Plasma bullet splitting behavior of a positive streamer initiated in an atmospheric pressure argon plasma jet

Atmospheric pressure plasma jet opens up extensive potential applications and becomes a hot issue in low temperature plasma research in which a guided streamer regime is normally involved. The dynamics of the streamer head (also referred to as a plasma bullet) are crucial to the distribution of active species. Previous studies have revealed that the guided streamer operates either in a single bullet (SB) mode or in a double bullet mode. In this paper, we report the streamer splits phenomenon in an argon plasma jet excited with a pulse voltage. Results indicate that the split of the plasma bullet only appears with a high voltage amplitude (Va), otherwise, the streamer always keeps in the SB mode. With increasing Va, the distance that the SB travels (ds) increases. With the addition of trace oxygen in the working gas, ds is reduced. However, the influence on ds with the addition of trace nitrogen can be ignored. Only when the flow rate of added nitrogen is high, ds is also reduced. Moreover, the intensities increase with increasing voltage amplitude, while the durations reduce for the discharges at the rising and falling edges of applied voltage. In addition, the spatial distributions of streamer velocity and plasma parameters are compared for the plasma jet with different Va. The split of the plasma bullet is attributed to the Penning ionization in the interfacial layer between the working argon stream and the ambient air.