Dielectric-barrier discharges (silent discharges) are used on a large industrial scale. They combine the advantages of non-equilibrium plasma properties with the ease of atmospheric-pressure operation. A prominent feature is the simple scalability from small laboratory reactors to large industrial installations with megawatt input powers. Efficient and cost-effective all-solid-state power supplies are available. The preferred frequency range lies between 1 kHz and 10 MHz, the preferred pressure range between 10 kPa and 500 kPa. Industrial applications include ozone generation, pollution control, surface treatment, high power CO2 lasers, ultraviolet excimer lamps, excimer based mercury-free fluorescent lamps, and flat large-area plasma displays. Depending on the application and the operating conditions the discharge can have pronounced filamentary structure or fairly diffuse appearance. History, discharge physics, and plasma chemistry of dielectric-barrier discharges and their applications are discussed in detail.

https://www3.nd.edu/~sst/teaching/AME60637/reading/2003_PCPP_Kogelschatz_dbd_review.pdf

Dielectric-barrier Discharges: Their History, Discharge Physics, and Industrial Applications

Active flow control is a topic in full expansion due to associated industrial applications of huge importance, particularly for aeronautics. Among all flow control methods, such as the use of mechanical flaps, wall synthetic jets or MEMS, plasma-based devices are very promising. The main advantages of such systems are their robustness, simplicity, low power consumption and ability for real-time control at high frequency. This paper is a review of the worldwide works on this topic, from its origin to the present. It is divided into two main parts. The first one is dedicated to the recent knowledge concerning the electric wind induced by surface non-thermal plasma actuators, acting in air at atmospheric pressure. Typically, it can reach 8 m s−1 at a distance of 0.5 mm from the wall. In the second part, works concerning active airflow control by these plasma actuators are presented. Very efficient results have been obtained for low-velocity subsonic airflows (typically U∞ ≤ 30 m s−1 and Reynolds number of a few 105), and promising results at higher velocities indicate that plasma actuators could be used in aeronautics.

https://iopscience.iop.org/article/10.1088/0022-3727/40/3/S01/pdf

Airflow control by non-thermal plasma actuators

The term plasma actuator has now been a part of the fluid dynamics flow-control vernacular for more than a decade. A particular type of plasma actuator that has gained wide use is based on a single–dielectric barrier discharge (SDBD) mechanism that has desirable features for use in air at atmospheric pressures. For these actuators, the mechanism of flow control is through a generated body-force vector field that couples with the momentum in the external flow. The body force can be derived from first principles, and the effect of plasma actuators can be easily incorporated into flow solvers so that their placement and operation can be optimized. They have been used in a wide range of internal and external flow applications. Although initially considered useful only at low speeds, plasma actuators are effective in a number of applications at high subsonic, transonic, and supersonic Mach numbers, owing largely to more optimized actuator designs that were developed through better understanding and modeling of...

Dielectric Barrier Discharge Plasma Actuators for Flow Control

In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

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Plasma assisted ignition and combustion

Reactive species in non-equilibrium atmospheric-pressure plasmas: Generation, transport, and biological effects

The barrier discharge: basic properties and applications to surface treatment

The technique of spatially resolved cross-correlation spectroscopy (CCS) is used to carry out diagnostic measurements of the barrier discharge (BD) in air at atmospheric pressure. Quantitative estimates for electric field strength E(x,t) and for relative electron density ne(x,t)/nemax are derived from the experimentally determined spatio-temporal distributions of the luminosity for the spectral bands of the 0-0 transitions of the second positive system of N2 (λ = 337.1 nm) and the first negative system of N2+ (λ = 391.5 nm). These results are used to test the validity of some physical models of electrical breakdown in a BD. The influence of the spatio-temporal structure of the discharge on the chemical kinetics of ozone synthesis is studied by means of a semi-empirical method based on the results of spatially resolved CCS measurements.

https://iopscience.iop.org/article/10.1088/0022-3727/34/21/309/pdf

Spatio-temporally resolved spectroscopic diagnostics of the barrier discharge in air at atmospheric pressure

The ratios of intensities of the spectral bands of molecular nitrogen corresponding to transitions N + (B 2 � + g ,v = 0) → N + (X 2 � + ,v = 0), N2(C 3 � u ,v = 0) → N2(B 3 � g ,v = 0) and N2(C 3 � u ,v = 2) → N2(B 3 � g ,v = 5) as a function of the applied electric field strength were measured for air in the pressure range of 300 to 10 5 Pa. The non-self-sustaining dc discharge in a parallel-plane gap was used for excitation of gas molecules. The reduced field strength was varied in the range of (150–5000) × 10 −21 Vm 2 . The measured ratio of intensities as a function of electric field strength is compared with the theoretical estimates made by other authors. The obtained intensity ratio versus field strength curves can be used for field strength estimation in plasmas if the nitrogen molecules are excited dominantly from the ground state directly by the electron impact. (Some figures in this article are in colour only in the electronic version)

http://iopscience.iop.org/article/10.1088/0022-3727/38/21/010/pdf

Intensity ratio of spectral bands of nitrogen as a measure of electric field strength in plasmas

Polyethylene (PE) samples were activated by an atmospheric pressure plasma jet. The improvement in adhesive bond strength is attributed to the incorporation of oxygen-containing functional groups into the PE surface. Optical emission spectroscopy in combination with XPS analysis shows differences in the surface reactions for a plasma jet operated with air or pure nitrogen. The results indicate that the surface modifications take place in two different environments with respect to location and time: (a) reactions while the substrate is hit by the plasma jet, and (b) reactions outside the plasma jet after the treatment.

Atmospheric Pressure Plasma Jet Treatment of Polyethylene Surfaces for Adhesion Improvement

Dielectric barrier discharges (DBD) at atmospheric pressure are presented as a tool to create organosilicon deposits on technical planar aluminium substrates (up to 15 × 8 cm2) by admixing small amounts of hexamethyldisiloxane (HMDSO) and tetraethoxysilane (TEOS) to the carrier gas of the discharges. Using barrier materials of different specific capacities (2.6 × 104 and 3.2 pF/cm2) in two electrode arrangements operated at less than 1 W, the influence of the filament properties on the deposition is studied. In comparison to these arrangements, a third electrode setup with a barrier of the specific capacity of 2.9 pF/cm2 is operated at approximately 50 W to study the influence of the specific energy of the plasma (energy per molecule) on the deposition process. The plasma chemical process was studied qualitatively by Gas Chromatography, and properties of the plasma-treated substrates were examined by means of X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) spectroscopy, as well as visually.

Hans-Erich Wagner

Papers

The barrier discharge: basic properties and applications to surface treatment

Spatio-temporally resolved spectroscopic diagnostics of the barrier discharge in air at atmospheric pressure

Intensity ratio of spectral bands of nitrogen as a measure of electric field strength in plasmas

Atmospheric Pressure Plasma Jet Treatment of Polyethylene Surfaces for Adhesion Improvement

Deposition Process Based on Organosilicon Precursors in Dielectric Barrier Discharges at Atmospheric Pressure—A Comparison