The understanding of self-organized patterns in spatially extended nonlinear dissipative systems is one of the most challenging subjects in modern natural sciences. Such patterns are also referred to as dissipative structures. We review this phenomenon in planar low temperature dc gas-discharge devices with a high ohmic barrier. It is demonstrated that for these systems a deep qualitative understanding of dissipative structures can be obtained from the point of view of synergetics. At the same time, a major contribution can be made to the general understanding of dissipative structures. The discharge spaces of the experimentally investigated systems, to good approximation, have translational and rotational symmetry by contraction. Nevertheless, a given system may exhibit stable current density distributions and related patterns that break these symmetries. Among the experimentally observed fundamental patterns one finds homogeneous isotropic states, fronts, periodic patterns, labyrinth structures, rotating spirals, target patterns and localized filaments. In addition, structures are observed that have the former as elementary building blocks. Finally, defect structures as well as irregular patterns are common phenomena. Such structures have been detected in numerous other driven nonlinear dissipative systems, as there are ac gas-discharge devices, semiconductors, chemical solutions, electrical networks and biological systems. Therefore, from the experimental observations it is concluded that the patterns in planar low temperature dc gas-discharge devices exhibit universal behavior. From the theoretical point of view, dissipative structures of the aforementioned kind are also referred to as attractors. The possible sets of attractors are an important characteristic of the system. The number and/or qualitative nature of attractors may change when changing parameters. The related bifurcation behavior is a central issue of the synergetic approach chosen in the present article. A short review of possible theoretical approaches reveals that a theoretical description of the experimentally observed patterns is far from being satisfactory. Bearing this in mind, a qualitative model of the reaction-diffusion type is considered. Surprisingly enough, this model allows for a qualitative description of almost all fundamental patterns that have been observed experimentally. Also, so far the predictive power of this model is unmatched.

Synergetic aspects of gas-discharge: lateral patterns in dc systems with a high ohmic barrier

Cylindrical microdischarge cavities 200–400 μm in diameter and 0.5–5 mm in depth have been fabricated in silicon and operated at room temperature with neon or nitrogen at specific power loadings beyond 10 kW/cm3. The discharges are azimuthally uniform and stable operation at N2 and Ne pressures exceeding 1 atm and ∼600 Torr, respectively, has been realized for 400 μm diameter devices. Spectroscopic measurements on neon discharges demonstrate that the device behaves as a hollow cathode discharge for pressures >50 Torr. As evidenced by emission from Ne and Ne+ (2P,2F) states as well as N2 (C→B) fluorescence (316–492 nm), these discharge devices are intense sources of ultraviolet and visible radiation and are suitable for fabrication as arrays.

Microdischarge devices fabricated in silicon

Barrier discharges are increasingly used as a cost-effective configuration to produce non-equilibrium plasmas at atmospheric pressure. This way, copious amounts of electrons, ions, free radicals and excited species can be generated without significant heating of the background gas. In most applications the barrier is made of dielectric material. Major applications utilizing mainly dielectric barriers include ozone generation, surface cleaning and modification, polymer and textile treatment, sterilization, pollution control, CO2 lasers, excimer lamps, plasma display panels (flat TV screens). More recent research efforts are devoted to biomedical applications and to plasma actuators for flow control. Sinusoidal feeding voltages at various frequencies as well as pulsed excitation schemes are used. Volume as well as surface barrier discharges can exist in the form of filamentary, regularly patterned or diffuse, laterally homogeneous discharges. The physical effects leading to collective phenomena in volume and surface barrier discharges are discussed in detail. Special attention is paid to self- organization of current filaments and pattern formation. Major similarities of the two types of barrier discharges are elaborated.

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Collective phenomena in volume and surface barrier discharges

This review focuses on one of the fundamental phenomena that occur upon application of sufficiently strong electric fields to gases, namely the formation and propagation of ionization waves-streamers. The dynamics of streamers is controlled by strongly nonlinear coupling, in localized streamer tip regions, between enhanced (due to charge separation) electric field and ionization and transport of charged species in the enhanced field. Streamers appear in nature (as initial stages of sparks and lightning, as huge structures-sprites above thunderclouds), and are also found in numerous technological applications of electrical discharges. Here we discuss the fundamental physics of the guided streamer-like structures-plasma bullets which are produced in cold atmospheric-pressure plasma jets. Plasma bullets are guided ionization waves moving in a thin column of a jet of plasma forming gases (e.g.,He or Ar) expanding into ambient air. In contrast to streamers in a free (unbounded) space that propagate in a stochastic manner and often branch, guided ionization waves are repetitive and highly-reproducible and propagate along the same path-the jet axis. This property of guided streamers, in comparison with streamers in a free space, enables many advanced time-resolved experimental studies of ionization waves with nanosecond precision. In particular, experimental studies on manipulation of streamers by external electric fields and streamer interactions are critically examined. This review also introduces the basic theories and recent advances on the experimental and computational studies of guided streamers, in particular related to the propagation dynamics of ionization waves and the various parameters of relevance to plasma streamers. This knowledge is very useful to optimize the efficacy of applications of plasma streamer discharges in various fields ranging from health care and medicine to materials science and nanotechnology.

