Breathing Mode Effects on Hall Thruster Plasma Quantities and Channel Wall Power Loss

Abstract

Breathing mode instabilities, axially-oriented waves between 5-40 kHz, have been observed in Hall thruster operation since the earliest days of experimental research, including their ability to grow large enough to extinguish the working plasma. Recent forays into higher power Hall thrusters and extended mission durations highlight the need to understand the mechanisms and consequences of the breathing mode. While experiments in the last 20 years have increased the understanding of the time dependent behavior of plasma within the channel, analytical and numerical models have struggled to accurately replicate the oscillation or predict its effects. This thesis presents a partial-D fluid model to numerically solve for plasma and neutral density, ion and electron velocity, and mass utilization in a radially- and azimuthally-symmetric SPT-type Hall thruster. After an ideal steady state solution converges, these quantities evolve in the presence of a driven sinusoidal oscillation of the electric field, which simulates a breathing mode oscillation. Separate simulations vary the frequency and amplitude of the driven oscillations to test spatial and temporal variations of the acceleration region. Then, analysis focuses on how the oscillations affect plasma quantities and key contributors to channel wall power loss. This work provides clarification on how the breathing mode perturbs the plasma and how this compares with experiments in the literature.