Experimental Studies of the High-Frequency Oscillation Structure in the Discharge Channel of a Hall Thruster in Two Stable Discharge Modes

The structure of high-frequency oscillations in the plasma of a Hall thruster (HT) is studied experimentally in two different stable discharge modes: the “jet” mode and the “bell” mode. The discharge modes under study differ in the geometrical shape of the plasma plume and in the main integral characteristics of the thruster, such as the anode efficiency, driving force, and the specific momentum and thermal conditions of the construction achieved at almost identical input parameters. The studies are mainly performed in the frequency range of 5 to 150 MHz. It is shown that, in this frequency range, the oscillations represent the set of the azimuthal wave harmonics that propagate in the direction coinciding with the electron drift direction and obey the almost linear dispersion relation. An explicit correlation is found between the spectral composition of the waves and the type of the discharge mode.