Characteristics and mechanism of moniliform plasma plume in atmospheric argon jet

Abstract

Atmospheric pressure plasma jet can produce a kind of remote plasma plume in open air atmosphere. Different from the usual conical plasma plume found in the literature, a spatially periodical swelling plasma plume is generated in an atmospheric pressure argon plasma jet excited with a low-frequency biased sinusoidal voltage. By optical and electrical methods as well as optical emission spectroscopy, discharge characteristics and formation mechanism of the plasma plume with spatially periodical swells are studied. Experimental results show that length of the plasma plume increases with the increase of flow rate. Moreover, the plume initiates once in each negative half voltage cycle and it does not initiate in positive half voltage cycle. Through high-speed imaging, a negative streamer is found to propagate along argon flow for the swelling plasma plume. There is a strong discharge near the nozzle of the plasma jet, which initiates once per voltage half cycle and provides welling positions downstream with active species. These active species can significantly enhance the discharge and induce the formation of a swell. Furthermore, optical emission spectrum is used to investigate spatial distribution of excited electron temperature and averaged excited electron temperature as a function of gas flow rate. Finally, a qualitative explanation is given for the experimental results discussed above.