Guided ionization waves : theory and experiments

Dielectric barrier discharges (DBDs) operating in a transient glow discharge regime offer a large variety of self-organized filamentary static or dynamical structures and constitute an excellent physical system for the study of nonlinear dynamics and pattern formation. The plasma filaments of DBDs can exhibit particle-like behavior, with motion, generation, annihilation, and scattering as well as collective effects leading to self-organized structures (hexagons, stripes, concentric rings, spirals, etc) that are typical of reaction–diffusion systems. The purpose of this paper is to analyze the detailed physics of pattern formation in DBDs on the basis of numerical fluid simulations and experiments in order to provide a deeper understanding of the nonlinear mechanisms responsible for the self-organization and dynamics of filaments.

https://iopscience.iop.org/article/10.1088/0963-0252/23/5/054003/pdf

Pattern formation and dynamics of plasma filaments in dielectric barrier discharges

In this paper, we report the experimental results on the characteristics of plasma patterns with different planar electrode shapes in dielectric barrier glow discharge. The formation and the evolution of the discharge patterns at different voltages were investigated. The results show that the plasma patterns in this glow-barrier system form at the beginning of the discharge pulse. The limited size of planar electrodes and the electric field distribution are important factors for the pattern formation.

Pattern formation and boundary effect in dielectric barrier glow discharge.

The nonlinear phenomenon is very popular in dielectric barrier discharge (DBD) plasmas. There are at least three kinds of spatial and temporal nonlinear phenomena appearing synchronously or asynchronously in DBDs, i.e. self-organized patterns, striations and chaos. This paper describes the recent research and progress in understanding the nature of these nonlinear phenomena. Patterns are macroscopic structures with certain spatial and/or temporal periodicities generated through selforganization of microscopic parameters. The physics of patterns in DBDs is mainly associated with lateral dynamic behaviors or the lateral non-local effect of charged particles resulting in the lateral development or non-uniformity of discharge. Striations are ionization waves with unique properties determined by transport phenomena, ionization processes and electron kinetics in current-carrying plasmas. The physics of striations in DBDs is mainly associated with the advances in non-local electron kinetics in spatially inhomogeneous plasmas. Chaos is a kind of random and non-periodic phenomenon occurring in a determined dynamic system, following a series of certain rules while exhibiting random locomotion, and is regarded as an intrinsic and ubiquitous phenomenon in a nonlinear dynamic system. An evolution trajectory including period-doubling bifurcation to chaos was observed in DBDs or DBD-derived plasmas. In a common sense, it is believed that the formation of all the three nonlinear phenomena in a DBD system should be related to the non-local transversal and/or longitudinal dynamics of space charges (i.e. non-local effect) or the localized electric field interaction. Future work is still needed on the underlying physics and should be directed to pursuing the unification of these nonlinear phenomena in DBD.

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Nonlinear phenomena in dielectric barrier discharges: pattern, striation and chaos

The experimental and calculated results of uniformity in a glow dielectric barrier discharge (DBD) under sub-atmospheric pressures are reported. Driven by a square-wave power source, the discharge in a parallel-electrode DBD system shows uniform or various lateral structures under different conditions. There exists a critical frequency below which the DBD is uniform for almost all the applied voltages. Above the critical frequency, a non-uniform (patterned) discharge is observed and the patterned structures change with frequency and voltage. A two-dimensional fluid modeling is performed on this DBD system which shows similar results in agreement with the experiments. The simulations reveal that the distribution of the space electron density at the beginning of each voltage pulse plays an important role in achieving the uniformity. Uniform space charge results in a uniform DBD. The patterned DBD always evolves from the initial uniform state to the eventual non-uniform one. During this process, the space electrons form a patterned distribution ahead of the surface charges and lead to non-uniform discharge channels.

https://iopscience.iop.org/article/10.1088/0963-0252/21/1/015008/pdf

Uniformity of a dielectric barrier glow discharge: experiments and two-dimensional modeling

The effect of volume and surface charges on the structure of glow dielectric barrier discharge (DBD) has been investigated numerically by using two-dimensional (2D) fluid modeling. The local increase of volume or surface charges induces a kind of activation-inhibition effect, which enhances the local volume discharge and inhibits the discharge in neighborhoods, resulting in non-uniform discharge. The activation-inhibition effect due to the non-uniform volume and/or surface charges depends on the non-uniformity itself and the applied voltage. The activation-inhibition of non-uniform charges has different effects on the volume charges and the accumulated surface charges. The distribution of remaining free charges (seed electrons) in volume at the beginning of voltage pulse plays a key role for the glow DBD structure, resulting in a patterned DBD, when the seed electrons are non-uniform at higher frequency and moderate voltage or uniform DBD, when the seed electrons are uniform at lower frequency or high voltage. The distribution of surface charges is not the determining factor but a result of the formed DBD structure.

Effect of volume and surface charges on discharge structure of glow dielectric barrier discharge

In this paper, the numerical study has been performed on the xenon positive column discharges of mercury-free fluorescent lamp. The plasma discharge characteristics are analyzed by numerical simulation based on two-dimensional fluid model. The effects of cell geometry, such as the dielectric layer, the electrode width, the electrode gap, and the cell height, and the filling gas including the pressure and the xenon percentage are investigated in terms of discharge current and discharge efficiency. The results show that a long transient positive column will form in the xenon lamp when applying ac sinusoidal power and the lamp can operate in a large range of voltage and frequency. The front dielectric layer of the cell plays an important role in the xenon lamp while the back layer has little effect. The ratio of electrode gap to cell height should be large to achieve a long positive column xenon lamp and higher efficiency. Increase of pressure or xenon concentration results in an increase of discharge efficiency and voltage. The discussions will be helpful for the design of commercial xenon lamp cells.

Feng He

Papers

Pattern formation and boundary effect in dielectric barrier glow discharge.

Nonlinear phenomena in dielectric barrier discharges: pattern, striation and chaos

Uniformity of a dielectric barrier glow discharge: experiments and two-dimensional modeling

Effect of volume and surface charges on discharge structure of glow dielectric barrier discharge

Numerical study on xenon positive column discharges of mercury-free lamp