Two-Dimensional Full-Fluid Simulations for Low Temperature Rotating Spokes

A Penning-type low-temperature plasma configuration is simulated using a two-dimensional (2D) full-fluid moment model. A quasineutral, unperturbed plasma diffuses to absorbing walls, creating sheaths and density gradients, and giving rise to ExB and diamagnetic drifts for the magnetized electrons. This leads to charge separation in the azimuthal direction, which gives rise to instabilities due to a radial ExB drift. Such spokes and spoke-like structures have been observed in several low-temperature plasma settings, such as magnetron discharges 1 , Hall-effect thrusters 2 , and Penning discharges 3 . Results show the development of different wave modes in the azimuthal direction, depending on the magnetic field strength. For all cases where electrons are magnetized, radial nonuniformities arise and lead to an m=1 mode akin to the rotating spokes observed experimentally. The growth rates of the instability are studied for the different field strengths. The effect of the background neutral gas density is investigated through electron-neutral collisions. It is observed that the collisional drag term causes higher mode structures of rotating spokes to be sustained for longer times.