Zengqian Yin

Square pattern formation in a gas discharge system

The square pattern is observed in dielectric barrier discharge in argon for the first time. The hexagon pattern and the mixture of hexagon and square structure are also observed. The square pattern can remain stable for several tens of minutes. The spatio-temporal dynamics of square pattern formation is investigated by optical method. The measurement results show that the square pattern is an interleaving of two square patterns, which is the reason of the stability of square pattern.

Spatio-temporal dynamics of discharge domains in a dielectric barrier discharge device

The spatio-temporal correlation of discharge filaments in dielectric barrier discharges in air at atmospheric pressure is studied using an optical method. The stable filament patterns are achieved by using water electrodes, which serve both as coolants and transparent media for observation. It is found that the time interval between the two discharges of a filament in two consecutive half-cycles alternates between the long one and the short one, in general. An equation describing breakdown/termination of discharges is suggested by considering the effect of accumulated charges on the dielectric surface, and the experimental phenomena mentioned above can be explained using this equation. It is found in our experiments that the mapping of the delay time sequence for a filament has metastability with certain fluctuation features. The stable filament pattern can be divided into discharge domains. Each domain consists of several neighbouring filaments. The discharges of the filaments inside a domain are cooperatively correlated, while those of neighbouring domains are most likely competitively correlated.

A simple device of generating glow discharge plasma in atmospheric pressure argon

Atmospheric pressure glow discharge is realized in argon by using a plasma needle. With increasing the applied voltage, uniform plasma increases in scale from a small region near the needle tip to a plasma plume with a length of about 20mm. The discharge mechanism is discussed based on the light emission waveforms from the plasma. Optical emission spectroscopy is used to determine excited electron temperature and vibrational temperature, and the results indicate that the excited electron temperature and the molecular vibrational temperature are about 6000 and 2300K, respectively.

Spatio-temporal patterns in dielectric barrier discharge in air/argon at atmospheric pressure

A rich variety of patterns including travelling hexagon, travelling square, quasi-crystal, static hexagon and stripe have been studied in a dielectric barrier discharge system. The phase diagram of pattern types as a function of air concentration and the applied voltage is given. The spatio-temporal correlations between discharge filaments in these patterns are measured in a nanosecond time scale by an optical method. It is found that the travelling pattern is an interleaving of two sub-patterns with a temporal sequence inversion in consecutive half-cycles.

Hexagon and stripe patterns in dielectric barrier streamer discharge

We present a specially designed dielectric barrier discharge (DBD) system for the study of pattern formation. Hexagon and stripe patterns have been observed in a streamer discharge in a DBD for the first time. The phase diagram of pattern types as a function of applied voltage is given.

Numerical simulation of operation modes in atmospheric pressure uniform barrier discharge excited by a saw-tooth voltage

The characteristics of dielectric barrier discharge excited by a saw-tooth voltage are simulated in atmospheric pressure helium based on a one-dimensional fluid model. A stepped discharge is obtained per half voltage cycle with gas gap width less than 2 mm by the simulation, which is different to the pulsed discharge excited by a sinusoidal voltage. For the stepped discharge, the plateau duration increases with increasing the voltage amplitude and decreasing the gas gap. Therefore, uniform discharge with high temporal duty ratio can be realized with small gap through increasing the voltage amplitude. The maximal densities of both electron and ion appear near the anode and the electric field is almost uniformly distributed along the gap, which indicates that the stepped discharge belongs to a Townsend mode. In contrast to the stepped discharge with small gas gap, a pulsed discharge can be obtained with large gas gap. Through analyzing the spatial density distributions of electron and ion and the electric field, the pulsed discharge is in a glow mode. The voltage-current (V-I) characteristics are analyzed for the above mentioned discharges under different gas gaps, from which the different discharge modes are verified.

Temporal symmetry of individual filaments in different spatial symmetry filaments pattern in a dielectric barrier discharge

The temporal behavior of individual filament in different spatial symmetry filaments patterns in dielectric barrier discharge is investigated by using an optical method. A series of return maps of the discharge moments of individual filaments is given. It is found that the temporal symmetry of individual filament changes with the change of the spatial symmetry of filaments pattern as the applied voltage increases. The role of wall charges for this phenomenon is analyzed.

Spatiotemporal dynamics of discharge filaments in dielectric barrier discharges

A pair of water electrodes used in dielectric barrier discharge was served as coolant and transparent conductors for observation. Stable filamentary discharge was formed after cleaning discharges with high applied voltages. The temporal behavior of discharge of single filament can be measured with a lens-imaging and PMT system. The two-dimensional filamentary pattern can be divided into discharge domains with different shapes. Each discharge domain consists of several neighboring filaments. Their discharges overlap in time inside the domain. The temporal order of discharges of two filaments inside a domain or two neighboring domains can be alternately opposite for positive and negative half-cycles. The experimental results can be interpreted with breakdown-charge diffusion model.

Dielectric barrier discharge image processing by Photoshop

In this paper, the filamentary pattern of dielectric barrier discharge has been processed by using Photoshop, the coordinates of each filament can also be obtained. By using Photoshop two different ways have been used to analyze the spatial order of the pattern formation in dielectric barrier discharge. The results show that the distance of the neighbor filaments at U equals 14 kV and d equals 0.9 mm is about 1.8 mm. In the scope of the experimental error, the results from the two different methods are similar.

Image Processing of Discharge Pattern by Spatial Fourier Transform Method

In this paper, the method of Spatial Fourier Transform has been used to investigate the pattern formation dynamics in a dielectric barrier discharge (DBD) system. With this method, patterns formed in the DBD system can be transformed into smooth frequency spectrum. The frequency constitution of discharge pattern can be analyzed. In our experiment mixed gas of 96% Ar and 4% air at 0.9 atm is used as working gas. The experimental results show that the discharge pattern with increasing the applied voltage undergoes a scenario: stochastic discharge filaments, hexagon pattern, square pattern, honeycomb structure. The different kinds of patterns were transformed into Fourier space by two-dimension Spatial Fourier Transform. The spectra of patterns were given and analyzed in this paper. It was found that different discharge patterns correspond to different frequency spectrum, furthermore, the better the stability of the pattern, the clearer the frequency spectrum. Therefore, the pattern transition procedure from one discharge pattern to another can also be studied by the frequency spectrum. Consequently, Spatial Fourier Transform is a better method to research the pattern formation dynamics in gas discharge system.