Dec 2004 Simulation of Low Energy backgrounds in the ILC IR Impact on feedback BPMs FONT collaboration  QMUL: P Burrows, G Christian, C Clarke, G White, S Molloy Tony Hartin - QMUL

Apr 2005 Talk Outline Model feedback BPMs in Geant description of 2x10 mrad and 2mrad IR Geant mods for low Energy transport Compare Monte Carlo packages (Geant3,Geant4, EGS) at low energies

Apr 2005 Geant 3 model 2x10mrad & 2mrad IR models Strips placed on the wall of the beampipe Guinea-Pig pair particles and photons tracked with different kinetic energy cuts Solenoid field -T. Maruyama, Quad fields – latest MAD optics Stripline BPM

Apr 2005 BPM noise from backgrounds Noise form factor sinc(π.f.T) Secondary emission down to 100 eV needs to be considered Geant3 minimum transport is 10 keV! Copper strips with 1 mm gap to wall Noise from secondary charges crossing strip-wall gap ~1pm error for each charge absorbed or emitted. 1e6 hits per b.c. would be a problem!

Apr 2005 BPM hits Single 12 Gev e+ Multiple hits through showering Origin of hits: Inner beampipe Cylindrical mask Calorimeter 20% direct hits from IP

Apr 2005 Geant3 energy cuts for particle transport – default 1 MeV - minimum 10 keV 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 Energy spectrum of BPM hits

Apr 2005 Transport Code Low E cuts Geant3 1 MeV default, 10 keV min Low E recode to 100eV Computing time – 1 day per b.c. on Dual Opteron. 1 keV minimum LowE package available -> 250eV EGS EGSnrc - 1 keV minimum KEK (low-energy) Extensions to EGS4 100 eV

Apr 2005 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

Apr 2005 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

Apr 2005 Geant3 total BPM hits – headon IR model lowE mods reveal significant increase in BPM hits at 100eV cut 6000 hits per strip per b.c NOT in the danger zone Neutron impacts can be considered in Geant4 lowE – number of secondaries will increase

Apr 2005 Geant3 – 2x10 mrad IR model Angular asymmetry in BPM hits 7000 hits per strip per b.c but only 15% are charges

Apr 2005 G3 to G4 code conversion recipe Call GRFILE(21,’2x10mrad.geom’,’ON’) after call to GGCLOS in G3 code Build rztog4 in geant4 source code Rztog4 creates geant4 call_list Geant4 inputs call_list and creates logical volumes Magnetic fields described and associated with geant4 logical volumes

Apr 2005 Future Plans Convert 2x10mrad and 2mrad schemes + feedback BPMs from Geant3 -> Geant4 Run EGS, Geant4 and Geant3-mod in the lowE regime and compare results Investigate dependence on bunch shape, and y offsets