Electron cross field transport modeling in radial-axial hybrid hall thruster simulations.

摘要

A Hall thruster is an electric propulsion device capable of providing continuous low thrust while maintaining high efficiency and propellant utilization. The present study is concerned with the modeling of the interior channel and near-field region of a Hall thruster using a radial-axial hybrid simulation which treats the electrons as a quasi-one-dimensional fluid and the heavy particles using a particle-in-cell approach. A primary challenge in the modeling of Hall thrusters is the treatment of the poorly understood electron conductivity. In most regions of the channel and near-field, the experimentally-determined electron mobility substantially exceeds the classical value. Two possible mechanisms for this anomalous transport are electron wall interactions and azimuthal fluctuations. Since radial-axial codes cannot capture the azimuthal electron dynamics, ad-hoc transport models are frequently imposed.;This work focuses on the development of improved methods for simulating electron transport in radial-axial hybrid Hall thruster simulations. While the implementation of an experimentally-based electron transport model results in reasonable predictions of plasma properties, a second method has been developed which does not require laboratory measurements. Motivated by experimental observations in Hall thrusters and magnetized fusion devices, this semi-empirical model assumes a high base level of transport, but reduces the anomalous transport level in regions of strong axial shear in the azimuthal electron flow. Results are presented which show that this transport model based on shear-suppression of fluctuation-enhanced transport is also capable of predicting reasonable agreement with experimental measurements after optimization of two adjustable parameters. Lastly, the remaining chapters focus on better understanding of the fluctuation-induced transport level in the absence of shear using linearized perturbation models. While it is shown that the axial waves simulated by the hybrid simulation do not result in anomalous transport, coupling of these axial waves into tilted axial-azimuthal waves has the potential to produce the anomalous transport levels observed experimentally. Simulation results also suggest that the experimentally-observed region of reduced mobility near the channel exit may coincide with a transition from azimuthal to axial waves.