DESIGN AND PERFORMANCE OF AN ANNULAR MAGNETOPLASMADYNAMIC THRUSTER

In this paper both theoretical and experimental results are presented that demonstrate the effects of electrode geometry on the operation of the magnetoplasmadynamic (MPD) arcjet and describe the "onset" phenomenon not as a single phenomenon but as two distinct phenomena-one in which thruster efficiency is drastically reduced due to an anode depletion mechanism and the other when thruster lifetime is decreased due to enhanced erosion. Theory and data both show that the electrode current concentrations can be locally changed by varying the channel's interelectrode separation. The experiment (conducted on a large radius annular geometry) shows a clear separation between an anode depletion description of onset (caused by the radial component of the thrust vector), indicated by the growth of a large anode voltage drop, and onset indicated by the appearance of unsteady large amplitude voltage oscillations which are attributed to convective motion of large concentrated anode arcs.