Study of the instabilities in radial-azimuthal and axial-azimuthal 2D PIC simulations of a Hall Thruster

Plasma propulsions systems such as Hall Thrusters (HTs) use an electric field perpendicular to the magnetic field to produce the thrust. The differential drift between electrons and ions in the ExB direction can origin several instabilities, among which the Electron Cyclotron Drift Instability (ECDI) in the direction perpendicular to the magnetic field and the Modified Two-Streams Instability (MTSI), with also a component along the magnetic field. We have derived and validated a stability condition for the appearance of the MTSI modes in 2D Particle-In-Cell (PIC) simulations of the radial-azimuthal plane of a HT. Furthermore, we have investigated their effects on the main discharge parameters.The plasma instabilities play a very important role also in the axial-azimuthal plane of a HT. In particular, we are addressing, using PIC simulations, the Ion Transit Time Instability (ITTI) and how it can be related to the electron emission temperature at the cathode and to the presence of a virtual third dimension in the radial direction. This third dimension may strongly affect the discharge behaviour, especially the Breathing Mode characteristics.