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Experimental investigation of a surface DBD plasma actuator at atmospheric pressure in different N 2 /O 2 gas mixtures

This paper presents an investigation of the influence of nitrogen and oxygen on the behavior of a surface dielectric barrier discharge (SDBD) used for active flow control. The SDBD operated in a controlled atmosphere under several N 2 /O 2 gas mixture ratios. For each gas mixture, the consumed power was measured as a function of voltage amplitude. Then, for a given applied high voltage, the plasma morphology was recorded and commented and lastly, ionic wind velocity measurements were performed. Results show that the induced ionic wind velocity is mainly due to oxygen negative ions during the negative half-cycle. Nevertheless, the contribution of nitrogen to velocity is not negligible during the positive half-cycle. Moreover, the propagation of negative spark filaments during the negative half-cycle is linked to the proportion of O 2 in the gas mixture. Increasing this proportion beyond 20% leads to a shift in the saturation effect to lower voltages an...

Pure air?plasma bullets propagating inside microcapillaries and in ambient air

This paper reports on the characterization of air?plasma bullets in microcapillary tubes and in ambient air, obtained without the use of inert or noble gases. The bullets were produced by nanosecond repetitively pulsed discharges, applied in a dielectric barrier discharge configuration. The anode was a tungsten wire with a diameter of50?? m, centered in the microcapillary, while the cathode was a silver ring, fixed on the outer surface of the fused silica tube. The effects of the applied voltage and the inner diameter of the microcapillary tube on the plasma behavior were investigated. Inside the tubes, while the topology of the bullets seems to be strongly dependent on the diameter, their velocity is only a function of the amplitude of the applied voltage. In ambient air, the propagation of air bullets with a velocity of about 1.25???10 5?m?s ?1 is observed.

Real time characterization of polymer surface modifications by an atmospheric-pressure plasma jet: Electrically coupled versus remote mode

We characterize and distinguish two regimes of atmospheric pressure plasma (APP) polymer interactions depending on whether the electrical interaction of the plasma plume with the surface is significant (coupled) or not (remote). When the plasma is coupled to the surface, localized energy deposition by charged species in filaments dominates the interactions with the surface and produces contained damaged areas with high etch rates that decrease rapidly with plasma source-to-sample distance. For remote APP surface treatments, when only reactive neutral species interact with the surface, we established specific surface-chemical changes and very slow etching of polymer films. Remote treatments appear uniform with etch rates that are highly sensitive to feed gas chemistry and APP source temperature.

Effect of dielectric barrier discharge plasma actuators on non-equilibrium hypersonic flows

A numerical study employing discontinuous Galerkin method demonstrating net surface heat reduction for a cylindrical body in Mach 17 hypersonic flow is presented. This application focuses on using sinusoidal dielectric barrier discharge plasma actuators to inject momentum near the stagnation point. A 5 species finite rate air chemistry model completes the picture by analyzing the effect of the actuator on the flow chemistry. With low velocity near the stagnation point, the plasma actuator sufficiently modifies the fluid momentum. This results in redistribution of the integrated surface heating load on the body. Specifically, a particular configuration of normally pinching plasma actuation is predicted to reduce the surface heat flux at the stagnation point. An average reduction of 0.246% for the integrated and a maximum reduction of 7.68% are reported for the surface heat flux. The temperature contours in the fluid flow (with maximum temperature over 12 000 K) are pinched away from the stagnation point, thus resulting in reduced thermal load. Plasma actuation in this configuration also affects the species concentration distribution near the wall, in addition to the temperature gradient. The combined effect of both, thus results in an average reduction of 0.0986% and a maximum reduction of 4.04% for non-equilibrium calculations. Thus, this study successfully demonstrates the impact of sinusoidal dielectric barrier discharge plasma actuation on the reduction of thermal load on a hypersonic body.

Breakdown characteristics in pulsed-driven dielectric barrier discharges: influence of the pre-breakdown phase due to volume memory effects

The pre-phase of the breakdown of pulsed-driven dielectric barrier discharges (DBDs) was investigated by fast optical and electrical measurements on double-sided DBDs with a 1 mm gap in a gas mixture of 0.1 vol% O 2 in N 2 at atmospheric pressure. Depending on the pulse width (the pause time between subsequent DBDs), four different breakdown regimes of the following discharge were observed. By systematically reducing the pulse width, the breakdown characteristics could be changed from a single cathode-directed propagation (positive streamer) to simultaneous cathode- and anode-directed propagations (positive and negative streamer) and no propagation at all for sub-μs pulse times. For all cases, different spatio-temporal emission structures in the pre-phase were observed. The experimental results were compared with time-dependent, spatially one-dimensional fluid model calculations. The modelling results confirmed that different pre-ionisation conditions, i.e. co...

Dynamics of energy coupling and thermalization in barrier discharges over dielectric and weakly conducting surfaces on µ s to ms time scales

The paper presents experiments characterizing discharge development and energy coupling in a surface dielectric barrier discharge (SDBD), atmospheric air plasmas over dielectric and weakly conducting surfaces, over a wide range of time scales and electrical conductivities. The experiments are done using nanosecond pulse (NS) both single polarity and alternating polarity) and ac voltage waveforms. Discharge development and mechanisms of coupling with quiescent air are analysed using nanosecond gate camera imaging, schlieren imaging, and laser differential interferometry. It is shown that NS SDBD plasmas generate stochastic, localized, near-surface perturbations on a long time scale (>100  μ s) after the discharge pulse. These perturbations, entirely different from compression waves generated on a short time scale (~1–10  μ s), are caused by discharge contraction and originate from the ends of the filaments. Surface conductivity has almost no effect on discharge behavi...

Flow and Discharge Development in an Argon Atmospheric Pressure Plasma Jet Observed by ICCD and PLIF Imaging

In this paper, a megahertz atmospheric pressure plasma jet is investigated regarding its discharge pattern in correlation with the flow. Single-shot imaging shows plasma streamer development in a flow pattern determined by turbulent interaction with the atmosphere. Planar laser-induced fluorescence imaging on hydroxyl shows the flow pattern. The discharge pattern is streamerlike. Here, it can be observed that the streamer exhibits a hook-like structure at the end, which might also be attributed to the gas flow pattern.

An Atmospheric Cold Plasma Jet With a Good Uniformity, Robust Stability, and High Intensity Over a Large Area

To gain a cold atmospheric pressure helium plasma jet with good uniformity, robust stability, and high intensity over a larger area, a novel dielectric barrier discharge plasma jet generator with a honeycomb-like powered electrode and a gas shielding is proposed in this paper. The innovative design has been demonstrated to facilitate more homogeneous treatment and a higher degree of insusceptibility in plasma stability to variations of samples in their material properties, physical dimensions, and structures.

Electrode-Embedded Atmospheric Pressure Plasma Jet Device for Humid Environment

A newly designed atmospheric pressure plasma jet that can generate plasma without an external power line for use in an inhospitable humid environment is proposed. A four-bore tube is employed as the delivery conduit, and wire electrodes are inserted into two diagonal hollows. As the wire electrodes are completely isolated inside the hollows of the multibore glass tube, there is no contact with the environment at the end of the device where the jet is produced. Two identical plasma plumes can be generated not only in the ambient air but also under water, thereby enabling tissue and wound treatments in a humid environment, such as oral medicine and endodontic care.

Visualization of the Distribution of Oxidizing Substances in an Atmospheric Pressure Plasma Jet

A chemical interaction between an atmospheric pressure plasma jet and liquid media is of great interest for biomedical applications. In this paper, the visualization method and typical results of the 2-D distribution of oxidizing substances generated by the plasma jet were reported using the gel visualization reagent. The plasma jet generator consists of a glass tube and two electrodes. As a result, the distribution of oxidizing substances was able to be visualized around the contact point between the plasma jet and the reagent in atmospheric air. The interesting distribution patterns depending on the supplied gas were visually obtained by the reagent. In addition, its relative concentration distribution was also obtained by an absorbance measurement.

OH Radicals Distribution in a Nanosecond Pulsed Atmospheric Pressure Plasma Jet

Using the laser-induced fluorescence technique (LIF), the distribution of OH radicals in a nanosecond pulsed room-temperature atmospheric plasma jet was studied in this paper. The OH LIF signals are much stronger on both ends than at the center after the first discharge pulse, which means donut-shaped LIF signals. As the number of discharge pulses increased, the donut-shaped LIF signals fade away and the intensity of OH LIF signals is increased significantly. After about 11 discharge pulses (at (1251~mu ) s), the OH LIF intensity reaches to a saturation value, which is over ten times larger than that generated during the first discharge pulse at (1~mu ) s.

Flame and Trident Plasma Emissions of Single Rectangular-Shaped Atmospheric Pressure Plasma Jet

A single atmospheric pressure plasma jet device using a rectangular tube has been proposed for generating the intense glow plasmas. Two plasma regimes were found to exist in the same plasma structure under changes of gas flow rate and applied voltage conditions: the flame plasma regime and the trident plasma regime. When the gas flow rate and applied voltage were at low values, the flame glow plasma was produced, whereas the trident glow plasma was produced when the gas flow rate and applied voltage were at high values. Under identical electrical driving and gas conditions in each plasma regimes, the optical intensity of the trident plasma regime was approximately two times larger than the flame plasma regime. This highly energetic trident plasma jet is useful in developing novel applications requiring strong atmospheric pressure discharge processes by using very simplified structures, easy fabrication, potable and light weight, wide area, patterning generation, and low manufacturing and maintenance cost compared with the vacuum plasmas.

Behavior of Atmospheric Pressure Plasma Jet in External Electric Field

We report here the behavior of the atmospheric pressure plasma jet when passing through a dc electric field between two parallel plates. The deflection of the plasma plume was observed by using an intensified charge-coupled device camera. The external field affects both the length and the width of the plasma plume. The plasma jet first deflects toward the positive plate, then turns to the opposite direction. The result indicates that the plasma plume is induced by high-energy electron beam from the temporal cathode.

