David Rene Jovel
Prof. Mitchell Walker

will propose a doctoral thesis entitled,

Impedance Characterization of a Hall Effect Thruster Discharge in a Ground-based Vacuum Test Facility

On

Tuesday, January 10 at 12:00 p.m.
Montgomery Knight Building 317
 

Abstract
In-space electric propulsion (EP) is an attractive candidate for many space architectures due to its high specific impulse values in the 1000s of seconds and high engine efficiencies greater than 50%. The performance of EP devices allows users to effectively increase the payload mass fraction per launch, thereby maximizing the overall productivity of the mission. Of the different EP types available, Hall effect thrusters (HETs) offer competitive performance and are presently the most commonly flown supporting electric orbit-raising and station-keeping maneuvers. Prior to installing a HET on a spacecraft and operating it in space, the thruster is tested on Earth inside vacuum test facilities. Based on in-flight data, HETs are known to perform differently in space than when operated inside ground-based vacuum test facilities. This is because the HET plume, consisting of ions, electrons, and neutrals, emanating from the thruster physically interacts with its local operating environment. Examining the two operational environments closely, we see that the physical properties of metallic vacuum chambers, and the elevated pressures they maintain, are vastly different from the space plasma environment observed in low-Earth orbit and beyond.

The proposed work investigates the effect that ground-based vacuum test facilities have on the impedance of HET plasma discharges. In this work, the impedance is the effective resistance and reactance of the HET discharge as an electrical load. The HET discharge is comprised of the various ion and electron currents required for ionization inside the thruster’s discharge channel and ion beam neutralization in the HET plume. This works posits that the degree of electrical coupling between the HET plume and metallic vacuum test facility effects the impedance of the thruster. A method to vary the electron current to the test facility walls was developed. The test campaign consists of electrically biasing a large electrode to different voltages to change the degree of electrical coupling between the HET plume and the metallic vacuum test facility. An array of 46 witness plate electrodes line the facility walls to provide a spatial resolution of the plasma environment with respect to the HET’s location. A novel impedance measurement technique was designed to characterize the effective impedance of the HET discharge as the plume electrically couples to the electrode. In addition to this, a plasma-physics-based equivalent circuit model was developed to map the dominant ion and electron current pathways between the HET plume and the metallic vacuum test facility walls.

Committee

• Prof. Mitchell Walker – School of Aerospace Engineering (advisor)
• Prof. Wenting Sun– School of Aerospace Engineering
• Prof. Lukas Graber – School of Electrical and Computer Engineering