Two Problems Involving Imperfect Conductivity in a Collisionless Plasma.

The first problem deals with magnetic merging, the process by which magnetic field lines in a plasma change their topology. The Sonnerup merging model, in which merging takes place in the boundary between two regions of oppositely directed magnetic field, is extended to allow plasma flow parallel to the boundary. Solutions in the extended model are found to exist as long as the change in the quantity across the boundary does not exceed a critical magnitude dependent on the field strengths and plasma densities. The second problem concerns current interruption in a collisionless plasma, the process by which currents in a plasma above a critical magnetide are spontaneously reduced by a mechanism of anomalous resistivity. A new mechanism is proposed in which a growing electrostatic wave traps current-carrying particles within the potential of the wave, thus reducing the current.