Physics, simulation and diagnostics of Hall effect thrusters

TLDR

Scaling laws for anomalous electron mobility have not yet been derived, and hybrid models must rely on empirical transport coefficients inferred from PIC results or LIF measurements of the ion velocity distribution function. This paper aims to better understand and quantify charged particle transport in Hall effect thrusters by validating PIC model predictions of azimuthal instability through collective scattering experiments. The study combines particle‑in‑cell and hybrid models with laser‑induced fluorescence and collective scattering experiments to investigate anomalous electron transport, showing that high‑frequency, short‑wavelength azimuthal instabilities drive plasma turbulence and transport. Experimental results provide the first direct evidence of the predicted azimuthal instability, confirming that plasma turbulence drives anomalous transport and demonstrating the synergy between models and experiments for a quantitative understanding of HET physics.

Abstract

This paper presents recent efforts to better understand and quantify charged particle transport in Hall effect thrusters (HETs). Particle-in-cell (PIC) models, hybrid models, laser induced fluorescence (LIF) measurements and collective scattering (CS) experiments are combined to get a better insight into anomalous electron transport in HETs and to increase the predictive capabilities of simulation codes.PIC models have demonstrated that plasma turbulence associated with the development of a high frequency, short wavelength azimuthal instability can be responsible for anomalous transport. Scaling laws for anomalous electron mobility have not yet been derived and hybrid models, which are more practical than PIC models for parametric studies, must use empirical, adjustable transport coefficients that can be inferred from PIC results or LIF measurements of the ion velocity distribution function. CS experiments are aimed at validating the PIC model predictions of the azimuthal instability. The CS results show the first direct experimental evidence of the azimuthal instability predicted by the PIC code. The paper illustrates the synergy between experiments and models toward a complete and quantitative understanding of the physics of HETs.