Experimental study on the emission spectra of microwave plasma at atmospheric pressure

With increasing peak voltage applied to a plasma jet, surface discharge patterns are formed on the dielectric target, which include diffuse spot, single ring, and concentric triple rings. During the evolvement of these patterns, the number of positive current pulses increases and there is only one negative pulse per voltage cycle. Fast photography reveals that all of these patterns originate from temporal superposition of negative and positive surface discharges. The negative surface discharge is always diffused for each pattern. However, the positive surface discharges in a streamer regime are more complicated. The first positive streamer per voltage cycle is short, which propagates along radial spokes that are distributed symmetrically, resulting in a central spot of each pattern. The last positive streamer per voltage cycle is long, which propagates along a straight line at a lower peak voltage and bifurcates randomly at a higher peak voltage, resulting in diffuse background of each pattern. Other positive streamers also bifurcate after traveling certain distance from the center, and then propagate along an arc, leading to the formation of ring in patterns. The propagation behaviors of these positive streamers are discussed qualitatively by analyzing the influence of applied electric field, residual charges, and air diffusion.

Section: Resultsmentioning

confidence: 99%

Spatial‐temporal evolutions of surface discharge patterns generated on dielectric target interacted with a plasma jet

Ren

Jia

et al. 2019

“…Therefore, the intensity ratio of 391.4 to 337.1 nm is an indicator for electron temperature, which is positively proportional to electric field strength. [22,55] Hence, electric field strength can be reflected from an intensity ratio of 391.4 to 337.1 nm. This method has also been reported in Paris et al [49] To implement a precise investigation of the spatial distribution of field strength for D p2 , spectra are captured with a spatial resolution better than 0.1 mm.…”

Section: Resultsmentioning

confidence: 99%

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

Zhao

et al. 2022

Streamer behaviors, related to discharge patterns, can determine the distribution of active species, which play an important role in the applications of the plasma jet. In this article, petal-like patterns formed on the substrate are observed for the first time downstream of an argon plasma jet. The penta-petalous pattern is taken as an example to discuss the pattern formation mechanism, which results from two positive discharges (D p1 and D p2 ) and one negative discharge (D n ) in every voltage cycle. Fast photography is implemented to reveal the complicated streamer dynamics of D p2 . Results indicate that D p2 with a low Q undergoes a stripe phase, a homogeneous phase, and a branch phase. The complicated streamer dynamics of D p2 are analyzed based on optical emission spectra.

“…As mentioned above, the serpentine trajectory of the streamer presents a peak near an ion cloud and E reaches a minimum in front of an ion cloud. Primarily determined by E, [59,85] T e reaches a minimum once in front of a peak of the snake-like plume. Moreover, as a function of E, the first Townsend ionization coefficient (α) dominates the secondary electron avalanches (electron production process).…”

Section: Methodsmentioning

confidence: 99%

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

Ran

et al. 2023

Plasma plume morphology, related to streamer behavior and active‐species distribution of plasma jets, is important for fixed‐point and precise treatment of workpieces. For a peculiar snake‐like plume, discharge aspects are investigated with varying argon flow rate (Q) in this paper. Results indicate that the plume length and distance between two neighboring peaks of the snake‐like plume increase with increasing Q. Fast photography indicates that the snake‐like plume is composed of positive streamers propagating along a reproducible serpentine trajectory, which occurs once per voltage cycle. Based on optical emission spectroscopy, electron temperature, electron density, and vibrational temperature are investigated with varying Q. All these phenomena are qualitatively analyzed finally.