Effect of the magnetic field topology on azimuthal spoke oscillations in Hall thruster*

Low-frequency (typically <100 kHz) spoke oscillations are commonly observed in ExB devices including Hall thrusters, magnetron discharges etc. The spoke mode manifests itself as strong perturbations in plasma density that propagate in the ExB direction perpendicular to the crossed electric (E) and magnetic (B) fields, generating substantial components in electric field in this ExB direction [1]. In Hall thrusters, the spoke propagates in the azimuthal direction. The most prominent spoke oscillations are usually observed inside the thruster channel near the anode electrode [2]. In this work, we report the effect of the magnetic field topology in this thruster region on spoke oscillations, correlate this effect with measured plasma properties [3] and relate these experimental results to a collisionless Simon-Hoh instability [1].

[1] I. D. Kaganovich et al., Phys. Plasmas 27, 120601 (2020)

[2] J. B. Parker, Y. Raitses, and N. J. Fisch, Appl. Phys. Lett. 97, 091501 (2010)

[3] L. Dorf, Y. Raitses and N. J. Fisch, Phys. Plasmas 13, 057104 (2006)