Thrust production mechanisms in Hollow cathode microthrusters

Hollow cathode have recently been investigated at the University of Southampton as potential standalone microthrusters. Thrust measurements suggest that in some cases, hollow cathodes are able to generate specific impulse of over 1000s with xenon. The means by which hollow cathodes are able to generate such high levels of specific impulse is not clearly understood. This paper explores thrust production mechanisms in the T5, T6 and XIPS hollow cathodes based on thrust performance and ion energy measurements. Analysis suggests the total thrust produced includes components of gas dynamic thrust particularly as a result of an intense electron pressure at the cathode exit, but also shows evidence for magneto-hydro-dynamic (MHD) forces at high currents and low flow rates arising from the self-induced azimuthal magnetic field within the orifice and resulting cross-field interaction plasma. Data may also suggest ion acceleration due to plasma potential hills. While this initial characterization can only loosely attribute the relative magnitude each mechanism plays it does show evidence for each. This research shows that with further development based on an understanding of the thrust mechanism, hollow cathodes thrusters could present significant refinements to the technology of electric propulsion.