The Influences of Water and Oxygen Contents on Length of Atmospheric Pressure Plasma Jets in Ar/H<sub>2</sub>O and Ar/O<sub>2</sub> Mixtures

Images are taken to study the influence of applied voltage and O2 or H2O vapor content on discharge evolution and jet length of atmospheric pressure plasma jet in Ar/O2 and Ar/H2O mixtures. Three discharge modes of corona, dielectric barrier discharge, and jet with the increase of applied voltage are identified, and the breakdown voltage and jet generated voltage are different for O2 and H2O adding. The jet length decreases with the increase of O2 and H2O content, and this may be due to their quenching effect on excitation and ionization particles.

Induced Liquid Phase Flow by RF Ar Cold Atmospheric Pressure Plasma Jet

The plasma of an atmospheric pressure plasma jet strongly interferes with a liquid when it just touches the liquid surface. The gas flow of the jet exerts a force on the liquid surface pushing it downward, while the plasma exerts a force that is partly counteracting the gas flow induced force. The downward force in the center of the liquid recipient causes the liquid to circulate with a circulation time of (sim 2) s. Due to this circulation the color change of a dye proceeds homogeneously.

Emission Characteristics of Surface Microdischarge in Atmospheric-Pressure He/N<sub>2</sub> Mixture

The surface microdischarge in atmospheric-pressure He/N2 mixture is studied with an emphasis on its emission characteristics. It is found that the emission intensity and the pattern shape are strongly dependent on the N2 concentration. The UV emission intensity increases by a factor of nine with the N2 concentration up to 5%, after that it decreases moderately. Meanwhile, the luminous pattern expands and then shrinks from grounded mesh edge to the mesh center in the positive half-cycle, while it gradually brightens and then darkens in the central region of a mesh for the negative half-cycle, which is mainly attributed to the distribution of surface charge. In the case of [N2] (=~2) %–5%, the UV-Vis emission intensity is stronger and the emission pattern is comparable to spatial homogenous, thus benefiting the light emission applications.

Fibroblast Cell Morphology Altered by Low-Temperature Atmospheric Pressure Plasma

Low-temperature atmospheric pressure plasmas (LTAPPs) have garnered great scientific interest in recent years because of their chemically reactive properties. The LTAPP is currently being studied for potential applications in the field of plasma medicine including, but not limited to, wound healing and cancer therapy. In this paper, images of fibroblast cells exposed to different treatment times of LTAPP are presented. The results reveal the morphological cell changes associated with LTAPP treatment and indicate the potential use of LTAPP to alter physical attributes of mammalian cells.

Low Temperature Plasma Causes Double-Strand Break DNA Damage in Primary Epithelial Cells Cultured From a Human Prostate Tumor

Research in the new field of plasma medicine continues to demonstrate the efficacy of low temperature plasmas (LTPs) for numerous biomedical applications. Responses such as reduction in cell viability and cell death for cancer therapy, cell proliferation for wound healing, and bacterial inactivation have been observed as a result of plasma treatment. In this paper, we applied LTP to prostate cancer primary cells derived from patient tumour tissue to inflict irreparable DNA damage.

High-Speed Multi-Imaging of Repetitive Unipolar Nanosecond-Pulsed DBDs

Dielectric barrier discharges (DBDs) are being studied for a wide range of biomedical and industrial applications. In this paper, qualitative results coming from synchronized high-speed and Schlieren multi-imaging of a unipolar nanosecond-pulsed DBD are presented, with the final aim of showing plasma structure, filament movement, and refractive index gradients in different interelectrode gaps and counter electrode materials.

iCCD Imaging of the Transition From Uncoupled to Coupled Mode in a Plasma Source for Biomedical and Materials Treatment Applications

Intense and energetic atmospheric plasma was achieved by jet-to-jet coupling using an array of plasma jets arranged in an axisymmetric structure. To highlight the effects of pulse repetition frequency, peak voltage and mass flow rate on the transition from a coupled mode to an uncoupled one, qualitative results coming from iCCD imaging of a nanopulsed Gatling machine gun-like plasma source will be shown. Moreover, results on surface modifications and bacterial inactivation will be presented.

Raw Food Sterilization of Flexible Dielectric Barrier Discharge Device Using Biocompatible Tubing

A flexible dielectric barrier discharge (DBD) using biocompatible tubing was fabricated for food sterilization in ambient air. Even though the selected poultry medium had a complex geometry, DBD was easily created due to the high flexibility of the tubing and metal wire. DBD was produced at the peak voltage of 7.5 kV (Vpp of 15 kV) and frequency of 32 kHz. It is expected, from the emission spectrum of the plasma, that chemical reaction of the hydroxyl and nitrogen species within the plasma can effectively sterilize the poultry sample. Consequently, this fast reaction at room temperature makes plasma sterilization a viable alternative to conventional food sterilization processes.

Adding of Nitrogen in Helium DBD: Consequences on the Self-Organization of the Discharge

Depending on the operating conditions, different regimes can be obtained in a dielectric barrier discharge (DBD): filamentary, diffuse/homogeneous, or self-organized. For a plane-to-plane DBD operated at high frequency (150 kHz) and at atmospheric pressure in helium gas, we show that the addition of a small amount of nitrogen induces a transition from the homogenous regime to a self-organized regime characterized by the appearance of several stable strips always located at the same position.

Airflow Control by DBD Actuator Over an MDA Airfoil

Efforts have been performed on utilizing the dielectric barrier discharge actuator to control the flow separation over the top of the flap of a three-element airfoil. Images of the flow fields visualized by a particle image velocimetry system with actuators off and on at the free-stream speeds of 20 and 30 m/s are presented.

Effect of Pulse Rise time on Plasma Plume Propagation Velocity

Atmospheric pressure plasma jets driven by a pulsed dc power supply have several advantages over the traditional jets driven by an ac power supply. However, how the pulse rise time affects the characteristic of the plasma jets is not clearly known. In this paper, the simulation results of a plasma jet driven by pulsed dc voltages with different pulse rise time (t_{mathrm {mathbf {rise}}}) are presented. It shows that, the shorter the pulse rise time (t_{mathrm {{rise}}}) is, the faster the head of the plasma jet propagates.

Study on the Effects of Dielectric Barrier Discharge on the Bunsen Flame Structure With OH-PLIF Technique

Nonthermal equilibrium plasma has been reported to be potentially applicable in many combustion scenarios. In this paper, the effects of dielectric barrier discharge (DBD) on the flame structure of a Bunsen flame have been investigated by using the OH planar laser-induced fluorescence technique. Results show that the increase of discharge intensity significantly enhances the local burning. In coaxial-cylinder DBD reactor, the flame structure can be varied from conic shape to M shape with discharge power increasing.

Visualization of a Coaxial Dielectric Barrier Discharge Driven by a Sub-ns Rising High-Voltage Pulse and Its Reflections

Dielectric barrier discharges generated in a coaxial tip to cylinder configuration at atmospheric pressure by a 5-ns high-voltage pulse with sub-ns rise time were investigated with a fast intensified CCD camera. Different discharge characteristics were found for the breakdown during the pulse itself and in the subsequent reflections of the pulse. There is a transition from a complete diffuse regime to a breakdown in constricted channels, which finally cross the whole gap.

Effect of Pulse Polarity on Nanosecond Surface Dielectric Barrier Discharge

This paper presents the optical emission characteristics of a surface dielectric barrier discharge sustained by repetitive nanosecond pulses with different polarities in the subsonic airflows. The plasma images presented here show that the positive polarity pulsed discharge is stable in the airflows, appearing as a brush-type discharge. While the negative polarity pulsed discharge plasma becomes a filamentary pattern that is evidently spatial inhomogeneous in quiescent air, it behaves unstable in airflows.

Dynamics of Mode Transition in Air Dielectric Barrier Discharge by Controlling Pressures

In general, parameter pressure (times ) gap distance (p (times ) d) in dielectric barrier discharge is used to control the electrical breakdown and plasma characteristics. In this paper, we investigate the critical pd value for air discharge transition from filamentary to homogeneous mode by controlling the pressure. Dynamics of the air discharge show that the discharge transits from filamentary to homogeneous mode when the operating pressure decreases from 9 to 4 kPa. With 1-mm thickness alumina applied pulsed power, the critical pd value obtaining homogeneous air plasma is 40 kPamm.

Comparison of (mu ) s- and ns-Pulse Gliding Discharges in Air Flow

Pulsed power can provide instantaneously high power density to generate atmospheric nonthermal plasma in open air. In this paper, using two power supplies including a (mu ) s-pulse generator with a rise time of 300 ns and a pulsewidth of 5 (mu ) s and a ns-pulse generator of a rise time of 70 ns and a pulsewidth of 100 ns, pulsed gliding discharges are created with point-to-point electrodes in open air. Discharge images with these two generators under different flow rates are presented for a brief comparison of (mu ) s- and ns-pulse gliding discharges in air flow.

Propagation of a Dielectric Barrier Discharge in a Multichannel Mixing Chip Microreactor

An atmospheric-pressure dielectric barrier discharge was generated inside a T-type mixing multichannel chip microreactor in argon, at peak-to-peak voltages of 3.0 kV, and a frequency of 10 kHz. Time-resolved imaging and current-voltage measurements revealed temporal and spatial variation of the discharge, and the appearance of discharge nonuniformities that are considered to arise due to small pressure differences caused by the microchannel geometry, and the mixing of gas flows in regions where the channels connect.

Rotating Concentric Spot-Ring Pattern in a Dielectric Barrier Discharge System

The rotating concentric spot-ring pattern in a dielectric barrier discharge is investigated in different time scales. From a series of frames with 2-ms exposure taken by a high-speed video camera, it is found that the two rings rotate with different rotating periods and the rotating direction of the inner ring changes with time. The instantaneous image with 10- $mu{rm s}$ exposure shows the appearance of the surface discharge besides the volume discharge. The change of the orientation of the surface discharge leads to the size of the spot in outer ring changing with rotation.

