Author Archives: RSS - PlasMedFeed

Improving Plasma Regeneration Conditions of Pt–Sn/Al 2 O 3 in Naphtha Catalytic Reforming Process Using Atmospheric DBD Plasma System

Abstract The catalytic naphtha reforming is one of the largest processes of petroleum industry that is used to rebuild the low-octane hydrocarbons in the naphtha to more valuable high-octane gasoline called reformate without changing the boiling point range. An atmospheric pressure pin to plate dielectric barrier discharge (DBD) plasma was used to remove carbonaceous contaminant from the coked Pt–Sn/Al2O3 catalysts during the naphtha reforming process. The effects of treatment time and flow ratios of O2/Ar and O2/He on the carbon content of the coked catalysts were investigated. The produced radicals and active species of the plasma process were identified by optical emission spectroscopy. To confirm removing the coke from the catalyst, thermal gravimetric/differential thermal analysis and temperature programmed oxidation analysis were done. Effects of treatment time and flow ratios of O2/Ar and O2/He on the carbon content of the coked catalysts were investigated by applying elemental analysis. The results of X-ray diffraction, X-ray fluorescence, Brunauer–Emmett–Teller, and CO adsorption showed that the structure and specifications of regenerated catalysts remained without significant changes during the plasma treating. The catalyst performance test revealed that DBD plasma regenerated catalysts increased the aromatic content of the feed as well as the fresh catalysts. The results showed that the plasma treatment method for regeneration of Pt–Sn/Al2O3 can be applied at lower temperature and pressure relative to the thermal regeneration method. Graphical Abstract

Numerical investigation of plasma-actuator force-term estimations from flow experiments

The accuracy of the experimental force-term estimation for cold, dielectric barrier discharge (DBD) plasma actuators based on fluid-velocity information is investigated by means of numerical simulations for cases without and with a laminar base flow. First, a wall jet induced by a steady planar body force similar to that induced by a plasma actuator under quiescent-air conditions is simulated. Second, the same steady force is applied to stabilise a laminar two-dimensional zero-pressure-gradient boundary-layer flow under the usual assumption of force independence. For both cases the force distribution is reconstructed applying two different methods to eliminate the pressure gradients unknown from experiments. The method based on the vorticity transport equation requires the force to be dominated by one component only. It is found that its accuracy is unaffected by a base flow but strongly dependent on the characteristics of the force distribution. The other method is based on the...

Nitrogen Atmospheric-Pressure-Plasma-Jet Induced Oxidation of SnO x Thin Films

Abstract SnOx thin films that were rf-sputter-deposited under various gas flow ratios ([O2]/([O2] + [Ar]) OFR = 3.0, 3.6, 4.2 and 4.8 %) were rapidly annealed using atmospheric pressure plasma jets (APPJs) in temperature range of ~350–386 °C for up to 5 min. The original electron probe micro-analysis [O] contents in the as-deposited films were ~25, ~30, ~35 and ~40 % for films deposited at ([O2]/([O2] + [Ar]) gas flow ratios OFR = 3.0, 3.6, 4.2 and 4.8 %, respectively. APPJ annealing increased the [O] content to ~35 % for films deposited at OFR = 3.0 and 3.6 %, where the [O] content remained in similar levels for films deposited at OFR = 4.2 and 4.8 %. Crystalline metallic Sn was identified in films as-deposited at OFR = 3.0 and 3.6 %; on the other hand, an X-ray amorphous SnOx phase was identified in films as-deposited at OFR = 4.2 and 4.8 %. Crystallization and oxidation by APPJ annealing improved the transmittance and blue-shifted the absorption band edge to ~420 nm. All APPJ-annealed films exhibit n-type conductivity that may be contributed by the mixed phases of SnO, SnO2 and a small amount of Sn.

Thomson scattering on non-thermal atmospheric pressure plasma jets

To characterize non-thermal atmospheric pressure plasmas experimentally, a large variety of methods and techniques is available, each having its own specific possibilities and limitations. A rewarding method to investigate these plasma sources is laser Thomson scattering. However, that is challenging. Non-thermal atmospheric pressure plasmas (gas temperatures close to room temperature and electron temperatures of a few eV) have usually small dimensions (below 1 mm) and a low degree of ionization (below 10 −4 ). Here an overview is presented of how Thomson scattering can be applied to such plasmas and used to measure directly spatially and temporally resolved the electron density and energy distribution. A general description of the scattering of photons and the guidelines for an experimental setup of this active diagnostic are provided. Special attention is given to the design concepts required to achieve the maximum signal photon flux with a minimum of unwanted signals...

Localized pulsed nanosecond discharges in a counterflow nonpremixed flame environment

A flame is a very unusual environment for the development of a gas discharge, since it presents strong gradients in temperature, composition, and pre-ionization. In this paper we examine how such an environment impacts the development of the plasma when using repetitive pulsed nanosecond discharges, one of the main strategies used in the field of plasma assisted combustion. Experiments were performed in a counterflow nonpremixed burner with parallel electrodes at the nozzle exits and nanosecond-resolved photography of the plasma emission is presented. It was shown that the discharge development in stratified media may take place in the form of a dielectric barrier discharge with a localized energy deposition. In the experiments presented the discharge energy was coupled to the flame front because of the high rate of chemi-ionization and the gas density decrease in the flame.

Synthesis of hard hydrogenated amorphous carbon films by atmospheric pressure filamentary dielectric barrier discharge

In this study, the authors synthesized a-C:H films by filamentary dielectric barrier discharge (FDBD) to improve their mechanical properties compared to the films synthesized by glow DBD (GDBD), which is generally used for atmospheric pressure plasma enhanced chemical vapor deposition. The discharge type was transited from GDBD to FDBD by increasing the gap between the electrodes from 1 to 4 mm. The hydrogen concentration of the a-C:H films synthesized by FDBD was reduced compared to that of the films synthesized by GDBD. The hardness of the films increased from 3.7 to 11.9 GPa by using FDBD. These results show that the hard a-C:H films can be synthesized at room temperature in a large area by FDBD.

Cavity ring-down spectroscopy for atmospheric pressure plasma jet analysis

Pulsed cavity ring-down spectroscopy (CRDS) is a direct absorption, highly sensitive, versatile technique suitable for the analysis of a wide range of plasmas. CRDS belongs to a wide class of cavity-enhanced spectroscopies. This work briefly describes the basic principles of CRDS and summarizes the main literature specifically related to applications for atmospheric pressure plasma jets (APPJ). Emphasis is given to the temporal resolution and pulsed character of the plasma sources. As an example we present in more detail the determination of metastable helium density in the ##IMG## [http://ej.iop.org/images/0963-0252/24/5/054004/psst517579ieqn001.gif] {$2\text{s}{}_{~}^{3}{{\text{S}}_{1}}$} state produced in a single-electrode atmospheric pressure plasma jet driven by a pulsed high-voltage waveform. Measured He( ##IMG## [http://ej.iop.org/images/0963-0252/24/5/054004/psst517579ieqn002.gif] {${}_{~}^{3}{{\text{S}}_{1}}$} ) number densit...

Phase resolved analysis of the homogeneity of a diffuse dielectric barrier discharge

Cold atmospheric pressure plasmas have already proven their ability of supporting the healing process of chronic wounds. Especially simple configurations like a dielectric barrier discharge (DBD), comprising of one driven electrode which is coated with a dielectric layer, are of interest, because they are cost-effective and easy to handle. The homogeneity of such plasmas during treatment is necessary since the whole wound should be treated evenly. In this investigation phase resolved optical emission spectroscopy is used to investigate the homogeneity of a DBD. Electron densities and reduced electric field distributions are determined with temporal and spatial resolution and the differences for applied positive and negative voltage pulses are studied.

Impact of ns -DBD plasma actuation on the boundary layer transition using convective heat transfer measurements

This paper demonstrates that the impact of nanosecond pulsed dielectric barrier discharge ( ns -DBD) actuators on the structure of the boundary layer can be investigated using quantitative convective heat transfer measurements. For the experiments, the flow over a flat plate with a C4 leading edge thickness distribution was examined at low speed incompressible flow (6.6–11.5 m s −1 ). An ns -DBD plasma actuator was mounted 5 mm downstream of the leading edge and several experiments were conducted giving particular emphasis on the effect of actuation frequency and the freestream velocity. Local heat transfer distributions were measured using the transient liquid crystal technique with and without plasma activated. As a result, any effect of plasma on the structure of the boundary layer is interpreted by local heat transfer coefficient distributions which are compared with laminar and turbulent boundary layer correlations. The heat transfer results, which are a...

Atmospheric Pressure Plasma Polymerization of Super-Hydrophobic Nano-films Using Hexamethyldisilazane Monomer

Abstract The super-hydrophobic nano-films were synthesized by atmospheric pressure plasma jet using hexamethyldisilazane. In this paper, the atmospheric pressure plasma jet reacting with air was used to determine the formation of plasma polymerized nano-film. The atmospheric pressure plasma polymerized nano-film surface properties were determined by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and atomic forced microscopy. Specifically, it has been observed that atmospheric pressure plasma polymerization with the appropriate monomer gas flow rate cause the formation of the super-hydrophobic film. The surface properties of atmospheric pressure plasma polymerized nano-films were determined as the Cassie–Baxter state. It was examined that super-hydrophobic nano-film surface exhibits the organosilicon sphere stacking structure. Such sphere stacking structure does not only cause the hydrophobicity, it also stabilizes the Cassie regime, and thus favors the water repellency.

Review on VUV to MIR absorption spectroscopy of atmospheric pressure plasma jets

Absorption spectroscopy (AS) represents a reliable method for the characterization of cold atmospheric pressure plasma jets. The method’s simplicity stands out in comparison to competing diagnostic techniques. AS is an in situ , non-invasive technique giving absolute densities, free of calibration procedures, which other diagnostics, such as laser-induced fluorescence or optical emission spectroscopy, have to rely on. Ground state densities can be determined without the knowledge of the influence of collisional quenching. Therefore, absolute densities determined by absorption spectroscopy can be taken as calibration for other methods. In this paper, fundamentals of absorption spectroscopy are presented as an entrance to the topic. In the second part of the manuscript, a review of AS performed on cold atmospheric pressure plasma jets, as they are used e.g. in the field of plasma medicine, is presented. The focus is set on special techniques overcoming not only the drawback ...

Generation of In-Package Cold Plasma and Efficacy Assessment Using Methylene Blue

Abstract In-package cold plasma processing is highly desirable in the food and biomedical industries as it allows for efficient sterilisation, and prevents against post-packaging contamination. The sensitivity of methylene blue dye to the reactive species generated from cold plasma is tested in this work for possible use as a marker of process efficacy. A large gap dielectric barrier discharge (DBD) operating in air was employed to generate the plasma discharge within the sealed package. The discolouration of methylene blue dye placed inside the package was studied as a function of DBD operation time, applied voltage and spatial position. Ozone concentrations were measured immediately after treatment as an indicator of one of the key meta-stables produced by the approach with values of up to 1800 ppm recorded. Visible absorption spectra and pH changes of the dye were measured. A decrease in peak absorbance of the dyes and pH was observed as a function of treatment time and ozone concentration. Optical emission spectroscopy of the discharge revealed the generation of excited nitrogen and reactive oxygen species. The results of kinetic modelling revealed that the dye discolouration can be used as a suitable marker reaction for treatment times within the order of 30 s.

