Modeling of channel wall erosion in Hall Effect Thrusters

Hall Effect Thrusters (HETs) are used for satellites applications, particularly orbiting at Low/Geo Earth Orbit (LEO/GEO) for telecommunications and government spacecraft because of their efficiency and competitiveness if compared to other electric propulsion devices. Furthermore, HETs have great potential because, in the future, they could be used for orbit transfers and interplanetary space missions. The erosion of HETs channel walls represents the main limiting factor of thrusters lifetime. Experimental characterization of erosion is expensive and time consuming, since thrusters lifetime is in the order of thousands of hours, hence the need of computational models which can accurately predict erosion is increasingly important. Computational tools can be a very handy tool also during the design process as it can help designers foresee how changes in the project will affect lifetime. In this thesis an effort has been put into developing an erosion model which can predict erosion in HETs using data for sputtering of Xe ions on ceramics in energy ranges close to HETs operating conditions. In particular a brief overview of electric propulsion, focusing on HETs, is given. Erosion process, sputtering and plasma modeling, past and current erosion models will be presented. An erosion model will be developed, based on experimental data for sputtering at very low energies and at high temperature. It will be applied to a model of the SPT-100 and results will be compared to experimental wall profiles. The aim of this thesis is to develop an erosion model as self consistent as possible, which uses as few empirical coefficients as possible, so that it could be used to predict erosion in HETs accelerating channel without knowing a priori the erosion profiles on which to adapt the coefficients such as the Threshold Energy E_{th}.