1. 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

2. 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

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

4. Geometry
spacecraft
payload
area
Alex Howard, CERN Slide4

5. 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

6. 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

7. 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

8. 6secs and Convergence of Charging Rate
Alex Howard, CERN Slide8

9. 6secs and Convergence of Charging Rate
Initial indications of charging rate
Alex Howard, CERN Slide9

10. 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

11. 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

12. 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