Experiment and simulation of the characteristics and mechanisms of self-oscillations in parallel-plate glow discharges

Abstract

This paper presents experimental results of the characteristics appearance and the mechanism of self-oscillation in a parallel-plate glow discharge with argon as the discharge gas at 266 Pa. The cathode and anode are molybdenum plates with a diameter of 3 cm. The distance between the electrodes is 1 cm. Discharge average voltage and current vary between 300 V and 500 μA, respectively. Light emission from the electrode gap is measured by a charge coupled device camera and argon spectra are recorded of emission lines at 650–800 nm. Results show that self-oscillations exist in the negative differential resistance region in the static V–I curve. An obvious negative differential resistance also can be observed in the dynamic of the V–I curve for the self-oscillations. The appearance and disappearance of the self-oscillating phenomenon are companied with an obvious change in all of the discharge current, discharge images, and electron excited temperature. It can be determined that the self-oscillation is a mode transition between low-current stage of Townsend discharge and high-current stage of glow discharge. The frequency range of self-oscillations starts with 0.4 k Hz up to 24 k Hz in dependence of the average discharge current and the external capacitors. When the self-oscillation disappears, the luminescence shows a significant radial contraction, the electron excitation temperature rise obviously. The frequency of oscillations exhibits a substantial linear increase with the average discharge current and decreases with the increase in the external capacitance from 0 pF up to 250 pF. A resistance–capacitance circuit model is used to simulate the self-oscillation discharge in this experimental glow discharge. Results show that the waveforms simulated by this circuit model are well consistent with those obtained experimentally at different average discharge currents and external parallel capacitances. The equivalent plasma resistance decreases with an increase in the average discharge current. The theory of charge and discharge of a capacitor provides good insights into the characteristics and mechanism of self-oscillations in parallel-plate discharges.