Dielectric barrier surface discharges (DBD) have the potential to act as flush mounted flow control devices for separation control and other aeronautic applications. A pulse-sustained plasma with the ions driven by a DC bias voltage is proposed for optimum performance. While characterizing these devices, it was found that their performance is severely limited by surface charge build-up. That charge builds up rapidly and remains for as long as hours. Work in this paper shows that the surface charge can be mitigated by using a reversing DC bias potential or by using a constant DC bias potential with a partially covered electrode.

Dynamics of the controlled streamer-to-spark transition in atmospheric-pressure air is simulated. Results of calculation show that at proper selection of the parameters (the feeding capacitor, the ballast resistor) of power-supply electric circuit it is possible to produce non-thermal plasma filaments of radii about 10−2 cm, the mean gas temperature inside the filament being about 2000-3000 K and the electron number density being 1013–1014 cm−3.

The paper highlights applications of some atmospheric pressure plasmas (dc-corona, streamer and spark and ac-Dielectric Barrier Discharges) to aerosol processes for Materials and Environment (filtration, diagnostics).The production of vapor i.e. condensable gaseous species, leads to nano-sized particles by physical and chemical routes of nucleation in these AP plasmas: (i) when dc streamer and spark filamentary discharges as well as ac filamentary dielectric barrier discharges interact with metal or dielectric surfaces, and (ii) when discharges induce reactions with gaseous precursors in volume. It is shown how composition, size and structure of primary nano-particles are related to plasma parameters (energy, number per unit surface and time and thermal gradients).Then the growth by coagulation controls the final size of agglomerates versus plasma parameters and transit time in and after the plasma. Charging and electro-thermal collection are depicted to account for the related potential applications of controlled kinematics of charged aerosol.

This paper is a state of the art of the understanding on the physics of homogeneous dielectric barrier discharges at atmospheric pressure. It is based on the analysis of present and previous work about the behavior of these discharges and the conditions to get them. Mechanisms controlling the homogeneity during gas breakdown and discharge development are successively discussed. The breakdown has to be a Townsend one, the ionization has to be slow enough to avoid a large avalanche development. During the breakdown, the discharge homogeneity is related to the ratio of the secondary emission at the cathode (γ coefficient) on the ionization in the gas bulk (α coefficient). Higher is this ratio, higher is the pressure × gas gap product (Pd) value for which a Townsend breakdown is obtained. Among the phenomena enhancing the secondary emission there is the negative charge of the dielectric on the cathode surface, the trapping of ions in the gas and the existence of excited state having a long lifetime compared to the time between two consecutive discharges. The first phenomenon is always present when the electrodes are covered by a solid dielectric, the second one is related to the formation of a positive column and the third one is specific of the gas. During the discharge development, the homogeneity is mainly controlled by the voltage or the current imposed by the electrical circuit/electrode configuration and by the gas ability to be slowly ionized. Larger is the contribution of a multiple step ionization process like Penning ionization, higher will be the working domain of the discharge. A decrease of the gas voltage during the discharge development is a solution to enhance the contribution of this process. After 20 years of research a lot of mechanisms have been understood however there is still open questions like the nature of the Inhibited homogeneous DBD, surface energy transfers, role of attachment and detachment...

The paper reviews a current state of the art in the in-line plasma treatment of low-cost materials and opportunities for the use of the so-called Diffuse Coplanar Surface Dielectric Barrier Discharge (DCSBD). A brief outline of physical mechanism and basic properties of DCSBD is given. The results presented on the ambient air plasma treatments of textile, paper, wood, and glass illustrate that DCSBD offers outstanding performance with extremely low energy consumption for large area, uniform surface modifications of materials under continuous process conditions.

