Side and front fast imaging of solid and liquid fed ablative pulsed plasma thruster’s discharge

Ultra-fast camera imaging is used to capture temporal evolution of the plasma discharge in an ablative Pulsed Plasma Thruster (PPT) fueled with solid polytetrafluoroethylene (PTFE) and liquid perfluoropolyether (PFPE), with the goal of comparing the mechanism of the expelled mass acceleration and getting insight into the physics of the processes involved in the discharge maintenance and impulse bit production. The fast photos are taken from two viewpoints (non-simultaneously), directing camera parallel (side view) and perpendicular (front view) to the ablative surface of the propellants, and are correlated with the relevant phases of the discharge current. Side view images reveal the presence of two distinct exhaust fractions, velocities of which differ by an order of magnitude. The speed of the faster fraction is comparable with the median of the ionized particles velocity expelled by the thruster. The vividness of the slow propagating component of the ablated mass, which mostly corresponds to neutral particles (based on velocity estimation) and lower mass bit of PFPE shots hint towards better propellant utilization by a liquid-fed PPT. Front view images confirm stable localization of PFPE discharge, forced by design of the propellant supplying plenum, whereas PTFE discharge is characterized by irregular path that covers an area of the propellant surface in random. The last half-period of the discharge is accompanied by vortices near the cathode spots. They are supposedly formed by evaporated electrode’s material and their trajectories imply further recombination in collisions with the electrodes, making this part of evaporated copper undetectable for charged particles diagnostics. • Front view full-band fast photography of an ablative Pulsed Plasma Thruster discharge. • Reduction of the exposed ablative propellant area diminishes late time ablation. • The ignition processes of PTFE-fed and PFPE-fed PPTs noticeably differ.