Fucheng Liu

Self-Organized Gas-Discharge Patterns in a Dielectric-Barrier Discharge System

A rich variety of gas-discharge patterns have been observed in a specially designed dielectric-barrier discharge system with two liquid electrodes. The patterns presented here include square-lattice pattern, square-texture pattern, square-superlattice pattern, hexagonal superlattice state, multiarmed-spiral pattern, hollow-hexagonal pattern, and rotating-wheels pattern.

Simulation of stationary glow patterns in dielectric barrier discharges at atmospheric pressure

Self-organized stationary patterns in dielectric barrier discharges operating in glow regime at atmospheric pressure are investigated by a self-consistent two-dimensional fluid model. The simulation results show that two different modes, namely, the diffuse mode and the static patterned mode, can be formed in different ranges of the driving frequency. The discharge operates in Townsend regime in the diffuse mode, while it operates in a glow regime inside the filaments and in a Townsend regime outside the filaments in the stable pattered mode. The forming process of the stationary filaments can be divided into three stages, namely, destabilizing stage, self-assembling stage, and stable stage. The space charge associated with residual electron density and surface charge is responsible for the formation of these stationary glow patterns.

Core dynamics of a multi-armed spiral pattern in a dielectric barrier discharge

Stable multi-armed spiral patterns have been observed in a gas discharge by using water electrodes. It is found that the multi-armed spirals in our experiments generally result from the interaction between a single-armed spiral pattern and dislocations. The number of spiral arms can be increased or decreased depending on the topological charge of the dislocation when it glides into the spiral core. The complex spatiotemporal dynamics of the multi-armed spiral tips has also been investigated. The spiral tips rotate about a common circle for a two-armed spiral pattern. The core dynamics of a three-armed spiral pattern involves intermittent pairwise collision of tips at or near their tips, and it is more complex for a four-armed spiral pattern.

Formation of side discharges in dielectric barrier discharge

Pattern formation and self-organization are fascinating phenomena found widely in nature and in laboratory environment such as dielectric barrier discharge (DBD). Significant efforts have been made to explain the dynamic pattern formation. In DBD, the formation of side discharges is generally supposed to be a key factor responsible for diversity and spatial-temporal symmetry breaking of pattern formation. However, it is still not clear how such discharges are induced. Here, we present the observations of side discharges in a filamentary dielectric barrier discharge from both numerical simulations and experiments. Two-dimensional particle-in-cell simulations with Monte Carlo collisions included have revealed formation dynamics of side discharges, suggesting that transverse plasma diffusion and ion induced secondary electron emission play critical roles. Moreover, a novel honeycomb superlattice pattern is observed in experiment, where the side discharges associated with honeycomb superlattice are verified by utilizing a high speed camera. Experimental observations and numerical simulation are in good agreement.

A complex pattern with hexagonal lattice and white-eye stripe in dielectric barrier discharge

A novel type of white-eye pattern in a dielectric barrier discharge system has been investigated in this paper. It is a superposition of a hexagonal lattice and a white-eye stripe in appearance and evolves from a white-eye square grid state with the applied voltage increasing. Its spatio-temporal dynamics obtained by an intensified charge-coupled device shows that it consists of three transient rectangular sublattices. The spatiotemporally resolved evolutions of the molecular vibrational temperature and electron density of the pattern are measured by optical emission spectra. The evolution of surface charge distribution is given and its effect on the self-organized pattern formation is discussed.

Mechanisms of fine structure formation in dielectric barrier discharges

The evolution of two successive filamentary discharges in dielectric barrier discharge (DBD) has been studied by the use of two-dimensional particle-in-cell simulations with Monte Carlo collisions included. It is shown that these filamentary discharges involve the interplay between the external field, the surface charge field, and the space charge field. This leads to a few fine structures emerging, such as the weak discharge occurring at the zero-crossing point of the ac voltage, the splitting phenomenon of filaments, and the coexistence of positive and negative surface charges at footprints of the filamentary discharges. Our simulation results reveal the underlying physics governing the discharge and explain the dynamical behaviors of the DBD filaments observed in experiments.

Numerical simulations of superlattice patterns in dielectric barrier discharges at atmospheric pressure

This paper presents the numerical investigation on superlatticepatterns in atmospheric pressure glow discharges in dielectric barrier discharges by using a self-consistent 2D fluid model. It is found that the superlatticepattern is an interleaving of two filamentary sub-patterns with alternate spatial and temporal characteristics. The competition between the volume ionization and the memory effects of both surface charges and space charges is expected to the formation mechanism of this superlatticepattern.

Image processing on the patterns in dielectric barrier discharge at atmospheric pressure

Pattern formation is a process by which a spatially uniform state loses stability to a non-uniform state. A usual effective method for studying the property of patterns is to take pictures or record images of the patterns with digital cameras and get useful information from them. In this work, the structure, the spatial frequency spectrum of the patterns, the precise location of the discharge filaments center and the distribution of the light emission density of filaments are analyzed with Matlab6.1. This work can provide a beneficial reference for researchers who study pattern dynamics in DBD system or other systems.

A dot-line square super-lattice pattern with surface discharge in dielectric barrier discharge

We report a dot-line square super-lattice pattern with surface discharge (DLSSPSD) in a dielectric barrier discharge system and show for the first time that the surface discharge can promote the formation of volume discharge (VD). The pattern consists of three different discharge morphologies, namely, bright spots, dim spots, and bright lines. The spatiotemporal dynamics of the DLSSPSD are studied using an intensified charge-coupled device camera, a photomultiplier, and a high-speed video camera. The results show that the VD located at the dim spots and bright lines is generated on both the rising and falling edges of the voltage. It is found that the high surface charge density transferred by the surface discharge of the bright spots promotes the formation of VD at the dim spots and bright lines.We report a dot-line square super-lattice pattern with surface discharge (DLSSPSD) in a dielectric barrier discharge system and show for the first time that the surface discharge can promote the formation of volume discharge (VD). The pattern consists of three different discharge morphologies, namely, bright spots, dim spots, and bright lines. The spatiotemporal dynamics of the DLSSPSD are studied using an intensified charge-coupled device camera, a photomultiplier, and a high-speed video camera. The results show that the VD located at the dim spots and bright lines is generated on both the rising and falling edges of the voltage. It is found that the high surface charge density transferred by the surface discharge of the bright spots promotes the formation of VD at the dim spots and bright lines.

Rotation of a single vortex in dusty plasma

A single vortex is obtained in radio-frequency capacitive discharge in argon gas. The dust subsystem is confined in the horizontal plane with an asymmetrical saw structure placed on the lower electrode. The vortex rotates as a whole along the long side of the saw-teeth. Asymmetry of the saw structure plays an important role in the rotation of the vortex. Nonzero curl of the total force resulting from the local ion flow and the electric field in the plasma sheath could be attributed to the persistent rotation of vortex.