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Simulation of Low Energy backgrounds in the TESLA IR

Simulation of Low Energy backgrounds in the TESLA 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 TESLA IR Geant mods for low Energy transport

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Simulation of Low Energy backgrounds in the TESLA IR

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  1. Simulation of Low Energy backgrounds in the TESLA 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 TESLA IR • Geant mods for low Energy transport • Compare Monte Carlo packages (Geant3,Geant4, EGS) at low energies • BPM experimental tests at SLAC ESA

  3. FONT elements - BPM • BPM provides input to beam based feedback system (see Phil’s talk) • Incident impacts on BPM affect performance BPMs sited behind masks

  4. BPM performance • 4 Copper strips in total • Susceptible to noise from absorbed charge and secondary emission F(R,Solid Angle,bunch charge) • 1pm error for each charge absorbed or emitted. 1e6 hits per b.c. would be a problem! • low energy impacts affect strip charge

  5. Geant 3 model • IR model adopted from Brahms • Strips placed on the wall of the beampipe • Guinea-Pig pair particles and photons tracked with different kinetic energy cuts • 4 Tesla Magnetic Field included as per Brahms default 10 cm Cu strips

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

  7. Energy spectrum of BPM hits • Geant3 energy cuts for particle transport – default 1 MeV - minimum 10 k.e.cut • 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

  8. Transport Code Low E cuts • Geant3 • 1 MeV default, 10 keV min • Low E recode to 100eV • Computing time – 1 week per b.c. • Runs much faster than G4! • . • 1 keV minimum • LowE package available -> 250eV • EGS • EGSnrc - 1 keV minimum • KEK (low-energy)Extensions to EGS4 100 eV

  9. 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

  10. 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

  11. Geant 3 recoding sanity checks -Cu disc model • Fire 100 identical Incident electrons at Cu strip • Emergent flux for different E cuts • LowE mods reveal more secondaries

  12. Geant3 total BPM hits - lowE • lowE mods reveal significant increase in BPM hits at 100eV cut • 6000 hits per strip per b.c NOT in the danger zone • G4 lowE secomdaries indicate the number of hits is probably greater • Neutron impacts not yet considered

  13. Detector BKG (NLC) F.O.N.T. G.R.White: 11/09/2014 • Insertion of feedback system at z=4.3 m has no impact on secondary detector backgrounds arising from pair background • Past studies suggest backgrounds adversely effected only when feedback system installed forward of z=3 m

  14. Possible experimental tests at SLAC-ESA(Christian/Clarke) • Possible test of BPM performance at ESA with expected pair background at ILC – use radiator at ESA to mimic ILC pair background • 2 options – Thin target (~5-10% X0) in IR-mockup at ESA or Thick target (~30% X0) at end of linac to produce secondary spray beam in A-line • Built simple GEANT3 model for thin target option • First-step – benchmark model against EGS simulation of Keller/Woods for thin radiator

  15. Comparison of GEANT/EGS models – first results GEANT model 1 million incident electrons @25 GeV 10% X0 carbon radiator #particles E>500KeV hitting scoring plane 3m from target EGS model (Keller)

  16. Future Plans • Convert TESLA IR + feedback BPMs from Geant3 -> Geant4 • Compare low Energy performance of EGS, Geant4 and Geant3-mod • Gauge impact of crossing angle and other suggested TESLA IR mods

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