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The interest in the use of atmospheric-pressure plasma jets (APPJs) is constantly growing. APPJs offer various ranges for applications, such as wound healing, cancer treatment, and dental care. The complex plasma chemistry plays an important role in each of these fields but is often poorly understood. In this paper, the production of atomic oxygen in a radio frequency helium–oxygen plasma is investigated by means of a numerical simulation. A 1-D discharge of an atmospheric-pressure plasma jet is created with the plasma module of COMSOL Multiphysics, using a set of 25 reactions. Many 1-D simulations usually cannot estimate the power deposition in a correct way because of suspected arising losses, such as radiation and inefficiencies of the external circuit. In order to match the experimental power deposition of 13 W, high voltages (855 V) are required in the model. Such high voltages cause changes in the plasma characteristics like a switch in the glow mode. The impact of the voltage on the plasma is investigated by the comparison of a low-voltage (325 V) simulation, which matches the experimental oxygen production, and a high-voltage (855 V) simulation, which matches the experimental power deposition. Outcomes of this paper further support the idea that the power deposition measured in experiments is higher than the actual power deposition coupled to the plasma. [ABSTRACT FROM AUTHOR]

This paper embodies the results of experimental studies of a dielectric barrier discharge low-temperature nonequilibrium plasma reactor that runs in air and nitrogen at atmospheric-pressure conceived for surface treatment applications. A homemade reactor, of typical plane-to-plane geometry with the dielectric covering the upper electrode which is stressed by a high voltage (40 kV, 3–20 kHz) is used. Electrical signals (current and voltage), optical emission spectroscopy records, and total light emission measured by photomultiplier have been analyzed and used to distinguish different plasma regimes which are studied for the treatment of a lignocellulosic material (sugarcane bagasse). In the filamentary discharge regime, the gas temperature of few tens of degree Celsius above the ambient one was determined, the electronic temperature of some electronvolts and electron density in the range of 1012–1013 cm−3 were estimated. Plasma treated pellets of sugarcane bagasse were analyzed by diffuse reflectance infrared Fourier transform spectrometry and the relative results obtained under filamentary discharge regime have shown significant degradation of the lignin macromolecule. It has been shown important modifications on the lignocellulosic material, namely, the plasma attacks drastically the lignin bonds. Strong modification of lignin was observed near wavenumber of 3400 cm−1, due to stretching vibrations of OH, and for the band 1114 cm−1 which is related to C=C and C=O stretching. Severe decrease of the band intensity 1596 cm−1, which due to C=C stretching and C=O, is also a result of the treatments done in this paper. [ABSTRACT FROM AUTHOR]

Chemical oxidation and the bactericidal capabilities of nonthermal plasma discharges can be used in different practical applications, such as biodecontamination, sterilisation of medical equipment, waste water treatment, syn-gas treatment, and others. In this paper, the oxidation and biodecontamination effects of impulsive plasma discharge, which propagate across a liquid sample/air interface (surface discharges), and through the bulk of a liquid sample (direct discharges), have been investigated. The oxidizing capability was analyzed by measuring the degree of decolorization of indigo carmine dye in water solutions. Gram-negative and gram-positive bacterias, E. coli and S. aureus, respectively, were used as model microorganisms in the investigation of the biocidal effects of plasma discharges. Surface and direct plasma discharges were generated by high-voltage impulses of both polarities, with the magnitudes of 20, 24, and 28 kV, and the chemical oxidation and biodecontamination capabilities of such discharges have been obtained and analyzed. It has been established that the defining factor in the chemical and biological effects of plasma discharges is the normalized delivered charge (dose). The results obtained in this paper show that surface discharges have greater biodecontamination capability as compared with direct transient plasma discharges. Also, it was shown that the decontamination rate of E. coli is more than double than that of S. aureus. [ABSTRACT FROM AUTHOR]

In this paper, we characterize a Transparent Cathode Discharge (TCD), a type of Inertial Electrostatic Confinement (IEC) plasma, operated in helium and argon in the pressure range of 1–100 Pa. The discharge was investigated using a combination of electrical and optical diagnostic techniques. The imaging of the discharge indicated distinct operating regimes related to the background gas pressure, with each mode being characterized by different patterns of optical emission. The spectroscopic analysis of the optical emission showed that this mode structure represented an electron-driven discharge at higher pressures, and a discharge sustained by the activity of energetic heavy particles at lower pressures. The high-pressure discharge is shown to be assisted by the hollow cathode effect toward its low-pressure limit, and the visible color of emission from the discharge in helium is found to provide a convenient diagnosis of active species. The identification of a stable discharge mode in which energetic heavy particles are responsible for collisional processes has the potential to lead to new industrial applications based on this novel heavy particle-driven reactive plasma source. [ABSTRACT FROM AUTHOR]

