Sheath Effects in Computational Hall Thruster Modeling

Justin Koo, University of Michigan

The works of Fife [1], Garrigues [2] and Koo [3] have developed computational Hall thruster modeling to a level where qualitative features of the plasma and electric field can be reproduced. However, these results are possible only with the use of relatively simple-minded corrections to the electron mobility and wall-collision rate. The corrections, although justifiably based on experimental observations, are not rigorously defined by the actual physics governing these processes. Since the dependence of the solution on these corrections is very strong, if computational Hall thruster modeling is ever to take on a predictive role, a much more accurate method of determining these corrections must be discovered.


Recent sheath models by many researchers, including Meezan [4], have included various forms of not only secondary electron emission, but also elastic electron scattering off the sheath without wall impingement. This scattering off a “rough" sheath seems to offer some promise as a physical explanation for elevated near-wall conductivity. Better estimates of the wall-collision rate and electron mobility will be used to improve an existing hybrid particle-in-cell, Monte Carlo collisions (PIC-MCC) model.


Due to observed discrepancies between computational and experimental results, other improvements to the model are also planned. These include the addition of a diffusion term in the calculation of the electron current and the study of additional mobility mechanisms in the plume (bohm-type mobility).


The primary focus of this presentation is to study changes in electron-wall collision rates and electron mobility due to elastic scattering effects. The improved wall-collision rate and electron mobility correction factors are used in an existing hybrid PIC-MCC Hall thruster model to provide comparisons to relevant experimental data.


References

Full references will be available at presentation.

Abstract Author(s): Justin W. Koo and Iain D. Boyd<br />Department of Aerospace Engineering<br />University of Michigan<br />Ann Arbor, Michigan 48109