Flexible Dielectric Barrier Discharge Reactor With Water and Teflon Dielectric Layers

Flexible dielectric barrier discharge (DBD) was demonstrated using water and Teflon dielectric layers at atmospheric pressure. The flexible DBD reactor is composed of copper electrodes and two main dielectric layers of water and Teflon tubes, which cover each electrode inserted in urethane tubes. Since dielectric materials are easy to bend, DBD can be generated in various geometries. In addition, water layer provides the reliable cooling of insulation surface exposed to atmospheric plasma. Therefore, a stable plasma discharge during a long time operation is achieved regardless of the flow rate of plasma forming gas.

Inducing a Dielectric Barrier Discharge Plasma Within a Package

Cold atmospheric plasma offers significant potential as a nonthermal decontamination tool for food and medical applications. We present results of a dielectric barrier discharge (DBD) plasma induced in a gas confined by a polymer package. The resultant discharge and contained afterglow are found to have a strong antimicrobial effect.

Characteristics of a Dielectric Barrier Discharge Reactor With Two L-Shaped Electrodes Working in Helium

We report the characteristics of a dielectric barrier discharge reactor consisting of two L-shaped electrodes separated by a central slit. The macroscopic discharge behaviors were investigated on the basis of time-averaged discharge images obtained for different applied voltages. The mechanism for achieving a homogeneous discharge mode was explained by analyzing the spectral light emissions from He I ( (lambda =706) nm) and O I ( (lambda =777) nm) lines.

Development of a Single Filament Pulsed Dielectric Barrier Discharge in Volume and on Surface

Pulsed-driven dielectric barrier discharges were recorded in a single filament arrangement with a 1-mm gap in a N2–O2 gas mixture at atmospheric pressure with a fast ICCD camera. The comparison of spectrally-integrated and spectrally-resolved emissions for the second positive system (SPS) and the first negative system (FNS) of N2 reveals different structures in the volume and on the dielectric surfaces. A propagation of surface discharges with approximately the same velocity is visible on both electrodes, but with a higher intensity of the FNS on the cathode and of the SPS on the anode. This indicates a higher electric field strength in the discharges on the cathode surface.

Deflection of Streamer Path in DC Electric Potential

Nonequilibrium atmospheric plasma jets are associated with sequence of streamer breakdowns developing in helium-air mixture. In this paper, propagation of the streamer in plane capacitor is photographed, and deflection toward the positive capacitor plate is analyzed.

Glow Modes in Radio Frequency Atmospheric Discharge Operating With and Without Anodized Electrodes

A comparison of the visual appearance of the glow modes in radio frequency (RF) atmospheric pressure glow discharge (APGD) with bare electrodes and dielectric barrier discharge (DBD) using anodized electrodes is presented. In (alpha ) mode, both RF APGD and RF DBD remain volumetric, stable, and uniform. In (gamma ) mode, the RF APGD shrinks into a constricted plasma column. On the other hand, RF DBD in (gamma ) mode is stable, horizontally uniform, and retains the same volume as that in (alpha ) mode without plasma constriction.

Importance of Plasma Thermal Energy Transfer for Plasma Jet Systems

Atmospheric pressure plasma systems are routinely used to treat the surfaces of thermally sensitive materials. There are wide ranges of commercial plasma jet systems available, and for the end user, it can be difficult to directly compare the power outputs of these sources. This paper evaluates the use of a thermal imaging technique in order to provide a semiquantitative evaluation of energy output from plasma jets. The evaluation involved a comparison of the thermal energy transfer obtained from three commercially available atmospheric pressure plasma jet systems: 1) PlasmaTreat’s Openair; 2) Dow Corning’s PlasmaStream; and 3) SurFx’s Atomflo.

On the Bullet-Streamer Dualism

Formerly so-called bullet jets have been in the focus of atmospheric pressure plasma jet research of the past years. In this paper, two perspectives of the dynamic phenomenon are presented. Averaged, the dynamics appears as a bright spot—the so-called bullet—traveling from the plasma jet nozzle. In single shot it is revealed that the discharge mode in fact is a streamer-type discharge leaving the jet nozzle into the ambient.

Investigation on Atmospheric Pressure Plasma Jet Array in Ar

An atmospheric pressure plasma jet linear array consisting of five jet units is developed; the influences of applied voltage amplitude, frequency of the power supply, and Ar flow rate on its characteristics are investigated using lighting emission images. The results show that the length and shape of the jet array vary with variation in these parameters, and the optimum operation conditions for the maximum length jet array are at applied voltage of 8.5 kV, frequency of 20 kHz, and gas flow rate of 20 L/min.

Atmospheric Pressure Plasma Jet Array With Multivariate Cells

A large-scale atmospheric pressure plasma jet (APPJ) device with variable discharge cells is developed using a special designed electrode configuration, and a maximum of fifteen APPJ cells work simultaneously. The properties of APPJ arrays are investigated from plasma profile and statistical parameters. From one to fifteen cells, the peak value of discharge current rises gradually when increasing cell numbers. The APPJ images and current waveforms present good synchronism and repeatability of discharge, and the effective plasma area up to 20 cm (^{vphantom {big (}2}) is achieved.

Dynamic Evolution of Helium Atmospheric Pressure Plasma Jet With ITO-PET Electrodes

A helium atmospheric pressure plasma jet configured with transparent double ring electrodes is driven by an ac high voltage power, and its dynamic evolution in a whole cycle is carefully investigated with ns scale intensified-charge coupled device images. During the positive current pulse, a plasma bullet appears at downstream of active electrode and donut shape plasma presents inside ground electrode, respectively, and wave-packet-like behavior emerges in Dielectric Barrier Discharge (DBD) zone. However, for negative current pulse, the phenomena with double plasma bullets occur beneath active electrode, and plasma inside ground electrode is formed via overflow of diffuse plasma in DBD zone.

Influence of Oxygen Impurity on the Atmospheric Pressure Helium Plasma Jet Behavior

Trace of oxygen adding to the helium atmospheric pressure plasma jet can make the jet behave differently, such as dimming the plume and changing the jet length as well as the discharge current. Moreover, with certain specific ratio of oxygen/helium, double-bullet phenomenon could be captured by intensified charge couple device. The speeds of the bullets are estimated to be several kilometers per second.

Spatio-Temporally Resolved Mapping of Helium Metastable Density in an Atmospheric Pressure Plasma Jet

Tunable diode laser absorption spectroscopy was used to measure the spatio-temporal evolution of helium metastable atoms He $(2^{3}{rm S})$ in an atmospheric plasma jet. The production of these atoms is clearly correlated to the propagation of an ionization wave, the so-called plasma bullet. Whatever the applied voltage, the spatial structure of the density rapidly evolves from a donut shape to a conical form as the plasma propagates. For applied voltages higher than 4.5 kV, a complex transient structure appears at the tip of the jet.

Study of Cold Ar Atmospheric Pressure Plasma Jet Generated With the Tapered Quartz Tube

In this paper, a cold atmospheric-pressure plasma jet is generated in argon using a single-electrode configuration with the tapered quartz tube. The design of quartz tube is based on the theory of wind tunnel. The lower portion of the tube is divided into two parts: 1) contraction section and 2) test section. Electrical and optical diagnostics are conducted on a plasma jet device, the experimental results show that when the contraction ratio gets higher, the velocity of exit flow is more evenly distributed and the length of atmospheric pressure plasma jet is longer. It shows that a high-concentrated structure is effective to make the argon gas flow more stable and faster.

Decomposition of sugars under non-thermal dielectric barrier discharge plasma

Abstract: Solutions of ribose, glucose, and sucrose in water and phosphate buffer were treated with non-thermal plasma generated by using a dielectric barrier discharge (DBD) device and the oxidation products were characterized by 1H NMR and GC–MS. Our results demonstrate that these sugars are decomposed to formic acid, glycolic acid, glyceric acid, tartronic acid, tartaric acid, acetic acid, and oxalic acid after direct exposure to DBD plasma. The concentrations of these compounds are time-dependent with plasma treatment. The decomposition mechanisms of these sugars under the DBD plasma are also proposed in this study.

The bidirectional character of O 2 concentration in pulsed dielectric barrier discharges in O 2 /N 2 gas mixtures

This paper presents experimental results on the influence of O 2 on the characteristics of dielectric barrier discharges (DBDs) at one and at half atmospheric pressure. Gas mixtures of 0.1–10 vol % O 2 in N 2 were investigated, as well as in virtually pure N 2 . Electrical data, simultaneous streak and intensified charge-coupled device images were recorded in pulsed driven dielectric barrier discharges of 0.8 mm gap in a single filament arrangement. The O 2 concentration is shown to have a significant impact on the electrical characteristics, the temporal DBD development and its breakdown inception. Higher O 2 concentrations (above 0.1 vol %) led to an ignition delay, a shorter discharge duration, increased discharge radius, higher discharge current maxima and larger velocities of the cathode directed streamers. For O 2 concentrations below 0.01 vol %—i.e. nearly pure nitrogen—some of these effects were reversed...

Post-discharge gas composition of a large-gap DBD in humid air by UV–Vis absorption spectroscopy

Large gap dielectric barrier discharges (DBD) provide non-thermal, non-equilibrium plasmas that can generate specific gas chemistry with enhanced bactericidal effects when working in humid air. The present study investigates the post-discharge gas composition of such plasmas operated in humid air using UV–Vis (200–800 nm) absorption spectroscopy. Absorbance spectra have been de-convoluted using direct deconvolution and iterative methods and results are correlated to the DBD electrical parameters. The high-voltage (56 and 70 kV rms) DBD plasma generated at 50 Hz frequency in a closed container over a 20 mm gap in air with relative humidity (RH) of 5–70% has been characterized by I – V and capacitive methods. The post-discharge gas composition at each RH is assessed by UV–Vis absorption spectroscopy for plasma exposure times of 15–120 s. The concentration of ozone and nitrogen oxides (O 3 , NO 2 , NO 3 , N 2 O 4 )...

