Investigation of the discharge characteristics of the T6 hollow cathode operating on several inert gases and Kr/Xe mixture

Rudwan, I.F.M. Ahmed and Gabriel, S.B. (2002) Investigation of the discharge characteristics of the T6 hollow cathode operating on several inert gases and Kr/Xe mixture. 11th International Congress on Plasma Physics. ICPP2002, Sydney, Australia. 14 - 18 Jul 2002. pp. 294-297 .

Abstract

Xenon is currently the propellant of choice for gridded ion thrusters. But in order to make deep space missions feasible, an increase in the Specific Impulse (SI) that these thrusters can achieve is necessary. One method of achieving this is to use a propellant with a lower atomic mass (e.g. argon). However, the feasibility of operating the hollow cathode using these alternative propellants has to be demonstrated. Moreover, interest in decreasing the propellant cost in missions and ground testing (especially life tests) have led to the comprehensive discharge characterisation of several gases that will be presented in this paper. The tests were carried out in diode configuration using a T6 hollow cathode with an enclosed keeper design employing xenon, krypton, argon and a Kr/Xe mix.
The discharge initiation tests were undertaken with a view to investigate some of the factors thought to influence the starting potential such as mass flow rate and tip temperature. It was found that, for mass flow rates ranging from 0.2–1.1 mg/s and cathode tip temperatures ranging from 900–1300°C, the breakdown potential was less than 50V for argon, less than 25V for krypton, less than 21V for xenon and less than 35V for the Kr/Xe mix. The discharge initiation results were then compared to those obtained by Fearn et al. [8] with a T5 cathode operating on mercury and with a T6 cathode utilising an open keeper design using xenon propellant [3]. Steady state discharge behaviour was also investigated under a range of operating conditions. Spot to plume mode transitions were observed in argon, krypton and Kr/Xe discharges.

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