Streamer dynamics involved in a complex striated plume generated by an atmospheric pressure argon plasma jet

Abstract The morphology of the plasma plume in atmospheric pressure plasma jet (APPJ) is a mapping of the spatial distribution of reactive species, which is actually determined by the dynamic behavior of streamers. Different to a simple striated plume (SSP) reported previously, a complex striated plume (CSP) is generated for the first time in an argon APPJ under higher peak voltage ( V p ), with which peculiar streamer dynamics are explored. Results show that the CSP evolves from the SSP with increasing V p . Besides, raising driving frequency ( f ) and decreasing argon flow rate ( Q ) also make the SSP transition to the CSP. For both the SSP and the CSP, the distance between two adjacent ridges (or grooves) decreases with decreasing Q or increasing f . For the SSP, the discharges only appear at the negative voltage polarity. Besides these negative discharges, a discharge initiates at the positive voltage polarity for the CSP. Fast photography reveals that the SSP is solid with ridges and grooves alternately distributed along the flow direction, which originates from the propagation of a negative streamer. In addition to the solid SSP, a hollow SSP originating from a positive streamer is formed during the positive discharge of the CSP, suggesting that the CSP is a superposition of the solid SSP and the hollow SSP. The formation mechanism of the solid SSP and the hollow SSP is discussed through analyzing the negative-ion rings in the mixing layer between the argon stream and ambient air. By optical emission spectroscopy, spatial distribution of active species including OH (A 2 Σ + ) and N 2 (C 3 Π u ) is obtained. Moreover, temporal evolutions of intensity ratios for spectral lines are studied to reflect electron density and electron temperature for the negative and positive streamers. In addition, line intensity ratios and gas temperature are investigated as functions of V p , f , and Q .