Cross-field electron transport through a rotating spoke in Hall thrusters

A rotating spoke was observed in cylindrical and annular Hall thrusters [1, 2]. In the cylindrical Hall thrusters with a cusp-shape magnetic field topology, the spoke rotates with a speed of 1-3 km/s in the ExB direction, which is substantially less than the local E$\times $B speed of 30 km/s [2]. In recent experiments, the cross-field electron transport induced by the spoke was directly measured for the first time using a segmented anode. Approximately 50{\%} of the total current is found to pass through the spoke. The cross-field transport mechanism has been explored using emissive and biased electrostatic probes and high speed imaging. The findings reveal a perturbed electric field which enhances electron transport across the field.\\[4pt] [1] G. S. Janes and R. S. Lowder, Phys. Fluids \textbf{9}, 1115 (1966)\\[0pt] [2] J. B. Parker, Y. Raitses, and N. J. Fisch, Appl. Phys. Lett. \textbf{97}, 091501 (2010).