Role of thermionic emission in the formation of negative electric potential and oscillations in low pressure discharges

In this paper, we discuss the results from the two-dimensional computational investigation of the role of thermionic cathode emission in the formation of the negative (reverse) potential near the emissive cathode (LaB6 tablet). Two modes of discharge behavior are considered-high- and low-pressure modes. We show that the region of the negative potential (for that of the emitting cathode) is enclosed in a semi-sphere bounded by the line where the electric field changes its direction. This sheath region was distorted by the movement of the emitting points in horizontal and vertical directions. The unstable behavior of the high pressure discharge and self-excited oscillations of plasma parameters were observed. At low pressure the potential reversal and oscillations were not so pronounced.