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.

Discharge aspects of a snake‐like plasma plume generated by an atmospheric pressure plasma jet with variable argon flow rate

“…Apparently, the propagation of the positive streamer is accomplished by successive generations of secondary electron avalanches. [36,54] Hence, the positive streamer propagates along the argon flow direction along a straight line (30 ns). At 60 ns, a curved trajectory is present.…”

“…After the streamer passes position 2, the ion cloud will reinforce E and maximal E appears again in front of the ion cloud, leading to the backward deflection of the streamer. [54,57] As a result, a peak of the serpentine trajectory is present for the propagating streamer. From the analysis mentioned above, it can be inferred λ is determined by the distance between two neighboring ion clouds, which equals to the product of vT. As a result, λ increases with increasing Q (Figure 3a).…”

“…[52,53] In addition, a stable snake-like plume has been generated downstream of the jet tube using a biased sinusoidal voltage. [54] Although preliminary investigations have been conducted for the snake-like plume, detailed studies need to be conducted about the discharge aspects to elucidate the mechanism of the snake-like streamer.…”

Complicated streamer dynamics in petal‐like patterns formed on the substrate downstream of an argon plasma jet

“…Therefore, the needle tip stretches out from the jet nozzle to avoid this obstruction, which has no interference with the formation of the surface pattern. Similar to the method used in Wu et al [ 24 ] a transistor‐transistor‐logic (TTL) signal produced by a signal generator (Tektronix AFG 3052 C) is used to trigger the ICCD (or an electron‐multiplying ICCD [emICCD, PI MAX4]) and the oscilloscope synchronously. Therefore, images can be captured with variable delay time in reference to the discharge.…”

“…[12] In addition, streamers tend to swell at the regions with residual meta-stables due to discharge enhancement, resulting in a plume with periodical swells. [22,23] Owing to electrostatic repellence, streamers present a curved propagation to detour residual positive ions, leading to a meandering plume, [24] or a hollow plume. [25] In brief, resulting from different streamer behaviors, free plasma jet presents distinctive plume morphologies.…”