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Low Energy backgrounds in the TESLA IR

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 Modify Geant3 for low Energy transport

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Low Energy backgrounds in the TESLA IR

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  1. 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 • Modify Geant3 for low Energy transport • Compare to other Monte Carlo packages (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 • Noise susceptible to absorbed charge and secondary emission • 1pm error for each charge absorbed or emitted. 10e5 hits would be a problem! • low energy e-s add 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 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. Geant3 mod for Low Energy Transport • Geant3 X-section parametrization wrong below 10kev • 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. Transport Code Low E cuts • Geant3 • 1 Mev default, 10 kev min, recode to <100eV • . • LowE package available -> 250ev • EGS • KEK (low-energy)Extensions to EGS4 < 100 eV

  10. Geant 3 recoding sanity checks -Cu disc model • Fire 100 identical Incident electrons at Cu strip • Emergent flux for different E cuts • G3 mods agree with G4

  11. Geant 3 recoding sanity checks -Cu disc model • Fire 100 identical Incident electrons at Cu strip • Emergent flux for different E cuts • G3 mods agree with G4

  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 • Need to push lowE cut even lower

  13. Detector BKG (NLC) F.O.N.T. G.R.White: 13/10/2014 • 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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