Dec 2004Dec 2004

Simulation of Low Energy Simulation of Low Energy backgrounds in the ILC IRbackgrounds in the ILC IR

Impact on feedback BPMsImpact on feedback BPMs

FONT collaboration

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

Tony Hartin - QMUL

Apr 2005Apr 2005

Talk OutlineTalk Outline

Model feedback BPMs in Geant Model feedback BPMs in Geant description of 2x10 mrad and 2mrad IRdescription of 2x10 mrad and 2mrad 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

Apr 2005Apr 2005

Geant 3 modelGeant 3 model2x10mrad & 2mrad IR 2x10mrad & 2mrad IR modelsmodels

Strips placed on the wall of Strips placed on the wall of the beampipethe beampipe

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

Solenoid field -T. Maruyama, Solenoid field -T. Maruyama, Quad fields – latest Quad fields – latest MAD opticsMAD optics

Stripline BPM

Apr 2005Apr 2005

BPM noise from backgroundsBPM noise from backgrounds

Noise form factor sinc(Noise form factor sinc(ππ.f.T).f.T)

Secondary emission down to Secondary emission down to 100 eV needs to be 100 eV needs to be consideredconsidered

Geant3 minimum transport is Geant3 minimum transport is 10 keV!10 keV!

Copper strips with 1 mm gap to wallCopper strips with 1 mm gap to wall

Noise from secondary charges crossing strip-wall gapNoise from secondary charges crossing strip-wall gap

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

Apr 2005Apr 2005

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

Apr 2005Apr 2005

Geant3 energy cuts for particle Geant3 energy cuts for particle transport – default 1 MeV - minimum transport – default 1 MeV - minimum 10 keV10 keV

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

Apr 2005Apr 2005

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 day per b.c. on Dual OpteronComputing time – 1 day per b.c. on Dual Opteron

..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

Apr 2005Apr 2005

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

Apr 2005Apr 2005

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

Apr 2005Apr 2005

Geant3 total BPM hits – headon IR Geant3 total BPM hits – headon IR modelmodel

lowE mods reveal lowE mods reveal significant increase in BPM significant increase in BPM hits at 100eV cuthits at 100eV cut

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

Neutron impacts can be Neutron impacts can be considered in Geant4 lowE considered in Geant4 lowE – number of secondaries – number of secondaries will increasewill increase

Apr 2005Apr 2005

Geant3 – 2x10 mrad IR modelGeant3 – 2x10 mrad IR modelAngular asymmetry in Angular asymmetry in BPM hitsBPM hits

7000 hits per strip per b.c 7000 hits per strip per b.c but only 15% are chargesbut only 15% are charges

Apr 2005Apr 2005

G3 to G4 code conversion recipeG3 to G4 code conversion recipe

Call GRFILE(21,’2x10mrad.geom’,’ON’) after call to Call GRFILE(21,’2x10mrad.geom’,’ON’) after call to GGCLOS in G3 codeGGCLOS in G3 code

Build rztog4 in geant4 source codeBuild rztog4 in geant4 source code

Rztog4 creates geant4 call_listRztog4 creates geant4 call_list

Geant4 inputs call_list and creates logical volumesGeant4 inputs call_list and creates logical volumes

Magnetic fields described and associated with geant4 Magnetic fields described and associated with geant4 logical volumeslogical volumes

Apr 2005Apr 2005

Future PlansFuture Plans

Convert 2x10mrad and 2mrad schemes + Convert 2x10mrad and 2mrad schemes + feedback BPMs from Geant3 -> Geant4feedback BPMs from Geant3 -> Geant4

Run EGS, Geant4 and Geant3-mod in the Run EGS, Geant4 and Geant3-mod in the lowE regime and compare resultslowE regime and compare results

Investigate dependence on bunch shape, Investigate dependence on bunch shape, and y offsetsand y offsets