Exogenous nitric oxide (NO) generated by NO-plasma treatment modulates osteoprogenitor cells early differentiation

In this study, we investigated whether nitric oxide (NO) generated using a non-thermal plasma system can mediate osteoblastic differentiation of osteoprogenitor cells without creating toxicity. Our objective was to create an NO delivery mechanism using NO-dielectric barrier discharge (DBD) plasma that can generate and transport NO with controlled concentration to the area of interest to regulate osteoprogenitor cell activity. We built a non-thermal atmospheric pressure DBD plasma nozzle system based on our previously published design and similar designs in the literature. The electrical and spectral analyses demonstrated that N 2 dissociated into NO under typical DBD voltage–current characteristics. We treated osteoprogenitor cells (MC3T3-E1) using NO-plasma treatment system. Our results demonstrated that we could control NO concentration within cell culture media and could introduce NO into the intracellular space using NO-plasma treatment with various treatment times...

Radial structures of atmospheric-pressure glow discharges with multiple current pulses in helium

Radial structures of atmospheric pressure glow discharges in dielectric barrier discharge with multiple current pulses are investigated by a self-consistent two-dimensional fluid model. The simulation results show that the discharge current densities at different radial positions do not reach their peaks simultaneously, indicating that there exists a radial non-uniform structure. The time delay between the plasma ignitions in different positions become larger and larger in the successive current pulses. It is argued that the radial non-uniformity originates from the edge effects in the first current pulse, and grows in the successive current pulses by the activation-inhibition mechanism.

Silicon-based quantum dots: synthesis, surface and composition tuning with atmospheric pressure plasmas

The synthesis of silicon and silicon-based quantum dots (diameter < 5 nm) is discussed. Specifically the synthesis of Si-based quantum dots (QDs) by atmospheric pressure plasmas is reviewed and the most recent developments are also reported. Atmospheric pressure plasmas are then compared with other synthesis methods that include low pressure plasmas, wet chemistry, electrochemical etching and laser-based methods. Finally, progress in the synthesis of alloyed silicon QDs is discussed where the nanoscale Si–Sn and Si–C systems are reported. The report also includes a theoretical analysis that highlights some fundamental differences offered by plasmas at atmospheric pressure and that may provide opportunities for novel materials with advantageous properties.

Atmospheric-pressure dielectric barrier discharge with capillary injection for gas-phase nanoparticle synthesis

We present an atmospheric-pressure dielectric barrier discharge (DBD) reactor for gas-phase nanoparticle synthesis. Nickel nanoparticles are synthesized by homogenous nucleation from nickelocene vapor and characterized online by aerosol mobility measurements. The effects of residence time and precursor concentration on particle growth are studied. We find that narrower distributions of smaller particles are produced by decreasing the precursor concentration, in agreement with vapor nucleation theory, but larger particles and aggregates form at higher gas flow rates where the mean residence time should be reduced, suggesting a cooling effect that leads to enhanced particle nucleation. In comparison, incorporating a capillary gas injector to alter the velocity profile is found to significantly reduce particle size and agglomeration. These results suggest that capillary gas injection is a better approach to decreasing the mean residence time and narrowing the residence time distrib...

Temporally resolved ozone distribution of a time modulated RF atmospheric pressure argon plasma jet: flow, chemical reaction, and transient vortex

The ozone density distribution in the effluent of a time modulated RF atmospheric pressure plasma jet (APPJ) is investigated by time and spatially resolved by UV absorption spectroscopy. The plasma jet is operated with an averaged dissipated power of 6.5 W and gas flow rate 2 slm argon  +2% O 2 . The modulation frequency of the RF power is 50 Hz with a duty cycle of 50%. To investigate the production and destruction mechanism of ozone in the plasma effluent, the atomic oxygen and gas temperature is also obtained by TALIF and Rayleigh scattering, respectively. A temporal increase in ozone density is observed close to the quartz tube exit when the plasma is switched off due to the decrease in O density and gas temperature. Ozone absorption at different axial positions indicates that the ozone distribution is dominated by the convection induced by the gas flow and allows estimating the on-axis local gas velocity in the jet effluent. Transient vortex structures occurring dur...

Addendum to ‘velocity-information based force-term estimation of dielectric barrier discharge plasma actuators’

In a recent publication (Kriegseis et al 2013 J. Phys. D: Appl. Phys . 46 055202) we contrasted the variety of published strategies to estimate magnitude and distribution of the body force produced by dielectric barrier discharge plasma actuators. All approaches were applied to an identical set of velocity data, which was experimentally obtained by means of particle image velocimetry. Particularly, the determined force distributions of the above paper turned out to be beneficial for subsequent efforts to derive empirical plasma-actuator models. The purpose of this addendum, therefore, is to provide both the velocity data and the determined force distributions as discussed in the original publication. As such, a comparison of different empirical models based on identical velocity data becomes possible. In addition, numericists can directly implement the published force fields in so as to perform computational studies of discharge-based flow control.

Addendum to ?velocity-information based force-term estimation of dielectric barrier discharge plasma actuators?

In a recent publication (Kriegseis et al 2013 J. Phys. D: Appl. Phys . 46 055202) we contrasted the variety of published strategies to estimate magnitude and distribution of the body force produced by dielectric barrier discharge plasma actuators. All approaches were applied to an identical set of velocity data, which was experimentally obtained by means of particle image velocimetry. Particularly, the determined force distributions of the above paper turned out to be beneficial for subsequent efforts to derive empirical plasma-actuator models. The purpose of this addendum, therefore, is to provide both the velocity data and the determined force distributions as discussed in the original publication. As such, a comparison of different empirical models based on identical velocity data becomes possible. In addition, numericists can directly implement the published force fields in so as to perform computational studies of discharge-based flow control.

Nanosecond-Resolved Discharge Processes Revealing Detailed Mechanisms of Nonequilibrium Atmospheric-Pressure Plasma Jet of Helium

Nanosecond-resolved photographs of the nonequilibrium atmospheric-pressure plasma jet of helium, generated with the conventional dielectric barrier discharge device, were obtained at different sections of the experimental setup and at different development stages of the discharges, showing that various distinct mechanisms are simultaneous in operation. The streamer from the outer edge of active electrode sitting at downstream side forms a jet in air, which only turns out to be hollow when approaching the orifice of the gas conduct. The streamer from the inner edge temporally lags behind, and it propagates along a helical path and initiates the glow discharge when arriving at the ground electrode. The electron deposit beneath the active electrode expands inward from both sides, displaying a soliton-like behavior; while the very compact ion deposit beneath the ground electrode, a typical ionic streamer, extends outward from the inner edge of the electrode. The velocities of the jet in air and of the streamer between electrodes are much larger than those at other parts of the device. The resolution of these particular processes and features can improve the implementation of this valuable cold plasma source.

Dielectric Barrier Discharge Processing of trans -CF 3 CH=CHF and CF 3 C(O)CF(CF 3 ) 2 , Their Mixtures with Air, N 2 , CO 2 and Analysis of Their Decomposition Products

Abstract The experimental study of the degradation of gaseous dielectrics after processing in the dielectric barrier discharge (DBD) is presented. Two pure gases trans-CF3CH=CHF (HFO-1234ze(E)), perfluoroketone CF3C(O)CF(CF3)2 (C5K), and also the following mixtures 75 %HFO-1234ze(E):25 %N2, 12 %C5K:88 %N2, 18.5 %C5K:81.5 %dry air, 9 %C5K:57.5 %HFO-1234ze(E):33.5 %N2, 9 %C5K:56 %HFO-1234ze(E):35 %CO2 have been used as test-gases. A content of the decomposition products of the gases before and after a 5-h workout in the barrier discharge has been determined by means of the chromatography-mass spectrometry and gas chromatography methods. Dilution of C5K with dry air greatly increases the degree of conversion of the source gas in the barrier discharge. Dilution of HFO-1234ze(E) and C5K with nitrogen, and the use of ternary mixtures 9 %C5K:57.5 %HFO-1234ze(E):33.5 %N2 and 9 %C5K:56 %HFO-1234ze(E):35 %CO2 significantly reduces the degree of conversion of the mixture compared with the source gases in the barrier discharge. After the DBD processing of two test-gases a large quantity of toxic C3F6 was found in pure C5K, and also a large number of highly toxic CF3CCH was found in pure HFO-1234ze(E). The least amount of toxic products after the DBD processing was detected in mixtures HFO-1234ze(E):N2 and C5K:HFO-1234ze(E):N2. The mixture C5K:HFO-1234ze(E):N2 has the best features among studied mixtures.

Nonlocal behavior of the excitation rate in highly collisional RF discharges

The present work focuses on the fundamental aspects of atmospheric pressure plasma electropositive discharges operated in the ohmically heated ##IMG## [http://ej.iop.org/images/0963-0252/24/4/044004/psst514481ieqn001.gif] {$\Omega$} mode, the electron heating and the excitation (ionization) rate. We find that the two do not necessarily have similar profiles and can show peaks at different locations, the ionization rate being much more sensitive to the electric field compared to the sensitivity to the electric field of the electron heating. This suggests an explanation for the discrepancies between the profiles of the power absorbed by electrons and the excitation patterns previously reported in the literature and observed in the present study. The excitation rate profile can then be explained by analyzing overlapping of the electron heating and the electric field profiles. Surprisingly, it has been discovered that the excitation dynamics exhibits nonlocal b...

The relation between the production efficiency of nitrogen atoms and the electrical characteristics of a dielectric barrier discharge

In a nitrogen plasma jet, atomic nitrogen is the longest lived radical species and, through recombination, gives rise to highly reactive excited nitrogen species. In this paper, the atomic nitrogen concentration in the effluent of a nitrogen-fed dielectric barrier discharge (DBD) is determined by using direct 2D imaging of the visible FPS emission. The relationship between radical production and the electrical characteristics of the discharge is assessed by making use of an electrical model which assumes only a part of the electrode area is discharged every half-cycle. For the pure nitrogen jet used here, the specific energy input per nitrogen atom is found to be 320  ±  20 eV atom −1 , comparable to the specific energy for other atomic nitrogen sources in the literature. It is shown that the production efficiency of atomic nitrogen does not depend on the amplitude of the applied voltage of the DBD and any increase in radical production is due to an increase of the elect...

Saffman-Taylor–like instability in a narrow gap induced by dielectric barrier discharge

Author(s): Shang-Yan Hou and Hong-Yu Chu

This work is inspired by the expansion of the plasma bubble in a narrow gap reported by Chu and Lee [Phys. Rev. Lett. 107, 225001 (2011)]. We report the unstable phenomena of the plasma-liquid interface with different curvature in a Hele-Shaw cell. Dielectric barrier discharge is produced in the cel…


[Phys. Rev. E 92, 013101] Published Wed Jul 01, 2015

Precise energy and temperature measurements in dielectric barrier discharges at atmospheric pressure

A specially designed dielectric barrier discharge (DBD) cell and associated equipment has been used to carry out precise measurements of electrical energy, ##IMG## [http://ej.iop.org/images/0963-0252/24/4/045004/psst514889ieqn001.gif] {${{E}_{\text{g}}}$} , dissipated per discharge cycle of the applied ac voltage, V a over the frequency range 5  ⩽   ##IMG## [http://ej.iop.org/images/0963-0252/24/4/045004/psst514889ieqn002.gif] {$f$}   ⩽  50 kHz. Twin pairs of several different dielectric materials (2.54 cm diameter discs, thicknesses = 2.0 or ca. 0.1 mm) with relative permittivities between 2.1  ⩽   ##IMG## [http://ej.iop.org/images/0963-0252/24/4/045004/psst514889ieqn003.gif] {$K{{'}^{{}}}$}   ⩽  9.5 were used as dielectric barriers in DBDs of four different gases: He, Ne, Ar and N 2 . Much of the work relates to the study of atmospheric pressure glow discharge (APGD) plasma in flowing He g...