The generation of singlet delta oxygen states (O2(a1Δg )) by microplasmas has been studied experimentally. In the present paper, it is shown that micro-cathode sustained discharges (MCSD's) can be used to produce high fluxes of O2(a1Δg ) at atmospheric pressure. In He/O2/NO mixtures, O2(a1Δg ) number densities higher than 1016 cm−3 can be generated by this 3-electrode configuration and transported over distances of some tens of cm. In fact, at total flow rates up to 30 ln/min, O2(a1Δg ) fluxes above 10 mmol/h were measured in the MCSD afterglow, at 26 cm downstream. As a result, MCSD's appear to be very efficient and suitable tools for the continuous production of large amounts of O2(a1Δg ) at atmospheric pressure, which could give rise to a wide range of new applications, namely biological. The effect of different parameters such as gas flows and mixtures, and discharge current are discussed in the paper.

We present an experimental study of pattern formation in a Dielectric Barrier Discharge in Neon at 100 torr and 1 mm gap. An intensified CCD camera is used to analyze the time evolution of the patterns during one cycle of the voltage waveform. The formation of a hexagonal pattern of filaments in a transient, glow-like regime is observed, followed by a honeycomb structure that corresponds to a Townsend discharge occurring outside the regions delimited by the previous filaments. A 2D fluid model can qualitatively reproduce these features and is used to help interpreting the experimental results.

Three dielectric barrier discharge jets have been analyzed mainly by spectroscopic methods. Power densities, electron concentrations, and heavy particle temperatures are in the same range for the jets. All three jets are excited by sinusoidal voltages with kilohertz frequencies. High speed imaging proves that for quite different excitation schemes the jet plasma consists of isolated, fast moving, light-emitting structures. These so-called plasma bullets are emitted at a certain phase of the excitation voltage and occur in one half-cycle only.

Dielectric barrier discharges (DBD) in air at atmospheric pressure and at low frequency are mainly constituted of thin transient plasma filaments (or microdischarges) with radii of a few hundreds of micrometers. In this work, we consider a point-to-plane geometry with the dielectric covering the plane electrode. Plasma filaments are initiated by streamers, starting from the high-field region close to the point electrode. The plasma filaments deposit charges on the dielectric plate which screen the electric field and lead to an extinction of the discharge filaments. In this work we experimentally demonstrate the synchronous start of several filaments in a time range of less than a few tens of nanoseconds and we show that the charges deposited on the dielectric have a strong impact on the discharge structure. This is validated using a simple electrostatic model. Then, the dynamics of the 2D streamer propagation in the gas gap and its interaction with the dielectric plane is calculated. The influence of space charges and surface charges on the discharge structure are discussed and compared with the experiment.

Properties of pulsed corona streamers are measured and simulated in full three spatial dimensions (3D). Stereo photography is used to measure branching angles and to investigate whether apparent streamers reconnections are real. 3D simulations of two parallel streamers show that they can repel each other electrostatically, but that they also can merge due to photoionization. The electrostatic interaction of several streamers becomes evident through theoretical investigations of a periodic array of streamers.

The reaction kinetics of photochemical ozone (O3) generation in humid air and oxygen (O2) using efficient, narrow band vacuum ultra violet (VUV) 172 nm xenon excimer lamps is discussed. Trace amounts of water (H2O) vapor in the process gas leads to hydroxyl (OH) and hydroperoxy (HO2) radical formation. These radicals drive a catalytic O3 destruction cycle limiting O3 saturation concentration. This catalytic O3 destruction cycle was included into a quantitative kinetic model describing photochemical O3 production. Experimental O3 saturation concentrations obtained with coaxial VUV driven photochemical O3 generators compare satisfactorily with the models predictions.

Microplasmas inside confined cavities, pores and capillaries of dielectric materials present a great potential for various environmental applications. The paper briefly introduces the physical properties of the AC microplasmas generated by the discharges inside porous ceramics foams and focuses on their chemical effects in various mixtures of nitrogen and oxygen. Ozone formation as an example tool to evaluate the chemical potential of the microplasmas was investigated as a function of discharge power, gas mixture composition and total gas flow rate.

An experimental study is carried out to clarify the mechanism of the ozone zero phenomenon. Temporal variations of both the discharge characteristics and the metallic electrode surface in the ozone generator are investigated by the Lissajous figure method and Auger electron spectroscopy (AES), respectively. The AES results suggest that a number of oxygen atoms penetrate into the stainless-steel electrode owing to the exposure to ozone. Such a surface change would result in the temporal variation of the discharge characteristics of the generator.

