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Ann. Geophys., 20, 365-376, 2002
www.ann-geophys.net/20/365/2002/
© European Geosciences Union 2002
Electrostatic interaction between Interball-2 and the ambient plasma. 1. Determination of the spacecraft potential from current calculations
M. Bouhram1, N. Dubouloz1,2, M. Hamelin1, S. A. Grigoriev3, M. Malingre1, K. Torkar4, M. V. Veselov5, Y. Galperin5, J. Hanasz6, S. Perraut7, R. Schreiber8, and L. V. Zinin3
1CETP-CNRS, 4 Avenue de Neptune, 94100 Saint-Maur, France
2LPCE-CNRS, 45071 Orleans Cedex, France
3Mathematical Dept., Kaliningrad State University, 236041 Kaliningrad, Russia
4Space Research Institute, A. A. S., Inffeldgasse 12, A-8010 Graz, Austria
5Space Research Institute, R. A. S., Profsoyuznaya 84/32, 117810 Moscow, Russia
6Space Research Centre, P. A. S., ul. Rabianska 8, 87-100 Torun, Poland
7CETP-CNRS, 10-12 Avenue de l’Europe, 78140 Velizy, France
8N. Copernicus Astronomical Centre, P. A. S., ul. Rabianska 8, 87-100 Torun, Poland
Correspondence to: M. Bouhram
(mehdi.bouhram@cetp.ipsl.fr)
Abstract. The Interball-2
spacecraft travels at altitudes extending up to 20 000 km, and becomes
positively charged due to the low-plasma densities encountered and the
photoemission on its sunlit surface. Therefore, a knowledge of the spacecraft
potential Fs is required for
correcting accurately thermal ion measurements on Interball-2. The
determination of Fs is based
on the balance of currents between escaping photoelectrons and incoming plasma
electrons. A three-dimensional model of the potential structure surrounding
Interball-2, including a realistic geometry and neglecting the space-charge
densities, is used to find, through particle simulations, current-voltage
relations of impacting plasma electrons Ie (Fs
) and escaping photoelectrons Iph (Fs
). The inferred relations are compared to analytic relationships in order to
quantify the effects of the spacecraft geometry, the ambient magnetic field B0
and the electron temperature Te . We found that the complex geometry
has a weak effect on the inferred currents, while the presence of B0
tends to decrease their values. Providing that the photoemission saturation
current density Jph0 is known, a relation between Fs
and the plasma density Ne can be derived by using the current
balance. Since Jph0 is critical to this process, simultaneous
measurements of Ne from Z-mode observations in the plasmapause, and
data on the potential difference Fs
- Fp between the spacecraft
and an electric probe (p) are used in order to reverse the process. A value Jph0
~ = 32 µAm-2 is estimated, close to laboratory tests, but less than
typical measurements in space. Using this value, Ne and Fs
can be derived systematically from electric field measurements without any
additional calculation. These values are needed for correcting the
distributions of low-energy ions measured by the Hyperboloid experiment on
Interball-2. The effects of the potential structure on ion trajectories
reaching Hyperboloid are discussed quantitatively in a companion paper.
Key words. Space plasma physics
(charged particle motion and acceleration; numerical simulation studies;
spacecraft sheaths, wakes, charging)
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