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                  cosmicray_charging advanced example

                     Henrique Araujo & Peter Wass
                       Imperial College London

                              April 2004

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This Geant4 example was derived from an application aimed at
simulating the electrostatic charging of isolated test masses in the
LISA mission by galactic cosmic ray protons and helium nuclei. This
work was supported by the European Space Agency through the SEPTIMESS
project under Contract No. 16339/02/NL/FM.

LISA, the Laser Interferometer Space Antenna for the detection of
gravitational waves, is a joint ESA/NASA mission composed of three
identical spacecraft orbiting the Sun in a triangular formation, each
containing two cubic test masses in pure geodesic (drag free) motion. 
The interferometric measurements between different spacecraft
are affected by the accrual of charge in the test masses caused by the
interaction of energetic cosmic rays.

With this example we intend to demonstrate an application of Geant4 to
space environment simulations, using an extensive set of physics
models spanning from TeV energies down to a few hundred eV. This code
retains most (but not all) of the complex spacecraft and sensor
geometry implemented for the original purpose. In particular, some
complex elements of the inertial sensor surrounding the test masses
have not been included. Differential energy spectra for protons, He-4
and He-3 nuclei at solar minimum conditions are the only input macros
provided. The remaining application classes have been kept unchanged.

A Software Users' Manual suitable for Geant4 users of all levels is
distributed with this application (/docs). The technical description
of the original software package, including further software
documentation, physics analysis and a similar effort for the precursor
ESA mission LISA Pathfinder are available from the SEPTIMESS project
website at http://reat.space.qinetiq.com/septimess/ or from
http://astro.ic.ac.uk/~haraujo/SEPTIMESS/ .

Any queries regarding this example or the original work can be
directed to h.araujo@imperial.ac.uk.
