Study and modeling of the anomalous axial electron transport in fluid simulations*

Hall Thrusters (HTs) are a technologically advanced system that are nowadays widely used in space propulsion. Understanding the physics of these devices is crucial to their optimization. In this work, we present a fluid analytical model to describe electron transport in a HT. Using the results of a hybrid kinetic/fluid simulation (i.e. particle-in-cell charged species and fluid neutrals), we challenge this model. Subsequently, we show how anomalous axial transport can be correlated with azimuthal plasma dynamics, and hence with azimuthal instabilities.

In particular, we discuss the appropriateness and limitations of using the anomalous collision frequency as a proxy for anomalous transport in fluid codes. Despite numerous efforts in this direction by the community, we show that the approach of artificially increasing the collision frequency is not always valid.

We eventually propose a different method, to be used in fluid models, that takes into account the oscillations or turbulent viscosity of the plasma, inducing the electron anomalous transport. This method has been implemented in a 1D purely axial fluid model to account for the transport generated by the azimuthal plasma dynamic, which is not simulated. The results of this model are presented and discussed.