Comparison of Hollow Cathode Discharge Plasma Configurations

Hollow cathodes are used in plasma contactor and electric propulsion devices to provide electrons for sustaining plasma discharges. Based on previous cathode life tests where erosion was observed on hollow cathode assembly components, it is desirable to understand the plasma flow field downstream of hollow cathodes. Plasma flow field measurements are presented herein for hollow cathode generated plasmas using both local and remotely located plasma diagnostics. Two cathode discharges are presented: 1) an open, no magnetic field configuration and 2) a setup simulating an ion thruster discharge chamber. In the open cathode configuration, large amplitude plasma potential oscillations, ranging from 20 V to 85 V within a 34 V discharge, were observed using a floating emissive probe. These oscillations were observed over a dc potential profile that contained a clear potential hill structure. A remotely located electrostatic analyzer (ESA) was used to measure the energy of ions produced within the plasma, and energies were detected that met and in some cases exceeded the peak plasma potentials detected by the emissive probe. In the prototype NSTAR-like discharge chamber configuration, plasma potentials from the emissive probe agreed with ion energies recorded by the remotely located ESA. A correlation model wa