Low-frequency cathode plume oscillations in a 5-30A LaB6 cathode

A 20A LaB6 hollow cathode, designed to be coupled with a 5kW class Hall thruster under development at SITAEL, has been experimentally evaluated to understand the plasma plume parameters and the low-frequency dynamics of the plasma expanding outside the cathode exit plane. The investigation has been performed with the aid of triple Langmuir probes, mounted on an articulated arm capable of scanning the cathode plume along the cathode axis. The cathode has been investigated with two orifice diameters. The results show that a lowfrequency (1-4kHz) oscillation establishes in the cathode plume starting 3mm away from the keeper exit plane and expanding in the entire plume region. This low-frequency oscillation has been related to ionization instabilities, and it was found to disappear with a smaller diameter orifice.