Post-discharge gas composition of a large-gap DBD in humid air by UV?Vis absorption spectroscopy

Large gap dielectric barrier discharges (DBD) provide non-thermal, non-equilibrium plasmas that can generate specific gas chemistry with enhanced bactericidal effects when working in humid air. The present study investigates the post-discharge gas composition of such plasmas operated in humid air using UV?Vis (200?800?nm) absorption spectroscopy. Absorbance spectra have been de-convoluted using direct deconvolution and iterative methods and results are correlated to the DBD electrical parameters. The high-voltage (56 and 70?kV rms) DBD plasma generated at 50?Hz frequency in a closed container over a 20?mm gap in air with relative humidity (RH) of 5?70% has been characterized by I ? V and capacitive methods. The post-discharge gas composition at each RH is assessed by UV?Vis absorption spectroscopy for plasma exposure times of 15?120?s. The concentration of ozone and nitrogen oxides (O 3 , NO 2 , NO 3 , N 2 O 4 )...

Permanent hydrophilization of outer and inner surfaces of polytetrafluoroethylene tubes using ambient air plasma generated by surface dielectric barrier discharges

We present an atmospheric pressure ambient air plasma technique developed for technically simple treatment of inner and/or outer surfaces of plastic tubes and other hollow dielectric bodies. It is based on surface dielectric barrier discharge generating visually diffuse plasma layers along the treated dielectric surfaces using water-solution electrodes. The observed visual uniformity and measured plasma rotational and vibrational temperatures of 333 K and 2350 K indicate that the discharge can be readily applied to material surface treatment without significant thermal effect. This is exemplified by the obtained permanent surface hydrophilization of polytetrafluoroethylene tubes related to the replacement of a high fraction (more than 80%) of the surface fluorine determined by X-ray photoelectron spectroscopy. A tentative explanation of the discharge mechanism based on high-speed camera observations and the discharge current and voltage of measurements is outlined.

Power coupling and electrical characterization of a radio-frequency micro atmospheric pressure plasma jet

We propose an efficient RF power coupling scheme for a micro atmospheric pressure plasma jet operating in helium. The discharge gap is used as a resonant element in a series LC circuit. In resonance, the voltage across the discharge gap is amplified and the ignition of the plasma is enabled with the input RF power as low as 0.5 W. High power coupling efficiency and simplicity of the circuit allow accurate electrical characterization of the discharge. Systematic measurements of the dissipated power as a function of the applied voltage are reported for the discharge operating in helium with molecular admixtures of N 2 and O 2 .

Production of reactive species using vacuum ultraviolet photodissociation as a tool for studying their effects in plasma medicine: simulations and measurements

We propose a method for producing OH, H, O, O 3 , and O 2 ( a 1 Δ g ) using the vacuum ultraviolet photodissociation of H 2 O and O 2 as a tool for studying the reaction processes of plasma medicine. For photodissociation, an H 2 O/He or O 2 /He mixture flowing in a quartz tube is irradiated by a Xe 2 or Kr 2 excimer lamp. The effluent can be applied to a target. Simulations show that the Xe 2 lamp method can produce OH radicals within 0.1–1 ppm in the effluent at 5 mm from a quartz tube nozzle. This is comparable to those produced by a helium atmospheric-pressure plasma jet (He-APPJ) currently used in plasma medicine. The Xe 2 lamp method also produces H atoms of, at most, 6 ppm. In contrast, the maximum O densities produced by the Xe 2 and Kr 2 lamp methods are 0.15 ppm and 2.5 ppm, respectively; these are much lower than those from H...

Plasma–Catalyst Synergy During Methanol Steam Reforming in Dielectric Barrier Discharge Micro-plasma Reactors for Hydrogen Production

Abstract Non-thermal plasma is an effective technology that produces hydrogen from methanol by plasma reforming. In this study, hydrogen was produced via methanol steam reforming in a dielectric barrier discharge micro-plasma reactor filled with a Cu/Al2O3 catalyst. Comparative experimental results obtained using the reactor with and without catalyst are reported. The methanol conversion and hydrogen yield with the activated catalyst were 17.89 and 21.86 % higher than those without the catalyst. The primary gaseous products changed from H2 and CO to H2 and CO2 after adding the Cu/Al2O3 catalyst. Methanol conversion increased with the discharge frequency and input power and decreased with an increase in the liquid feed rate. Methanol conversion reached 78.48 % over the Cu/Al2O3 catalyst at a 1.0 steam-to-carbon ratio, an 18.00 ± 0.05 kHz discharge frequency, 18.70 W of input power, 10.0 mL/min Ar flow rate and 0.0165 mL/min liquid feed rate. A plausible mechanism for hydrogen generation during steam–methanol reforming using the plasma–catalyst synergy effect is presented.

Electron properties in an atmospheric helium plasma jet determined by Thomson scattering

In this work we present Thomson scattering measurements on a nanosecond pulsed high voltage dielectric barrier discharge (DBD)-like helium plasma jet, operated in ambient air. With the low detection limit offered by a triple grating spectrograph equipped with a high quantum efficiency intensified charge-coupled device (ICCD) camera, temporally and spatially resolved electron densities and mean energies have been mapped. 7 kV peak with 250 ns width pulses at 20 kHz are applied to the inner cylindrical shaped electrode of a DBD. This results in a peculiar hollow electron density profile in the vicinity of the jet nozzle with maximum values of n e = 5 × 10 18  m −3 and mean energies of up to 2.5 eV. Further downstream, the profile collapses radially and contracts. A much higher electron density is found (2 × 10 19  m −3 ) while the mean energy is lower (0.5 eV).

CO and byproduct formation during CO 2 reduction in dielectric barrier discharges

The dissociation of CO2 and the formation of CO, O3, and O2 were studied in a dielectric barrier discharge (DBD) at atmospheric pressure by means of ex-situ infrared absorption spectroscopy. CO mixing ratios of 0.1%–4.4% were determined for specific injected energies between 0.1 and 20 eV per molecule (0.3–70 kJ/l). A lower limit of the gas temperature of 320–480 K was estimated from the wall temperature of the quartz reactor as measured with an infrared camera. The formation of CO in the DBD could be described as function of the total number of transferred charges during the residence time of the gas in the active plasma zone. An almost stoichiometric CO:O2 ratio of 2:1 was observed along with a strongly temperature dependent O3 production up to 0.075%. Although the ideal range for an efficient CO2 dissociation in plasmas of 1 eV per molecule for the specific injected energy was covered, the energy efficiency remained below 5% for all conditions. The present results indicate a reaction mechanism which is initiated by electron impact processes followed by charge transfer reactions and non-negligible surface enhanced O and CO recombination. While electron-driven CO2 dissociation is relatively energy inefficient by itself, fast O recombination and the low gas temperatures inhibit the synergistic reuse of atomic oxygen in a secondary CO2 + O dissociation step.

Methane conversion in surface- and volume-type dielectric barrier discharges generated in the presence of metal-mesh electrodes

Methane gas conversion was studied in customized flow-type reactors with different dielectric barrier discharge generated in Ar-CH4-O2 gas mixtures. Different reactor geometries (with either volume or surface-type discharges) and different electrode materials were compared, and gas temperatures during methane conversion processes were evaluated. The discharge was generated by applying either a conventional sinusoid or nanosecond-pulsed voltage. The methane conversion rate was as high as ∼99% with the total gas flow rate of 15 sccm, while the temperatures did not exceed 450 K. No significant effect of electrode material (stainless steel, aluminum, or CuO coated copper) was found, confirming that the conversion temperatures were much lower than those required for activity of typical catalysts. The reactor geometry, flow rate, and oxygen amount could be used to govern both the methane conversion rate and the fractions of components in the final product.

Experimental and modelling study of organization phenomena in dielectric barrier discharges with structurally inhomogeneous wood substrates

The spatial organization of dielectric barrier discharges operating at atmospheric pressure in the presence of complex wood substrates was analysed using optical imaging, current–voltage ( I – V ) characteristics, and optical emission spectroscopy combined with a collisional–radiative model to extract the average electron energy. The structural inhomogeneities of selected wood species produced non-uniform light emission patterns while maintaining homogeneous-like I – V characteristics and spatially uniform average electron energy. Based on a simple electrical model of the discharge, this localization was ascribed, at least partially, to a spatial modulation of the relative dielectric permittivity on ‘early’ versus ‘late’ wood affecting the local voltage applied to the gas, and thus the local discharge current.

Pattern formation and dynamics of plasma filaments in dielectric barrier discharges

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.

A temporal multi-scale algorithm for efficient fluid modeling of a one-dimensional gas discharge

In this study, we present a temporal multi-scale algorithm (TMA) for efficient fluid modeling of a one-dimensional gas discharge with complex plasma chemistry. A helium dielectric barrier discharge driven by a power source with a frequency of 25 kHz is used as an example to demonstrate the superior capability of the TMA in accelerating fluid modeling simulations, while maintaining the same accuracy as compared to lengthy benchmarking fluid modeling using a single time-scale approach. The plasma chemistry considers 36 species and 121 reaction channels, which include some impurities such as nitrogen (25 ppm), oxygen (10 ppm) and water vapor (1 ppm), in addition to the helium itself. The results show that the runtime using the TMA can be dramatically reduced to 4% (25 times faster) with a relative difference of spatially averaged number densities generally less than 1% for all species between the TMA and the benchmarking cases when five initial cycles, five supplementary cycles and ...

Computational study of the interaction of cold atmospheric helium plasma jets with surfaces

We describe a computational modeling study of a cold atmospheric pressure plasma jet interacting with a dielectric surface placed normal to the jet axis. The plasma jet is generated by the application of a nanosecond pulse voltage applied to a dielectric tube through which the jet issues into ambient air. A base fluid flow field is pre-computed using a Navier–Stokes model for the helium jet impinging on the dielectric target surface with a two-species description for laminar diffusional mixing of the helium and ambient air streams. A self-consistent, multiple species, two-temperature model is used to describe the non-equilibrium plasma discharge dynamics in the presence of the base jet flow field. A single nanosecond pulse discharge event starting from initial breakdown in the dielectric tube, to propagation into the open gap, and finally the interaction with the dielectric surface is simulated. Initially, the plasma forms within the dielectric tube and propagates along the tube ...

