Numerical Simulations of the Electrodynamic Interactions Between a Satellite and Plasma.

The problem of solving the electrodynamic interactions between a satellite and plasma is a difficult one. Analytical treatments are generally based on several approximations and idealizations. In the real situation in space, the interactions involve a satellite having sizes much larger than the electron Larmor radius and having sizes of the order of the ion Larmor radius. There is relative motion between the satellite and the plasma, and an arbitrary orientation of the magnetic field with respect to the relative motion. In such a situation, the theoretical treatment of the plasma dynamics is highly involved. In this work (dissertation), we have attempted to solve this problem by means of numerical simulations. Our numerical model is based on the Particle-In -Cell (PIC) method for treating the plasma and the Poisson equation for the potentials around the satellite. It includes all the essential features mentioned above. Simulations were performed without the relative motion, showing results in fair agreement with available theory. In particular, we found the current collection by the satellite biased at positive potentials gives a current in agreement with the well-known Parker-Murphy theoretical results. We found that there were oscillations in the potential distributions due to plasma instabilities, but these do not effect the time averaged current values. When a relative motion between the satellite and plasma is included in the simulation, the sheath structures and the current collection processes are examined in detail. We find that there is an elongation of the equipotential surfaces along the magnetic field lines, and they are inclined with respect to the magnetic field lines, when the current continuity is properly employed in the simulation. Most importantly, we find that there is an enhancement in the current collected by a satellite, when there is a relative drift between the satellite and the plasma. We have also performed two-dimensional simulations to examine some specific features of satellite-plasma interactions brought out from the three-dimensional model; specifically the effects of a relatively small drift velocity on the potential distributions are examined.