Nanosecond-Resolved Discharge Processes Revealing Detailed Mechanisms of Nonequilibrium Atmospheric-Pressure Plasma Jet of Helium

Nanosecond-resolved photographs of the nonequilibrium atmospheric-pressure plasma jet of helium, generated with the conventional dielectric barrier discharge device, were obtained at different sections of the experimental setup and at different development stages of the discharges, showing that various distinct mechanisms are simultaneous in operation. The streamer from the outer edge of active electrode sitting at downstream side forms a jet in air, which only turns out to be hollow when approaching the orifice of the gas conduct. The streamer from the inner edge temporally lags behind, and it propagates along a helical path and initiates the glow discharge when arriving at the ground electrode. The electron deposit beneath the active electrode expands inward from both sides, displaying a soliton-like behavior; while the very compact ion deposit beneath the ground electrode, a typical ionic streamer, extends outward from the inner edge of the electrode. The velocities of the jet in air and of the streamer between electrodes are much larger than those at other parts of the device. The resolution of these particular processes and features can improve the implementation of this valuable cold plasma source.