Plume measurements of a 1 J ablative pulsed plasma thruster fed with non-volatile liquid propellant

Abstract The exhaust plume of a 1 J ablative pulsed plasma thruster (APPT) fed with non-volatile liquid propellant (perfluoropolyether—PFPE) was studied experimentally with electric probes. A Faraday cup and retarding potential analyzer were used with a time-of-flight approach to determine the shape and ion content of the plume, including the energy and velocity distributions of individual ion species. It was found that the plume was composed mainly of fluorine ions, with charge-states up to 6+. Other constituents of PFPE (carbon and oxygen) were detected in very low quantities. The results for liquid PFPE were similar to those obtained earlier for solid polytetrafluoroethylene (Teflon), with the exception of a larger contribution of highly ionized fluorine species. The plume measurements allowed calculation of efficiency factors and comparison with thruster efficiency. The obtained distributions of ions as well as the large relative abundance of high charge-state ions were indicative of a lack of thermal equilibrium in the plasma of APPT.