Diagnostics and performance of a low-power MPD thruster with appliedmagnetic nozzle

Abstract

This study evaluates the performance of a 50-150-kW thruster which was j-scale of a bench mark magnetoplasmadynamic (MPD) thruster; it was operated with and without applied magnetic nozzle fields. Capacitors (14 jnF) and inductors (80 /uH) in networks produced relatively constant currents for about 450 /us to generate the applied magnetic nozzle, and currents up to 2.3-kA constant for about 300 /us to drive the thruster. With the solid copper electrode, the applied magnetic field was excluded from the thrust chamber because of the short duration of the experiments. The i -scale device was mass starved below m = 0.135 g/s; this was equivalent to 2 g/s for a full-scale MPD thruster with the same ml A. With m > 0.25 g/s, the device was found to operate smoothly and with tittle evident erosion. Current-voltage records were similar with and without applied magnetic nozzle fields, indicating little effect of the external nozzles on the power deposition. The current plume in the expansion region outside the thruster chamber was reduced in axial extent with the application of the magnetic nozzle in this transient experiment. Momentum flux in the exhaust flow was measured by local pressure probes. For the same arc power, impact pressures with magnetic nozzles applied were 3-4 times larger than the self-field cases. Also, impact pressure increased with thruster power. For the 1.15and 2.30-kA cases, thrust from integrated impact pressure increased by a factor of 1.6 with magnetic nozzles applied. Local electron density and temperature were determined using Langmuir probes; these values along with impact pressure were used to determine flow velocity. For the 1.15and 2.30-kA cases, values of exhaust velocity increased by factors of 1.1 and 1.6, respectively, when the magnetic nozzles were applied.