Study on Performance Enhancement of an Electrothermal Pulsed Plasma Thruster

We designed a pulsed plasma thruster (PPT) with a propellant feeding mechanism using two poly-tetra-fluoroethylene (PTFE) bars as propellants. Both the PPT and capacitors were mounted on a thrust stand with a 1-m-long arm developed for precise measurement of impulse bit. The initial thrust performance showed impulse bit per joule of 43-48 μNs/J, specific impulse of 470-500 s and thrust efficiency of 10-12% with stored energy of 4.5-14.6J. 10000-shots operation was conducted with a stored energy of 8.8J. As a result, each PTFE bar was supplied in a length of approximately 2 mm, and a total impulse of approximately 3.6 Ns was obtained, though both the impulse bit and the thrust efficiency gradually decreased with shot number because of uneven receding of the PTFE surface. In order to investigate physical phenomena in a whole system, an unsteady numerical calculation was performed, which simultaneously simulates unsteady phenomena of discharge, heat transfer to/inside the PTFE, ablation from the PTFE surface and plasma flow. The calculated discharge current waveform and the PTFE mass loss showed good agreements with experimental results. The uneven shape of the PTFE surface after 10000-shots operation was also qualitatively explained with the calculation.