Simulation and Analysis for Astroparticle Experiments The LISA Gravitational Wave Interferometer Implementation within Geant4 Simulation output from the GRID and predictions Conclusions Future work Alex Howard, CERN Alex Howard, CERN Slide1

Geant4 Simulation of Test-Mass Charging in the LISA Mission   Very long base-line: 1 million km Very high precision: < 1nm – 1pm (!) Alex Howard, CERN Slide2

charge management system Test-Mass Charging charging rate fluctuations Lorentz + Coulomb forces p shielding charge management system Alex Howard, CERN Slide3

Geometry spacecraft payload area Alex Howard, CERN Slide4

LISA Environment 1. Protons from solar flares Localised in time 2. Extragalactic cosmic rays Protons, Alphas Isotropic flux MeV – TeV energies peak ~ 500 MeV/nucleon Jursa AS (ed) 1985 previous G3 simulations Jafry et al. 1996, 1997 G4 simulation Alex Howard, CERN Slide5

Physics List EM processes (LowE) Electrons, Gammas, etc Atomic de-excitation Hadrons (no hFluorescence) Hadronic processes Elastic (LE+HE) Inelastic (LE+HE) Nuclear de-excitation Absorption/Annihilation Photonuclear (g, e, m) Neutrons (HP, LE, HE) Decays Decay in flight (no RDM) Secondaries Cuts: (250 eV), 1um - 5um Kill e- outside caging Alex Howard, CERN Slide6

OUTPUT from Grid Running Over 100 jobs have been run on the grid to try and estimate the charging rate in the proof mass and test different cuts and processes within Geant4. 1.9 million events have been run in ~300 hours of CPU time Alex Howard, CERN Slide7

6secs and Convergence of Charging Rate Alex Howard, CERN Slide8

6secs and Convergence of Charging Rate Initial indications of charging rate Alex Howard, CERN Slide9

Results I Charging rate 2 days in parallel !!! G4 result: 58 +e/s 45 s exposure ~ 10,000,000 events 1 charging event ~ 2,000 events ~ 40,000 events/day/CPU 2 days in parallel !!! Charging rate G4 result: 58 +e/s (G3 result: 11 +e/s) 52 +e/s 6 +e/s Alex Howard, CERN Slide10

Results II Cuts (~0.1 um) 250 eV 52 +e/s 1 um 8.77 keV 41 +e/s 2 um 30.7 keV 40 +e/s 5 um 53.2 keV 42 +e/s Energy of Primary, MeV Decreasing the production threshold from 10 keV (G3, G4EM) to 250 eV (G4LowE) leads to a ~20% increase of the charging rate! Alex Howard, CERN Slide11

Conclusions The LISA Gravitational Wave spacecraft has been simulated in order to estimate the proof mass charging due to the space environment Charging rate increased ~5 times relative to G3 simulation: more physics, wider primary energy, geometry and lower cuts Alex Howard, CERN Slide12