Analysis of electromagnetic instabilities in magnetoplasmadynamic thrusters

In recent years, theory, modeling, and experimental studies have contributed to an improved understanding of the physics underlying electrostatic propulsion technologies. This research has focused, in particular, on Hall thrusters, aiming to clarify complex physics: plasma-wall interaction, the presence and role of plasma instabilities and their connection to anomalous transport, and fundamental plasma properties. Electromagnetic devices like magnetoplasmadynamic thrusters (MPDTs), while lacking a comparable flight heritage, possess certain advantages and are increasingly being considered as options for high-thrust electric propulsion in the future. As such, there is a need for targeted research efforts to advance this technology.

One way in which such progress may be gained is through an analysis of the instabilities excited in such architectures and the development of an understanding of their connection to thruster performance. This work focuses on the analysis of the electromagnetic dispersion relation relevant to the coaxial plasma channel of a low power MPDT prototype. The range of solutions is constrained based on plasma parameters determined in two ways: (i) from diagnostics measurements, and (ii) from an MHD code. In this way, specific modes susceptible to excitation can be investigated, and a new detection strategy devised. As has been observed with various kinetic instabilities in Hall thrusters (the electron cyclotron drift instability, ion-ion two stream instability, and others), a complex interplay between modes may govern important aspects of discharge operation. Elucidating such features in MPDTs will be key to their future optimization and development.