Combined effects of electron partial thermalization and secondary emission in Hall thruster discharges

Abstract

A model of the plasma interaction with the ceramic walls of a Hall thruster chamber is presented that takes into account partial thermalization of the electron distribution function. A model of secondary electron emission with both elastically reflected and true-secondary electrons is considered. The plasma response is found to differ substantially from low to high thermalization. The different roles of the bulk and emitted populations of electrons are discussed. Plasma fluxes to the wall are independent of the thermalization level except in the very-low thermalization limit, when the tail of the distribution function of bulk electrons is highly depleted. To the contrary, energy losses to the walls and the sheath charge saturation limit depend strongly on the level of thermalization. Elastically reflected electrons affect significantly the plasma response by modifying the fluxes of primary and secondary electrons at the walls. Emphasis is put on obtaining analytical expressions for main plasma magnitudes, which can be implemented in two-dimensional models of the whole plasma discharge.