Effect of the reference electrode size on the ionization instability in the plasma sheath of a small positively biased electrode

It is well known that additional ionization in the vicinity of a positively biased electrode immersed into a weakly ionized plasma is responsible for a hysteresis in the electrode current-voltage characteristics and the current self-oscillations rise. Here we show both experimentally and theoretically that under certain conditions these phenomena cannot be correctly interpreted once considered separately from the reference electrode current-voltage characteristics. It is shown that small electrodes can be separated into three groups according to the relation between the electrode and the reference electrode areas. Each group is characterized by its own dependence of the collected current on the bias voltage.