A novel measurment of net erosion and plasma-material interaction in plasma thrusters

Abstract

The lifetime of plasma thrusters is usually limited not by depletion of the propellant supply, but by erosion of the magnetic circuit from plasma particles bombarding the walls of the acceleration channel leading eventually to catastrophic engine failure. As erosion is the primary failure mode of these systems, understanding the erosion physics, plasma-material interactions (PMI), and the relationship between them is of utmost importance for extending the lifetime of high power and other next generation engines. A new measurement technique has been developed that uses lithium depth markers implanted in a thruster wall material. Nuclear Reaction Analysis (NRA) on the implanted material gives net erosion measurements while simultaneous Rutherford Backscattering Spectroscopy (RBS) quantifies the plasma retention and contamination in the surface layers. This insight into the surface composition and PMI is one of the major advantages of this technique when compared to other measurement methods. As an initial assessment of this technique's applicability for plasma thrusters, it has been applied to samples of Boron Nitride exposed to the plume of a Xenon fueled BHT-200 Hall thruster and the results are presented.