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

Dec 2004 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

Dec 2004 FONT elements - BPM BPMs sited behind masks BPM provides input to beam based feedback system (see Phil’s talk) Incident impacts on BPM affect performance

Dec 2004 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

Dec 2004 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

Dec 2004 BPM hits Single 12 Gev e+ Multiple hits through showering Origin of hits: Inner beampipe Cylindrical mask Calorimeter 20% direct hits from IP

Dec 2004 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 Energy spectrum of BPM hits

Dec 2004 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

Dec 2004 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

Dec 2004 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

Dec 2004 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

Dec 2004 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

Dec 2004 G.R.White: 10/02/2016 F.O.N.T. 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 2004 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% X 0 ) in IR- mockup at ESA or Thick target (~30% X 0 ) 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

Dec 2004 Comparison of GEANT/EGS models – first results 1 million incident GeV 10% X 0 carbon radiator #particles E>500KeV hitting scoring plane 3m from target GEANT model EGS model (Keller)

Dec 2004 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