Stabilisation of a three-dimensional boundary layer by base-flow manipulation using plasma actuators

The applicability of dielectric barrier discharge plasma actuators for controlling the crossflow-vortex-induced laminar breakdown in a three-dimensional swept-wing-type boundary-layer flow is investigated using direct numerical simulation. Similar to the classical application of suction at the wall the aim is to modify the quasi two-dimensional base flow and to weaken primary crossflow (CF) instability, mainly due to a reduction of the basic CF. Not only localised volumetric forcing by plasma actuators but also CF counter-blowing and spots with a moving wall are investigated to identify effective fundamental mechanisms. It is found that counter blowing always results in partial blockage of the flow and eventually increased CF velocity, whereas moving-wall spots can slightly reduce the CF and the amplitude of crossflow vortices. Using discrete volumetric forcing a significant attenuation even of finite-amplitude crossflow vortices and thus a distinct transition delay is achieved.

Atomic oxygen dynamics in an air dielectric barrier discharge: a combined diagnostic and modeling approach

Cold atmospheric pressure plasmas are a promising alternative therapy for treatment of chronic wounds, as they have already shown in clinical trials. In this study an air dielectric barrier discharge (DBD) developed for therapeutic use in dermatology is characterized with respect to the plasma produced reactive oxygen species, namely atomic oxygen and ozone, which are known to be of great importance to wound healing. To understand the plasma chemistry of the applied DBD, xenon-calibrated two-photon laser-induced fluorescence spectroscopy and optical absorption spectroscopy are applied. The measured spatial distributions are shown and compared to each other. A model of the afterglow chemistry based on optical emission spectroscopy is developed to cross-check the measurement results and obtain insight into the dynamics of the considered reactive oxygen species. The atomic oxygen density is found to be located mostly between the electrodes with a maximum density of ##IMG##

Temperature Controllable Atmospheric Plasma Source

An atmospheric pressure plasma source in which the gas temperature can be accurately controlled from below freezing point up to a high temperature has been developed. In general plasma devices, an electrical discharge is passed through a gas at about room temperature to generate plasma, so the plasma is at a temperature higher than room temperature; moreover, the gas temperature is determined by the discharge condition such as discharge power and plasma gas flow rate, so accurate temperature control is difficult. In the plasma source that has been developed in this research, the gas that is to be supplied to the discharge unit is first cooled using a gas cooler and then heated by a heater. The gas temperature of the produced plasma is measured, and feedback is sent to the heater. Thus, plasma at a desired temperature can be generated. Gas temperature control of the plasma over a range from −54 °C to +160 °C with a standard deviation of 1 °C was realized. Spectroscopic characteristics of generated plasma were investigated. This plasma source/technique will realize that effective plasma is applicable for heat-sensitive materials such as paper, textile, polymer, and especially human tissue. Furthermore, it enables us to generate the plasma at optimal gas temperature for chemical reaction of each plasma treatment.

Discharge Plasma Combined With Bauxite Residue for Biodiesel Exhaust Cleaning: A Case Study on NO<sub> x</sub> Removal

Experiments were conducted at laboratory level to treat the oxides of nitrogen (NOx) present in raw and dry biodiesel exhaust utilizing a combination of electric discharge plasma and bauxite residue, i.e., red mud, an industrial waste byproduct from the aluminum industry. In this paper, the adsorption and a possible catalytic property of bauxite residue are discussed. Nonthermal plasma was generated using dielectric barrier discharges initiated by ac/repetitive pulse energization. The effect of corona electrodes on the plasma generation was qualitatively studied through NOx cleaning. The plasma reactor and adsorbent reactors were connected in cascade while treating the exhaust. The diesel generator, running on biodiesel fuel, was electrically loaded to study the effectiveness of the cascade system in cleaning the exhaust. Interestingly, under the laboratory conditions studied, plasma–bauxite residue combination has shown good synergistic properties and enhanced the NOx removal up to about 90%. With proper scaling up, the suggested cascade system may become an economically feasible option to treat the exhaust in larger installations. The results were discussed emphasizing the role of bauxite residue as an adsorbent and as a room temperature catalyst.

The Configuration Effects of Electrode on the Performance of Dielectric Barrier Discharge Reactor for NO<sub> x</sub> Removal

In this paper, a dielectric barrier discharge cylindrical reactor has been analyzed in order to increase the efficiency of nitrogen oxide (NOx )removal from the simulated gas under the room temperature. The effects of electrode shape as well as electrode diameter and electrode length are investigated in the nonthermal plasma reactor. Two different electrode configurations (rod and screw thread electrodes) are examined. The experimental result shows that for the rod electrode, NOx removal efficiency is enhanced by increasing the electrode diameter. However, the screw thread electrode is more effective in decreasing NOx concentration. Finally, the results showed that the average input power requirement for NOx removal can be reduced almost 14% using a 1-mm screw thread electrode instead of a rod electrode.

Selective production of atomic oxygen by laser photolysis as a tool for studying the effect of atomic oxygen in plasma medicine

We propose a method for selectively producing O atoms by the laser photolysis of O ##IMG## [http://ej.iop.org/images/0022-3727/48/27/275201/d514654ieqn001.gif] {$_{3}$} as a tool for studying the therapeutic effect of O atoms in plasma medicine. A KrF excimer laser (248 nm) irradiates an O ##IMG## [http://ej.iop.org/images/0022-3727/48/27/275201/d514654ieqn002.gif] {$_{3}$} /He mixture flowing in a quartz tube to photodissociate O ##IMG## [http://ej.iop.org/images/0022-3727/48/27/275201/d514654ieqn003.gif] {$_{3}$} , which leads to the production of O atoms. The effluent from the quartz tube nozzle can be applied to a target (cells, bacteria, or an affected part). Simulations show that 500 ppm O atoms can be continuously supplied to a target surface at a distance of 3 mm from the quartz tube nozzle if an O ##IMG## [http://ej.iop.org/images/0022-3727/48/27/275201/d514654ieqn004.gif] {$_{3}$} (2000...

Uncertainty and error in complex plasma chemistry models

Chemistry models that include dozens of species and hundreds to thousands of reactions are common in low-temperature plasma physics. The rate constants used in such models are uncertain, because they are obtained from some combination of experiments and approximate theories. Since the predictions of these models are a function of the rate constants, these predictions must also be uncertain. However, systematic investigations of the influence of uncertain rate constants on model predictions are rare to non-existent. In this work we examine a particular chemistry model, for helium–oxygen plasmas. This chemistry is of topical interest because of its relevance to biomedical applications of atmospheric pressure plasmas. We trace the primary sources for every rate constant in the model, and hence associate an error bar (or equivalently, an uncertainty) with each. We then use a Monte Carlo procedure to quantify the uncertainty in predicted plasma species densities caused by the uncertai...

Formation of reactive oxygen and nitrogen species by repetitive negatively pulsed helium atmospheric pressure plasma jets propagating into humid air

Atmospheric pressure plasma jets have many beneficial effects in their use in surface treatment and, in particular, plasma medicine. One of these benefits is the controlled production of reactive oxygen and nitrogen species (RONS) in the active discharge through the molecular gases added to the primary noble gas in the input mixture, and through the interaction of reactive species in the plasma effluent with the ambient air. In this computational investigation, a parametric study was performed on the production of RONS in a multiply pulsed atmospheric pressure plasma jet sustained in a He/O 2 mixture and flowing into ambient humid air. The consequences of flow rate, O 2 fraction, voltage, and repetition rate on reactant densities after a single discharge pulse, after 30 pulses, and after the same total elapsed time were investigated. At the end of the first discharge pulse, voltage has the greatest influence on RONS production. However, the systematic trends f...

Propagation mechanisms of guided streamers in plasma jets: the influence of electronegativity of the surrounding gas

Atmospheric pressure plasma jets for biomedical applications are often sustained in He with small amounts of, for example, O 2 impurities and typically propagate into ambient air. The resulting poorly controlled generation of reactive species has motivated the use of gas shields to control the interaction of the plasma plume with the ambient gas. The use of different gases in the shield yields different behavior in the plasma plume. In this paper, we discuss results from experimental and computational investigations of He plasma jets having attaching and non-attaching gas shields. We found that negative ion formation in the He-air mixing region significantly affects the ionization wave dynamics and promotes the propagation of negative guided streamers through an electrostatic focusing mechanism. Results from standard and phase resolved optical emission spectroscopy ratios of emission from states of N 2 and He imply different electric fields in the plasma plume...

Gas purification by the plasma-oxidation of a rotating sacrificial electrode

A novel approach for the purification of inert gases by means of a dielectric barrier discharge (DBD) plasma has been demonstrated for argon and nitrogen. A rotating sacrificial electrode has been employed together with an electrode cleaning system to remove passivating product films during the plasma processing and thus enhance capacity and reaction rates. The purification of nitrogen using this approach was shown to be quite successful. The conditioning of technical argon yielded rotational temperatures well beyond 150 °C, thus being unable to remove the water content effectively.

Characterization of Physical, Mechanical and Chemical Properties of Quiscal Fibres: The Influence of Atmospheric DBD Plasma Treatment

Abstract This paper reports the first attempt of characterizing various physical, mechanical and chemical properties of Quiscal fibres, used by the native communities in Chile and investigating the influence of atmospheric dielectric barrier discharge plasma treatment on various properties such as diameter and linear density, fat, wax and impurity%, moisture regain, chemical elements and groups, thermal degradation, surface morphology, etc. According to the experimental observations, Quiscal fibre has lower tenacity than most of the technical grade natural fibres such as sisal, hemp, flax, etc., and plasma treatment at optimum dose improved its tenacity to the level of sisal fibres. Plasma treatment also reduced the amount of fat, wax and other foreign impurities present in Quiscal fibres as well as removed lignin and hemicellulose partially from the fibre structure. Plasma treatment led to functionalization of Quiscal fibre surface with chemical groups, as revealed from attenuated total reflection spectroscopy and also confirmed from the elemental analysis using energy dispersive X-ray technique and pH and conductivity measurements of fibre aqueous extract. The wetting behavior of Quiscal fibre also improved considerably through plasma treatment. However, untreated and plasma treated Quiscal fibres showed similar thermal degradation behavior, except the final degradation stage, in which plasma treated fibres showed higher stability and incomplete degradation unlike the untreated fibres. The experimental results suggested that the plasma treated Quiscal fibres, like other technical grade natural fibres, can find potential application as reinforcement of composite materials for various industrial applications.

The impingement of a kHz helium atmospheric pressure plasma jet on a dielectric surface

A parametric study of the impingement of a helium kHz atmospheric pressure plasma jet on a flat glass surface was performed by means of time-resolved intensified charge-coupled device imaging. The development of the plasma on the target is linked to the plasma evolution in the source and governed by the power supply. The glass surface takes part in the elongation of the plasma jet by the virtue of two mechanisms: the local enhancement of the electric field and the supply of pre-deposited charge. The evidence for the pre-deposited charge is the formation of a sheath on the glass surface, and the faint discharge formed on the glass surface during the negative voltage slope starting at the maximum of the negative current peak. The influence of the gas flow dynamics taking into account various gas flows, incident angles and distances is more important for the behaviour of the discharge on the surface than the voltage amplitude or the geometry of the source. The capacitance of the tar...

Characterization of atmospheric pressure plasma treated pure cashmere and wool/cashmere textiles: Treatment in air/water vapor mixture

Publication date: 15 September 2015 Source:Applied Surface Science, Volume 349 Author(s): Stefano Zanini , Elisa Grimoldi , Attilio Citterio , Claudia Riccardi We performed atmospheric pressure plasma treatments of pure cashmere and wool/cashmere textiles with a dielectric barrier discharge (DBD) in humid air (air/water vapor mixtures). Treatment parameters have been optimized in order to enhance the wettability of the fabrics without changing their bulk properties as well as their touch. A deep characterization has been performed to study the wettability, the surface morphologies, the chemical composition and the mechanical properties of the plasma treated textiles. The chemical properties of the plasma treated samples were investigated with attenuated total reflectance Fourier transform infrared (FTIR/ATR) spectroscopy and X-ray photoelectron microscopy (XPS). The analyses reveal a surface oxidation of the treated fabrics, which enhances their surface wettability. Morphological characterization of the treated fibers with scanning electron microscopy (SEM) reveals minor etching effects, an essential feature for the maintenance of the textile softness.