In this paper, the dual-frequency atmospheric-pressure glow discharge is operated in helium with a small amount of oxygen. It is found that the plasma density increases, but the reactive atomic oxygen density decreases with high-frequency (HF) power. The plasma density also increases with low-frequency (LF) power, but it is weak as with HF power. However, the reactive atomic oxygen density increases with LF power. It shows that HF power is in favor of excited helium, but LF power is in favor of producing reactive O, N2, and OH. The discharge intensity decreases with oxygen gas admixture in working gas due to its electronegative nature. The generation rate of reactive oxygen atom has a trend of increasing first and then decreasing after 0.3% oxygen gas admixture. [ABSTRACT FROM AUTHOR]

Gas flow plays an important role in determining the discharge properties in microwave plasma torches sustained by the propagating surface wave. This paper aims to investigate the gas flow effects on the plasma column length, the surface wave propagation, and the heavy species temperature in a surface wave plasma torch operated at atmospheric pressure. The steady-state discharges of pure argon gas at atmospheric pressure under different gas inflow rates in the plasma torch are characterized by an improved 2-D axisymmetric fluid model. The obtained results demonstrate that increasing the gas inflow rate is able to decrease the surface wave propagation distance, accelerating the contraction of the plasma column length. The discharge instability is found to be motivated by the disappearance of the sustaining surface wave at high gas inflow rates. Besides, a temperature drop of about 64 °C is observed at the temperature-maximum point of the glass tube with an increase in the gas inflow rate from 1 to $16\,\,\text {L}\cdot \text {min}^{-1}$. Therefore, for the surface wave plasma torch operated with only the axial gas flow, increasing the gas inflow rate cannot solve the glass overheating problem. [ABSTRACT FROM AUTHOR]

To realize the broadest potential of nonthermal atmospheric-pressure plasma (APP) technology, there is a need to develop low-cost, compact devices that can be used for portable applications. One of the greatest impediments to this is the power supplies and/or electronics needed to generate breakdown at atmospheric pressure. Piezoelectric transformers (PTs) are solid-state transformers that can produce large gains in voltage, which along with their modest size, makes them attractive candidates for use in plasma production. In this paper, we use a low-voltage power supply in line with a PT to produce an APP jet (APPJ). While operating at the resonance frequency of the PT (88 kHz), plasma jets were generated with input voltages as low as 10 V. The electrical and optical characteristics of the piezoelectric-driven jet were compared to an APPJ produced with a high-voltage sine wave of comparable operating frequency. Both APPJs were examined in helium and argon for a variety of different flow rates and operating voltages. In argon, the length of the jets was nearly identical for all operating parameters but produced different discharge currents. In helium, the discharge currents were similar but the lengths of the jet differed. Optical emission spectroscopy showed similar chemical composition between the two jets for both feed gases. Together, the results suggest that the piezoelectric material has an influence beyond simply amplifying voltage but can be successfully integrated to meet the requirements needed for plasma production. [ABSTRACT FROM AUTHOR]

In this paper, Ar–H2 plasma is studied by the nonintrusive optical emission spectroscopy method. The emission spectra of excited species of hydrogen and argon are observed and measured. The effect of an increase in hydrogen gas flow in the Ar–H2 plasma is studied experimentally. The variation in peak intensity and broadening of $\text{H}_{\alpha }$ line with increased hydrogen gas flow rates is examined. It is noticed that the peak intensity of $\text{H}_{\alpha }$ line is very sensitive to hydrogen gas flow rate while the broadening of the line is found to be constant. The broadening of $\text{H}_{\alpha }$ line is observed to be a Lorentzian profile. In addition to this observation, the electron temperature was computed using Boltzmann’s plot method. It is learned that the theoretical and the experimentally evaluated electron densities are not in close agreement with each other. Therefore, the estimation of electron density from the electron temperature will not always be a reliable method in the case of such atmospheric plasma. The saturation effect of electron density and the quenching of Ar I emission lines are also observed and discussed. [ABSTRACT FROM AUTHOR]

This paper is aimed to identify the mechanism that atmospheric pressure plasma jet (APPJ) damages malignant melanoma (B16-BL6 cells) cultured in vitro through the induction of oxidative stress. After being exposed to APPJ with different time durations, the reactive species of H2O2 and NO2− inside cell culture medium, together with a series of biochemical parameters including the cell viability, cell morphology, DNA damage, intracellular reactive oxygen species (ROS) and antioxidant capacity, are measured. The results reveal that there are obvious increases of H2O2 and NO2− in the plasma-irradiated medium. And the cell viability, intracellular total antioxidant capability (T-AOC), and glutathione (GSH) contents decrease with the exposure to APPJ in a time-dependent manner compared with the untreated cells, i.e., 0-s group ($p < 0.05$). Besides, the intracellular malondialdehyde (MDA), ROS contents, and the degree of cellular damage increase significantly with 30, 60, and 90 s of plasma treatment ($p < 0.05$). Furthermore, the pretreatment with N-acetyl cysteine, which is a free radical scavenger, can markedly prevent the decrease of cell viability, T-AOC, and GSH content, the increase of MDA, ROS contents, and the degree of cellular damage caused by 90-s exposure to APPJ. These research findings suggest that low-temperature plasma exerts its cytotoxic effects on melanoma cancer cells mainly through the ROS inside cells induced by reactive oxygen and nitrogen species generated in gaseous and liquid phases, which ultimately cause oxidative stress-evoked damage to cellular components. [ABSTRACT FROM AUTHOR]

