Streamers Initiated by a Capacitive Discharge at Air Pressure 0.2–6 Torr

The paper presents a study of diffuse plasma jets (DPJs), which have a red color and consist of streamers (ionization waves). It has been found that plasma generated in air at pressures of 0.2–4 Torr by a repetitively pulsed capacitive discharge in a dielectric tube initiates two DPJs in one pulse, each with up to three streamers. It has been found that two streamers propagating from the circular electrodes in opposite directions are formed by one voltage pulse of positive polarity. Using an ICCD camera and a silicon PMT, it is shown that the arrival of the front edge of a positive streamer in the region finally reached by the front edge of a negative streamer that was generated first at the front edge of the negative voltage pulse leads to the formation of a third thin streamer in the form of a cone with a small apex angle. It has been found that the direction of motion of the third streamer coincides with the direction of the streamers initiating it, but its speed is two orders of magnitude lower. It is shown that, at low air pressures, the speed of the first positive streamers is higher than that of the negative streamers and the distance to which they propagate at a generator voltage of 7 kV and an air pressure of 0.2 Torr exceeds 1 m.