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Ann. Geophys., 19, 1483-1489, 2001
www.ann-geophys.net/19/1483/2001/
© European Geosciences Union 2001
Four-point high time resolution information on electron densities by the electric field experiments (EFW) on Cluster
A. Pedersen1, P. Décréau2, C.-P. Escoubet3, G. Gustafsson4, H. Laakso3, P.-A. Lindqvist5, B. Lybekk1, A. Masson3, F. Mozer6, and A. Vaivads4
1University of Oslo, Norway
2LPCE/CNES, Orleans, France
3Space Science Department, ESTEC, Noordwijk, The Netherlands
4University of Uppsala, Sweden
5Royal Institute of Technology, Stockholm, Sweden
6SSL, University of California, Berkeley, USA
Abstract. For accurate measurements
of electric fields, spherical double probes are electronically controlled to be
at a positive potential of approximately 1 V relative to the ambient
magnetospheric plasma. The spacecraft will acquire a potential which balances
the photoelectrons escaping to the plasma and the electron flux collected from
the plasma. The probe-to-plasma potential difference can be measured with a
time resolution of a fraction of a second, and provides information on the
electron density over a wide range of electron densities from the lobes (~ 0.01
cm-3) to the magnetosheath (>10 cm-3) and the
plasmasphere (>100 cm-3). This technique has been perfected and
calibrated against other density measurements on GEOS, ISEE-1, CRRES, GEOTAIL
and POLAR. The Cluster spacecraft potential measurements opens the way for new
approaches, particularly near boundaries and gradients where four-point
measurements will provide information never obtained before. Another
interesting point is that onboard data storage of this simple parameter can be
done for complete orbits and thereby will provide background information for
the shorter full data collection periods on Cluster. Preliminary calibrations
against other density measurements on Cluster will be reported.
Key words. Magnetospheric physics
(magnetopause, cusp, and boundary layers) Space plasma physics (spacecraft
sheaths, wakes, charging; instruments and techniques)
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