Atmospheric air diffuse array-needles dielectric barrier discharge excited by positive, negative, and bipolar nanosecond pulses in large electrode gap

In this paper, positive, negative, and bipolar nanosecond pulses are employed to generate stable and diffuse discharge plasma using array needles-plate electrode configuration at atmospheric pressure. A comparison study of discharge images, electrical characteristics, optical emission spectra, and plasma vibrational temperature and rotational temperatures in three pulsed polarity discharges is carried on under different discharge conditions. It is found that bipolar pulse is beneficial to the excitation of diffuse dielectric barrier discharge, which can generate a room temperature plasma with more homogeneous and higher discharge intensity compared with unipolar discharges. Under the condition of 6 mm electrode gap distance, 26 kV pulse peak voltage, and 150 Hz pulse repetition rate, the emission intensity of N2 (C3Πu → B3Πg) of the bipolar pulsed discharge is 4 times higher than the unipolar discharge (both positive and negative), while the plasma gas temperature is kept at 300 K, which is about 10–20 K lower than the unipolar discharge plasma.

Study on Modes of the Pulsed Dielectric Barrier Discharges at Atmospheric Pressure in Helium

For the dielectric barrier discharge (DBD) at atmospheric pressure in helium excited by repetitive voltage pulses (called the pulsed DBD), two discharge modes, atmospheric pressure glow DBD (APGD), and atmospheric pressure Townsend DBD (APTD), have been numerically investigated by means of a 1-D fluid model. The influences of several important operation parameters, i.e., voltage growth rate (r_{rm vg}) , gap width (d_{g}) , dielectric thickness (d_{s}) , and dielectric constant (varepsilon _{r}) , on the discharge modes have been explored. Especially, the parameter regions in which each discharge mode located have been presented, in an effort to indicate the effects of the interaction of (r_{rm vg}) , (d_{g}) , and (d_{s}) on the discharge modes. This paper shows that there are two discharge modes in the pulsed DBD, relying on the used discharge parameters, and the obtained significant results are as follows. Based on the axial distributions of electric field, electron density, and ion density in the gap at the time point where the first discharge occurs, the discharge in APGD is of the following evident characteristics: 1) there are both cathode fall and quasi-neutral plasma bulk and 2) the electron density is evident large, when compared with those for the discharge in APTD. The increase of voltage growth rate or the increase of the capacitance of dielectrics by decreasing (d_{s}) or by increa- ing (varepsilon _{r}) can induce the transition of the discharge mode from APTD to APGD. With the use of efficient large gap width, APGD is easier to be driven. In particular, to what extent can the discharge be affected by a discharge parameter? This is still governed by other parameters and is shown using the regions of the parameters in which each discharge mode located.

Plasma Parameter Estimation in Capillary Single Barrier DBD Source Using Space Resolved Plasma Spectroscopy and PIC Simulation

To estimate plasma parameters in a dielectric barrier discharge (DBD)-based single barrier capillary source, a spatio-temporal plasma spectroscopy and a particle-in-cell simulation code OOPIC-Pro has been used. The developed DBD source consists of a 10-cm length capillary source with diagonally opposite striped electrodes pasted on the cylindrically hollow quartz tube of 4-mm outer and 2-mm inner diameters, respectively. The plasma has been produced in helium atmosphere using pulsed power source with 2–5 kV, 30-kHz square pulse having pulsewidth (2~mu ) s at different operating pressures. For space resolved plasma diagnostic, a high-resolution intensified charge coupled device camera has been used. The images of the discharge patterns of this pulsed DBD source have been compared with the simulation results and certain useful discharge parameters have been obtained. The obtained electron density in plasma from simulation has been compared with discharge resistivity method, which is found to be in close agreement. The filamentary and diffused discharge patterns have also been analyzed based on the electrical discharge patterns obtained from the simulation, which provides additional insight in such narrow DBD discharges.

Evaluation of pathogen inactivation on sliced cheese induced by encapsulated atmospheric pressure dielectric barrier discharge plasma

Publication date: April 2015 Source:Food Microbiology, Volume 46 Author(s): Hae In Yong , Hyun-Joo Kim , Sanghoo Park , Amali U. Alahakoon , Kijung Kim , Wonho Choe , Cheorun Jo Pathogen inactivation induced by atmospheric pressure dielectric barrier discharge (DBD) (250 W, 15 kHz, air discharge) produced in a rectangular plastic container and the effect of post-treatment storage time on inactivation were evaluated using agar plates and cheese slices. When agar plates were treated with plasma, populations of Escherichia coli, Salmonella Typhimurium, and Listeria monocytogenes showed 3.57, 6.69, and 6.53 decimal reductions at 60 s, 45 s, and 7 min, respectively. When the pathogens tested were inoculated on cheese slices, 2.67, 3.10, and 1.65 decimal reductions were achieved at the same respective treatment times. The post-treatment storage duration following plasma treatment potently affected further reduction in pathogen populations. Therefore, the newly developed encapsulated DBD-plasma system for use in a container can be applied to improve the safety of sliced cheese, and increasing post-treatment storage time can greatly enhance the system's pathogen-inactivation efficiency.

Flexible thin-layer dielectric barrier discharge plasma treatment of pork butt and beef loin: Effects on pathogen inactivation and meat-quality attributes

Publication date: April 2015 Source:Food Microbiology, Volume 46 Author(s): Dinesh D. Jayasena , Hyun Joo Kim , Hae In Yong , Sanghoo Park , Kijung Kim , Wonho Choe , Cheorun Jo The effects of a flexible thin-layer dielectric barrier discharge (DBD) plasma system using a sealed package on microbial inactivation and quality attributes of fresh pork and beef were tested. Following a 10-min treatment, the microbial-load reductions of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella Typhimurium were 2.04, 2.54, and 2.68 Log CFU/g in pork-butt samples and 1.90, 2.57, and 2.58 Log CFU/g in beef-loin samples, respectively. Colorimetric analysis showed that DBD-plasma treatment did not significantly affect L* values (lightness) of pork and beef samples, but lowered a* values (redness) significantly after 5- and 7.5-min exposures. The plasma treatment significantly influenced lipid oxidation only after a 10-min exposure. The texture of both types of meat was unaffected by plasma treatment. All sensory parameters of treated and non-treated samples were comparable except for taste, which was negatively influenced by the plasma treatment (P &lt; 0.05). This thin-layer DBD-plasma system can be applied to inactivate foodborne pathogens. The observed minor deterioration of meat quality might be prevented by the use of hurdle technology.

Effects of pulse parameters on the atmospheric-pressure dielectric barrier discharges driven by the high-voltage pulses in Ar and N 2

In this work, the atmospheric-pressure dielectric barrier discharges in Ar and N 2 excited by repetitive voltage pulses have been numerically studied using a 1D fluid model. The differences between the discharge characteristics for Ar and N 2 have been presented when changing the parameters of the applied pulse voltage. In this work we present the following significant results. With an increase of the amplitude of the applied pulse voltage, the increase of the maximum discharge current density in Ar is evident, compared with N 2 ; and the discharge mode changes from the weak atmospheric-pressure glow discharge (APGD) to the standard APGD for Ar, and from the atmospheric-pressure Townsend discharge to the APGD for N 2 . In addition, the increase of the averaged electron density in N 2 is more evident than that in Ar, especially when the standard APGD occurs in N 2 . The increasing frequency leads to lower maximum discharge c...

One-equation modeling and validation of dielectric barrier discharge plasma actuator thrust

Dielectric barrier discharge (DBD) plasma actuators with an asymmetric electrode configuration can generate a wall-bounded jet without mechanical moving parts, which require considerable modifications of existing aeronautical objects and which incur high maintenance costs. Despite this potential, one factor preventing the wider application of such actuators is the lack of a reliable actuator model. It is difficult to develop such a model because calculating the ion-electric field and fluid interaction consume a high amount calculation effort during the numerical analysis. Thus, the authors proposed a semi-empirical model which predicted the thrust of plasma actuators with a simple equation. It gave a numeric thrust value, and we implemented the value on a computational fluid dynamics (CFD) solver to describe the two-dimensional flow field induced by the actuator. However, the model had a narrow validation range, depending on the empirical formula, and it did not fully consider en...

Plasma-Catalytic Oxidation of Toluene on Mn<sub class=”a-plus-plus”>x</sub>O<sub class=”a-plus-plus”>y</sub> at Atmospheric Pressure and Room Temperature

Abstract MnxOy/SBA-15 catalysts were prepared via the impregnation method and utilized for toluene removal in dielectric barrier discharge plasma at atmospheric pressure and room temperature. The catalysts were characterized by X-ray diffraction, N2 adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, and O2 temperature-programmed desorption methods. The characterization results indicated that manganese loading did not influence the 2D-hexagonal mesoporous structure of SBA-15. The catalyst had various oxidation states of manganese (Mn2+, Mn3+, and Mn4+), with Mn3+ being the dominant oxidation state. Toluene removal was investigated in the environment of pure N2 and 80 % N2 + 20 % O2 plasma, showing that the toluene removal efficiency and CO2 selectivity were noticeably increased by MnxOy/SBA-15, especially in the presence of 5 % Mn/SBA-15. This activity was closely related to the high dispersion of 5 % Mn on SBA-15 and the lowest reduction temperature exhibited by this catalyst. Mn loading increased the yield of CO2 in the N2 plasma and promoted the deep oxidation of toluene. During toluene oxidation, oxygen exchange might follow a pathway, wherein bulk oxygen was released from the MnxOy/SBA-15 surface; gas-phase O2 subsequently filled up the vacancies created on the oxide. Each of the manganese oxidation states played an important role; Mn2O3 was considered as a bridge for oxygen exchange between the gas phase and the catalyst, and Mn3O4 mediated transfer of oxygen between the catalyst and toluene.

