Plasma Oscillations of Partially Magnetized E×B Discharge with Multiple Ion Species

In various E×B sources, plasma oscillations in the ranges of tens of kHz occur due to relatively high ionization rates and different degrees of magnetization between electrons and ions. Plasma oscillation in E×B sources is directly related to device efficiency. In-depth studies on the correlation between ion mass and oscillation frequency in Hall thrusters and magnetron devices with a single inert gas discharge have been carried out. In the case of ion implantation E×B sources using molecular gas or mixed gas, several ion species exist and plasma oscillations are expected to be more complicated. However, plasma oscillations considering the existence of multiple ion species have not yet been observed experimentally nor theoretically. With Ar/Kr mixed gas discharges, we investigated the basic characteristics of plasma oscillation in the mixed gas discharge of E×B sources. The proportion of ion species is changed by adjusting the gas-mixture ratio, and the frequency and mode number of the plasma oscillations are analyzed through the Beall technique. Also, characteristics of the oscillations were investigated with varying magnetic fields. Finally, the frequency of plasma oscillations is predicted through the analytical model to compare with the experimentally obtained values.