Plasma for cancer treatment

Plasma medicine is a relatively new field that grew from research in application of low-temperature (or cold) atmospheric plasmas in bioengineering. One of the most promising applications of cold atmospheric plasma (CAP) is cancer therapy. Convincing evidence of CAP selectivity towards the cancer cells has been accumulated. This review summarizes the state of the art of this emerging field, presenting various aspects of CAP application in cancer such as the role of reactive species (reactive oxygen and nitrogen), cell cycle modification, in vivo application, CAP interaction with cancer cells in conjunction with nanoparticles, and computational oncology applied to CAP.

Continuum emission-based electron diagnostics for atmospheric pressure plasmas and characteristics of nanosecond-pulsed argon plasma jets

Electron diagnostics based on electron–neutral atom (e–a) bremsstrahlung in the UV and visible range emitted from atmospheric pressure plasmas is presented. Since the spectral emissivity of the e–a bremsstrahlung is determined by electron density ( n e ) and mean electron temperature ( T e ) representing the Maxwellian electron energy distribution, their diagnostics is possible. As an example, emission spectra measured from capacitive discharges are presented, which show good agreement with the theoretically calculated emissivity of the e–a bremsstrahlung. For a single pin electrode nanosecond-pulsed plasma jet (n-PPJ) in argon, we investigate the electron properties and the temporal behavior of the positive streamers. Streamers with many branches are clearly observed inside the dielectric tube, while a few main streamers propagate outside the tube along the jet axis. A two-dimensional (2D) measurement of the time-averaged T e distri...

Surface modification of polyester synthetic leather with tetramethylsilane by atmospheric pressure plasma

Publication date: 15 August 2015 Source:Applied Surface Science, Volume 346 Author(s): C.W. Kan , C.H. Kwong , S.P. Ng Much works have been done on synthetic materials but scarcely on synthetic leather owing to its surface structures in terms of porosity and roughness. This paper examines the use of atmospheric pressure plasma (APP) treatment for improving the surface performance of polyester synthetic leather by use of a precursor, tetramethylsilane (TMS). Plasma deposition is regarded as an effective, simple and single-step method with low pollution. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) confirm the deposition of organosilanes on the sample's surface. The results showed that under a particular combination of treatment parameters, a hydrophobic surface was achieved on the APP treated sample with sessile drop static contact angle of 138°. The hydrophobic surface is stable without hydrophilic recovery 30 days after plasma treatment.

Electron density measurement in atmospheric pressure plasma jets: Stark broadening of hydrogenated and non-hydrogenated lines

Electron density is one of the key parameters in the physics of a gas discharge. In this contribution the application of the Stark broadening method to determine the electron density in low temperature atmospheric pressure plasma jets is discussed. An overview of the available theoretical Stark broadening calculations of hydrogenated and non-hydrogenated atomic lines is presented. The difficulty in the evaluation of the fine structure splitting of lines, which is important at low electron density, is analysed and recommendations on the applicability of the method for low ionization degree plasmas are given. Different emission line broadening mechanisms under atmospheric pressure conditions are discussed and an experimental line profile fitting procedure for the determination of the Stark broadening contribution is suggested. Available experimental data is carefully analysed for the Stark broadening of lines in plasma jets excited over a wide range of frequencies from dc to MW and...

Plasma Apparatuses for Biomedical Applications

Plasma-jet systems and plasma devices of dielectric barrier discharge (DBD) are introduced for biomedical applications. To achieve the purpose of being safe and user friendly, these devices have been developed to avoid electric shock and thermal damage. These types of plasma equipment operate with a sinusoidal voltage of kilovolts at a low frequency of several tens of kilohertz. The plasma jets have been developed with the specific ground-electrode structures according to the various gases in use, such as inert gases, molecular gases, or mixture gases, and air. The Ar-plasma jet with the external ground electrode is operated in a low current of 1–2 mA with the voltage of 1–2 kV. The stable air-jet plasma/plume exiting from a small hole at the cold metal-cap nozzle of the ground electrode can be obtained in a low current of 0.5–1 mA for safety with the voltage of 5–10 kV. Both types of ground electrode, the external electrode and the metal-cap electrode, are applicable to the plasma jets of molecular or mixture gases. The devices for DBD plasmas are shown to be the new advents of plasma stamp, plasma stick, plasma comb, and plasma roller, which operate with the voltage of 2–3 kV.

Robert Barker Memorial Session: Leadership in Plasma Science and Applications

This paper summarizes the Dr. Robert J. Barker memorial session at the IEEE International Conference on Plasma Science 2014. Each section summarizes progress in a plasma research area strongly influenced by Dr. Barker’s leadership: 1) plasma medicine; 2) atmospheric-pressure plasmas; 3) high-power microwaves; 4) pulsed power; and 5) numerical simulation of plasmas. He had a profound influence on these and other plasma science applications, as well as on numerous individual researchers. He will be missed greatly.

Transfer of a cold atmospheric pressure plasma jet through a long flexible plastic tube

This work proposes an experimental configuration for the generation of a cold atmospheric pressure plasma jet at the downstream end of a long flexible plastic tube. The device consists of a cylindrical dielectric chamber where an insulated metal rod that serves as high-voltage electrode is inserted. The chamber is connected to a long (up to 4 m) commercial flexible plastic tube, equipped with a thin floating Cu wire. The wire penetrates a few mm inside the discharge chamber, passes freely (with no special support) along the plastic tube and terminates a few millimeters before the tube end. The system is flushed with Ar and the dielectric barrier discharge (DBD) is ignited inside the dielectric chamber by a low frequency ac power supply. The gas flow is guided by the plastic tube while the metal wire, when in contact with the plasma inside the DBD reactor, acquires plasma potential. There is no discharge inside the plastic tube, however an Ar plasma jet can be extracted from the d...

A novel method of calculating the energy deposition curve of nanosecond pulsed surface dielectric barrier discharge

To obtain the energy deposition curve is very important in the fields to which nanosecond pulse dielectric barrier discharges (NPDBDs) are applied. It helps the understanding of the discharge physics and fast gas heating. In this paper, an equivalent circuit model, composed of three capacitances, is introduced and a method of calculating the energy deposition curve is proposed for a nanosecond pulse surface dielectric barrier discharge (NPSDBD) plasma actuator. The capacitance C d and the energy deposition curve E R are determined by mathematically proving that the mapping from C d to E R is bijective and numerically searching one C d that satisfies the requirement for E R to be a monotonically non-decreasing function. It is found that the value of capacitance C d varies with the amplitude of applied pulse voltage due to the change of discharge area and is depend...

Influence of applied voltage waveforms on the performance of surface dielectric barrier discharge reactor for decomposition of naphthalene

This paper is aimed at investigating the effect of applied voltage waveform on the surface dielectric barrier discharge (SDBD) in order to improve its capability in decomposing naphthalene in air. Five symmetric waveforms (sine, sinc, square, pulse and triangle) are used in this study in addition to two asymmetric waveforms (positive- and negative- ramp). The results show that the discharge activity is strongly affected by the applied voltage waveform, where the SDBD in case of the sine and triangle waveforms is more filamentary when compared with the other waveforms. Although the discharge period of the sine and triangle waveforms is high, the rms value of its current is lower than that in the case of the square and pulse waveforms. The SDBD reactor is more efficient to decompose the naphthalene when it operates in filamentary mode than that in diffuse-like mode. This is why the highest decomposition efficiency and energy efficiency are achieved in sine and triangle waveforms. F...

Quantitative schlieren diagnostics for the determination of ambient species density, gas temperature and calorimetric power of cold atmospheric plasma jets

A measurement and evaluation technique for performing quantitative Schlieren diagnostics on an argon-operated cold atmospheric plasma jet is presented. Combined with computational fluid dynamics simulations, the method not only yields the temporally averaged ambient air density and temperature in the effluent of the fully turbulent jet, but also allows for an estimation of the calorimetric power deposited by the plasma. The change of the refractive index due to mixing of argon and air is in the same range as caused by the temperature increase of less than 35 K in the effluent of the plasma jet. The Schlieren contrast therefore needs to be corrected for the contribution from ambient air diffusion. The Schlieren system can be calibrated accurately using the signal obtained from the argon flow when the plasma is turned off. The temperature measured in this way is compared to the value obtained using a fibre-optics temperature probe and shows excellent agreement. By fitting a h...

Hydrophobic–Hydrophilic Character of Hexamethyldisiloxane Films Polymerized by Atmospheric Pressure Plasma Jet

Abstract This paper reports on polymerization of hexamethyldisiloxane (HMDSO) using an atmospheric pressure dielectric barrier discharge plasma jet. The aim of the study is to contribute to the knowledge of thin film deposition using a low cost technique of atmospheric pressure plasma. The monomer HMDSO was used as a precursor for polymerization. The discharge was powered using a laboratory made resonant power supply working with sinusoidal voltage signal at a frequency of 8 kHz. The coatings were characterized using Fourier transform infrared spectroscopy, atomic force microscopy, growth rates and surface free energy measurements. The hydrophobic nature of the films was found to be decreased with increasing the plasma power. Fourier transform infrared spectroscopy gave an indication of the dominated inorganic content of the surface at higher discharge. An average growth rate of 220 nm min−1 was achieved at a monomer flow rate of 5 sccm and discharge power of 12.5 W. The films obtained using plasma jet were found to be stable in aqueous media and well adhered with substrate.

Gas temperature in transient CO 2 plasma measured by Raman scattering

Rotational Raman scattering on the vibrational ground state of CO 2 was performed to determine the gas temperature in narrow-gap dielectric barrier discharges (DBDs). The Raman spectrometer was equipped with a straightforward spectral filtering to mask ca. 30 cm −1 (0.85 nm) centered around the excitation wavelength of 532 nm. Linearisation of the observed transitions ( J = 18–42) was applied to retrieve gas temperatures in discharge gaps of 1 mm. The DBD was operated in pure CO 2 at atmospheric pressure and non-negligible gas heating of about 160 K was observed at 33 W injected power. Based on a simplified energy balance the gas temperature measurements were extrapolated to a broad range of injected plasma power values (0–60 W).

Surface roughening of ground fused silica processed by atmospheric inductively coupled plasma

Publication date: 30 June 2015 Source:Applied Surface Science, Volume 341 Author(s): Qiang Xin , Na Li , Jun Wang , Bo Wang , Guo Li , Fei Ding , Huiliang Jin Subsurface damage (SSD) is a defect that is inevitably induced during mechanical processes, such as grinding and polishing. This defect dramatically reduces the mechanical strength and the laser damage thresholds of optical elements. Compared with traditional mechanical machining, atmospheric pressure plasma processing (APPP) is a relatively novel technology that induces almost no SSD during the processing of silica-based optical materials. In this paper, a form of APPP, inductively coupled plasma (ICP), is used to process fused silica substrates with fluorocarbon precursor under atmospheric pressure. The surface morphology evolution of ICP-processed substrates was observed and characterized by confocal laser scanning microscope (CLSM), field emission scanning electron microscope (SEM), and atomic force microscopy (AFM). The results show that the roughness evolves with the etching depth, and the roughness evolution is a single-peaked curve. This curve results from the opening and the coalescing of surface cracks and fractures. The coalescence procedure of these microstructures was simulated with two common etched pits on a polished fused silica surface. Understanding the roughness evolution of plasma-processed surface might be helpful in optimizing the optical fabrication chain that contains APPP.

