Development of low power Hall thrusters

Abstract : Three different types of sub kilowatt class Hail thrusters tor on-board propulsion of small to mid size satellites are being developed at Busek. This paper describes their performance focusing on plasma behavior outside of the thrusters end contrasts the typical Hail thruster plasma with that encountered in MHD generators end accelerators researched in the past and familiar to the plasmadynamic community. A simple performance predicting analytical model. applicable to all sizes of thrusters also is presented. It adequately matches the measured thrust and specific impulse expressed in terms of primary electron loss parameter, and an overall voltage loss which includes the loss in the plasma bridge between the external cathode and the thruster. The external plasma plume was surveyed using a Faraday cup and an emissive probe to measure the beam current and the plasma potential. These measurements. together with the model support our visual observation that the plume. of a well performing thruster. forms at its center a highly conductive jet with sharply defined cone shaped boundaries. These boundaries were tentatively identified as an ion acoustic shock. The preliminary data and analysis indicate that the plasma downstream of the ion acoustic shock is at least partially responsible for the widely reported correlation between increasing test tank pressure and an increase in performance of Hall thrusters.