Infrared Spectroscopy of <span class=”a-plus-plus inline-equation id-i-eq1″> <span class=”a-plus-plus equation-source format-t-e-x”>\(\hbox {CH}_4/\hbox {N}_{2}\)</span> </span> and <span class=”a-plus-plus inline-equation id-i-eq2″> <span class=”a-plus-plus equation-source format-t-e-x”>\(\hbox {C}_{2}\hbox {H}_{m}/\hbox {N}_{2}\)</span> </span> (<span class=”a-plus-plus inline-equation id-i-eq3″> <span class=”a-plus-plus equation-source format-t-e-x”>\({m = 2, 4, 6}\)</span> </span>) Gas Mixtures in a Dielectric Barrier Discharge

Abstract Fourier transform infrared spectroscopy of \(\hbox {CH}_{4}/\hbox {N}_{2}\) and \(\hbox {C}_{2}\hbox {H}_{m}/\hbox {N}_2\) ( \(m = 2, 4, 6\) ) gas mixtures in a medium pressure (300 mbar) dielectric barrier discharge was performed. Consumption of the initial gas and formation of other hydrocarbon and of nitrogen-containing HCN and \(\hbox {NH}_{3}\) molecules was observed. \(\hbox {NH}_{3}\) formation was further confirmed by laser absorption measurements. The experimental result for \(\hbox {NH}_{3}\) is at variance with simulation results.

Effect of TiO2 addition on the microstructure and nanomechanical properties of Al2O3 Suspension Plasma Sprayed coatings

Publication date: 15 October 2014 Source:Applied Surface Science, Volume 316 Author(s): E. Bannier , M. Vicent , E. Rayón , R. Benavente , M.D. Salvador , E. Sánchez Alumina–titania coatings are widely used in industry for wear, abrasion or corrosion protection components. Such layers are commonly deposited by atmospheric plasma spraying (APS) using powder as feedstock. In this study, both Al2O3 and Al2O3–13wt% TiO2 coatings were deposited on austenitic stainless steel coupons by suspension plasma spraying (SPS). Two commercial suspensions of nanosized Al2O3 and TiO2 particles were used as starting materials. The coatings microstructure and phase composition were fully characterised using FEG-SEM and XRD techniques. Nanoindentation technique was used to determine the coatings hardness and elastic modulus properties. Results have shown that the addition of titania to alumina SPS coatings causes different crystalline phases and a higher powder melting rate is reached. The higher melted material achieved, when titania is added leads to higher hardness and elastic modulus when the same spraying parameters are used.

Influence of N<sub class=”a-plus-plus”>2</sub>/O<sub class=”a-plus-plus”>2</sub> Mixtures on Decomposition of Naphthalene in Surface Dielectric Barrier Discharge Based Reactor

Abstract The decomposition of naphthalene in surface dielectric barrier discharge (SDBD) based reactor is investigated in different carrier gases (air, nitrogen, and oxygen) in order to understand the reaction mechanism of the decomposition process. The decomposition efficiency of naphthalene is determined at different oxygen content (from 0 to 10 vol%) and different input power. The highest decomposition efficiency is obtained in nitrogen at low input power, due to the role played by the nitrogen excited species in the decomposition process. In addition, the decomposition efficiency is decreased with increasing the oxygen content at a low input power. At a relatively high input power, the decomposition efficiency reached its maximum value in pure oxygen. Moreover, the decomposition efficiency decreases with the increase of the oxygen content reaching minimum value at a small content of oxygen (~3 vol% O2) and relatively high input power, and then increases at higher oxygen content. The results show that the decomposition of naphthalene in the present reactor could be treated as a first order reaction with respect to the concentration of naphthalene.

Influence of voltage magnitude on the dynamic behavior of a stable helium atmospheric pressure plasma jet

Effects of voltage magnitude on the development of a stable helium atmospheric pressure plasma jet are investigated by current measurements and high temporal-resolution streak images. Generated by a coaxial dielectric barrier discharge structure, the entire discharge can be classified into three regions: discharges in the tube gap, downstream jet, and up-streamer. The discharge morphologies of each region are analyzed. In the positive discharge phase, there are two discharges in the tube gap between the electrodes; the first one is ignited as corona and then developed into streamer corona, and the second one is similar with positive glow. The downstream jet is ignited independently from the discharge in the tube gap. Referred as “plasma bullet,” the dynamic behavior of the jet can be well described as a positive streamer. Under specific applied voltage, the jet is found to be composed by double bullets in which case the jet length decreases since that less charge is carried by the first bullet. The up-streamer can be captured as long as the discharge in the tube gap is activated. Propagating with velocity of ∼4 km/s, the up-streamer can be regarded as the extension of the first discharge in the tube gap. In the negative discharge phase, the discharge is confined in the tube gap with nearly symmetrical morphology with the positive one. Besides, with the rising of voltage, the negative discharge is initially intensified and then turns weaker after surpassing certain voltage, which may provide suitable condition for the occurrence of double-bullet phenomenon.

Vibration of Discharge Filaments in a Dielectric Barrier Discharge

The vibration of discharge filaments in a concentric spotring pattern in a dielectric barrier discharge is investigated by high-speed camera. The pattern, consisting of several sparsely and densely arranged-spot rings, bifurcates from a vibrating hexagonal superlattice. The discharge spots vibrate between two neighboring densely arranged-spot rings. The vibration period, generally ranging from 12 to 24 ms, increases with the increase of radius and argon concentration. The instantaneous images taken by a high-speed framing camera show that most of the vibrating spots and static spots discharge asynchronously. Based on the forces exerted on one vibrating spot by two neighboring static spots, a set of dynamical equations are developed to explain the vibration.

Inactivation Effect of Surface Microdischarge Plasma on Bacillus cereus

A kind of nonequilibrium air plasma based on surface microdischarge is developed, behaving as per editing aspect. Please confirm the change. as large homogeneous scalable discharge area. Its inactivation effect on Bacillus cereus is investigated and 5.3-log reduction in cell viability is achieved within 150-s exposure. The pH value, hydroxyl (OH), and nitric oxide (NO) concentration in the extracellular solution after plasma treatments are detected. In addition, a transmission electron microscope is utilized to observe the cell damage from the morphology. Some potential chemical and biomedical processes involved are discussed. It is considered that the oxidation effect of reactive oxygen species plays a crucial role, and the nitration effect as well as the synergistic effect in the acid milieu, jointly contribute to the NAP-induced bactericidal process.

Acetic Acid Decomposition in a Coaxial Dielectric Barrier Discharge Tube with Mist Flow

Abstract Non-thermal plasmas can be used for water treatment system because they allow free radical generation without heating. Advanced oxidation processes using non-thermal plasmas have been developed to decompose persistent organic pollutants. In this study, a water treatment method that involves spraying a solution into a coaxial dielectric barrier discharge (DBD) tube using an air, argon or oxygen carrier gas was investigated. The alumina DBD tube had an inner high-voltage electrode and an outer ground electrode. Acetic acid was used as the decomposition target because acetic acid is a known persistent organic material. An acetic acid solution, diluted 10,000 times in purified water, was atomized by an ultrasonic atomizer unit and introduced into the DBD tube. The residence time of the droplets sprayed into the discharge area was almost 7 ms. Acetic acid was effectively decomposed and the decomposition ratio reached almost 80 % when Ar was employed as the carrier gas. This is due to the very fine droplets in the sprayed mist having a large specific surface area and OH radicals being able to react directly in solution. Furthermore, the results suggest that the chemical processes involved in acetic acid decomposition can be controlled by varying the carrier gas composition.

Plasma-Enhanced Methane Direct Conversion over Particle-Size Adjusted MO<sub class=”a-plus-plus”>x</sub>/Al<sub class=”a-plus-plus”>2</sub>O<sub class=”a-plus-plus”>3</sub> (M = Ti and Mg) Catalysts

Abstract Non-oxidative methane activation over particle-size adjusted alumina catalysts loaded with metal oxide (Al2O3, MgO/Al2O3, and TiO2/Al2O3) was investigated with a dielectric barrier discharge reactor using 10 % CH4 in Ar at plasma induced temperature. Plasma-assisted catalytic activity for direct conversion of methane over the catalysts was compared with that using plasma only. Catalyst hybrid reaction in a non-thermal discharge showed that MgO/Al2O3 had the highest activity for methane conversion. C2, C3, and C4 hydrocarbons were formed as products; ethane, ethylene, and acetylene were predominant over all catalysts. The effect of varying particle size of the MgO/Al2O3 catalyst was also examined. The conversion of methane over MgO/Al2O3 dramatically increased with decreasing catalyst particle size from 1.70 to 0.25 mm. It is interesting to note that distribution of C2 hydrocarbons was tuned by changing the particle size of the catalyst. It was also observed that the gas flow rate, frequency, and power supplied affected direct conversion of methane and selectivity of products significantly.

Surface modification of polymeric materials by cold atmospheric plasma jet

Publication date: 30 September 2014 Source:Applied Surface Science, Volume 314 Author(s): K.G. Kostov , T.M.C. Nishime , A.H.R. Castro , A. Toth , L.R.O. Hein In this work we report the surface modification of different engineering polymers, such as, polyethylene terephthalate (PET), polyethylene (PE) and polypropylene (PP) by an atmospheric pressure plasma jet (APPJ). It was operated with Ar gas using 10kV, 37kHz, sine wave as an excitation source. The aim of this study is to determine the optimal treatment conditions and also to compare the polymer surface modification induced by plasma jet with the one obtained by another atmospheric pressure plasma source – the dielectric barrier discharge (DBD). The samples were exposed to the plasma jet effluent using a scanning procedure, which allowed achieving a uniform surface modification. The wettability assessments of all polymers reveal that the treatment leads to reduction of more than 40° in the water contact angle (WCA). Changes in surface composition and chemical bonding were analyzed by x-ray photoelectron spectroscopy (XPS) and Fourier-Transformed Infrared spectroscopy (FTIR) that both detected incorporation of oxygen-related functional groups. Surface morphology of polymer samples was investigated by Atomic Force Microscopy (AFM) and an increase of polymer roughness after the APPJ treatment was found. The plasma-treated polymers exhibited hydrophobic recovery expressed in reduction of the O-content of the surface upon rinsing with water. This process was caused by the dissolution of low molecular weight oxidized materials (LMWOMs) formed on the surface as a result of the plasma exposure.

