Resistive plasma detachment in nozzle based coaxial thrusters

Abstract

Nozzle based coaxial plasma thruster constitute potentially attractive electric propulsion engines that are both compact (with high thrust density) and robust. The coaxial plasma thruster can be viewed as an evolutionary state of magnetoplasmadynamic (MPD) thruster development that may satisfy the demanding performance requirements of Space Exploration Initiative (SEI) relevant cargo or piloted missions. Previous work (Schoenberg et al., AIAA Technical Report 91‐3570) has shown that ideal magnetohydrodynamics (MHD) plays a major role in multi‐megawatt coaxial plasma thruster dynamics, particularly in the behavior of high‐grade plasma acceleration by a converging‐diverging magnetic nozzle. In this paper, we examine the detachment of high‐grad MHD plasma from a magnetic nozzle by resistive diffusion. A quantitative description of the resistive detachment process is derived. Included is a discussion of non‐ideal MHD effects, including classical and anomalous resistivity, that can enhance the detachment. This analysis supports the hypothesis that magnetic nozzle design for high‐performance thruster operation requires an optimization between the conflicting requirements of efficient plasma acceleration and plasma detachment. A qualitative prescription for such an optimized magnetic nozzle design is discussed.