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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 19, issue 10/12 | Copyright

Special issue: CLUSTER

Ann. Geophys., 19, 1721-1730, 2001
https://doi.org/10.5194/angeo-19-1721-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 Sep 2001

30 Sep 2001

Cluster PEACE observations of electrons of spacecraft origin

S. Szita1, A. N. Fazakerley1, P. J. Carter1, A. M. James1, P. Trávnícek2,1, G. Watson1, M. André3, A. Eriksson3, and K. Torkar4 S. Szita et al.
  • 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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