Inactivation of Shiga toxin-producing Escherichia coli O104:H4 using cold atmospheric pressure plasma

Publication date: September 2015 Source:Journal of Bioscience and Bioengineering, Volume 120, Issue 3 Author(s): Matthias Baier, Traute Janßen, Lothar H. Wieler, Jörg Ehlbeck, Dietrich Knorr, Oliver Schlüter From cultivation to the end of the post-harvest chain, heat-sensitive fresh produce is exposed to a variety of sources of pathogenic microorganisms. If contaminated, effective gentle means of sanitation are necessary to reduce bacterial pathogen load below their infective dose. The occurrence of rare or new serotypes raises the question of their tenacity to inactivation processes. In this study the antibacterial efficiency of cold plasma by an atmospheric pressure plasma-jet was examined against the Shiga toxin-producing outbreak strain Escherichia coli O104:H4. Argon was transformed into non-thermal plasma at a power input of 8 W and a gas flow of 5 L min−1. Basic tests were performed on polysaccharide gel discs, including the more common E. coli O157:H7 and non-pathogenic E. coli DSM 1116. At 5 mm treatment distance and 105 cfu cm−2 initial bacterial count, plasma reduced E. coli O104:H4 after 60 s by 4.6 ± 0.6 log, E. coli O157:H7 after 45 s by 4.5 ± 0.6 log, and E. coli DSM 1116 after 30 s by 4.4 ± 1.1 log. On the surface of corn salad leaves, gentle plasma application at 17 mm reduced 104 cfu cm−2 of E. coli O104:H4 by 3.3 ± 1.1 log after 2 min, whereas E. coli O157:H7 was inactivated by 3.2 ± 1.1 log after 60 s. In conclusion, plasma treatment has the potential to reduce pathogens such as E. coli O104:H4 on the surface of fresh produce. However, a serotype-specific adaptation of the process parameters is required.

Atmospheric Plasma Jet-Enhanced Anodization and Nanoparticle Synthesis

Atmospheric-pressure discharge in the tubular capillary plasma jet was studied to reveal the possibility to accelerate anodization of aluminum foils and fabricate alumina nanoparticles in liquid acids. Two different positions of the atmospheric pressure plasma jet relatively to the acid electrolyte and aluminum electrode were studied. Whereas at larger distances, only slight oxidation was obtained, the nanoporous surface and alumina nanoparticles were produced at closer (3–5 mm) distances. The mode with arcing (sparking) resulted in the film of alumina nanoparticles. The obtained results could be useful for the cheap and convenient synthesis of nanoparticles and nanostructured surfaces for various applications, including medical, biological, energy conversion, and nanoelectronic devices.

Characterization of a Cold Atmospheric Pressure Plasma Jet Device Driven by Nanosecond Voltage Pulses

The structure, fluid-dynamic behavior, temperature, and radiation emission of a cold atmospheric pressure plasma jet driven by high-voltage pulses with rise time and duration of a few nanoseconds have been investigated. Intensified charge-coupled device (iCCD) imaging revealed that the discharge starts when voltage values of 5–10 kV are reached on the rising front of the applied voltage pulse; the discharge then propagates downstream the source outlet with a velocity around $10^{7}$ – $10^{8}$ cm/s. Light emission was observed to increase and decrease periodically and repetitively during discharge propagation. The structure of the plasma plume presents a single front or either several branched subfronts, depending on the operating conditions; merging results of investigations by means of Schlieren and iCCD imaging suggests that branching of the discharge front occurs in spatial regions where the flow is turbulent. By means of optical emission spectroscopy, discharge emission was observed in the ultraviolet-visible (UV-VIS) spectral range (N2, N2+, OH, and NO emission bands); total UV irradiance was lower than 1 $mu $ W/ $mathrm{cm}^{2}$ even at short distances from the device outlet (<15 mm). Plasma plume temperature does not exceed 45 °C for all the tested operating conditions and values close to ambient temperature were measured around 10 mm downstream the source outlet.

Inactivation of Candida albicans by Cold Atmospheric Pressure Plasma Jet

Nonthermal atmospheric pressure plasma jets (APPJs) are characterized by very reactive chemistry without the need of elevated temperatures. Also, plasma jets are capable of producing cold plasma plumes that are not spatially confined by electrodes, which makes them very attractive for biomedical applications. In this paper, we investigate the antimicrobial efficiency of a simple plasma jet device operating with pure He as working gas. The device was driven by an ac power supply operated at 31.0 kHz, 13.0 kV amplitude with mean power around 1.8 W. The jet was directed perpendicularly on a standard Petri dish (Ø $90~{rm mm}times 15$ mm) filled with agar. The jet fungicidal efficiency was tested against Candida albicans (reference strains SC 5314 and ATCC 18804) and five clinical isolates from previously obtained denture stomatitis lesions. In this paper, the effects of treatment time and distance to the target were evaluated. In most treatments the samples did not have direct contact with the plasma plume; therefore, the reactive oxygen species produced by interaction between the plasma jet and ambient air were the principal inactivate agent.

Guest Editorial The Second Special Issue on Atmospheric Pressure Plasma Jets and Their Applications

It has been about two and a half years since the publication of the first IEEE Special Issue dedicated to the “Atmospheric Pressure Plasma Jets and Their Applications” in November 2012. Fig. 1 shows the publications on the atmospheric pressure plasma jet (APPJ) in the last decade from Web of Science. It clearly shows that this topic has been significantly grown in the past one decade and is still growing.

Nitrogen Shielding of an Argon Plasma Jet and Its Effects on Human Immune Cells

Atmospheric pressure plasmas are widely used in research for biomedical or clinical applications. Reactive oxygen species and reactive nitrogen species (RNS) produced by plasmas are thought to be of major significance in plasma-cell interactions. Different applications, however, may demand for different plasma properties. Tailoring plasma devices by modulating the supply gas or the surrounding is a suitable way to alter reactive species composition, vacuum ultra violet emission, or temperature. Treatment regimens involving availability of oxygen or humidity may lead to increased hydrogen peroxide deposition in liquids and thus will be toxic to cells. Using an atmospheric pressure argon plasma jet, we applied a nitrogen gas curtain to its visible effluent during treatment of human immune cells. The curtain deprived the plasma of molecular oxygen. This excluded gas-phase oxygen plasma chemistry and led to generation of highly energetic metastables. Planar laser-induced fluorescence spectroscopy verified laminar gas flow and complete elimination of surrounding air by the gas curtain. We used human immune cells to monitor cytotoxic effects as they are highly relevant in potential clinical plasma applications, e.g., treatment of chronic wounds. Air curtain plasma treatment led to significantly higher cytotoxicity compared with nitrogen curtain plasma treatment. Scavenging of hydrogen peroxide abrogated cell death in both gas curtain conditions. This indicated a negligible contribution of highly energetic metastables or increased gas temperature to cytotoxicity. Finally, the results suggested an oxygen-independent generation of hydrogen peroxide pointing to an indirect role of UV or RNS in plasma-mediated cytotoxicity.

Field-emitting Townsend regime of surface dielectric barrier discharges emerging at high pressure up to supercritical conditions

Surface dielectric barrier discharges (DBDs) in CO 2 from atmospheric pressure up to supercritical conditions generated using 10 kHz ac excitation are investigated experimentally. Using current–voltage and charge–voltage measurements, imaging, optical emission spectroscopy, and spontaneous Raman spectroscopy, we identify and characterize a field-emitting Townsend discharge regime that emerges above 0.7 MPa. An electrical model enables the calculation of the discharge-induced capacitances of the plasma and the dielectric, as well as the space-averaged values of the surface potential and the potential drop across the discharge. The space-averaged Laplacian field is accounted for in the circuit model by including the capacitance due to the fringe electric field from the electrode edge. The electrical characteristics are demonstrated to fit the description of atmospheric-pressure Townsend DBDs (Naudé et al 2005 J. Phys. D: Appl. Phys. [http://dx.doi.or...]

Deposition of ZnO Thin Films by an Atmospheric Pressure Plasma Jet-Assisted Process: The Selection of Precursors

The deposition ZnO thin films using an atmospheric pressure plasmas jet (APPJ)-assisted process using different precursors is presented. In this process, nebulized salt solutions droplets or precursor vapor were injected into the downstream of the APPJ to perform deposition of ZnO thin films. Zinc chloride (ZC)-, zinc acetate (ZA)-, and zinc nitrate (ZN)-containing solution and zinc acetylacetonate (ZAA) were precursors tested. For all precursors tested, formation of ZnO was observed based on X-ray diffraction analysis. ZC, however, was the only precursor that yields smooth films, which yields average transmittance in the visible wavelength range well >70%. When ZN, ZA, and ZAA were used as the precursors, rather rough films were obtained due to the fact that these precursors decomposed and formed ZnO readily upon heating. A high rate of volume nucleation, therefore, occurs in the gas phase. The above observation serves as the guideline for the selection of precursors for APPJ-assisted thin-film deposition processes.

Comparative Study of Pulsed Dielectric Barrier Discharges in Argon and Nitrogen at Atmospheric Pressure

In this paper, the mechanisms and characteristics of the pulsed dielectric barrier discharges in Ar and N2 at atmospheric pressure are analyzed and compared by means of numerical simulation based on the 1-D fluid model. Under different operating conditions, including gap width $d_{g}$ , dielectric thickness $d_{s}$ , and relative dielectric constant $varepsilon _{r}$ , the important characteristic quantities of describing the discharge, i.e., maximum discharge current density $J_{m}$ , averaged electron density $mathrm{N}_{e-mathrm {ave}}$ , and averaged dissipated power density $P_{mathrm {ave}}$ , are observed and studied in detail. This paper gives the following significant results. In Ar, the discharge occurs after the gap voltage has reached its maximum and is in the form of two short discharge current density pulses. In N2, the discharge starts from the increase of the gap voltage and presents the smooth development in a longer time being nearly equal to the pulsewidth. For the two gases, $J_{m}$ , $mathrm{N}_{e-mathrm {ave}}$ , and $P_{mathrm {ave}}$ decrease with the increase of $d_{!g}$ , and these characteristic quantities decrease with the increase of $d_{s}$ , or with the decrease of $varepsilon _{r}$ . In addition, the discharges in Ar maintain in the atmospheric pressure glow discharge (APGD), but the discharges in N2 operate in the varying discharge modes, including the APGD, the weak APGD, and the atmospheric pressure Townsend discharge. The development of the APGD in N2 requires the smaller gap width, the thinner dielectric thickness, and the larger relative dielectric constant.

Pulsed Atmospheric-Pressure DBD Plasma Produced in Small-Diameter Tubes

This paper presents the experimental results on the characterization of plasma produced in narrow tubes using a pulsed dielectric barrier discharge (DBD), working in helium or helium–oxygen gas mixture at atmospheric pressure, in a symmetrical configuration of external electrodes. This paper focuses on the effect induced by the total gas flow rate and gas composition on the characteristics of pulsed DBD. Using tunable diode laser absorption spectroscopy, ultraviolet absorption, and optical emission spectroscopy, complementary information on the reactive species (O, O3, N2, and N2+) present in the discharge has been obtained. It results that the excited species generated by direct electron excitation (as He and N2) follow the evolution of their precursors with increasing gas flow rate, while those created by chain reactions (as N2+, O, and O3) depend on the collective behavior of all their precursors, regardless of the fact that these are originating from the feeding gas or are coming from impurities. At specific energies, between 5 and 50 J/L, and a gas temperature of 315 ± 20 K, the atmospheric-pressure plasma is able to produce 1014−1015 m−3 of O (35S2) or (1.5− $2.8)times 10^{15}~{rm cm}^{-3}$ of O3, depending on the feeding gas composition and its flow rate. Low gas temperature and high density of reactive species could make the present DBD arrangement suitable for medical applications.

