Revealing phase transitions and instabilities in pseudospark discharges

Abstract

AbstractPseudospark discharge is a low‐pressure high‐voltage pulsed discharge with hollow electrodes, and the overall discharge experiences several distinctive sub‐phases. The instability phenomena, characterised by the sudden oscillations or distortions of discharge voltage and current, restrict the applications of pseudospark discharge. This study presents an investigation into phase transitions and instabilities in pseudospark discharge by combining the evidences from multiple discharge waveforms, time‐resolved images, electron beam current profiles, 2D kinetic simulation results, and the spectral line emission of cathode material. The process of a normal pseudospark discharge is firstly discussed, and the threshold conditions of the transition from the superdense glow discharge (SGD) phase to the high current phase with arc cathode spots are addressed. According to temporal profiles and voltage‐current characteristics, two types and four occurrences of instabilities are distinguished: type I—in the pre‐breakdown phase; type II‐1—in the SGD phase; type II‐2—in the transition of cathode spots propagating from cathode hole edge to cathode plane; type II‐3—in the re‐initiation of spots near current reversal. It is found that the instability of type I is caused by the stepwise penetration of virtual anode plasma, and type II is closely related to the cyclic nature and finite lifetime of cathode spots. It is induced by the fact that the decay of cathode spots is faster than the formation under certain conditions, and the existing spots are not able to provide the current required by the external circuit. Important features and the suppression methods of the instabilities are discussed based on the proposed mechanisms.