Self-deformation has been observed for an atmospheric pressure diffuse discharge initiated in the air gap between a needle anode and a water cathode, which undergoes a morphology scenario from a cone, an axially symmetric horn, to a rectangular horn as time elapses. During the self-deformation process, pH value and electric conductivity of the water cathode vary with time. Moreover, electrical measurements indicate that applied voltage and discharge current are time-invariant for the conical discharge, while periodically pulsed for the other two discharges. This may suggest different formation mechanisms of them. Hence, fast photography is implemented by a high-speed video camera and an intensified charge coupled device. Results indicate that the diffuse discharges with different morphologies belong to a glow discharge regime. Among them, the conical discharge is composed of stationary micro-discharge, and the horn-shaped discharges consist of moving micro-discharge. Moreover, the axially symmetric horn is a self-rotating version of the rectangular horn. Furthermore, the rectangular horn originates from the swing of a micro-discharge filament like a pendulum motion. Finally, qualitative explanations are given for the experimental phenomena mentioned above.

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Pattern formation is a very interesting phenomenon formed above a water anode in atmospheric pressure glow discharge. Up to now, concentric-ring patterns only less than four rings have been observed in experiments. In this paper, atmospheric pressure glow discharge above a water anode is conducted to produce diversified concentric-ring patterns. Results indicate that as time elapses, the number of concentric rings increases continuously and up to five rings have been found in the concentric-ring patterns. Moreover, the ring number increases continuously with increasing discharge current. The electrical conductivity of the anode plays an important role in the transition of the concentric patterns due to its positive relation with ionic strength. Hence, the electrical conductivity of the water anode is investigated as a function of time and discharge current. From optical emission spectrum, gas temperature and intensity ratio related with density and temperature of electron have been calculated. The various concentric-ring patterns mentioned above have been simulated at last with an autocatalytic reaction model.

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.

In a rod-water geometry, self-organized patterns are formed on the water surface of an atmospheric glow discharge excited by a square-wave voltage, which include a disk with an encircling ring and concentric triple rings with varying air gap widths. The diameter of these patterns slightly increases with the increasing gap width. Although a square-wave voltage is used, waveforms of voltage and current indicate that the discharge belongs to a periodical liquid-anode discharge. By fast photography, spatial and temporal evolutions of these self-organized patterns indicate that honeycomb patterns are prone to be generated with a wider gap. Moreover, these honeycomb patterns finally lead to the formation of the concentric triple rings and the disk with an encircling ring with wider gaps. Within the scope of our knowledge, this is the first observation of honeycomb patterns in a liquid-anode discharge.