Three dimensional numerical models for the current collection of a highly biased satellite in space

Since probe theory was developed, the problem of current collection by a charged spherically or cylindrically symmetric body has been investigated by a number of authors (e.g. Parker and Murphy, 1967; Linson, 1969; Laframboise and Rubinstein, 1976). The purpose of this paper is to develop a fully three-dimensional particle simulation code which can be used to understand the physics of current collection in three dimensions and to analyze data resulting from the future TSS (Tethered Satellite System) missions.;In summary, it was found that the SIPS model (i.e. neglect the space charge effect) is most appropriate for studying the evolution of electron torus around a highly biased satellite in space. On the other hand, the SUPS model (i.e. include the space charge effect) would be appropriate for studying the influence of ion motion on current collection. The three dimensional self-consistent particle code developed in this dissertation can be used to study the physical phenomena resulted from highly charged bodies in a space plasma and predict the current collected by the system. This is especially applicable to the future reflight of the TSS experiments.;According to the configuration of TSS, we have constructed two types of particle simulation models, a simple-particle simulation (SIPS) model and a super-particle simulation (SUPS) model, to study the electron transient response and its asymptotic behavior around a three dimensional, high biased potential satellite. The potential distribution surrounding the satellite is determined by solving Laplace's equation in the SIPS model and by solving Poisson's equation in the SUPS model. Thus, the potential distribution in space is independent of the density distribution of the particles in the SIPS model but it does depend on the density distribution of the particles in the SUPS model. The evolution of the potential distribution in the SUPS model can be expressed by the following steps: (1) The potential distribution is spherically symmetric in the beginning; (2) The spheroid potential distribution occurs in the region close to the high potential satellite; (3) The dumbbell-shaped potential distribution eventually forms with a high potential region in the polar regions. When the spherical satellite is charged to a high positive potential and immersed in plasma with a uniform magnetic field, the formation of an electron torus in the equatorial plane and the elongation of the torus along the magnetic field can be found in both the SIPS and the SUPS models but the shape of the torus is different. The areas of high potential that exist in the polar regions in the SUPS model exaggerate the elongation of the electron torus along the magnetic field. In addition, the currents collected by the satellite with different magnetic field strength in both the SIPS and SUPS models are investigated in this study. Due to nonlinear effects in the SUPS model, the current collection curve oscillates during the first 10 plasma periods in the SUPS model (it does not appear in the SIPS model). From the parametric studies, we find that the oscillating phenomenon of the current collection curve occurs only when the magnetic field strength is less than 0.2 gauss for the present SUPS model.