Modeling Neutral Densities Downstreamof aGridded Ion Thruster

摘要

The details of amodel for determining the neutral density downstreamof a gridded ion thruster are presented. Anninvestigation of the sources of neutrals emanating from the NASA Evolutionary Xenon Thruster ion thrusterndetermined that the most significant contributors to the downstream neutral density include discharge chambernneutrals escaping through the perforated grids, neutrals escaping from the neutralizer, and vacuum facilitynbackground neutrals. For the neutral flux through the grids, near- and far-field equations are presented fornrigorously determining the neutral density downstreamof a cylindrical aperture.These equations are integrated intona spherically-domed convex grid geometry with a hexagonal array of apertures for determining neutral densitiesndownstream of the ion thruster grids. The neutrals escaping from an off-center neutralizer are also modelednassuming diffuse neutral emission from the neutralizer keeper orifice. Finally, the effect of the surrounding vacuumnfacility neutrals is included and assumed to be constant. Themodel is used to predict the neutral density downstreamnof the NASA Evolutionary Xenon Thruster ion thruster with and without neutralizer flow and a vacuum facilitynbackground pressure. The impacts of past simplifying assumptions for predicting downstreamneutral densities arenalso examined for the NASA Evolutionary Xenon Thruster ion thruster.