Naia Butler-Craig 
(Advisor: Prof. Walker)

will propose a doctoral thesis entitled, 

Experimental Investigation of the Effect of Varying Thruster Body Bias on Electron 
Pathways in the Near-field of a Magnetically-Shielded Hall Thruster 

On 

Thursday, May 8 at 9:30 a.m.  
Guggenheim 244 

 

Abstract 
Magnetically‑shielded Hall effect thrusters (HETs) commonly exhibit sputter erosion of the inner front pole cover (IFPC), yet the underlying mechanisms remain poorly understood. One leading hypothesis is that electrostatic potential pathways, which are shaped by the spatial distribution of electrons, create localized electric fields capable of accelerating ions toward the IFPC surface.

Previous Laser Thomson Scattering measurements have revealed a local electron pressure drop at the IFPC relative to the discharge channel. When collisional effects are neglected, this pressure drop serves as a proxy for a negative potential well, suggesting that the plasma structure near the pole cover may play a role in directing ions to the IFPC surface. Because the IFPC can be electrically biased through the thruster body, it can be used as a controllable boundary condition to probe how these electron-driven-near‑field plasma structures respond to variations in thruster body potential.

In our experimental campaign, electrically isolated stainless‑steel witness plates will be mounted on the IFPC and their bias swept from –15 V to +20 V in one‑volt increments, including the cathode‑tied configuration. High‑resolution current–voltage measurements will identify the thresholds at which net charged‑particle collection shifts between electron‑dominated and ion‑dominated regimes, directly revealing how body bias influences IFPC surface fluxes.

Under representative bias conditions identified in that first phase, two‑dimensional Laser Thomson Scattering scans will then map the distributions of electron density and temperature across the cathode centerline and the IFPC face. From these data, local electron pressure gradients will be calculated to infer the corresponding electric field structures. By correlating the bias thresholds from the witness‑plate diagnostics with the spatial variations in plasma parameters, we will determine how varying thruster body biases alters electron trajectories in the IFPC region.

Committee 

• Prof. Mitchell Walker – School of Aerospace Engineering (advisor)
• Prof. Sedina Tsikata – School of Aerospace Engineering
• Prof. Wenting Sun – School of Aerospace Engineering