Numerical Study on Heat Flow During Catalytic Dissociation of Ozone in a Dielectric Barrier Discharge Ozonizer

A simple heat flow model is established for numerical analysis of the effect of catalytic dissociation of ozone on electrode surface temperature in a coaxial cylindrical-type dielectric barrier discharge ozonizer. The amount of heat consumed by the ozone decomposition at the electrode surface is determined from the balance of heat flow among the discharge gas, electrode, and cooling water. Our calculation using the experimental data shows that the ozone decomposition by 1.6% in total ozone reaching the electrode surface is required to explain the observed temperature decrease from about 20 °C to 8 °C for a stainless steel electrode, while that by 4.5% is needed to explain the temperature decrease from about 20 °C to 19 °C for a copper electrode. The decomposition rates calculated in the discharge are about two orders of magnitude higher than those measured in gas flow downstream of a similar discharge.

Mass spectrometric investigation of the ionic species in a dielectric barrier discharge operating in helium-water vapour mixtures

Using advanced mass spectrometry the chemistry of ionic species present in an atmospheric-pressure parallel plate dielectric barrier discharge (DBD) with a single dielectric on the powered electrode have been identified. The discharge was driven in helium with controllable concentrations of water vapour using an excitation frequency of 10 kHz and an applied voltage of 1.2 kV. Both negative and positive ions were identified and their relative intensity determined with variation of water concentration in the discharge, inter-electrode spacing, gas residence time and nominal applied power. The most abundant negative ions were of the family ##IMG## [http://ej.iop.org/images/0022-3727/48/8/085202/d508212ieqn001.gif] {$\text{O}{{\text{H}}^{-}}{{eft({{\text{H}}_{2}}\text{O}\right)}_{n}}$} , while the positive ions were dominated by those of the form ##IMG## [http://ej.iop.org/images/0022-372...] {${{\rm{H}}^ + }{{\rm{(}}{{\rm{H}}_2}{\rm{O)}}_n}$}

Time-resolved optical emission imaging of an atmospheric plasma jet for different electrode positions with a constant electrode gap

The aim of this paper is to determine the influence of the position of the electrodes on the range of a plasma jet, for specific experimental conditions, by using time-resolved optical emission spectroscopy. The optimal position of the electrodes is determined for a fixed gas flow rate and applied excitation voltage. We characterize the helium plasma jet for different distances from the end of the glass tube, showing detailed results for four different electrode positions from the jet nozzle (7, 15, 30 and 50 mm). It was found that at the distance of 15 mm, the length of the plasma jet is at its maximum. The highest speeds of the plasma package travelling outside the glass tube of the atmospheric plasma jet are obtained for the same electrode configuration (15 mm from the jet nozzle). With the electrodes positioned at smaller distances from the nozzle, the plasma plume was much shorter, and at the larger distances the plasma did not even leave the glass tube.

Optical and electrical characteristics of air dielectric barrier discharges in mode transition at atmospheric pressure

Atmospheric pressure dielectric barrier discharges (DBDs) have a wide range of industrial applications, generally exhibiting either filamentary or diffuse (i.e. glow) discharges. The focus of this investigation is on the formation mechanisms of the discharge current pulse width, on the order of tens of microseconds, accompanied by a light source formation, which is called a light source (LS) mode in air DBDs at atmospheric pressure. From a macroscopic point of view, the characteristics of the discharge current in the LS mode are similar with those of the glow mode. The optical and electrical characteristics of air DBDs at atmospheric pressure are investigated in the transition from the filamentary mode to the LS mode by measuring the optical emission spectroscopy and electrical signals. It is shown that in the manual increasing voltage stage, the vibrational temperature almost never changes and the gas temperature, electron temperature, dielectric capacitance, gas voltage ( V

Decomposition of Ethanethiol Using Dielectric Barrier Discharge Combined with 185 nm UV-Light Technique

Abstract The removal of gaseous ethanethiol (EtSH) via dielectric barrier discharge (DBD) combined with 185 nm UV-light energized by a DBD power supply has been investigated. EtSH removal efficiency and energy yield had been examined as a function of EtSH initial concentration, input power, gas flow rate and relative humidity of gas flow. The results showed that DBD combined with 185 nm UV-light could improve EtSH removal efficiency by about 10.4 % and increase energy yield by 0.4 g (kWh)−1 as compared with DBD treatment only. When increasing initial EtSH concentration and flow rate, a higher energy yield was obtained. And EtSH removal efficiency increased as the relative humidity increased to about 70 %, then decreased when the humidity continue to increase. Moreover, the possible reaction pathways were proposed based on the products identified by FT-IR.

Particle densities of the pulsed dielectric barrier discharges in nitrogen at atmospheric pressure

Pulsed dielectric barrier discharges (DBDs) have become a promising solution to generate atmospheric-pressure non-equilibrium plasmas. In this work, a one-dimensional fluid model is carried out to research particle densities of the pulsed nitrogen DBDs at atmospheric pressure. Averaged particle densities, time evolutions of axial distributions of particle densities and influences of discharge gap distance d g on the particle densities are systematically illustrated and discussed. The calculation results show that averaged electron densities are lower than averaged N 2 + densities, but higher than other averaged ion densities. Time evolutions of axial distributions of electron, N + and N 2 + densities show two peaks during rising and falling phases of applied voltage when d g is 0.2 cm but present gradual increases during pulse width when d g is 0.6 cm, which are similar to those o...

Frequency of collisions between ion and neutral particles from the cloning characteristics of filamentary currents in an atmospheric pressure helium plasma jet

In this paper, a cold He atmospheric pressure plasma jet that is generated using a dielectric barrier discharge configuration device is presented. This device is equipped with double-grounded ring electrodes that are driven by a sinusoidal excitation voltage. The properties of the cloning of filamentous current are studied. The frequency of the collisions between the ion and the neutral particles is calculated by measuring the current phase difference between the filamentous current and its corresponding clone. The frequency of the collisions between the ion and the neutral particles is of the order of 10 8 Hz.

Current-Mode Approach in Power Supplies for DBD Excilamps: Review of 4 Topologies

This document reviews the current-mode supply approach for dielectric barrier discharge (DBD) excilamps. It briefly demonstrates why this mode assures the control of the power injected into the DBD. Considerations with the step-up transformer required for the correct operation of the current-mode are developed. This document shows and compares four different converter topologies that comply with this principle. This comparison is made in terms of electric efficiency and luminous efficacy using experimental measurements.

Ferroelectric crystals for the low-voltage operation of surface dielectric barrier discharges

Dielectric barrier discharges (DBD) are commonly used to generate surface plasmas in atmospheric conditions due to their broad operational scope. Yet, high input voltages are typically required to breakdown atmospheric air. Ferroelectric crystals, however, can be used in place of dielectrics in order to reduce the driving voltage required to generate a DBD. Ferroelectrics are unique in that they have spontaneous polarizations that can be reversed by an applied electric field and also typically have very large relative permittivities. By using a ferroelectric with a large permittivity and small coercive fields, the applied voltage required to generate a discharge was reduced to <600 V in atmospheric air, and a visible glow and current filaments consistent with polarization switching were observed. Analysis of the discharge showed that the onset voltage follows a power law relation with its capacitance. Furthermore, poling the ferroelectric with a large DC voltage before use also reduced the onset voltage of the discharge.

Surface activation of polyethylene with an argon atmospheric pressure plasma jet: Influence of applied power and flow rate

Publication date: 15 February 2015 Source:Applied Surface Science, Volume 328 Author(s): A. Van Deynse , P. Cools , C. Leys , N. De Geyter , R. Morent Atmospheric pressure plasma technology offers attractive perspectives to alter the surface properties of polymers. Within this context, the surface modification of polyethylene (LDPE) by an argon atmospheric pressure plasma jet (APPJ) is profoundly investigated in this work. The influence of two different parameters (applied power and argon flow rate) on the plasma jet characteristics and the LDPE surface properties is examined in detail. In a first step, the APPJ is electrically and visually characterized and visual inspection of the afterglow clearly shows that mainly a variation in argon flow rate can result in a changing afterglow length. A maximum afterglow length is obtained at an argon flow rate of 1–1.25slm, while higher gas flows result in turbulence leading to a shorter afterglow. Secondly, the surface modification of LDPE is examined using different analyzing techniques namely water contact angle (WCA) measurements for the wettability, X-ray photoelectron spectroscopy (XPS) for the chemical composition and atomic force microscopy (AFM) for the surface morphology determination. WCA measurements show that by increasing the applied power the wettability of the LDPE increases. Increasing the argon flow rate up to 1.25slm gives a decrease in WCA value or in other words an increased wettability. From 1.25slm on, an increase in argon flow rate during plasma treatment decreases the LDPE wettability as can be concluded from the increased WCA values. An increased wettability can be explained by the incorporation of oxygen moieties. By increasing the discharge power, the concentrations of all oxygen containing groups such as CO, CO and OCO increase. Increasing the flow rate up to 1.25slm results mainly in an increase in OCO groups. However, from a flow rate of 1.25slm on, the concentration of all oxygen groups again decreases. Based on these results, the appropriate settings for an efficient plasma treatment can easily be selected.

Experimental Study and Kinetic Modeling for Ethanol Treatment by Air Dielectric Barrier Discharges

Abstract This paper deals with the ethanol (EtOH) removal in both dry and humid air fed dielectric barrier discharges. The experimental results were compared to the predictions of a zero dimension kinetic model to elucidate the main chemical routes occurring in the plasma phase. This comparison shows that both the dissociative quenching of the nitrogen metastables and the oxidation reactions by the oxygen atom or the hydroxyl radical should be taken into account to explain the EtOH abatement in these kinds of discharges. The CH3CHOH radical seems to be the main product of the nitrogen dissociative collisions, whereas radicals issued from the α- and β-H atom cleavage are the dominant ethanol oxidation by-products. These radicals account for the production of acetaldehyde, the main by-product of the ethanol/air fed discharges investigated here. Apart the complete oxidation products, i.e. carbon oxides and water, aldehydes containing up to six carbon atoms, ketones, carboxylic acids, ozone, nitrogen oxides, nitric acid and organic nitrates were found in the exhaust gas. A kinetic pathway is proposed to explain the formation of the detected by-products. Water vapour addition to the feeding gas slightly improves the EtOH removal and promotes further oxidation of the main by-products, thus enhancing the CO2 selectivity. This behaviour could be ascribed to the higher amount of hydroxyl radicals, which could boost the production of the direct precursors of CO2.

Investigating antennas as ignition aid for automotive HID lamps

This paper considers the ignition of mercury-free high-intensity discharge (HID) lamps for car headlights. Due to safety reasons, these lamps need to have a fast run-up phase which is ensured, amongst other things, by a high Xe pressure of roughly 15 bar (cold) in the discharge vessel. The high Xe pressure causes an increased ignition voltage compared with former mercury-containing automotive HID lamps or low-pressure lamps used for general-lighting applications. The increase in ignition voltage can be limited if the electric field in front of the electrodes is raised by an uplifting of the electrical conductivity along the outer wall of the inner bulb either by a conductive layer on its surface or by a dielectric barrier discharge (DBD) within the outer bulb. This paper considers on the one hand conventional antennas deposited by physical vapour deposition (PVD) and on the other hand a combination of these antennas with a DBD within the outer-bulb operated in 100 mbar Ar a...

