Dynamic behaviors of helium atmospheric pressure plasma jet investigated by steak images

Summary form only given. Helium atmospheric pressure plasma jet (He-APPJ) was a kind a stable low-temperature plasma source which had been widely used in medical and industrial areas, but its physical mechanisms was not yet fully revealed. In the present study, streak camera was used to record the discharge processes. Compared to conventional devices such as ICCD and PMT, streak camera allowed continuous recording with high temporal resolution, therefore it was more precise and reliable.The He-APPJ was driven by 10 kHz sinusoidal voltage source in co-axial double-ring electrodes structure. Three distinguish discharge zones separated by the electrodes were observed and detailed analyzed under different voltage magnitudes. The experimental results shown that discharge in positive voltage phase was dominated over the whole discharge cycle. Double discharges were observed in the tube gap between electrodes, which were supposed to be positive streamer and glow discharge, respectively. Propagation speed of the streamer was about 40 km/s. Discharge beyond the upper electrode was resulted from the first streamer. The downstream jet was independent from discharge in the tube gap, which propagated with speed in the order of 1 km/s. What's more, with specific voltage magnitude, the jet was found to consist of two discharges, known as the “double bullet”. Space charge distribution modulated by the last discharge in negative phase might give rise to this phenomenon.