Axisymmetric Hybrid Plasma Model for Hall Effect Thrusters

Abstract

Hall Effect Thrusters (HETs) are nowadays widely used for satellite applications because of their efficiency and robustness compared to other electric propulsion devices. Computational modelling of plasma in HETs is interesting for several reasons: it can be used to predict thrusters’ operative life; moreover, it provides a better understanding of the physical behaviour of this device and can be used to optimize the next generation of thrusters. In this work, the discharge within the accelerating channel and near-plume of HETs has been modelled by means of an axisymmetric hybrid approach: a set of fluid equations for electrons has been solved to get electron temperatures, plasma potential and the discharge current, whereas a Particle-In-Cell (PIC) sub-model has been developed to capture the behaviour of neutrals and ions. A two-region electron mobility model has been incorporated. It includes electron–neutral/ion collisions and uses empirical constants, that vary as a continuous function of axial coordinates, to take into account electron–wall collisions and Bohm diffusion/SEE effects. An SPT-100 thruster has been selected for the verification of the model because of the availability of reliable numerical and experimental data. The results of the presented simulations show that the code is able to describe plasma discharge reproducing, with consistency, the physics within the accelerating channel of HETs. A small discrepancy in the experimental magnitude of ions’ expansion, due probably to boundary condition effects, has been found.

Resolving multi-dimensional plasma phenomena in Hall thrusters using the reduced-order particle-in-cell scheme

“…Accordingly, in this section, we present the results of our pseudo-2D axial-radial simulations and compare the results against 1D axial PIC simulations with and without a model to account for the plasma-wall interactions. To have a point of reference, the setup of all simulations is similar to a recent 2D hybrid fluid/PIC simulation from the literature [31], and our results are compared against those from the hybrid code. In this regard, it is important to highlight that an axial or axial-radial PIC simulation is not self-consistent with respect to electron mobility and, as a result, the same model as that in Ref.…”

“…In this regard, it is important to highlight that an axial or axial-radial PIC simulation is not self-consistent with respect to electron mobility and, as a result, the same model as that in Ref. [31] to account for the enhanced electrons' cross-field transport is included in our 1D and pseudo-2D simulations in this section. As such, since the choice of electrons' mobility model can have a dominant influence on the plasma dynamics, it was expected that the results would be mostly comparable, which will be seen in "Results and discussion" section to has been the case.…”

“…It is also important to recall that, as mentioned in "Introduction" section, by performing the single-region pseudo-2D axial-radial simulations, we aim to demonstrate preliminarily that this approach can provide a self-consistent method to capture an average effect of the plasma-wall collisions and the associated particles' momentum and energy loss in lieu of the ad-hoc models that have been proposed in the literature for this purpose [3,31].…”

“…The axial extent of the domain was chosen to be 3 cm compared to 6 cm in Ref. [31] in order to speed up the simulation by reducing the number of macroparticles. In the y-direction, however, the same extent of 1.5 cm as in Ref.…”

“…In the y-direction, however, the same extent of 1.5 cm as in Ref. [31] was used. The simulated operating condition is the same as that adopted in Ref.…”