Electron beams with a particle energy of typically 12 keV are used for collisional excitation of dense gases. The electrons are sent through ceramic membranes of only 300 nm thickness into gas targets. Excimer light emission from the pure rare gases and from gas mixtures are studied for the development of brilliant VUV and UV light sources. The application of the technology for gas kinetic studies is described and its potential for building very small electron beam pumped lasers is discussed.

The kinetic of the hydroxyl radical is studied in N2/O2/H2O mixtures with small amounts of acetone or isopropyl alcohol (0.5%). The radical density is measured in absolute value in the afterglow of a photo-triggered discharge, which generates an homogeneous transient non-equilibrium plasma, using a time resolved absorption measurement method. For dry mixtures, experimental results are compared to predictions of a self-consistent 0D discharge and kinetic model. It is shown that dissociation of the VOCs through quenching collisions of nitrogen metastable states plays an important role in the production of OH. Measurements can not be explained looking only at the oxidation of acetone or IPA by the oxygen atom. This result is reinforced by experimental results about the OH density in wet mixtures, with or without VOCs, compared to dry ones.

NO oxidation by simultaneous action of a dielectric barrier discharge and TiO2 photocatalyst was investigated as a function of the inlet gas composition (NO, O2, N2) and the input energy. Concentrations of various NOx species and ozone in the outlet were detected by the optical absorption spectroscopy. Higher content of O2 (10% and higher) increased the removal of NO and resulted in a higher output of N2O5. TiO2 coating on a reactor electrode resulted in the time-depending oxidation of NO. Initially the concentration of untreated NO fell below the level achieved without TiO2 but after few minutes the positive effect of TiO2 diminished. The initial decrease in NO level due to the presence of TiO2 coating is explainable by surface reactions of NO species and absorbed oxygen. After few minutes, the surface states responsible for the initial removal of NO saturated and the effect of TiO2 vanished.

In this study, the efficiency of different types of pulsed electrical discharges for the removal of organic pollutants from wastewater has been determined. Three discharge types, either in the water volume or in close proximity to the water surface are studied. The production of hydrogen peroxide in pure water, and the degradation of two typical pollutants (4-chlorophenol and 4-nitrophenol) is measured together with the amount of electrical energy dissipated in discharges. It is shown that the energy yield for the degradation of organic pollutants, expressed in terms of degraded moles per Joule, strongly depends on the discharge type. The highest efficiency is obtained with pulsed corona discharges in humid air above the water surface. A lower efficiency is found with spark discharges in water, and the less efficient process is constituted by streamer discharges in water. The influence of ferrous ions added to solutions is also very different according to the discharge type. This helps to get a better understanding of the degradation processes involved with the different discharge types.

Two DBD torch designs were used to investigate coatingand surface functionalization of small particles. One had an annulardischarge gap between coaxial quartz tubes, the second, suited forhigh throughput, used external shell electrodes on opposite sides ofa quartz tube. Several discharge sections could be used in flowdirection, with intermediate ports for particle and/or monomerinjection. Both torches were operated by a sinusoidal high voltage(13 kV, 20 kHz). The coaxial torch always showed a filamentarydischarge, while the shell-electrode design in He also produceddiffuse glow discharges. A variety of different precursors anddielectric as well as metallic particles of nanometer or micrometerdiameter were used.

The present work is an investigation of the chemical composition and growth profile of an hydrogenated amorphous carbon nitride film (a-CN:H) deposited by atmospheric pressure Townsend discharge in C2H4/N2. Various surface characterization techniques were used to evaluate the coatings properties (X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy, Profilometry, Scanning Electron Microscopy). The coating obtained presented a high N/C ratio and a high concentration of N-functionalities. The results revealed two different growth mechanisms depending on the residence time of the precursor molecules; at first, the growth is mainly due to radicals then a powder formation mechanism appears, therefore leading to different chemical composition and surface properties.