Direct investigation of near-surface plasma acceleration in a pulsed plasma thruster using a segmented anode

Abstract

The ablative pulsed plasma thruster (APPT) has been widely used on satellites due to its low electrical power requirements and structural simplicity. Recently, a segmented anode schematic has been proposed to increase the main discharge arc current density and the propellant mass ablation of APPTs while using the same input energy. In this work, a structurally similar multi-segmented anode was instead used for plasma measurements. The incentive behind the use of the multi-segmented anode was to measure the plasma propagation process and downstream current flow inside the discharge channel of the APPTs (volume between the electrodes). The multi-segmented anode divides the anode into multiple parts in order to directly measure and analyze the current flow for each anode segment as the APPT plasma moved downstream between the electrodes. This provided new information regarding the plasma propagation process between the electrodes. Local magnetic probe measurements were also conducted inside the APPT discharge channel. From the experimental results, distinct plasma progression towards the downstream direction was identified. The plasma reached a velocity of up to 25 km s−1 at only 5 mm from the propellant surface. In contrast, the downstream portion of the electrodes was found to contribute relatively little to the final velocity (an increase of ~16%). Furthermore, the base (1st) element of the multi-segmented anode (where the discharge arc is located) was found to carry over 5 times more current than downstream segments (which carry the maximum downstream plasma current). These results directly indicate that the downstream plasma carries relatively little current, thus resulting in a lower Lorentz force contribution and downstream acceleration. Instead, most of the plasma acceleration process occurs very near to the propellant surface.