Effects of the applied fields' strength on the plasma behavior and processes in ExB plasma discharges of various propellants: I. Electric field

Abstract: We present, in this two-part article, an extensive study on the influence that the magnitudes of the applied electric (E) and magnetic (B) fields have on a collisionless plasma discharge of xenon, krypton, and argon in a 2D radial-azimuthal configuration with perpendicular orientation of the fields. The dependency of the behavior and the underlying processes of ExB discharges on the strength of electromagnetic field and ion mass has not yet been studied in depth and in a manner that can distinguish the role of each individual factor. This has been, on the one hand, due to the significant computational cost of conventional high-fidelity particle-in-cell (PIC) codes that do not allow for extensive simulations over a broad parameter space within practical timeframes. On the other hand, the experimental efforts have been limited, in part, by the measurements' spatial and temporal resolution. In this sense, the notably reduced computational cost of the reduced-order PIC scheme enables to numerically cast light on the parametric variations in various aspects of the physics of ExB discharges, such as high resolution spatial-temporal mappings of the plasma instabilities. In part I of the article, we focus on the effects of the E-field intensity. We demonstrate that the intensity of the field determines two distinct plasma regimes, which are characterized by different dominant instability campaigns. At relatively low E-field magnitudes, the Modified Two Stream Instability (MTSI) is dominant, whereas, at relatively high E-field magnitudes, the MTSI is mitigated, and the Electron Cyclotron Drift Instability (ECDI) becomes dominant. These two regimes are identified for all studied propellants. Consequent to the change in the plasma regime, the radial distribution of the axial electron current density and the electron temperature anisotropy vary.