Observation of positive and negative nanosecond pulsed streamers in a coaxial electrode using a quadruple emICCD camera system

The environmental improvements by non-thermal plasma have been actively studied all over the world. Generally, a pulsed discharge having a time duration of 100s ns consists of two discharge phases including the streamer and glow discharges. It is also well known that the streamer heads always have the largest electric field during entire discharge process and meanwhile, the propagation behavior between electrodes is strongly influenced by the polarity of the applied voltage. In recent studies, the nanosecond (ns) pulse power generator with a short pulse duration of 5 ns achieved the higher energy efficiency for exhaust gas treatment and ozone generation than other discharge methods. However, the fundamental characteristics of ns pulsed discharge are still unclear. In our previous study, although several propagation processes of the discharge were revealed using a single high-speed gated emICCD camera, it could not clarify on the full details because the continuous propagation images were unable to obtain, therefore, a combination of different discharge shots were photographed by changing exposure onset time of the emICCD camera. In the present study, a newly developed high-speed imaging system combined with four emICCD cameras, which can observe the single ns pulsed discharge phenomenon at the same time. The propagation of the positive and negative streamer heads was observed using this imaging system. In the experiment, ns pulsed discharge was generated in a coaxial electrode. The propagation behavior such as propagation velocity, thickness of streamer heads, were compared in more detail between streamer heads with different voltage polarities. In addition, we analyzed obtained pictures by our program. This program was produced in our laboratory and this method is independent from past datas. We could confirm its currency in this study.