Charging of moving surfaces by corona discharges sustained in air

Atmospheric pressure corona discharges are used in electrophotographic (EP) printing technologies for charging imaging surfaces such as photoconductors. A typical corona discharge consists of a wire (or wire array) biased with a few hundred volts of dc plus a few kV of ac voltage. An electric discharge is produced around the corona wire from which electrons drift towards and charge the underlying dielectric surface. The surface charging reduces the voltage drop across the gap between the corona wire and the dielectric surface, which then terminates the discharge, as in a dielectric barrier discharge. In printing applications, this underlying surface is continuously moving throughout the charging process. For example, previously charged surfaces, which had reduced the local electric field and terminated the local discharge, are translated out of the field of view and are replaced with uncharged surface. The uncharged surface produces a rebound in the electric field in the vicinity of the corona wire which in turn results in re-ignition of the discharge. The discharge, so reignited, is then asymmetric. We found that in the idealized corona charging system we investigated, a negatively dc biased corona blade with a dielectric covered ground electrode, the discharge is initially sustained by electron impact ionization from the bulk plasma and then dominated by ionization from sheath accelerated secondary electrons. Depending on the speed of the underlying surface, the periodic re-ignition of the discharge can produce an oscillatory charging pattern on the moving surface.

Characterization of a Plasma Jet Produced by Spark Discharges in Argon Air Mixtures at Atmospheric Pressure

Abstract A stark difference in the electrical, optical and thermal properties of an atmospheric pressure plasma jet source exploiting spark discharges in a gas stream was reported when argon is used instead of air in the flow. Electrical probe results are discussed together with optical ones in order to investigate the discharge properties and the temporal structure of the different pulses of electrical current. If air-argon mixtures are used as feeding gas for the discharge, a sharp transition from a hot plume to a cold plasma jet is observed when argon content exceeds 90 %. Characteristics of the source are examined from the point of view of their utility as a tool for plasma treatment of materials. In this respect, a 10 % air in argon mixture corresponds to a promising oxidizing condition, as revealed by the pronounced peak in atomic oxygen emission intensity.

Experimental study on surface modification of PET films under bipolar nanosecond-pulse dielectric barrier discharge in atmospheric air

Publication date: 15 September 2014 Source:Applied Surface Science, Volume 313 Author(s): Yunfei Liu , Chunqiang Su , Xiang Ren , Chuan Fan , Wenwu Zhou , Feng Wang , Weidong Ding Dielectric barrier discharge (DBD) is widely used for surface modification of polymer films. In this paper, DBD characteristics under bipolar repetitive frequency nanosecond pulse in atmospheric air are studied and surface properties of polyethylene terephthalate films under homogeneous DBD and filamentary DBD modification are compared through scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and dielectric test equipment. It is found that the discharge is homogeneous when gap spacing d is less than 1.2mm and filamentary when d is within the range of 3.0mm to 5.8mm. SEM pictures reveal that films under homogeneous DBD present a smooth surface while intensive “gully-like” etches appear on the surface of the films under filamentary DBD, which can result in local insulation defects and is disadvantageous to surface modification. It is found from the XPS analysis that a number of oxygen-containing polar groups are introduced onto the surface of the film modified by homogeneous DBD compared with the untreated one. Experimental results for dielectric properties indicate that the three parameters: relative dielectric constant ɛ r , dielectric loss tangent tan δ and breakdown voltages V b are all changed in different degree after surface modification. And possible reason for the phenomenon is discussed.

Plasma actuator electron density measurement using microwave perturbation method

A cylindrical dielectric barrier discharge plasma under five different pressures is generated in an evacuated glass tube. This plasma volume is located at the center of a rectangular copper waveguide cavity, where the electric field is maximum for the first mode and the magnetic field is very close to zero. The microwave perturbation method is used to measure electron density and plasma frequency for these five pressures. Simulations by a commercial microwave simulator are comparable to the experimental results.

Effect of Ozone Addition to Lean NO<sub class=”a-plus-plus”>x</sub> Trap Method Using Plasma-Catalyst System

Abstract Although diesel vehicles have high energy efficiency, the removal of emitted NOx at low temperature persists as an important issue. This report presents an examination of low-temperature NOx removal using ozone injection and a plasma-lean NOx trap (LNT) catalyst system. Ozone is readily producible by a dielectric barrier discharge reactor using oxygen in air, and its injection to emitted NO enables oxidation to NO2 even at low temperatures. Results show that synergetic effects of ozone injection and plasma-LNT catalyst system enable low-temperature NOx removal.

Synergistic effect of gold nanoparticles and cold plasma on glioblastoma cancer therapy

Gold nanoparticles (AuNPs) have been investigated as a promising reagent for cancer therapy in various fields. In the meantime, cold atmospheric plasma has shown exquisite selectivity towards cancer cells. In this paper, we demonstrate that there is a synergy between gold nanoparticles and cold atmospheric plasma in cancer therapy. Specifically, the concentration of AuNPs plays an important role on plasma therapy. At an optimal concentration, gold nanoparticles can significantly induce glioblastoma (U87) cell death up to a 30% overall increase compared to the control group with the same plasma dosage but no AuNPs applied. The reactive oxygen species (ROS) intensity of the corresponding conditions has a reversed trend compared to cell viability. This matches with the theory that intracellular ROS accumulation results in oxidative stress, which further changes the intracellular pathways, causing damage to the proteins, lipids and DNA. Our results show that this synergy has great po...

Ultraviolet-B radiation enhancement in dielectric barrier discharge based xenon chloride exciplex source by air

A single barrier dielectric barrier discharge tube of quartz with multi-strip Titanium-Gold (Ti-Au) coatings have been developed and utilized for ultraviolet-B (UV-B) radiation production peaking at wavelength 308 nm. The observed radiation at this wavelength has been examined for the mixtures of the Xenon together with chlorine and air admixtures. The gas mixture composition, chlorine gas content, total gas pressure, and air pressure dependency of the UV intensity, has been analyzed. It is found that the larger concentration of Cl2 deteriorates the performance of the developed source and around 2% Cl2 in this source produced optimum results. Furthermore, an addition of air in the xenon and chlorine working gas environment leads to achieve same intensity of UV-B light but at lower working gas pressure where significant amount of gas is air.

Single dielectric barrier discharge characteristics in needle-to-plane configuration

Single dielectric barrier discharges (DBDs) in the ‘needle—submillimetric air gap—polymer barrier—plane’ configuration were investigated. The measurements of breakdown voltages, discharge current pulses, transferred charges and surface charge distributions for both needle polarities were conducted by the developed experimental setup. For the same gaps the breakdown voltage and the accumulated surface charge for the positive needle polarity are larger than the ones for the negative polarity. It is shown that the main contribution to the DBD current pulse and accumulated charge is determined by the surface phase of discharge process. Additionally the subsequent DBD development during one period of the applied voltage of triangular waveform was observed. The results indicate a ‘memory effect’ of the DBD development.

Dielectric barrier discharge at the triglycine sulfate crystal surface: the role of the electric field of the domain structure

Dielectric barrier discharges (DBD) at the triglycine sulfate crystal surface, generated in air under controlled gas pressure, have been investigated. Electrical characterization of these DBD discharges, produced at temperatures below as well as above the ferroelectric phase transition, are presented. The influence of the electric field of the domain structure on these DBD discharges are discussed in the frame of a model which takes into account the dynamics of the domain structure of the ferroelectric barrier under the action of an external voltage.

Removal of Volatile Organic Compounds (VOCs) at Room Temperature Using Dielectric Barrier Discharge and Plasma-Catalysis

Abstract Non-thermal plasma (NTP) was produced in a dielectric barrier discharge reactor for degradation of acetaldehyde and benzene, respectively. The effect of volatile organic compounds (VOCs) chemical structure on the reaction was investigated. In addition, acetaldehyde was removed in different background gas. The results showed that, no matter in nitrogen, air or oxygen, NTP technology always exhibited high acetaldehyde removal efficiency at ambient temperature. However, it also caused some toxicity by-product such as NOx and ozone. Meanwhile, some intermediates such as acetic acid, amine and nitromethane were formed and resulted in low carbon dioxide selectivity. To solve above problems, Co–OMS-2 catalysts were synthesized and combined with plasma. It was found that, the introduction of catalysts improved VOCs removal efficiency and inhibited by-product formation of plasma significantly. The plasma-catalysis system was operated in a recycling experiment to investigate its stability. The acetaldehyde removal efficiency can be kept at 100 % in the whole process. However, slight deactivation in ozone control was observed at the later stage of the experiment, which may be ascribed to deposition of VOCs on the catalysts surface and reduction of catalysts surface area.

Surface Analysis of Titanium Cleaning and Activation Processes: Non-thermal Plasma Versus Other Techniques

Abstract A medium pressure (5 kPa) dielectric barrier discharge operating in different atmospheres (air and argon) is used to develop a fast and easy way to remove adsorbed carbon contamination. Chemical and physical changes at the sample surface after plasma treatment are studied, making use of contact angle measurements, X-ray photoelectron spectroscopy analysis and atomic force microscopy measurements. The obtained results are compared with other chemical and thermal treatments typically used. This comparison shows that plasma treatment at medium pressure is able to remove up to 20 % more of the adsorbed carbon compared to the classical cleaning methods, while at the same time being less aggressive, leaving the sub-surface chemistry unchanged. Moreover, the analysis techniques give a fundamental insight in the reactions processes at the titanium surface when exposed to a medium pressure plasma.

Effect of Plasma Deposition Using Low-Power/Non-thermal Atmospheric Pressure Plasma on Promoting Adhesion of Composite Resin to Enamel

Abstract This study investigated the effect of monomer deposition through a low-power, non-thermal atmospheric pressure plasma (NT-APP) on adhesion of resin composite to enamel and its durability. The adhesion of resin composite to enamel and its durability were compared using micro-shear bond strength (MSBS) tests, with or without monomer deposition and before or after thermocycling (TC). The bond strength data were interpreted using Weibull analysis. Hydrophilicities of treated ceramic surfaces were compared with contact angle measurements. Surface characterization was performed with a Fourier transform infra-red spectrophotometer and X-ray photoelectron spectroscopy. The fracture mode at the interface was evaluated using a stereomicroscope and a scanning electron microscope. The plasma polymer deposition of benzene and 1,3-butadiene using the low-power NT-APP improved the MSBS of resin composite to enamel (p < 0.05). Surface characterization suggested improved wettability and changes in the chemical composition of the plasma-deposited enamel surface. However, the mean values of the MSBS of the plasma polymer-deposited groups decreased after TC (p < 0.05). After TC, the Weibull modulus (m) values increased in all the groups, especially in the plasma polymer-deposited groups. Plasma polymer deposition improved enamel adhesion but failed to improve durability in terms of mean bond strength. However, the plasma polymer deposition increased the Weibull modulus m after TC, which indicated that the scatter of the bond strength was narrowed with respect to durability.

