Design of a hollow cathode thruster: concepts, parameter study and initial test results

Abstract

Two electric propulsion concepts have been developed at Technische Universität Dresden as spin-off devices of regular hollow cathodes and initial testing has been conducted. Both devices represent millinewton thrusters that take advantage of thermionic electron emission using the low work function materials C12A7, LaB6, and thoriated tungsten in different design configurations. The first concept represents an electrothermal thruster which generates thrust by expanding and accelerating a heated propellant in a nozzle. Initial thrust measurement tests were carried out which showed thrust levels well above cold gas thrust, but low thrust efficiencies. The influence of different geometric parameters on the discharge properties and the performance is investigated and presented. The second thruster concept is a novel electromagnetic device in which charge carriers in a plasma discharge are accelerated by an applied magnetic field that is orthogonally oriented to the discharge current. Initial tests with C12A7 were not successful, but the functionality of the concept was shown by thrust measurements using a thoriated tungsten wire as an electron emitter.

An experimental study on the degradation of the C12A7 hollow cathode

“…It has been reported to have some unique features, including a lower operating temperature, good chemical stability and reported iodine compatibility, as well as some specific failure modes [11,12]. Rand, McDonald and Drobny et al reported the overheating and melting of electride emitters during hollow cathode operation [6,11,13]. Kottke et al compared the thermionic emission properties of LaB 6 and C12A7.…”