Erosion Measurements in a Diverging Cusped-Field Thruster (Pre Print)
AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIR/SPACE AND MISSILE PROPULSION DIV
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Results from a long duration test of a cusped-field plasma thruster operating at an anode power of 165 W are presented and discussed. Profile measurements of the boron nitride insulator were performed before and after the 204 h test, enabling the quantification of average erosion rates over a large portion of the interior. Unlike most Hall thrusters, the lifetime is not limited by erosion near the exit plane, due to the positioning of magnetic circuit elements. Additionally, the maximum erosion rate is found to be lower than rates measured in low-power Hall thrusters by at least 50. The lifetime of this laboratory prototype is estimated at 1220 h based on the time needed to erode through the insulator in one of the ring-cusps. Therefore, fortifying cusps with additional or a more durable material would increase the lifetime of future designs. A summary of long duration tests and erosion measurements in Hall thrusters is also provided. A concurrent analysis of deposition within the thruster shows the accumulation of a conductive and ferromagnetic material between cusps. Finally, estimates of electron temperature and ion loss widths near the wall are obtained based on measured distributions of erosion in each cusp. During the tests discussed here, the thruster operated in the high-current mode, characterized by strongly oscillatory anode currents. Erosion rates upstream of the exit cusp may be lower in the low-current mode, where anode current oscillation amplitudes are smaller by two orders of magnitude.
- Electric and Ion Propulsion