Dec 2004Dec 2004

Simulation of Low Energy Simulation of Low Energy backgrounds in the TESLA IRbackgrounds in the 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

Geant mods for low Energy transportGeant mods for low Energy transport

Compare Monte Carlo packages Compare Monte Carlo packages (Geant3,Geant4, EGS) at low energies(Geant3,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

Susceptible to noise from Susceptible to noise from absorbed charge and absorbed charge and secondary emission secondary emission F(R,Solid Angle,bunch charge)F(R,Solid Angle,bunch charge)

1pm error for each charge 1pm error for each charge absorbed or emitted. 1e6 hits absorbed or emitted. 1e6 hits per b.c. would be a problem!per b.c. would be a problem!

low energy impacts affect strip low energy impacts affect strip chargecharge

Dec 2004Dec 2004

Geant 3 modelGeant 3 model

IR 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 included as per Field included as per Brahms defaultBrahms default

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

Transport Code Low E cutsTransport Code Low E cutsGeant3Geant3

1 MeV default, 10 keV min1 MeV default, 10 keV minLow E recode to 100eVLow E recode to 100eVComputing time – 1 week per b.c.Computing time – 1 week per b.c.Runs much faster than G4!Runs much faster than G4!

..1 keV minimum1 keV minimumLowE package available -> 250eVLowE package available -> 250eV

EGSEGSEGSnrc - 1 keV minimumEGSnrc - 1 keV minimumKEK (low-energy)KEK (low-energy)Extensions to EGS4 100 eVExtensions to EGS4 100 eV

Dec 2004Dec 2004

Geant3/4 mod for Low Energy Geant3/4 mod for Low Energy TransportTransport

Geant3 X-section Geant3 X-section parametrization wrong parametrization wrong below 10kev cutbelow 10kev cut

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

Road test lowE mods – Road test lowE mods – Copper disc modelCopper disc 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 cutsLowE mods reveal more LowE mods reveal more secondariessecondaries

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 cutsLowE mods reveal more LowE mods reveal more secondariessecondaries

Dec 2004Dec 2004

Geant3 total BPM hits - lowEGeant3 total BPM hits - lowElowE mods reveal significant lowE mods reveal significant increase in BPM hits at 100eV increase in BPM hits at 100eV cutcut

6000 hits per strip per b.c NOT 6000 hits per strip per b.c NOT in the danger zonein the danger zone

G4 lowE secomdaries indicate G4 lowE secomdaries indicate the number of hits is probably the number of hits is probably greatergreater

Neutron impacts not yet Neutron impacts not yet consideredconsidered

Dec 2004Dec 2004

G.R.White: G.R.White: 21/04/2321/04/23

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 background

2 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 results

1 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