Extracted Current, Bias Voltage, and Ion Production of Cathodic Hollow-Cathode-Driven Plasma Contactors

Abstract

Plasma properties on extracted electron current–bias voltage characteristics are presented for three selected plasma contactor configurations: a hollow-cathode-only concept, a motive discharge chamber concept, and a passive discharge chamber concept. Measurements were used to demonstrate how one could achieve low impedance performance without being affected by space plasma properties or by consuming significant propellant mass and power. A one-dimensional model was applied to describe the plasma expansion process that occurs downstream of a cathodic contactor. The model matched well with experimental trends and indicated that the plasma ion production rate within and nearby the plasma contactor dominated the emission-bias behavior of the devices. High ion production rate at a given total mass flow resulted in high propellant utilization and low discharge loss. However, plasma potential measurements showed that an anode sheath limited the maximum propellant unitization to less than and led to a foldback in discharge loss curves. The anode sheath and foldback resulted in poor agreement with zero-dimensional energy balance models that do not model this process. Finally, it was found that the passive discharge chamber concept resulted in the lowest energy cost and a larger clamping extracted current compared with the hollow-cathode-only concept.