DBD-streamer mode transition of atmospheric-pressure plasma jet applied on water with varying distance and AC power

The discharge of atmospheric-pressure plasma jet (APPJ) applied on the water was studied by varying an air gap between a powered electrode and the water, and the alternating current power. It was found that the streamers were converged by the air flow to form a streamer bridge to allow current flow across the air gap to transition from a dielectric barrier discharge (DBD) mode to a streamer mode. Because the AC power alternates periodically, this study proposed an analysis without the parameter of time by the voltage amplitude to power characteristic. It was found that the longer distance required higher voltage amplitude and power to transition. Prior research of plasma rarely mentioned the real power and the reactive power, which are essential for electric devices. Because different discharge mode produces different species, this study proposed a simple method to analyze and predict discharge modes based on the power factor, which presents the relationship of the real power and the reactive power. It was found that the streamer mode had a higher power factor than the DBD mode, and thus the power factor decides the discharge mode. Therefore, a power factor analysis can be a systematic basis to produce the required discharge by changing the equivalent capacitance and resistance to change the reactive power and real power. This study proposed a simple method to analyze periodic discharge by the intensified charge-coupled device (ICCD). A period of the AC was divided into twelve timings. For each timing, each shot was configured to have the minimum exposure time to avoid the afterimage. Thousands of shots were overlapped into one snapshot to increase the fluorescence and make such snapshot more representative for the timing. Snapshots show that the streamer bridge was only formed in specific timings periodically.