Investigation of the effects of a pulsed electrode on a magnetized plasma

The electrodynamic tether is a device proposed to provide power to space vehicles in near earth orbit. The interaction of the tether with the ambient ionospheric plasma is still being investigated and is not well understood. Several models of this interaction are reviewed in this thesis. One model, the anisotropic contactor model, predicts the formation of electrostatic double layers near a current collecting plasma contactor. Detailed experiments performed at UCLA indicate the tether interaction with the ionosphere is more complicated than the anisotropic model predicts. In particular, it was found not to be possible to collect a steady state current from the laboratory plasma and no evidence of collected current levels above the electron saturation current was observed. This thesis reports results of experiments performed in a magnetized plasma with parameter ratios characteristic of the ionosphere. Current collecting probes, capacitive probes and magnetic loop probes were used to investigate the effects of a pulsed disc probe on the plasma. The results of this work indicate the pulsed electrode creates a complicated potential structure in the magnetized plasma and is also responsible for initiating a high frequency electrostatic instability in the plasma. In addition, observations of fluctuations in the current collected from the plasma support the idea that a steady state current can not be collected in the ionosphere.