Hybrid plasma simulations of a magnetically shielded Hall thruster

Abstract

Numerical simulations of a magnetically shielded Hall effect thruster with a centrally mounted cathode are performed with an axisymmetric hybrid particle-in-cell/fluid code and are partially validated with experimental data. A full description of the plasma discharge inside the thruster chamber and in the near plume is presented and discussed, with the aim of highlighting those features most dependent on the magnetic configuration and the central cathode. Compared to traditional magnetic configurations, the acceleration region is mainly outside the thruster, whereas high plasma densities and low temperatures are found inside the thruster. Thus, magnetic shielding does not decrease plasma currents to the walls, but reduces significantly the energy fluxes, yielding low heat loads and practically no wall erosion. The injection of neutrals at the central cathode generates a secondary plasma plume that merges with the main one and facilitates much the drift of electrons toward the chamber. Once inside, the magnetic topology is efficient in channeling electron current away from lateral walls. Current and power balances are analyzed to assess performances in detail.

Kinetic plasma dynamics in a radial model of a Hall thruster with a curved magnetic field

“…However, the magnetic topology in a HET is curved. Leaving apart modern magnetically-shielded HETs [6,7] with farfrom-radial 2D magnetic topologies, classical HETs implement a (near) symmetric magnetic lens topology, with the lens centered around the channel exit, reduces detrimental plasma fluxes to walls and enhances thruster performances [8][9][10]. The rationale for that configuration is that, to a first order approximation for near-cold electrons and as sketched in figure 1, magnetic field lines are expected to be isolines for the electric potential, so a negative curvature (i.e.…”

Using electron fluid models to analyze plasma thruster discharges

“…experimental data, such as thrust and discharge current [31] or, better, the time-averaged φ(z) or u zi (z) in the mid-channel location [32]. A certain consensus on α a (z) suggests it is smaller within the channel than in the near plume, and would present a minimum around the maximum of E z (z) [31][32][33][34].…”

“…experimental data, such as thrust and discharge current [31] or, better, the time-averaged φ(z) or u zi (z) in the mid-channel location [32]. A certain consensus on α a (z) suggests it is smaller within the channel than in the near plume, and would present a minimum around the maximum of E z (z) [31][32][33][34]. In EPTs with a quasi-axial magnetic field, α a = const is being used [35], partly due to the limited experimental evidence on anomalous diffusion in these devices.…”

“…For ceramic walls, as δ s increases, the sheath potential fall decreases and the electric field at the wall too. Before the normal sheath collapses, this electric field vanishes, and the sheath enters into the the charge saturation limit (CSL) and regime [43,96,97], which is the scenario adopted in many HET simulations [27,31,43,44]. Nonetheless, the exact sheath potential fall at the CSL is very sensitive to the ion and electron VDFs, and the classical result from Hobbs-Wesson [96] applies only to a fully replenished semi-Maxwellian VDF.…”

“…Fig.1Simulation of an axisymmetric MS-HET with HYPHEN for a configuration similar to[31]. a MFAM: magnetic lines are in blue and the ortoghonal family is in red; the black box is the location of the central cathode which emits electrons and neutrals.…”