Experimental Insights into Instability-Induced Cross-Field Transport in Hall Effect Thrusters

Hall effect thrusters are one of the mostly widely used forms of in space propulsion. Their ability to achieve high exhaust velocities translates to an order of magnitude higher fuel economy when compared to chemical rockets. These devices also are attractive due to their moderate to high thrust density, which stems from the quasi-neutral nature of the acceleration process. Despite a high level of maturity and decades of development efforts, there are aspects of the operation of Hall thruster—most notably the electron dynamics—that remain poorly understood. In particular, there is experimental and numerical evidence that the cross-field electron transport is non-classical, resulting from the onset of drift-driven instabilities. The lack of understanding of this non-classical process has precluded the development of fully predictive models for these thrusters. This work highlights recent experimental efforts to infer the growth and saturation of these instabilities. These measurements in turn are related through the framework of quasilinear theory to an effective electron transport. The experimental insights are leveraged to inspire closure models that represent the non-classical transport in a reduced fidelity fluid model. The predictive capability of this fluid model is assessed against experimental measurements.