The influence of ambient air species especially humidity is an ever-present challenge for atmospheric pressure plasma jet applications. Especially, where the plasma-induced effects are extremely sensitive to humidity, such as in the field of plasma medicine, an understanding of the influence of ambient species diffusion on plasma chemistry and on reactive component composition is crucial. In this paper, we investigate the influence of ambient humidity versus feed gas humidity on the production of reactive components by atmospheric pressure plasma jets. By the use of a shielding gas curtain, we control the surrounding atmosphere around the active effluent region of the investigated argon RF-plasma jet (kinpen) and control the gas humidity of the ambient gas. By quantum cascade laser absorption spectroscopy and by Fourier transformed infrared (IR) absorption spectroscopy, the effect of diffusing surrounding molecular species on the chemistry of the long-living reactive oxygen species is investigated. Mechanisms of H2O2 and O3 production are studied. In this paper, we have quantified the influence that ambient species, namely, water molecules, have on the reactive species’ generation in the gas phase. It is shown that the effect of ambient humidity is important for the long-living species production, feed gas humidity, however, has the much stronger effect. Finally, with the focus of applications in plasma medicine, the cell viability of human skin cells (HaCaT keratinocytes) as a function of feed gas and ambient gas humidity is compared. [ABSTRACT FROM PUBLISHER]

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~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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

This paper presents an experimental investigation of ionization waves’ (IWs’) propagation in a nanosecond-pulse dielectric barrier discharge at atmospheric pressure in air. The effect of the rise time and pulse duration on IW propagation is studied by an intensified charge-coupled device, and the mechanism of the discharge propagation is analyzed. The experimental results show that the discharge produced in the rise time of the applied voltage develops in a structure of discontinuous sphere, while the discharge produced in the falling time exhibits a continuous form due to the effect of space charge. Furthermore, the rise time of the applied voltage has a significant influence on the velocity of IWs, and the maximal velocity of IWs rapidly decreases from 0.08 to 0.008 mm/ns when the rise time of the applied voltage increases from 50 to 300 ns. However, the pulse width has almost no influence on the velocity of IWs. The electric field distortion caused by both the propagation of IWs and the accumulation of surface charges is responsible for the formation and propagation of IWs. [ABSTRACT FROM AUTHOR]

Surface dielectric barrier discharge (DBD) has recently received growing interest for enormous application potential in various fields. In this paper, the optical observation of surface DBD is conducted by an intensified charge-coupled device camera from top view in the atmospheric air. Spacial and transient characteristics of discharge phenomenon in atmospheric pressure air have been, respectively, visualized with the exposure time of 100 ms and 5 μs. The discharge area is obtained by calculating the number of pixels in MATLAB software at different electrical parameters and different high-voltage electrode configurations with microsecond time scale. Experimental measurements show that the diffuse discharge during the negative-half cycle has good uniformity and stability compared with filamentary discharge during the positive-half cycle. The results offer a new estimated method for the discharge area. [ABSTRACT FROM PUBLISHER]

The conventional ways of processing natural gas into more efficient and economical fuels usually have either low conversion rate or low energy efficiency. In this paper, a new approach of methane liquefaction is proposed. Instead of direct treatment of only natural gas, plasma-activated methane is reacting with liquid fuel. In this way, methane molecules are directly incorporated into liquid fuel to achieve liquefaction. Nanosecond-pulsed dielectric barrier discharge and atmospheric pressure glow discharge are used here to ensure no local heating in gas bubbles. Effects of both discharges on methane reaction with liquid fuel are investigated, and mass and chemical changes in liquid are observed. Preliminary results show fixation of methane in liquid fuel. [ABSTRACT FROM PUBLISHER]

