Mechanism of snake-like propagation for positive streamers in a meandering plasma plume excited by a positively biased sinusoidal voltage

Abstract

Being able to generate a remote plasma plume, the atmospheric pressure plasma jet has become an indispensable tool for extensive application fields. A plasma plume usually has a straight column morphology, which results from straight-line or stochastic snake-like propagations of streamers. The snake-like propagation of streamers is unclear in the mechanism. In this paper, a meandering plume is generated for the first time downstream of an argon plasma jet excited by a positively biased sinusoidal voltage, which transits from a straight column plume with an increasing bias voltage (Vb). Results indicate that the wavelength of the meandering plume is inversely proportional to voltage frequency and directly proportional to the gas flow rate. For every voltage cycle, integrated light emission from the meandering plume presents one pulse with low Vb and two pulses with high Vb. Fast photography reveals that the meandering plume results from repeated snake-like propagations of positive streamers due to the influence of ion clouds. To confirm the existence of ion clouds, an opposite argon flow is introduced. With wiping off ion clouds in the argon stream, the meandering plume gradually turns back to a straight column with an increasing opposite flow rate. All these phenomena mentioned above have been explained qualitatively on the basis of ion clouds. These results may shed light on the streamers' dynamics in the atmospheric pressure plasma jet.