Optical Boron Nitride Insulator Erosion Characterization of a 200 W Xenon Hall Thruster

Abstract

Abstract : Vacuum ultraviolet emission (137.9 nm) of boron neutrals sputtered from a 200 W xenon Hall thruster boron nitride insulator is evaluated as a diagnostic for real-time evaluation of thruster insulator erosion. Three Hall thruster plasma control variables are examined: ion energy (discharge potential), ion flux (propellant flow), and plasma conductivity (magnetic field strength). The boron emission, and hence the insulator erosion rate, varies linearly with ion energy and ion flux. A minimum erosion rate appears at intermediate magnetic field strengths. This may indicate that local plasma conductivity significantly affects the divergence of the plasma plume and hence thruster lifetime. The emission measurements of insulator erosion are supported by near field (^10 mm) xenon ion laser-induced fluorescence velocity measurements which confirm that changes in the magnetic field produce significant changes in the ion flow vectors. The near field plume appears to be relatively invariant to changes in the plasma density, but increased flow divergence may be attributed to changes in magnetic strength. Faraday probe plume divergence measurements in the far field (60 cm) show that some of these differences propagate into the far field.