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Ann. Geophys., 19, 1721-1730, 2001
www.ann-geophys.net/19/1721/2001/
© European Geosciences Union 2001
Cluster PEACE observations of electrons of spacecraft origin
S. Szita1, A. N. Fazakerley1, P. J. Carter1, A. M. James1, P. Trávnícek1,2, G. Watson1, M. André3, A. Eriksson3, and K. Torkar4
1Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey, RH5 6NT, UK
2Institute of Atmospheric Physics, Academy of Sciences of the Czech Republic
3Swedish Institute of Space Physics, Uppsala Division, Box 537, SE-75121 Uppsala, Sweden
4Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
Abstract. The two PEACE (Plasma
Electron And Current Experiment) sensors on board each Cluster spacecraft
sample the electron velocity distribution across the full 4<pi> solid
angle and the energy range 0.7 eV to 26 keV with a time resolution of 4 s. We
present high energy and angular resolution 3D observations of electrons of
spacecraft origin in the various environments encountered by the Cluster
constellation, including a lunar eclipse interval where the spacecraft
potential was reduced but remained positive, and periods of ASPOC (Active
Spacecraft POtential Control) operation which reduced the spacecraft potential.
We demonstrate how the spacecraft potential may be found from a gradient change
in the PEACE low energy spectrum, and show how the observed spacecraft
electrons are confined by the spacecraft potential. We identify an intense
component of the spacecraft electrons with energies equivalent to the
spacecraft potential, the arrival direction of which is seen to change when
ASPOC is switched on. Another spacecraft electron component, observed in the
sunward direction, is reduced in the eclipse but unaffected by ASPOC, and we
believe this component is produced in the analyser by solar UV. We find that
PEACE anodes with a look direction along the spacecraft surfaces are more
susceptible to spacecraft electron contamination than those which look
perpendicular to the surface, which justifies the decision to mount PEACE with
its field-of-view radially outward rather than tangentially.
Key words. Magnetosheric physics
(general or miscellaneous) Space plasma physics (spacecraft sheaths, wakes,
charging)
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