Current and Temperature Thresholds for Short-Term Oxygen Poisoning of Hollow Cathodes

Abstract

Hollow cathodes that operate with impurities in the xenon propellant exhibit poisoning of the emitter surface, resulting in a higher surface work function and increased operating temperatures. The goal of this paper is to provide insight Into the physical processes responsible for cathode degradation during short-duration oxygen poisoning over a range of discharge currents and surface temperatures. The experimental results presented here show that the cathode is more susceptible to poisoning at higher oxygen concentration levels, lower discharge currents, and lower initial insert temperatures. The threshold current at which the emitter surface becomes susceptible to oxygen poisoning was determined to be between 8.24 A and 10.17 A for an oxygen concentration level of 10 ppm, and between 10.17 A and 12.35 A for oxygen concentration levels of 50 and 100 ppm. To determine the threshold surface temperature, further work must be conducted to isolate the effects of xenon ion sputtering and surface temperature on cathode operation during poisoning.