Rotating spoke instabilities in a wall-less Hall thruster: simulations

K. Matyash, R. Schneider, S. Mazouffre, S. Tsikata and L. Grimaud
Plasma Sources Sci. Technol. 28, 044002 (2019)

The low-frequency rotating plasma instability (spoke) in the ISCT200 thruster operating in the
wall-less configuration was simulated with a 3 dimensional PIC MCC code. In the simulations
an m = 1 spoke rotating with a velocity of 6.5 km sāˆ’1 in the E Ɨ B direction was observed. The
rotating electron density structure in the spoke is accompanied by a strongly depleted region of
the neutral gas, which clearly shows that the spoke instability is of an ionization nature, similar to
the axial breathing mode oscillations. In the simulation the electron cross-field transport through
the spoke core was caused by diffusion in the high-frequency (4ā€“10 MHz), short-scale (3mm)
electric field oscillations. These short-scale oscillations play a crucial role in the thruster
discharge as over 70% of the electron current to the anode originates from the spoke core. The
rest of the current originates from the spoke front where the electron cross-field transport toward
the anode is due to the E Ɨ B drift in the spoke macroscopic azimuthal electric field.