Morphology evolution of an atmospheric pressure glow discharge initiated in the air gap between a liquid cathode and a needle anode

Self-deformation has been observed for an atmospheric pressure diffuse discharge initiated in the air gap between a needle anode and a water cathode, which undergoes a morphology scenario from a cone, an axially symmetric horn, to a rectangular horn as time elapses. During the self-deformation process, pH value and electric conductivity of the water cathode vary with time. Moreover, electrical measurements indicate that applied voltage and discharge current are time-invariant for the conical discharge, while periodically pulsed for the other two discharges. This may suggest different formation mechanisms of them. Hence, fast photography is implemented by a high-speed video camera and an intensified charge coupled device. Results indicate that the diffuse discharges with different morphologies belong to a glow discharge regime. Among them, the conical discharge is composed of stationary micro-discharge, and the horn-shaped discharges consist of moving micro-discharge. Moreover, the axially symmetric horn is a self-rotating version of the rectangular horn. Furthermore, the rectangular horn originates from the swing of a micro-discharge filament like a pendulum motion. Finally, qualitative explanations are given for the experimental phenomena mentioned above.