Fundamentals of Breakdown & Plasma Generation

In recent years, there has been a concerted research effort in theory, modeling, and experimentation focusing on electrostatic propulsion technologies. Research on Hall thrusters, in particular, aims to optimize thruster architecture and clarify complex physics: plasma-wall interaction, the presence and role of plasma instabilities and their connection to anomalous transport, and measure fundamental plasma properties. Electromagnetic propulsion devices like magnetoplasmadynamic thrusters (MPDTs), while lacking a comparable flight heritage, are increasingly being considered as options for high-thrust electric propulsion in the future. Several aspects of the basic physics of such architectures remain unclear. The nature of the instabilities excited in such architectures, and an understanding of their connection to thruster performance, is one important area requiring further investigation.

 

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 from diagnostics measurements and an MHD code. In this way, specific modes susceptible to excitation can be investigated, and a 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, non-linear interplay between modes may govern important aspects of discharge operation. Elucidating such features in MPDTs will ultimately be key to their future optimization and development.