Dec 2004Dec 2004

Low Energy backgrounds in Low Energy backgrounds in the TESLA IRthe TESLA IR

Impact on feedback BPMsImpact on feedback BPMs

FONT collaboration

QMUL: P Burrows, G Christian, C Clarke, G White, S Molloy

Tony Hartin - QMUL

Dec 2004Dec 2004

Talk OutlineTalk Outline

Model feedback BPMs in Geant description of Model feedback BPMs in Geant description of TESLA IRTESLA IR

Modify Geant3 for low Energy transportModify Geant3 for low Energy transport

Compare to other Monte Carlo packages Compare to other Monte Carlo packages (Geant4 EGS) at low energies(Geant4 EGS) at low energies

BPM experimental tests at SLAC ESABPM experimental tests at SLAC ESA

Dec 2004Dec 2004

FONT elements - BPMFONT elements - BPM

BPMs sited behind masks

BPM provides input to beam based BPM provides input to beam based feedback system (see Phil’s talk)feedback system (see Phil’s talk)

Incident impacts on BPM affect Incident impacts on BPM affect performance performance

Dec 2004Dec 2004

BPM performanceBPM performance4 Copper strips in total4 Copper strips in total

Noise susceptible to Noise susceptible to absorbed charge and absorbed charge and secondary emissionsecondary emission

1pm error for each 1pm error for each charge absorbed or charge absorbed or emitted. 10e5 hits would emitted. 10e5 hits would be a problem!be a problem!

low energy e-s add low energy e-s add chargecharge

Dec 2004Dec 2004

Geant 3 modelGeant 3 modelIR model adopted IR model adopted from Brahmsfrom Brahms

Strips placed on the Strips placed on the wall of the beampipewall of the beampipe

Guinea-Pig pair Guinea-Pig pair particles and photons particles and photons tracked with different tracked with different kinetic energy cutskinetic energy cuts

4 Tesla Magnetic 4 Tesla Magnetic Field includedField included

10 cm Cu strips

Dec 2004Dec 2004

BPM hitsBPM hitsSingle 12 Gev e+Single 12 Gev e+Multiple hits through showeringMultiple hits through showeringOrigin of hits:Origin of hits:

Inner beampipeInner beampipeCylindrical maskCylindrical maskCalorimeterCalorimeter20% direct hits from IP20% direct hits from IP

Dec 2004Dec 2004

Geant3 energy cuts for particle Geant3 energy cuts for particle transport – default 1 MeV - minimum transport – default 1 MeV - minimum 10 k.e.cut10 k.e.cut

BUT.. at least half the BPM hits have BUT.. at least half the BPM hits have k.e between 10 keV and 1 MeVk.e between 10 keV and 1 MeV

AND.. Eg e-/+ hits of just a few eV AND.. Eg e-/+ hits of just a few eV ionize BPM stripsionize BPM strips

Energy spectrum of BPM hitsEnergy spectrum of BPM hits

Dec 2004Dec 2004

Geant3 mod for Low Energy Geant3 mod for Low Energy TransportTransport

Geant3 X-section Geant3 X-section parametrization wrong parametrization wrong below 10kevbelow 10kev

Recode Geant3 to Recode Geant3 to parametrize real data parametrize real data from NEA sitefrom NEA site

Similar schemesSimilar schemesApostolakis 1999, Apostolakis 1999, Geant4 LowEGeant4 LowEKippen, New Astr Kippen, New Astr Rev (2004)Rev (2004)Y. Namito and H. Y. Namito and H. Hirayama, KEK Hirayama, KEK Internal 2000-4Internal 2000-4

Dec 2004Dec 2004

Transport Code Low E cutsTransport Code Low E cutsGeant3Geant3

1 Mev default, 10 kev min, 1 Mev default, 10 kev min, recode to <100eVrecode to <100eV

..LowE package available -> 250evLowE package available -> 250ev

EGSEGSKEK (low-energy)KEK (low-energy)Extensions to EGS4 < 100 eVExtensions to EGS4 < 100 eV

Dec 2004Dec 2004

Geant 3 recoding sanity checks -Cu Geant 3 recoding sanity checks -Cu disc modeldisc model

Fire 100 identical Incident Fire 100 identical Incident electrons at Cu stripelectrons at Cu stripEmergent flux for different Emergent flux for different E cutsE cutsG3 mods agree with G4G3 mods agree with G4

Dec 2004Dec 2004

Geant 3 recoding sanity checks -Cu Geant 3 recoding sanity checks -Cu disc modeldisc model

Fire 100 identical Incident Fire 100 identical Incident electrons at Cu stripelectrons at Cu stripEmergent flux for different Emergent flux for different E cutsE cutsG3 mods agree with G4G3 mods agree with G4

Dec 2004Dec 2004

Geant3 total BPM hits - lowEGeant3 total BPM hits - lowE

lowE mods reveal lowE mods reveal significant increase in significant increase in BPM hits at 100eV cutBPM hits at 100eV cut6000 hits per strip per 6000 hits per strip per b.c NOT in the danger b.c NOT in the danger zonezoneNeed to push lowE cut Need to push lowE cut even lowereven lower

Dec 2004Dec 2004

G.R.White: G.R.White: 03/05/2303/05/23

F.O.N.T.F.O.N.T. Detector BKG (NLC)Detector BKG (NLC)

•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

Dec 2004Dec 2004

Possible experimental tests at SLAC-ESAPossible experimental tests at SLAC-ESA(Christian/Clarke)(Christian/Clarke)

Possible test of BPM performance at ESA with Possible test of BPM performance at ESA with expected pair background at ILC – use radiator expected pair background at ILC – use radiator at ESA to mimic ILC pair backgroundat ESA to mimic ILC pair background2 options – Thin target (~5-10% X2 options – Thin target (~5-10% X00) in IR-) in IR-mockup at ESA or Thick target (~30% Xmockup at ESA or Thick target (~30% X00) at end ) at end of linac to produce secondary spray beam in A-of linac to produce secondary spray beam in A-linelineBuilt simple GEANT3 model for thin target optionBuilt simple GEANT3 model for thin target optionFirst-step – benchmark model against EGS First-step – benchmark model against EGS simulation of Keller/Woods for thin radiatorsimulation of Keller/Woods for thin radiator

Dec 2004Dec 2004

Comparison of GEANT/EGS models – first resultsComparison of GEANT/EGS models – first results1 million incident electrons @25 GeV

10% X0 carbon radiator

#particles E>500KeV hitting scoring plane 3m from target

GEANT model

EGS model (Keller)

Dec 2004Dec 2004

Future PlansFuture Plans

Convert TESLA IR + feedback BPMs from Convert TESLA IR + feedback BPMs from Geant3 -> Geant4Geant3 -> Geant4

Compare low Energy performance of Compare low Energy performance of EGS, Geant4 and Geant3-modEGS, Geant4 and Geant3-mod

Gauge impact of crossing angle and other Gauge impact of crossing angle and other suggested TESLA IR modssuggested TESLA IR mods