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Simulation of Low Energy backgrounds in the ILC IR

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. Talk Outline. Model feedback BPMs in Geant description of 2x10 mrad and 2mrad IR Geant mods for low Energy transport

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Simulation of Low Energy backgrounds in the ILC IR

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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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