Dispersion relation of high-frequency plasma oscillations in Hall thrusters

The dispersion relation of high-frequency plasma oscillations (>1MHz) in a Hall thruster is estimated from two point probe measurements. The probes are located outside the accelerating channel nearby the channel exit. The probe orientation allows us to investigate the evolution of azimuthal and axial wave numbers with the oscillation frequency. The azimuthal dispersion relation is nearly linear. The axial dispersion relation depends upon the probe position, which translates into a varying slope. The observed features of the two dispersion relations can be explained in terms of spatial structure of the high-frequency plasma instabilities.