Parametric evaluation of ion beam properties in the near-field plume of a low-voltage, liquid-fed pulsed magnetoplasmadynamic thruster

A parametric investigation of plume characteristics from a pulsed magnetoplasmadynamic thruster (PMPD) operating with the liquid monopropellant ASCENT is presented. Discharges across a range of driving voltages (200–400 V) and three interelectrode configurations were evaluated to assess their influence on beam behavior. Time-resolved current density mapping revealed symmetric plasma packet formation during both polarities of underdamped current oscillations, indicative of cathode–anode role reversal within each pulse. Peak current densities reached up to 180 A/cm2, corresponding to inferred number densities of 1013–1015 cm−3. Axial measurements of cumulative ion charge carried by the ejected plume suggest enhanced ion ejection with increased electrode separation, along with evidence of ionization persisting downstream of the thruster and substantial dissociative recombination. The total ion charge carried by the ejected plume increase and beam divergence narrows with increasing discharge voltage. Characteristic ion velocity was assessed for all tested conditions, revealing strong sensitivity to interelectrode spacing. Preliminary optical emission spectroscopy of the ejected plume was performed, providing insights into beam composition.