Global Stability Analysis of Azimuthal Oscillations in Hall Thrusters

A linearized time-dependent 2-D ( axial and azimuthal) fluid model of the Hall thruster discharge is presented. This model is used to carry out a global stability analysis of the plasma response, as opposed to the more common local stability analyses. Experimental results indicate the existence of low-frequency long-wave-length azimuthal oscillations in the direction of the E x B drift, usually referred to as spokes. The present model predicts the presence of such oscillations for typical Hall thruster conditions with a frequency and a growth rate similar to those found in experiments. Moreover, the comparison between the simulated spoke and the simulated breathing mode, a purely axial low-frequency oscillation typical in Hall thrusters, shows similar features in them. Additionally, the contribution of this azimuthal oscillation to electron conductivity is evaluated tentatively by computing the equivalent anomalous diffusion coefficient from the linear oscillations. The results show a possible contribution to anomalous diffusion in the rear part of the thruster.