New insights into the physics of rotating spokes in partially magnetized e × B plasmas

Regions of enhanced light emission rotating in the azimuthal direction ("rotating spokes") have been observed in different types of partially magnetized E × B plasma devices such as magnetron discharges and Hall thrusters. A two-dimensional Particle-In-Cell Monte Carlo Collision (PIC MCC) model is used to study the formation of these rotating structures. The model shows that these current driven rotating structures are the results of a Simon-Hoh instability evolving into an ionization instability. The spoke is sustained by local electron heating induced by ∇ B drift along a double layer separating the cathodic presheath from the plasma at a potential close to the anode potential. The PIC MCC simulations predict that spoke rotation can take place in the + E × B direction and in the - E × B direction depending on the magnetic field intensity.