Presence of energetic ions in hollow cathode discharge with low frequency oscillations

Low-power electric propulsion system has high application prospects. The matching small orifice cathode has become a research hotspot. Through the long-life-test, it is found that the small orifice cathode will also have serious erosion, which seriously affects the reliability of the cathode. This kind of erosion is caused by high-energy ion sputtering, which is usually observed only on the large orifice cathode. There is no clear mechanism research on the cause of such high-energy ions in the small orifice cathode plume region. This paper finds that when the energy of the cathode is mainly concentrated at low frequencies, energetic ions much higher than the discharge voltage will be generated in the cathode plume area. The measurement results of the ion energy distribution in the cathode plume area show that the energy of the ions generated near the keeper increase as the cathode oscillation intensifies. It is found that the oscillation phases of low-energy ions and high-energy ions are inconsistent by measuring the changes of different energy ions during the cathode oscillation period. The oscillation of low-energy ions is in the same phase with the cathode current, while that of high-energy ions is in the same phase with the discharge voltage. This means that the previously neglected oscillation of the cathode at the frequency of tens of kHz can also produce high-energy ions. Therefore, inhibiting the oscillation of this frequency band is of great significance to extend the life of the cathode.