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

TL;DR

This study investigates how varying magnetic field strengths influence plasma behavior and instabilities in ExB discharges with different propellants, revealing distinct regimes and the coexistence of instabilities at moderate fields.

Contribution

It provides a detailed analysis of plasma regimes and instability coexistence under different magnetic fields using PIC simulations, extending previous work to include magnetic field effects.

Findings

Two distinct plasma regimes identified based on magnetic field strength.

Coexistence of ECDI and MTSI observed at moderate magnetic fields.

Magnetic field influences the presence and dominance of plasma instabilities.

Abstract

We present in this part II the effects of the magnetic field intensity on the properties of the plasma discharge and the underlying phenomena for different propellant's ion mass. The plasma setup represents a perpendicular configuration of the electric and magnetic fields, with the electric field along the axial direction and the magnetic field along the radial direction. The magnetic field intensity is changed from 5 to 30 mT, with 5 mT increments. The propellant gases are xenon, krypton, and argon. The simulations are carried out using a particle-in-cell (PIC) code based on the computationally efficient reduced-order PIC scheme. Similar to the observations in part I, we show that, across all propellants, the variation in the intensity of the magnetic field yields two distinct regimes of the plasma, where either the Modified Two Stream Instability (MTSI) or the Electron Cyclotron Drift Instability (ECDI) are present. Nonetheless, a third plasma regime is also observed for cases with moderate values of the magnetic field intensity (15 and 20 mT), in which the ECDI and the MTSI co-exist with comparable amplitudes. This described change in the plasma regime becomes clearly reflected in the radial distribution of the axial electron current density and the electron temperature anisotropy. Contrary to the effect of the electric field magnitude in part I, we observed here that the MTSI is absent at the relatively low magnetic field intensities (5 and 10 mT). At the relatively high magnitudes of the magnetic field (25 and 30 mT), the MTSI becomes strongly present, a long-wavelength wave mode develops, and the ECDI does not excite. An exception to this latter observation was noticed for xenon, for which the ECDI's presence persists up to the magnetic field peak value of 25 mT.