Numerical treatment of a magnetized electron fluid model within an electromagnetic plasma thruster simulation code

Abstract

Plasma discharges in electromagnetic thrusters often operate with weakly-collisional, magnetized electrons. Macroscopic models of electrons provide affordable simulation times but require to be solved in magnetically aligned meshes so that large numerical diffusion does not ruin the solution. This works discusses suitable numerical schemes to solve the axisymmetric equations for the electric current continuity and the tensorial Ohm's law in such meshes, when bounded by the thruster cylindrical or annular chamber. A finite volume method is appropriate for the current continuity equation, even when meshes present singular magnetic points. Finite differences and weighted least squares methods are compared for the Ohm's law. The last method is more prone to producing numerical diffusion and should be used only in the boundary cells and requires a special formulation in the boundary faces. In addition, the use of the thermalized potential is suggested for an accurate computation of parallel electron current densities for very high conductivity. The numerical algorithms are tested in a hybrid (particle/fluid) simulation code of a helicon plasma thruster, for different magnetic fields, mesh refinement, and plume lengths. The different contributions to the electric current density are assessed and the formation and relevance of longitudinal electric current loops is discussed.1

Simulation of the plume of a magnetically enhanced plasma thruster with SPIS

“…Specifically it is computed with (Zhou et al. 2019) with the external boundary surface, the external normal to the surface and the unity vector parallel to the axis. The specific impulse is obtained by with the standard gravity.…”

“…The thrust F produced by the thruster is obtained by summing, for each species p, the contribution due to the momentum exchange and to the pressure. Specifically it is computed with (Zhou et al 2019)…”

Coupled plasma transport and electromagnetic wave simulation of an ECR thruster

“…The features of these two modules have been described in Refs. [41][42][43][44][46][47][48]. Their main aspects are described briefly in the next subsections.…”

“…In their low-frequency response, electrons are treated as a magnetized diffusive fluid [47]. The set of fluid equations is the following:…”

A software package for rigorously calculating optical plasma spectra and automatically retrieving plasma properties

“…6 Some of the parameters such as the electron tem-perature and density may be determined from information such as the line-to-continuum intensity [7][8][9][10][11] or the Stark line broadening. [12][13][14][15][16][17] All methods involving human intervention eventually become very inefficient and tedious as the number of lines in the emission spectrum increases and the quality of any human involved process is difficult to gauge quantitatively. In recent years, chemometric methods based on multivariate statistical analysis in various forms have been developed to partially mitigate the situation.…”