Experimental investigation of high-frequency drifting perturbations in Hall thrusters

High-frequency instabilities (1–10MHz) in a Hall thruster were studied with the use of six antennas installed in the external ceramic wall of the accelerating channel of the thruster. Azimuthal modes m⩾1 were evidenced in more or less complex shape of the antenna signal, propagating with azimuthal velocity close to the drift velocity in crossed electric and magnetic fields. These instabilities have the highest level at the exit part of the thruster. They were shown to correlate with low-frequency (10–30kHz) oscillations of the discharge current. Information on axial electric field variation is derived from the instabilities properties. The instabilities were characterized as a function of thruster operating parameters—discharge voltage and magnetic field.