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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

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
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
font elements bpm
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

bpm performance
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
geant 3 model
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

bpm hits
BPM hits
  • Single 12 Gev e+
  • Multiple hits through showering
  • Origin of hits:
      • Inner beampipe
      • Cylindrical mask
      • Calorimeter
      • 20% direct hits from IP
energy spectrum of bpm hits
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
transport code low e cuts
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
geant3 4 mod for low energy transport
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
road test lowe mods copper disc model
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
geant 3 recoding sanity checks cu disc model
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
geant3 total bpm hits lowe
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
slide13
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
possible experimental tests at slac esa christian clarke
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
comparison of geant egs models first results
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)

future plans
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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