Analysis of the self-pulsing operating mode of a microdischarge

The self?pulsing regime of a microhollow cathode discharge in argon is reported. The plasma is generated inside the hole drilled in an anode?dielectric?cathode device. The hole dimension ranges from 200 to 400??m and the gas pressure ranges from 40 to 200?Torr. It is shown by optical spectroscopy and fast CCD imaging that the current pulse is related to a fast expansion of the plasma outside the microhole on the cathode backside. The pulse current duration ranges from 0.4 to 2??s depending on the gas pressure. The self-pulsing regime occurs at medium current range (0.1?1?mA). At lower current the discharge is steady and the plasma is confined inside the hole (abnormal regime); at higher current, the plasma is steady and the plasma expands outside the hole on the cathode backside. The self-pulsing frequency is a linear function of the averaged discharge current and decreases with the device capacitance. The dependence of the self-pulsing characteristics (frequency, light emission, power deposition, etc) on the gas pressure follows a Paschen-like law; this is interpreted in considering that the fast expansion of the plasma outside the hole is similar to a gas breakdown. A simple electrical model, using a bistable voltage-controlled variable resistor to simulate the evolution of the plasma impedance, provides qualitative results in good agreement with the experiments.