Properties of Soil Treated With Ozone Generated by Surface Discharge

Chemical contamination in plants, soil, and ground water has become serious by overuse of pesticides and nitrogen fertilizers in agriculture. We propose the use of ozone generated by atmospheric pressure plasma for soil disinfection as one of the plasma applications into agriculture. Because ozone has strong oxidation potential to decompose organic substances in soil, it is considered to be one of the candidates as potential alternative to both pesticide and nitrogen fertilizer. In this paper, fundamental studies on changes in acidity and amounts of nitrogen nutrients, bacteria, mold, and soil DNA remained in soil after ozone treatment were carried out with a system using a quartz chamber. Surface barrier discharge that operates in atmospheric oxygen was used in the system as the ozone generator. In addition, growth of radishes that seeded on soils in pots that were treated by ozone diffusion method was also evaluated.

Hydrogen Production From Hydrocarbons With Use of Plasma Discharges Under High Pressure Condition

New H2 production system from hydrocarbons is under development that uses plasma discharges working in high pressure condition over 1.5 atm. Here methane and propane are tried at present. This system is objected to be installed on the moving vehicles and the produced H2 gas is directly supplied to the fuel cell on the vehicle. The hydrocarbons can be easily compressed into liquid state for storing in the conveyable tank, while H2 gas requires a lot of extra energy for compression. For those purposes three kinds of plasma discharge methods are tried: 1) corona discharge plasma system; 2) dielectric barrier discharge nonthermal plasma system; and 3) nonthermal plasma reactor filled with dielectric pellet catalysts. Clear decompositions of hydrocarbons to produce H2 gas have been observed without COx. Decomposed carbon powder is attached fully on the electrodes and no contamination on the chamber wall is observed.

Lithium Electrochemical and Electrochromic Properties of Atmospheric Pressure Plasma Jet-Synthesized Tungsten/Molybdenum Mixed Oxide Films for Flexible Electrochromic Devices

Lithium electrochemical and electrochromic (EC) performances of flexible tungsten/molybdenum mixed oxide (WMoxOyCz) films, deposited onto 40- $Omega $ /square flexible polyethylene terephthalate/indium tin oxide substrates at room temperature ( $sim 23$ °C) and at the short exposed durations of 19–26 s using an atmospheric-pressure plasma-enhanced chemical vapor deposition with an atmospheric pressure plasma jet (APPJ) at various precursor injection angles, are investigated. The flexible organo-tungsten–molybdenum oxide (WMoxOyCz) films have been identified for the remarkable EC performance for 200 cycles of reversible Li+ ion intercalation and deintercalation in a 1-M LiClO4-propylene carbonate electrolyte by a potential sweep switching measurement between −1 and 1 V at a scan rate of 50 mV/s, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The optical modulation ( $Delta T)$ is up to of 75.6% at a wavelength of 691.9 nm for WMoxOyCz films cosynthesized with an APPJ.

Novel Atmospheric Pressure Plasma Utilizing Symmetric Dielectric Barrier Discharge for Mass Spectrometry Applications

This paper develops a novel symmetric dielectric barrier discharge (DBD) plasma as an ion source for environmental mass spectrometry (MS) applications. The conventional linear-type DBD plasma generator suffers the drawback of floating voltage at the plasma outlet. This paper develops an innovative symmetric T-shaped DBD plasma generator to produce atmospheric plasma with zero-floating potential for high-sensitivity MS analysis. By changing the geometric configuration and the drive phase of the symmetric T-shaped DBD plasma generator, the resulting symmetric structural design can fully cancel the floating potential and noise signal. Therefore, the main objective of this paper is to compare the differences between traditional linear-type DBD and the symmetric T-shaped DBD designs using MS, spectroscopy, and some basic electrical measurements. The most suitable parameters are determined by changing the electrode design, voltage, temperature, gas flow rate, diameter, and other parameters of the plasma tube. The symmetric T-shaped design generator produces the zero-potential plasma that generates fewer ambient gas molecules to form ozone, NOx, water clusters, and other strong oxidizing molecules such that less damage to the MS samples occurs. This in turn results in a less fragmented ion signal and higher sensing performance for rapid MS applications. In addition, the proposed system can directly ionize gas, liquid, and solid samples at more than $10^{7}$ -cm $^{-3}$ ion concentration. Results show that more information-rich spectra can be obtained with the developed symmetric T-shaped DBD plasma generator compared with the typical linear-type DBD generator.

Plasma Medical Science for Cancer Therapy: Toward Cancer Therapy Using Nonthermal Atmospheric Pressure Plasma

We have been developing novel ultrahigh density atmospheric pressure plasma sources and succeeded in the selective killing ovarian cancer cells against normal ones. Furthermore, we have found out the plasma-activated medium (PAM) also killed glioblastoma brain tumor cells selectively against normal ones and the chemical products in the PAM have long lifetime healing effects. To clarify the mechanism, interactions of plasma with the organism and the medium where the organism belongs were investigated on the viewpoint of intracellular molecular mechanism.

Efficient Production of Hydrogen by DBD Type Plasma Discharges

A hydrogen production system using plasma discharges working in high pressure condition over 1.5 atm is under development. The original fuel for the system is hydrocarbons, such as methane or propane. For those purposes, mainly a dielectric barrier discharge nonthermal plasma system is employed. High efficient decompositions of hydrocarbons have been observed to produce hydrogen gas without COx. The production rate of hydrogen from methane or propane increases linearly with input energy for decomposition. This rate also has dependence on electrode temperature; higher temperature shows better decomposition rate. Decomposed carbon powder is attached fully on the electrodes without contamination on the surrounding vacuum chamber wall.

Direct Measurement of Metal Surface Temperature During Catalytic Dissociation of Ozone for Sensor Application

Temperature variation of a catalytic metal surface exposed to ozone produced in an atmospheric-pressure dielectric barrier discharge is examined by using a very thin thermocouple. The metal sheet is heated initially to a certain temperature ( $T_{1})$ using a resistive heater and, then, the ozone concentration is increased with the heater current unchanged. When $T_{1}$ is room temperature, the temperature of the metal sheet remains almost constant independent of ozone concentration. When $T_{1}$ is increased up to 80 °C, the temperature of the metal sheet decreases clearly with increasing ozone concentration due to enhanced catalytic dissociation of ozone at the metal surface. The rate of decrease in temperature for a stainless steel sheet is increased from nearly 0% to $sim 5.7$ % with increasing $T_{1}$ from room temperature to 80 °C, while that for a platinum sheet is increased further to $sim 17.5$ % at 80 °C due to stronger catalytic activity of platinum. The results confirm that the sensitivity for ozone is improved with a stronger catalytic metal heated to a higher temperature as the sensor body.

Dry Reforming of CH<sub>4</sub> With CO<sub>2</sub> to Generate Syngas by Combined Plasma Catalysis

The hybrid plasma catalysis system was investigated for dry reforming of methane (DRM) with CO2 to form syngas. First, dielectric barrier discharge (DBD) alone was evaluated for the effectiveness in conversion of CO2 and CH4, and with the applied voltage of 15.0–19.5 kV, and frequency of 200 Hz. The ratio of feeding gas (CH4/CO2) and total gas flow rate were controlled at 1 and 40 mL/min, respectively. The results indicate that conversions of CO2 and CH4 significantly increase with increasing applied voltage. The conversion of both greenhouse gases (CO2 and CH4) achieved the maximum value of 18.9% and 24.0%, respectively, at applied voltage of 19.5 kV. Selectivity of CO decreases from 53.6% to 42.4% as applied voltage is increased from 15.0 to 19.5 kV, while selectivity of H2 increases from 30.1% to 35.8%. In addition, the influences of gas flow rate and ratio of feeding gas were also explored for DBD-alone system, and the results indicate that energy efficiency of syngas generation can be significantly increased as the flow rate is increased. As a catalyst with a high dielectric constant is placed into the discharge zone, the conversions of two gases (CO2 and CH4) reach 27.3% and 31.2%, respectively, at applied voltage of 19.5 kV. Selectivity of CO decreases from 59.4% to 49.6% as applied voltage is increased from 15 to 19.5 kV, while selectivity of H2 increases from 32.0% to 38.3%. In the meantime, energy efficiency of syngas generation is increased by 0.3%. Overall, this paper indicates that combining DBD with a catalyst of high dielectric constant is a viable process for DRM.

Hydrophilic Stability of Plastic Surfaces Treated in Low- and Atmospheric-Pressure Radio-Frequency Plasmas

An atmospheric-pressure radio-frequency (RF) corona torch plasma and a low-pressure parallel-plate RF plasma are employed to increase hydrophilicity of polycarbonate and acrylonitrile butadiene styrene surfaces. The contact angle of water for the plastic surfaces is decreased by Ar plasma treatment in any condition, while the surface roughness is decreased, too, unexpectedly. The rate of decrease in contact angle versus treatment time in the atmospheric pressure plasma is about an order of magnitude higher than that in the low-pressure plasma. During postexposure of the plastic surfaces to ambient air, the contact angle is recovered gradually and saturated at a certain value depending on plasma treatment time. A longer plasma treatment time causes less recovery in contact angle. The results indicate that surface roughening as well as surface functionalization is responsible for improving the recovery characteristic and, hence, the hydrophilic stability.

The influence of partial surface discharging on the electrical characterization of DBDs

The determination of internal electrical discharge parameters, such as plasma current and burning voltage, in dielectric barrier discharges (DBDs) relies on an equivalent circuit based on series capacitances for the discharge gap and dielectric material. An effective dielectric capacitance for the discharge can be obtained from Q – V diagrams, also called Lissajous figures, during discharging, which may not be a constant for a given DBD geometry. It has been shown experimentally that microdischarges, which can consist of narrow channels in either diffuse or filamentary form, may not fully cover the available discharge area. Here, we report measurements of the effective dielectric capacitance as a function of applied voltage amplitude in a DBD plasma jet system operating in N 2 and derive equations to determine the conductively transferred charge, burning voltage and the proportion of the electrode surface over which discharging occurs when the effective diel...

Controlling plasma stimulated media in cancer treatment application

Cold atmospheric plasma (CAP) constitutes a “cocktail” of various reactive species. Accumulating evidence shows the effectiveness of CAP in killing cancer cells and decreasing the tumor size, which provides a solid basis for its potential use in cancer treatment. Currently, CAP is mainly used to directly treat cancer cells and trigger the death of cancer cells via apoptosis or necrosis. By altering the concentration of fetal bovine serum in Dulbecco's modified Eagle's medium and the temperature to store CAP stimulated media, we demonstrated controllable strategies to harness the stimulated media to kill glioblastoma cells in vitro. This study demonstrated the significant role of media in killing cancer cells via the CAP treatment.

Enhanced Adhesion Properties, Structure and Sintering Mechanism of Hydroxyapatite Coatings Obtained by Plasma Jet Deposition

Abstract Hydroxyapatite (HA) coatings were deposited on high purity titanium substrate by atmospheric plasma spraying (APS) with high electric energy input. Previously, the surface of the titanium was prepared by alkali etching with NaOH and subsequent diverse thermal treatments. The phase composition, structure and morphology of the nano-structured HA coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The XRD pattern showed that the coatings deposited by APS consisted mainly of HA with crystallite sizes between 15.5 and 31 nm and small quantities of the amorphous HA phase. The SEM observation showed that the as-deposited coatings had very different morphology with typical features of micro-structural patterns, which are desirable for improving the biological performances of HA coatings. AES analysis of various spots of the titanium substrate-coating interface showed the presence of an oxide layer with implanted Ca ions owing to the high kinetic energy of the plasma jet. This layer caused a significant increase in the measured adhesive strength, showing values in the range of 51.8–62.5 MPa. The sintering mechanism was studied using several approaches that show that the dominant sintering mechanism was volume diffusion.

