Simulation of low energy backgrounds in the tesla ir
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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


    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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