conversion recipe • Call GRFILE(21,’2x10mrad.geom’,’ON’) after call to GGCLOS in G3 code • Build rztog4 in geant4 source code • Rztog4 creates geant4 call_list • Geant4 inputs call_list and creates logical volumes • Magnetic fields described and associated with geant4 logical volumes

  13. Future Plans • Convert 2x10mrad and 2mrad schemes + feedback BPMs from Geant3 -> Geant4 • Run EGS, Geant4 and Geant3-mod in the lowE regime and compare results • Investigate dependence on bunch shape, and y offsets

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