Committee Members:

Professor Mitchell Walker – Georgia Tech

Professor Suresh Menon – Georgia Tech

Professor Jerry Seitzman– Georgia Tech

Professor Wenting Sun – Georgia Tech

Professor Sven Simon – Georgia Tech

ABSTRACT:

Helicon ion thrusters are high-efficiency, high-density plasma sources with applications in electric propulsion. Their ability to accelerate ions without the use of lifetime limiting electrodes sets them apart from traditional Gridded Ion Thrusters which require biased grids and neutralizing cathodes for optimal operation. The extended expected lifetime of Helicon ion thrusters makes them desirable for long duration missions and warrants continued research dedicated to their development.

In order for Helicon ion thruster performance to be properly evaluated enabling real world applications, thruster characterization must occur during operation in a ‘space-like’ environment such as a vacuum test facility. For other electric propulsion applications such as Hall-effect thrusters, differences in thruster performance characteristics occur between ground based test facilities and operation in space. Neutral ingestion, the recirculation of expelled neutral propellant back inside the thruster and exhaust plume, is the suspected cause of performance alteration.

This study considers the effect of facility back pressure and subsequent neutral ingestion on the thrust performance of Helicon ion thrusters by examining the effect on crucial plasma properties. Properties examined in this work include electron temperature, ion number density, the Ion Energy Distribution Function, and plasma potential recorded during operation of a replica of the Madison Helicon eXperiment (MadHeX). Plasma properties are measured during thruster operation for two distinct operating pressures. The effect of facility environment on Helicon ion thruster operation is examined using recorded experimental data and kinetic models.