Measurement of Ozone Production in Non-thermal Plasma Actuator Using Surface Dielectric Barrier Discharge

Abstract Plasma actuators for flow control are intensively studied, but the production of ozone by the surface dielectric barrier discharge used in the actuators has never been quantified. Since ozone is harmful to human health, it is important to quantify its production for an application of this type of actuator on a land vehicle. This paper describes an experimental study to measure the concentration of ozone produced by an actuator with different parameters: amplitude and frequency of the applied high voltage, and the electrode configuration (shape, spacing and length). The results show that, under our experimental conditions, the production of ozone is directly proportional to the power dissipation. The production rate was measured at 21 g/kWh. Although the rate is much lower than that of an industrial ozonizer, it is still far from being negligible and should be taken into account for the future application of these actuators.

2D Thermoluminescence imaging of dielectric surface long term charge memory of plasma surface interaction in DBD discharges

The charge trapping effect due to the exposure of alumina surfaces to plasma has been studied in a volume dielectric barrier discharge (DBD) in Ar and He noble gases. The long lasting charge trapping of alumina dielectric plates, used as barriers in DBDs, is evidenced by an ex situ thermoluminescence (TL) experiment performed with a standard and a custom two-dimensional (2D)-TL apparatus. The spatial density of trapped surface charges is found to be strongly correlated to the plasma morphology, and the surface spatial memory lasted for several minutes to hours after plasma exposure. In the case of Ar, the plasma channel impact signature on the surface shows a higher equivalent radiation dose with respect to the surface plasma wave and the post-discharge species signature. As a consequence, for the development of discharges, inside the dielectric surface the availability of lower energy trapped electrons is larger in the first region of plasma impact. The reported spatial m...


The second volume of Clinical Plasma Medicine starts its first issue as a focus issue to cover an important topic with huge practical relevance: plasma in dentistry. We are happy to gain Professor Stefan Rupf, Homburg/Saar, Germany, as guest editor for this section of the journal. Three manuscripts in this issue are dedicated to this topic but we are convinced that this will be continued. Two another articles of this issue give some new results of research on cold atmospheric plasma application in dermatology and wound healing. A letter written by colleagues from India opens up new perspectives of plasma application and is a first step to establish this journal as a discussion platform to exchange new ideas to extend the application field of plasmas in medicine.

Guest editorial

Plasma medicine has evolved rapidly in the past two decades, boosted by groundbreaking ideas in plasma physics as well as investments in research and development by national governments and national and international project management institutions. Clinic-associated research centers where established in Europe, America and Asia, which are systematically trying to make use of cold plasma in humans possible. Mention should be made here of the close cooperation of application-oriented workgroups and scientists conducting basic research. In the field of dermatology, good progress has been made on the path to establishing treatment methods using cold atmospheric plasma. Clinical studies were able to prove the technology׳s non-invasive potential very impressively. The broad spectrum of potential applications of atmospheric plasmas up to invasive procedures is being underlined by already established methods of treatment such as plasma coagulation and plasma ablation. In dentistry, the first investigations into the usability of plasma technology started at the beginning of the century. Eva Stoffels and Raymond Sladek were among the first to explore this field. As the most important diseases of the human mouth are of infectious nature, it was logical to direct the first approach to one of them, the dental caries. Press publications created the impression atmospheric plasma would soon replace the dentist׳s drill. As a result of this simplification, many further interesting developments in the field of dentistry went somewhat unnoticed for some time. The expectations on the plasma technology׳s performance to replace rotating preparation techniques were very unrealistic. Again and again it had to be stressed that there are different dental drills such as diamond-coated preparation instruments for working on enamel or removing existing restorations of metal or ceramics as well as specialized drills made of metal, plastics or ceramics. There is no use for cold atmospheric plasma in invasive treatments of the dentin or in removing old restoration material, as it cannot destroy the substances to be worked on. In contrast, there is great potential for the treatment of weakened dentin infected by caries. According to the traditional teaching, which was characterized by non-adhesive metals such as gold or amalgam, the latter was removed completely well beyond the infected area. The introduction of adhesive restoration techniques has overruled the maxim of complete removal of dentin affected by caries, evolving into a concept of caries management, focusing on stopping the progress of the caries process. Caries management today comprises the aspects of biofilm control, remineralization of enamel and of caries-affected dentin as well as the defect-adapted restoration of the tooth substance. Cold atmospheric plasma offers application potential for all these partial aspects. It is able to kill microorganisms in microstructures such as dentin tubules, to further the infiltration of restoration material or even regenerative material as well as to improve the adhesion of tooth-colored restoration materials. Thus, it may be concluded that cold atmospheric plasma may, if not replace the drill, at least significantly reduce its application on dentin, where it is most unpleasant and painful. The use of plasma technology may even be envisaged in the early stages of caries, in order to stop the destructive process and to prevent the use of the dental drill. In particular, the potential offered by an increase of the surface energy of treated tooth substances and the deposit of disinfecting and sealing materials may become important in the near future.

Antimicrobial effects of non-thermal atmospheric plasma as a novel root canal disinfectant

Abstract: This study aimed to investigate effects of non-thermal atmospheric plasma on an Enterococcus faecalis biofilm within the canals of extracted human teeth. A significant decrease in the number of CFU׳s was observed after 2min cold plasma treatment with an average kill rate of 99.999%. MTT assay showed a significant reduction in the viability of bacteria with a reduction rate of 98.939%. XTT assay showed a reduction of bacterial metabolic activity by 99.7%. Both 2min cold plasma and 6% NaOCl greatly reduced the viability and metabolic activity of E. faecalis bacteria, but there is no significant difference between them.

Computer simulations of plasma–biomolecule and plasma–tissue interactions for a better insight in plasma medicine

Plasma medicine is a rapidly evolving multidisciplinary field at the intersection of chemistry, biochemistry, physics, biology, medicine and bioengineering. It holds great potential in medical, health care, dentistry, surgical, food treatment and other applications. This multidisciplinary nature and variety of possible applications come along with an inherent and intrinsic complexity. Advancing plasma medicine to the stage that it becomes an everyday tool in its respective fields requires a fundamental understanding of the basic processes, which is lacking so far. However, some major advances have already been made through detailed experiments over the last 15 years. Complementary, computer simulations may provide insight that is difficult—if not impossible—to obtain through experiments. In this review, we aim to provide an overview of the various simulations that have been carried out in the context of plasma medicine so far, or that are relevant for plasma medicine. We focus ou...

Chemical modification of amino acids by atmospheric-pressure cold plasma in aqueous solution

Plasma medicine is an attractive new research area, but the principles of plasma modification of biomolecules in aqueous solution remain elusive. In this study, we investigated the chemical effects of atmospheric-pressure cold plasma on 20 naturally occurring amino acids in aqueous solution. High-resolution mass spectrometry revealed that chemical modifications of 14 amino acids were observed after plasma treatment: (i) hydroxylation and nitration of aromatic rings in tyrosine, phenylalanine and tryptophan; (ii) sulfonation and disulfide linkage formation of thiol groups in cysteine; (iii) sulfoxidation of methionine and (iv) amidation and ring-opening of five-membered rings in histidine and proline. A competitive reaction experiment using 20 amino acids demonstrated that sulfur-containing and aromatic amino acids were preferentially decreased by the plasma treatment. These data provide fundamental information for elucidating the mechanism of protein inactivation for biomedical p...

Atmospheric cold plasma inactivation of Escherichia coli, Salmonella enterica serovar Typhimurium and Listeria monocytogenes inoculated on fresh produce

Publication date: September 2014 Source:Food Microbiology, Volume 42 Author(s): D. Ziuzina , S. Patil , P.J. Cullen , K.M. Keener , P. Bourke Atmospheric cold plasma (ACP) represents a potential alternative to traditional methods for non-thermal decontamination of foods. In this study, the antimicrobial efficacy of a novel dielectric barrier discharge ACP device against Escherichia coli, Salmonella enterica Typhimurium and Listeria monocytogenes inoculated on cherry tomatoes and strawberries, was examined. Bacteria were spot inoculated on the produce surface, air dried and sealed inside a rigid polypropylene container. Samples were indirectly exposed (i.e. placed outside plasma discharge) to a high voltage (70 kVRMS) air ACP and subsequently stored at room temperature for 24 h. ACP treatment for 10, 60 and 120 s resulted in reduction of Salmonella, E. coli and L. monocytogenes populations on tomato to undetectable levels from initial populations of 3.1, 6.3, and 6.7 log10 CFU/sample, respectively. However, an extended ACP treatment time was necessary to reduce bacterial populations attached on the more complex surface of strawberries. Treatment time for 300 s resulted in reduction of E. coli, Salmonella and L. monocytogenes populations by 3.5, 3.8 and 4.2 log10 CFU/sample, respectively, and also effectively reduced the background microflora of tomatoes.

A nanosecond surface dielectric barrier discharge in air at high pressures and different polarities of applied pulses: transition to filamentary mode

The development of a nanosecond surface dielectric barrier discharge in air at pressures 1?6 bar is studied. At atmospheric pressure, the discharge develops as a set of streamers starting synchronously from the high-voltage electrode and propagating along the dielectric layer. Streamers cover the dielectric surface creating a ?quasi-uniform? plasma layer. At high pressures and high voltage amplitudes on the cathode, filamentation of the discharge is observed a few nanoseconds after the discharge starts. Parameters of the observed ?streamers-to-filaments? transition are measured; physics of transition is discussed on the basis of theoretical estimates and numerical modeling. Ionization-heating instability on the boundary of the cathode layer is suggested as a mechanism of filamentation.