DIAGNOSTICS AND PERFORMANCE OF A LOW-POWER MPD THRUSTER WITH APPLIED MAGNETIC NOZZLE

This study evaluates the performance of a 50-150-kW thruster which was 1/4-scale of a bench mark magnetoplasmadynamic (MPD) thruster; it was operated with and without applied magnetic nozzle fields. Capacitors (14 muF) and inductors (80 muH) in networks produced relatively consta nt currents for about 450 mus to generate the applied magnetic nozzle, and currents up to 2.3-kA constant for about 300 mus to drive the thr uster. With the solid copper electrode, the applied magnetic field was excluded from the thrust chamber because of the short duration of the experiments. The 1/4-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 th e same m/A. With m > 0.25 g/s, the device was found to operate smoothl y and with little evident erosion. Current-voltage records were simila r with and without applied magnetic nozzle fields, indicating little e ffect of the external nozzles on the power deposition. The current plu me in the expansion region outside the thruster chamber was reduced in axial extent with the application of the magnetic nozzle in this tran sient experiment. Momentum flux in the exhaust flow was measured by lo cal pressure probes. For the same arc power, impact pressures with mag netic nozzles applied were 3-4 times larger than the self-field cases. Also, impact pressure increased with thruster power. For the 1.15- an d 2.30-kA cases, thrust from integrated impact pressure increased by a factor of 1.6 with magnetic nozzles applied. Local electron density a nd temperature were determined using Langmuir probes; these values alo ng with impact pressure were used to determine flow velocity. For the 1. 15- and 2.30-kA cases, values of exhaust velocity increased by fact ors of 1.1 and 1.6, respectively, when the magnetic nozzles were appli ed.