Computational Simulation of Faraday Probe Measurements.

Abstract

Electric propulsion devices, including ion thrusters and Hall thrusters, are becoming increasingly popular for long duration space missions. Ground-based experimental testing of such devices is performed in vacuum chambers, which develop an unavoidable background gas due to pumping limitations and facility leakage. Besides directly altering the operating environment, the background gas may indirectly affect the performance of immersed plasma probe diagnostics.

This work focuses on computational modeling research conducted to evaluate the performance of a current-collecting Faraday probe. Initial findings from one dimensional analytical models of plasma sheaths are used as reference cases for subsequent modeling. A two dimensional, axisymmetric, hybrid electron fluid and Particle In Cell computational code is used for extensive simulation of the plasma flow around a representative Faraday probe geometry.

The hybrid fluid PIC code is used to simulate a range of inflowing plasma conditions, from a simple ion beam consistent with one dimensional models to a multiple component plasma representative of a low-power Hall thruster plume. These simulations produce profiles of plasma properties and simulated current measurements at the probe surface. Interpretation of the simulation results leads to recommendations for probe design and experimental techniques. Significant contributions of this work include the development and use of two new non-neutral detailed electron fluid models and the recent incorporation of multi grid capabilities.