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Ann. Geophys., 16, 1086-1096, 1998
www.ann-geophys.net/16/1086/1998/
© European Geosciences Union 1998
An experiment to study and control the Langmuir sheath around INTERBALL-2
K. Torkar1, M. V. Veselov2, V. V. Afonin2, H. Arends3, M. Fehringer4, G. Fremuth1, K. Fritzenwallner1, Y. I. Galperin2, A. I. Kozlov5, A. Pedersen6,*, S. Perraut7, W. Riedler1, F. Rüdenauer4, R. Schmidt3, A. Smit3, N. Valavanoglou8, and L. V. Zinin9
1SpaceResearch Institute, Austrian Academy of Sciences, Inffeldgasse 12, A-8010 Graz, Austria
E-mail: torkar@fiwf01.tu-graz.ac.at
2Space Research Institute, Russian Academy of Sciences, Moscow, Russia
3Space Science Division, ESA/ESTEC, NL-2200 AG Noordwijk, The Netherlands
4Austrian Research Centre Seibersdorf, A-2444 Seibersdorf, Austria
5NPO KVANT, Moscow, Russia
6Space Science Division, ESA/ESTEC, NL-2200 AG Noordwijk, The Netherlands
7CETP/IPSL, Orleans, France
8Department of Communications and Wave Propagation, Technical University Graz, Graz, Austria
9Kaliningrad State University, Kaliningrad, Russia
*Present address: Department of Physics, University of Oslo, Oslo, Norway
Abstract. The satellite INTERBALL-2 has an orbit with
high inclination (62.8°), covering the altitude range between a few hundred and
about 20000 km. The ambient plasma conditions along this orbit are highly
variable, and the interactions of this plasma with the spacecraft body as well
as the photo-electron sheath around it are considered to be interesting topics
for detailed studies. The electric potential of the spacecraft with respect to
the ambient plasma that develops as a result of the current equilibrium reacts
sensitively to variations of the boundary conditions. The measurement and
eventual control of this potential is a prerequisite for accurate measurements
of the thermal plasma. We describe the purpose and technical implementation of
an ion emitter instrument on-board INTERBALL-2 utilising ion beams at energies
of several thousand electron volts in order to reduce and stabilise the positive
spacecraft potential. First results of the active ion beam experiments, and
other measures taken on INTERBALL-2 to reduce charging are presented.
Furthermore, the approach and initial steps of modelling efforts of the sheath
in the vicinity of the INTERBALL-2 spacecraft are described together with some
estimates on the resulting spacecraft potential, and effects on thermal ion
measurements. It is concluded that even moderate spacecraft potentials as are
commonly observed on-board INTERBALL-2 can significantly distort the
measurements of ion distribution functions, especially in the presence of
strongly anisotropic distributions.
Key words. Space plasma physics (active perturbation
experiments; spacecraft sheaths · wakes · charging; instruments and
techniques).
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