Discharge characteristics and increased electron current during azimuthally nonuniform propellant supply in an anode layer Hall thruster

Discharge current components, such as electron, ion beam, and lost-to-wall currents, are obtained as functions of azimuthal propellant inhomogeneity in a Hall thruster. Discharge characteristics are discussed based on discharge current oscillation and radial-azimuthal discharge photography. A highly oscillative operation regime is found to be accompanied by radially enlarged expansion of discharge under limited electron currents. Further increases in neutral inhomogeneity lead to quiescent discharge combined with enhanced electron currents and an azimuthally separated ionization region. An axial one-dimensional classical view of electron flow is found to explain the observed electron current evolution only until moderate propellant inhomogeneity occurs. Through discharge image analysis, it is shown that plasma inhomogeneity increases linearly with respect to the input neutral particle inhomogeneity. The evolution of the inhomogeneity does not capture a stepwise increase in the electron current during discharge mode changes; however, the monotonic increase featured in each discharge regime shows that the azimuthal gradient of plasma properties can contribute to increased electron current. Lastly, the weakened magnetic barrier to electron flow resulting from axial-azimuthal variation in plasma structures is presented as another possible cause of increased electron current in nonuniform propellant operations.