Kinetic Simulation of Ion Thruster Plume Neutralization in a Vacuum Chamber

TL;DR

This study uses advanced simulation methods to analyze how ground vacuum chamber effects influence ion thruster plume neutralization, revealing key factors like chamber walls, neutralizer placement, and background pressure that alter plasma behavior.

Contribution

It provides detailed insights into how vacuum chamber environment impacts plume neutralization, highlighting the importance of simulation for understanding facility effects in thruster testing.

Findings

Chamber walls increase electric potential and electron temperature.

Neutralizer position affects electron extraction and plume neutralization.

Background pressure influences ion sheath formation and ion current paths.

Abstract

The electrical environment of a ground vacuum testing chamber creates facility effects for gridded ion thrusters. For example, it is well known that the plume from the thruster generates current paths that are very different from what occurs in space, and the neutralization of this plume is also different. For reasons such as this, it is important to clarify how the experimental testing environment affects plasma flows, but understanding this effect solely through ground experiments is difficult. To that end, this study utilizes particle-in-cell and direct simulation Monte Carlo methods to simulate xenon beam ions and electrons emitted from a neutralizer. First, we compare simulations conducted within the chamber to those conducted in space, demonstrating that grounded chamber walls increase the electric potential and electron temperature. Next, we investigate the impact of the neutralizer's position and the background pressure on the plume in the vacuum chamber. We find that as the neutralizer position moves closer to the location of maximum potential, more electrons are extracted, resulting in increased neutralization of the plume. We also observe that high background pressure generates slow charge-exchange ions, creating ion sheaths on the side walls that alter ion current paths. Finally, we discuss how the potential at the thruster and neutralizer exits affects the plume. The relative potential of the neutralizer to the vacuum chamber wall is observed to significantly influence the behavior of the electrons, thereby altering the degree of plume neutralization. These findings are shown to be consistent with experimental results in the literature and demonstrate the promise of high-performance simulation.