Semi-analytical model of ionization oscillations in Hall thrusters

Abstract

This thesis presents efforts to better understand the breathing-mode oscillation within Hall thrusters. These oscillations have been present and accepted within Hall thrusters for decades, but recent interest in the oscillation has occurred partly due to a possible connection between wall erosion and the oscillations. The first part of this thesis details a steady model of the ionization region in a Hall thruster that finds existence criteria for the steady solution under the hypothesis that the steady limits match the smooth sonic passage limits. Operation outside these limits would correspond to unsteady behavior which could result in either a periodic oscillatory behavior or plume extinguishment. To distinguish between periodic behavior and thruster extinguishment, an unsteady model of the ionization region is developed, but this model falls short of its goal. The transient model, however, is still useful for observation of the periodic nature of an oscillating Hall thruster. Next, an anode depletion model for Hall thrusters is formulated. This model explores one of the causes of thruster extinguishment, when the plasma cannot reach the anode. Finally, a new method for performing Boron Nitride erosion measurements is discussed and preliminary results are presented. This method imbeds Lithium ions into Boron Nitride. The depth of the Lithium can be measured before and after erosion or deposition to give a net erosion or accumulation measurement.