Field emission array cathode performance in electric propulsion system environments
The recent drive towards utilizing electric propulsion systems for micro spacecraft warrants the development of efficient, low power and low propellant consumption cathodes. Because of the lower limits on size, power and propellant consumption of hollow cathodes typically employed with Hall and ion thrusters, heaterless cathodes which require no propellant for operation are under investigation. The goal of this work is to develop such a cathode with efficient operation at microwatt power consumption levels. Although field emission arrays (FEAs) fulfill these requirements, they have not been tested in the hostile environments generated by Hall and ion thrusters (e.g., pressures on the order of 10-5 Torr). This report discusses the results of field emission array cathode (FEAC) testing in expected thruster environments, and modeling work to estimate cathode lifetime by predicting tip sputter rates from ion bombardment. Lifetime estimates are computed for molybdenum, silicon, hafnium carbide, and zirconium carbide tip materials in xenon- and argon-rich environments. FEA tip configurations fabricated by SRI and the University of Michigan are employed in this investigation.
