Computational Modeling of Expanding Plasma Plumes in Space Using a PIC-DSMCAlgorithm

摘要

A comprehensive computational model of the plume of a Hall Thruster is presented.Spacecraft-plume interaction issues are addressed by studying how a partially ionized plasma expands in three dimensions and interacts with the surfaces it encounters. A quantitative analysis of fundamental parameters is used to show that the plume is an unmagnetized, quasi-neutral plasma in which Charge Exchange collisions play a significant role. The electrons are shown to be isothermal and collisionless and the electron momentum equation is shown to reduce to the Boltzmann relationship. An axisymmetric computational model of the plume is described in detail. The model combines the Particle-in-Cell (PIC) and Direct Simulation Monte Carlo (DSMC) methods to create a quasi-neutral PIC-DSMC model. The resulting model is relatively fast and is used to model meter scale objects on workstation class computers. Comparisons are made to experimental data from multiple sources. The model is shown to have good agreement with macroscopic quantities such as current densities and sputtering rates but poor agreement with microscopic quantities like the ion distribution function. Disagreement is thought to be due to inadequicies in the plasma source model. Further results are presented showing the thruster operating in vacuum. 'Rules of thumb' are recommended for scaling erosion rates.