Atmospheric pressure plasma enhanced spatial ALD of silver

The authors have investigated the growth of thin silver films using a unique combination of atmospheric process elements: spatial atomic layer deposition and an atmospheric pressure surface dielectric barrier discharge plasma source. Silver films were grown on top of Si substrates with good purity as revealed by resistivity values as low as 18 μΩ cm and C- and F-levels below detection limits of energy dispersive x-ray analysis. The growth of the silver films starts through the nucleation of islands that subsequently coalesce. The authors show that the surface island morphology is dependent on surface diffusion, which can be controlled by temperature within the deposition temperature range of 100–120 °C.

Editorial

In recent years basic research in plasma medicine led to two fundamental insights about mechanisms of plasma effects on biological systems: Biological plasma effects are significantly caused by plasma induced changes of the liquid environment of cells.

Plasma-assisted conversion of CO 2 in a dielectric barrier discharge reactor: understanding the effect of packing materials

A cylindrical dielectric barrier discharge (DBD) reactor has been developed for the conversion of undiluted CO 2 into CO and O 2 at atmospheric pressure and low temperatures. Both the physical and chemical effects on reaction performance have been investigated for the addition of BaTiO 3 and glass beads into the discharge gap. The presence of these packing materials in the DBD reactor changes the physical characteristics of the discharge and leads to a shift of the discharge mode from a typical filamentary discharge with no packing to a combination of filamentary discharge and surface discharge with packing. Highest CO 2 conversion and energy efficiency are achieved when the BaTiO 3 beads are fully packed into the discharge gap. It is found that adding the BaTiO 3 beads into the plasma system enhances the average electric field and mean electron energy of the CO 2 discharge by a factor of two, which significant...

Oxy-nitroso shielding burst model of cold atmospheric plasma therapeutics

Abstract: It is postulated that cold atmospheric plasma (CAP) can trigger a therapeutic shielding response in tissue by creating a time- and space-localized, burst-like form of oxy-nitrosative stress on near-surface exposed cells through the flux of plasma-generated reactive oxygen and nitrogen species (RONS). RONS-exposed surface layers of cells communicate to the deeper levels of tissue via a form of the ‘bystander effect,’ similar to responses to other forms of cell stress. In this proposed model of CAP therapeutics, the plasma stimulates a cellular survival mechanism through which aerobic organisms shield themselves from infection and other challenges.

Surface Treatment of Polyimide Substrates Using Dielectric Barrier Discharge Reactors Based on L-Shaped Electrodes

Abstract Two dielectric barrier discharge reactors, based on L-shaped electrodes, were designed and fabricated for in-line surface treatment of polyimide (PI) substrates. Under homogeneous discharge mode, their surface treatment performance was evaluated in terms of water contact angles (WCAs) of PI film. Hydrophilicity of polymer films arises from the grafting of functional groups onto the polymer’s surface by O and N radicals. In our reactor, ambient air could be entrained into the discharge region, such that the WCA of PI film was effectively lowered without adding O2 or N2 gas. The PI film WCA decreased with increased applied voltage or with decreased motion speed of the substrate. A serial connection of the electrode lowered the WCA, whereas O2 addition only weakly affected the PI film hydrophilicity. The mechanisms underlying these phenomena were analyzed using the discharge current, the temporal and time-averaged discharge images, and the optical emission profiles.

Noise control of subsonic cavity flows using plasma actuated receptive channels

We introduce a passive receptive rectangular channel at the trailing edge of an open rectangular cavity to reduce the acoustic tones generated due to coherent shear layer impingement. The channel is numerically tested at Mach 0.3 using an unsteady three-dimensional large eddy simulation. Results show reduction in pressure fluctuations in the cavity due to which sound pressure levels are suppressed. Two linear dielectric barrier discharge plasma actuators are placed inside the channel to enhance the flow through it. Specifically, acoustic suppression of 7 dB was obtained for Mach 0.3 flow with the plasma actuated channel. Also, the drag coefficient for the cavity reduced by over three folds for the channel and over eight folds for the plasma actuated channel. Such a channel can be useful in noise and drag reduction for various applications, including weapons bay, landing gear and branched piping systems.

Atomic nitrogen: a parameter study of a micro-scale atmospheric pressure plasma jet by means of molecular beam mass spectrometry

Absolute atomic nitrogen densities (N) in the effluent of a micro-scale atmospheric pressure plasma jet ( µ -APPJ) operated in He with small admixtures of molecular nitrogen (N 2 ) are measured by means of molecular beam mass spectrometry. Focusing on changes of the external plasma parameters, the dependency of the atomic nitrogen density on the admixture of molecular nitrogen to the plasma, the variation of applied electrode voltage and the variation of distance between the jet nozzle and the sampling orifice of the mass spectrometer are analysed. When varying the N 2 admixture, a maximum density of atomic nitrogen of approximately 1.5  ×  10 14  cm −3 (~6 ppm) is reached at about 0.25% N 2 admixture. Moreover, the N density increases approximately linearly with the applied voltage. Both results are comparable to atomic oxygen (O) behaviour of the µ -APPJ operated at equal plasma conditions except for admixing molecular ...

Two-dimensional LIF measurements of humidity and OH density resulting from evaporated water from a wet surface in plasma for medical use

In plasma medicine, plasma is applied to a wet surface and is often accompanied by dry-gas flow. The dry-gas flow affects water evaporation from the wet surface and influences production of reactive species derived from water vapor, such as OH radicals. In this study, the effect of the dry-gas flow on two-dimensional distributions of humidity and OH radical density are examined by measuring them using laser-induced fluorescence (LIF). First, humidity is measured when nitrogen flows from a quartz tube of 4?mm inner diameter onto distilled water and agar media from 5?mm distance. NO gas is added to the nitrogen as a tracer and humidity is obtained from the quenching rate of NO molecules measured using LIF. This measurement has a spatial resolution of 0.2?mm 3 and a temporal resolution of less than 220?ns. The two-dimensional humidity distribution shows that the dry-gas flow pushes away water vapor evaporating from the wet surface. As a result, a low-humidity region is for...

An electric field in nanosecond surface dielectric barrier discharge at different polarities of the high voltage pulse: spectroscopy measurements and numerical modeling

The ratio of emission intensities of the second positive N 2 (C 3 Π u , v ′ = 0) → N 2 (B 3 Π g , v  = 0), 337.1 nm and first negative ##IMG## [http://ej.iop.org/images/0022-3727/47/48/485201/d503781ieqn001.gif] {$\text{N}_{2}^{+}$} (B ##IMG## [http://ej.iop.org/images/0022-3727/47/48/485201/d503781ieqn002.gif] {$^{2}\Sigma_{g}^{+},v\prime =0)$} → ##IMG## [http://ej.iop.org/images/0022-3727/47/48/485201/d503781ieqn003.gif] {$\text{N}_{2}^{+}$} (X ##IMG## [http://ej.iop.org/images/0022-3727/47/48/485201/d503781ieqn004.gif] {$^{2}\Sigma_{g}^{+},v=0)$} , 391.4 nm systems of nitrogen have been measured in a nanosecond surface dielectric barrier discharge (SDBD). The measurements were carried out in synthetic air for a pressure range 1–3 bar for different polarities of the high-voltage (HV) pulse. For all...

Investigation of Preionization Effects in Atmospheric Pulsed Discharge

Preionization for atmospheric pressure discharge plasma has been employed in several pulse gas lasers, while dielectric barrier discharge has often been utilized for ozone generators. A single ozone-generating device combining both preionization discharge and dielectric barrier discharge is investigated in this paper. The preionizing electrode configuration consisted of a wire-dielectric-plate with a 1.5-mm-thick aluminum oxide (Al2O3) barrier with relative permittivity $varepsilon _{mathit {r}}$ of about 10. Wire electrodes (0.8-mm diameter) and plate electrodes were all made of stainless steel. A barrier discharge was generated by applying a pulse voltage between the plate electrode and the wire electrodes across the dielectric, which was served as a preionizer. The main discharge was produced immediately after preionization by applying a high-voltage pulse between the wire-plate electrodes with a gap distance of 10 mm. This paper examines the temporal and spatial evolution of the discharge with and without preionization. Results from a high-speed framing camera indicate that preionization increases the volume of the main discharge, resulting in a streamer-like discharge system with preionization, which is an effective method for ozone generation.

Toluene Decomposition by a Two-stage Hybrid Plasma Catalyst System in Dry Air

This paper presents a two-stage hybrid plasma catalyst system for toluene decomposition in dry air. It consists of a dielectric barrier discharge reactor and a homemade Co–Mn catalyst bed reactor. At room temperature and under a bed gas hourly space velocity of up to 32 233 h $^{mathrm {-1}}$ , the decomposition efficiency is about 92.4% when plasma specific energy density is around 100 J/L. With increasing the catalyst bed temperature to about 350 K, almost 100% of the toluene and the plasma generated O3 are decomposed simultaneously. The Fourier transform infrared spectra show that the major reaction byproducts are CO2. By means of X-ray powder diffraction, X-ray photoelectron spectroscopy, and N2 physisorption diagnostics, we conclude that both Co3Mn3O4 and the lattice oxygen species play an important role in simultaneous toluene decomposition and ozone utilization.

Propagation of Plasma Diffusion Wave According to the Voltage Polarity in the Atmospheric Pressure Plasma Jet Columns

Propagation of optical signals measured along the atmospheric plasma-jet column according to the operational voltage polarity is analyzed with the electrostatic plasma-diffusion wave in terms of the characteristic speeds of plasma fluids, such as the plasma drift (u_{d}) , the gas flow (u_{b}) , and the plasma diffusion (u_{n}) . For the positive voltage, the ion wave propagates with the wave-packet velocity of (u_{rm g} sim c_{s}^{2}/u_{n}) , where (c_{s}) is the acoustic velocity along the whole column of plasma jet without any restrictions. The electron wave propagates backward with the group velocity of electron drift with (u_{rm g} sim -u_{ed}) toward the high voltage electrode right after passing of the frontline of ion wave-packet. For the negative voltage, the ion wave propagates on the high ionization column with the wave-packet velocity of (u_{rm g} sim c_{s}^{2}/u_{n}) . The electron wave propagates forward while its propagation mode varies from the group velocity of (u_{rm g} sim c_{s}^{2}/u_{n}) on a region of high electric field to the velocity of electron drift with (u_{rm g} sim +u_{ed}) on a low field region.

Simulation of the effect of plasma species on tumor growth and apoptosis

Tumor modeling is a technique that entails using mathematical and physical equations to describe the biological disease, most importantly uncontrolled cell growth and the tumor life cycle. The model utilized in this paper makes use of a three-dimensional hybrid discrete–continuum model to show the apoptotic effect a tumor volume undergoes when treated with reactive oxygen and nitrogen species from the cold atmospheric plasma. The results compare untreated and treated tumors of varying sizes by measuring spatiotemporal data to predict trends of tumor evolution. The simulation results show that the treated tumor death, irrespective of tumor volume, follows an exponential decay and that the untreated tumor follows an expected growth pattern. Future experiments and applications can lead to a predictive tumor model allowing for individualized treatment planning for the cold atmospheric plasma therapy.

Atmospheric pressure plasma jets interacting with liquid covered tissue: touching and not-touching the liquid

In the use of atmospheric pressure plasma jets in biological applications, the plasma-produced charged and neutral species in the plume of the jet often interact with a thin layer of liquid covering the tissue being treated. The plasma-produced reactivity must then penetrate through the liquid layer to reach the tissue. In this computational investigation, a plasma jet created by a single discharge pulse at three different voltages was directed onto a 200  µ m water layer covering tissue followed by a 10 s afterglow. The magnitude of the voltage and its pulse length determined if the ionization wave producing the plasma plume reached the surface of the liquid. When the ionization wave touches the surface, significantly more charged species were created in the water layer with H 3 O + aq , O 3 − aq , and O 2 − aq being the dominant terminal species. More aqueous OH aq , H 2

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...