This paper presents a correlated experimental and simulation study of an ionic electrospray thruster beam. The effects of vacuum chamber on the thruster beam are inferred through comparisons of laboratory measurements and simulations of the beam in an idealized chamber environment. While laboratory and simulation results agree qualitatively, the quantitative comparison shows that, for single positive polarity beams, the experimental measurement exhibits a more focused, higher density beam core and a flatter potential profile in the radial direction than the beam in simulation. This difference is mostly due to the background plasma generated in the vacuum chamber. The background plasma provides partial neutralization of the ion beam, thus reducing the radial direction beam spreading due to the space charge effect. The background plasma also cuts off the beam expansion process, thus reducing the radial direction potential gradient. Thus, vacuum chamber measurements of electrospray thruster beams will over-predict the density in the beam core region but under-predict beam potential with respect to ambient for the in-space condition.
Asher et al. (Wed,) studied this question.