An experiment to study and control the Langmuir sheath around INTERBALL-2
- 1SpaceResearch Institute, Austrian Academy of Sciences, Inffeldgasse 12, A-8010 Graz, Austria
- 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).