Alex Howard, CERN Slide1

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Simulation and Analysis for Astroparticle
Experiments

1. The LISA Gravitational Wave Interferometer
2. Implementation within Geant4
3. Simulation output from the GRID and predictions
4. Conclusions
5. Future work

• Alex Howard, CERN

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Geant4 Simulationof Test-Mass Chargingin the
LISA Mission
     

• Very long base-line
• 1 million km
• Very high precision
• lt 1nm 1pm (!)

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Test-Mass Charging
p
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Geometry
spacecraft
payload area
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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
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Physics List
EM processes (LowE) Electrons, Gammas, etc Atomic
de-excitation Hadrons (no hFluorescence)
Hadronic processes Elastic (LEHE) Inelastic
(LEHE) Nuclear de-excitation Absorption/Annihilat
ion Photonuclear (g, e, m) Neutrons (HP, LE, HE)
Decays Decay in flight (no RDM)
Secondaries Cuts (250 eV), 1um - 5um Kill e-
outside caging
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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

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6secs and Convergence of Charging Rate
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6secs and Convergence of Charging Rate
Initial indications of charging rate
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Results I
45 s exposure 10,000,000 events 1 charging
event 2,000 events 40,000 events/day/CPU
Charging rate
G4 result 58 e/s
(G3 result 11 e/s)
52 e/s
6 e/s
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Results II
Cuts
1 um 8.77 keV 41 e/s
(0.1 um) 250 eV 52 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!
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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