Nstar ion thruster plume impacts assessments

摘要

Tests were performed to establish 30-cm ion thruster plume impacts, including plume characterizations via near and far-field ion current measurements, contamination, and sputtering assessments. Current density measurements show that 95 percent of the beam was enclosed within a 22 deg half-angle and that the thrust vector shifted by less than 0.3 deg during throttling from 2.3 to 0.5 kW. The beam flatness parameter was found to be 0.47, and the ratio of doubly charged to singly charged ion current density decreased from 15 percent at 2.3 kW to 5 percent at 0.5kW. Quartz sample erosion measurements showed that the samples eroded at a rate of between 11 and 13 mu m/khr at 25 deg from the thruster axis, and that the rate dropped by a factor of four at 40 deg. Good agreement was obtained between extrapolated current densities and those calculated from tantalum target erosion measurements. Quartz crystal microbalance and witness plate measurements showed that ion beam sputtering of the tank resulted in a facility material backflux rate of approx 10 A/hr in a large space simulation chamber.