Ph.D. Defense

David Rene Jovel

(Advisor: Prof. Mitchell Walker)

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

On

Friday, December 8 

10:00 a.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 environment inside test facilities can replicate only some of the electrical boundary conditions observed in space. Specifically, most vacuum test facilities are metallic, electrically grounded, and finite in volume whereas the space environment possesses a low-density, cold plasma that varies in time due to space weather activity. Therefore, it is essential to understand how HETs electrically couple to, and are affected by, their local operating environment.

The purpose of this dissertation is to quantify the dynamic electrical characteristics of the HET discharge as it electrically interacts with the metal vacuum chamber. To accomplish this, a novel impedance measurement diagnostic was used to characterize the capacitive, inductive, and resistive characteristics of the HET discharge in the band 100 Hz – 300 kHz as the electron current to the facility walls was reduced. The results show that ground-based vacuum test facilities participate in the HET discharge circuit in three main ways: 1) adds capacitive effects that may suppress the inherent dynamic behavior of HETs via the plasma-chamber wall sheath, 2) reduces inductive effects due to the increased plasma densities contained within the facility, and 3) facilitates ion-electron neutralization processes via its electrically-conductive walls. Furthermore, this work in this dissertation shows that these artificial effects become more pronounced as the HET discharge current level increases.

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