Three-Dimensional Model for Erosion of a Hall-Effect Thruster Discharge Channel Wall

The erosion of the channel wall in Hall-effect thrusters limits the maximum thruster operating lifetime. Hall-effect thruster channel wall materials are often binary composites of BN and SiO2. The heterogeneity of the material drives the development of complex surface features and roughness during the erosion process. A three-dimensional model of the atomic sputtering of a heterogeneous material is developed. The model investigates, through a ray-tracing technique and empirical erosion rate models of each phase, the interaction between the plasma and the material microstructure. Simulated surface profiles are compared with experimental data collected from the eroded channel wall of the U.S. Air Force Research Laboratory/University of Michigan P5 Hall-effect thruster. The channel wall is composed of M26, a BN-SiO2 composite material. Simulated surface features and roughnesses for an ion incidence angle of 30 deg resemble those observed through scanning electron microscopy and optical profilometry of the P5 channel wall. Predicted root mean square roughnesses, for 30 deg ion incidence, of 8 mu m are within 33% of the 6 +/- 2.5 mu m root mean square measured experimentally. The composition of the channel wall surface is investigated via x-ray photoelectron spectroscopy and is comparable to prior work, but the reduction in the presence of BN with erosion is not adequately captured by this model.