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Ph.D Thesis Proposal
by Aaron M. Schinder
Dr. Mitchell Walker, Advisor School of Aerospace Engineering Georgia Institute of Technology Dr. John Yim NASA Glenn Research Center Dr. Julian J. Rimoli, Advisor School of Aerospace Engineering Georgia Institute of Technology Dr. Sven Simon School of Earth and Atmospheric Sciences Georgia Institute of Technology
INVESTIGATION OF HALL EFFECT THRUSTER CHANNEL WALL EROSION MECHANISMS
9:30-11:00 AM, Wednesday, October 7, 2015
EAS (Earth and Atmospheric Sciences) L1114
ABSTRACT:
Plasma erosion of the discharge channel wall of Hall effect thrusters (HETs) is the primary mechanism limiting their operational life. Work has been done to understand the ion sputtering of materials, and to apply models of the plasma discharge in a HET to simulate the erosion of the channel wall profile. While state-of-the-art engineering models have reproduced average azimuthal profiles of eroded channel walls, and predicted average erosion rates, there are still phenomena that are unexplained. One phenomenon of interest is the anomalous erosion ridges: Azimuthal saw-tooth shaped ridge structures grow during the long-duration operation of many HETs. A hypothesis, called the strain relief hypothesis (SRH), is proposed to explain the ridges as resulting from a growth process driven by the release of thermo-mechanical strain energy in the HET channel walls. The SRH is investigated theoretically, and certain qualitative aspects match. An experimental test has been performed in an attempt to isolate and detect growth processes driven by the presence of mechanical loads during plasma erosion. A growth process has been observed to occur in pre-roughened fused silica samples, however it does not depend on the applied mechanical load, and does not correspond to the predictions of the SRH. Observations to date are not consistent with the SRH. It is proposed to complete the work by performing two more exposures, with care taken to measure in real-time the applied load to the samples. To explain the growth process that does occur, an alternative hypothesis is proposed, and it is proposed to investigate the hypothesis for plausibility with a numerical model. Completion of this work should provide experimental verification of at least one growth process, which may eventually lead to the ability to predict and model the anomalous erosion ridge phenomenon in HETs and improve confidence in life modeling.
