Upon varying discharge current and gap width, several self‐organized patterns are observed in the anode layer of an atmospheric pressure glow discharge with miniature axial argon flow, including diffuse‐disk, single‐ring, disk‐ring, wheel‐spokes, and radial‐stripes patterns. Among them, the wheel‐spokes pattern is observed for the first time in atmospheric pressure glow discharge above a water anode. The conditions for generating the self‐organized patterns are also investigated. Fast photography results indicate that the patterns with low current and narrow gap are diffuse in nature, while those with high current and wide gap are composed of individual spots. This is further verified from waveforms of applied voltage and light emission signals. Moreover, the generation, movement, and disappearance of discrete spots are observed by a high‐speed video camera. Besides, the optical emission spectrum indicates that the glow discharge above the water surface is abundant with electronegative species, including O, NO, NH, and OH. Finally, the formation mechanism of diffuse and spotted anode layers is revealed.

In this Letter, a uniform air plasma plume with a fairly large scale is generated downstream of an air flow through interactions between a pair of argon plasma jets excited by a direct current power supply. With increasing power voltage, two separated plumes are first generated downstream of the pair of jets, which transit to the uniform planar plume with a fairly large scale. The planar plume elongates with the increasing air flow rate or power voltage. Moreover, the temperature of the planar plume is comparatively low with a maximum of about 80 °C, which is symmetrically distributed perpendicular to the pair of jets. For the separated plumes, discharge current is intermittently pulsed under a time-invariant gap voltage. However, both gap voltage and discharge current are periodically pulsed for the planar plume. High-speed video images reveal that the planar plasma plume stems from two discrete plumes flushing out of the pair of jets, which are soon merged together by a cathode-directed streamer due to interactions between them, leading to the generation of an arc-shaped filament. Due to the air flow, the arc-shaped filament keeps moving away from the jet vicinity until it quenches at last, which belongs to a glow discharge regime. In addition, surface modification of polyethylene terephthalate (PET) is performed with our planar plasma plume, which reveals that the hydrophilicity of the PET surface can be improved greatly.

Excited by a modulated sinusoidal voltage, self-organized filaments are generated in a parallel plate dielectric barrier discharge with a flowing mixture of argon and nitrogen at atmospheric pressure. With increasing off time of the modulated voltage, a single filament transits into a pair of filaments. Then, the self-organized filaments undergo a scenario from triangle, quadrilateral, pentagon, hexagon, and finally, to a ring composed of rotating filaments. During the transition process, the discharge current always presents a single pulse per half voltage cycle, whose amplitude increases for both positive and negative discharges. However, discharge current symmetry deteriorates. Moreover, with increasing off time, the inception voltage increases for the positive discharge, while it decreases for the negative discharge. For the hexagonal arranged filaments, temporal evolutions are implemented for the positive and negative discharges. The results reveal that the initiation in one current pulse seems to propagate opposite to the gas flow direction in the positive discharge, while advances along it in the negative discharge. By optical emission spectroscopy, the electron temperature and electron density are investigated via Boltzmann plotting and a line ratio from 738 nm to 750 nm, respectively. With increasing off time, both of them increase for the positive discharge, while they decrease for the negative discharge. What is more, both electron temperature and electron density increase as the inception voltage increases.

Excited by a modulated sinusoidal voltage, dielectric barrier discharge in atmospheric pressure helium has been investigated through a one-dimensional fluid model. Under a lower voltage amplitude, the discharge presents one current pulse per half sinusoidal cycle. The positive discharge is weaker than the negative one if the duty ratio of the modulated voltage is lower. When increasing the duty ratio, the intensity of the positive discharge increases and that of the negative discharge keeps approximately constant, which implies that the discharge symmetry is improved. A similar phenomenon regarding the discharge symmetry is also observed under a higher voltage amplitude despite the fact that a secondary discharge following a primary one is presented per half sinusoidal cycle. Besides the duty ratio, the discharge symmetry can be improved by increasing the voltage amplitude, especially under a lower duty ratio. These phenomena are qualitatively explained by analyzing the variation of the electron density when increasing the duty ratio. Results also indicate that the positive primary discharge at the peak moment belongs to a Townsend mode or a glow one, which is determined by the duty ratio and the voltage amplitude. Finally, the critical voltage for the Townsend mode transiting to the glow one is investigated as a function of the duty ratio.

Atmospheric pressure glow discharge above liquid electrode has extensive application potentials in biomedicine, chemical degradation,environmental protection,etc.In this paper,such a kind of discharge excited by a direct current voltage is generated through using a metal rod above water surface.Results show that the discharge has a ring shape on the water surface when the current is low.With increasing the discharge current,its diameter first increases,and then decreases after reaching a maximum,and finally slightly increases.In this process,the discharge transits from a conical shape to a column.Fast photography indicates that the conical discharge actually originates from the rotation of a discharge filament,which can be attributed to the effect of electronegative particles generated in the discharge channel. These electronegative particles,mainly including NO,NO2,NO3,O,O3 and OH,can increase electron attachment coefficient β,resulting in extinguishment of the original discharge channel.Due to a similar field value and a normal β coefficient,the breakdown conditions can be satisfied in a region adjacent to the original channel.Therefore,the discharge will move into the new region.Further investigation indicates that both the conical discharge and the column discharge are in a normal glow regime.By optical emission spectroscopy,it is found that the vibrational temperature,the rotational temperature and the intensity ratio of I391.4/I337.1 increase with increasing the current.Electron mobility decreases in the conical discharge due to voltage decreasing with the current.Hence,electrons have an increased possibility with which they are attracted by the electronegative particles to form negative ions.Consequently,with increasing the discharge current,more negative ions will be accumulated not only near the conical center,but also in the vicinity of the discharge channel.Obviously,there is repulsive force between the negative ions in the two regions.The repulsive force increases with increasing the discharge current,which leads to the ring diameter increasing with the current.Besides the negative ions,gas temperature plays another important role in the discharge.It increases with current increasing,leading to the decrease of gas density in the discharge channel.Hence,electrons have a reduced probability with which they are attached by electronegative particles.This factor will lead to a reduced force between less negative ions in the two regions.Consequently,after reaching its maximum,the ring diameter decreases with current increasing.If the current is high enough,the discharge channel will have a sufficiently high temperature and an adequately lower gas density, resulting in an increased electron energy as well as an increased α(the first Townsend ionization coefficient).Therefore, the discharge will be self-sustained in the original region,other than move into an adjacent region.Consequently,the column discharge appears with the current increasing to some extent.In the column discharge,more negative ions will be accumulated above the water surface with increasing the current.These negative ions extend along the water surface,which contributes to the slight diameter increase of the luminous column.These experimental results are of great significance for theoretically studying liquid anode discharge.