The effect of facility background pressure on hollow cathode operation

Abstract

The effect of facility background pressure on the operation of a hollow cathode in a Hall thruster-like axial magnetic field is experimentally characterized. Facility pressure was varied between 10 and 88 μTorr-Xe using a secondary flow of xenon into the test facility, and cathode operation was studied using a combination of telemetry and plasma diagnostic measurements. Increasing pressure resulted in decreased discharge voltage, cathode orifice plate temperature, and voltage and current oscillation magnitudes. The plasma diagnostics, which consisted of a radially mounted retarding potential analyzer and an ion saturation probe and emissive probe mounted to a fast reciprocating motion stage, showed that increasing pressure resulted in decreased radial high-energy ions, decreased centerline maximum plasma potential and electron temperature, and increased plasma density farther than 40 mm downstream of the cathode. The effects of background pressure on the cathode plume were largely constrained to between 50 and 100 mm downstream of the cathode, where the largest gradients of plasma potential and electron temperature occur. Experimental measurements were combined with neutral density simulations to identify that the confluence of changes in electron temperature, plasma density, and neutral density result in an increase of almost an order of magnitude in the calculated ionization rate in the same location. These results have implications for both standalone cathode tests and for improving the understanding of facility effects on cathode coupling in Hall thrusters.

Use of an accelerated testing method to characterize inner front pole cover erosion in a high power Hall thruster

“…The cathode ion energy measurements were performed with facility pressures approximately an order of magnitude higher than ambient pressures in the thruster tests. Recent measurements 33 have shown that the neutral density in the near-cathode region (within about 50 mm of the cathode orifice) is dominated by the neutral gas flow from the cathode and that plasma parameters in this region do not change significantly with changing facility pressure. These experiments included radial ion energy measurements using a retarding potential analyzer which yielded similarly high energies and showed that the peak energies decreased with increasing pressure.…”