Low-temperature atmospheric-pressure plasma jets (APPJs) are being increasingly used in surface activation, cleaning, wound care, and sterilization applications. The development of successful applications using these systems depends on the ability to tailor the active species generated in the plasma jets to match the treatment requirements. This paper presents an investigation of the effect of sinusoidal drive frequency (20–140 kHz), on a helium discharge formed using an APPJ. The discharge was formed in a large-orifice 16-mm-diameter quartz tube with a treatment area of \approx\! 2\ \cm^2 at the nozzle exit. Optical, polychromic emission, and thermographic imaging data were correlated with electrical measurements. These measurements indicated that the coupling efficiency was frequency dependent. As a result of differences in coupling efficiency, variations in active species (\N2, \N2^{+}, O, and NO) present in the discharge were observed. The concentration of active species was also dependent on the distance from the powered electrodes. As well as altering the concentration of active species in the discharge, changes in frequency resulted in higher discharge temperatures (25 ^\circ\C at 20 kHz to 40 ^\circ\C at 80 kHz). The temperature was measured on the quartz tube, and steady state was reached after 120 s. This paper presents a detailed analysis of the frequency/distance dependence on the active species in the discharge. This dependence makes it possible to control the active species present at the plasma jet orifice by tailoring the frequency and tube length. [ABSTRACT FROM PUBLISHER]

Inactivation kinetics of a nanosecond-pulsed plasma jet against a panel of common pathogenic microorganisms was studied to assist the design and development of nonthermal plasma-based treatment schemes for pathogenic infection control. We evaluated the effectiveness of our cold-plasma in vitro against microbes with varying cell wall and membrane characteristics: the Gram-positive organisms Staphylococcus aureus and Staphylococcus epidermidis, the Gram-negative organisms Pseudomonas aeruginosa and Escherichia coli, and the yeast Candida albicans. We found that all of the organisms tested in this paper were rendered nonculturable ( >99.99%) by the end of the short plasma treatment times ranging from 30 to 180 s. Our results indicate that the pathogenic bacteria and yeast tested in this paper can be effectively rendered noncultivable within seconds using the He/(1%)\O2 cold plasma, and that susceptibility to plasma may vary depending on the cell wall and membrane characteristics of the organisms in addition to the other resistant mechanisms of individual strain. [ABSTRACT FROM PUBLISHER]

In recent years, surface dielectric barrier discharge (SDBD) sustained by pulse power supply has been widely investigated due to its high efficiency and fast response. In this paper, in order to obtain the effect of the electrode length, dielectric thickness, and electrode width on the characteristics of SDBD driven by microsecond-pulse generator, experimental investigation on the SDBD actuator using a dielectric barrier of epoxy glass cloth is performed. The experimental results showed that both the current amplitude at the rising edge of the applied voltage and the consumption energy increased with the electrode length. Moreover, dielectric thickness slightly affected the displacement current, while the consumption energy decreased when the dielectric thickness increased. Furthermore, when the electrode width increased, the current at the rising edge of the applied voltage increased, but it would reach the saturation when the electrode width exceeded 3 mm. Both the instantaneous power and the consumption energy increased with the electrode width. The experimental results can provide reference for the optimal design of the SDBD actuator driven by microsecond pulses. [ABSTRACT FROM AUTHOR]

Our concern with plasma jets is the generation of pressure waves that influence the surface or the inside of targets. In this paper, the detection of pressure waves emitted from plasma jets was carried out using a fibered optical wave microphone, which works based on Fraunhofer diffraction for phase objects, with a synchronized high-speed camera observation of the dynamic behavior of plasma jets and their electrical properties. The electrode configuration of typical dielectric barrier discharge tubes was used in He gas flow. Effects of the amplitude and frequency of applied voltages and He gas flow rates on relationships among the irradiation of plasma jets, the generation of pressure waves, and current waveform were studied. Pressure waves were detectable by the fibered optical wave microphone, even though the irradiation of plasma jets from the glass tube was not observed with the high-speed camera. Frequency dependence on the generation of pressure waves was confirmed. [ABSTRACT FROM AUTHOR]

An atmospheric microwave plasma torch for the decomposition of \SF6 accompanying additive gases (\O2, compressed air) was investigated experimentally in this paper. Applied microwave power and additive gas species as effective parameters on destruction and removal efficiency (DRE) were considered. It was approved that compressed air is a more efficient additive gas for the removal of \SF6 compared to oxygen. Also, DRE is highly dependent on the variation of forward power. Highest efficiencies while using oxygen and compressed air as additive gases have been 98.4% and 99.1% (in 1100 W), respectively. In some case, the \N2 was also used with \SF6, resulting in a maximum efficiency (in 1100 W) of 99.4%. This paper approves that a microwave plasma torch sustained in atmospheric pressure can almost completely remove the \SF6 in semiconductor industry. [ABSTRACT FROM PUBLISHER]

Due to several urgent applications such as plasma medicine, atmospheric-pressure nonequilibrium plasma jets (APNP-Js) have attracted lots of attention in the past two decades. Researchers found that APNP-Js could be used in various applications of dentistry. In this paper, first, a brief review on APNP-Js is presented. Second, the details about the application of the APNP-Js in the oral cavity, one of the important practices of dentistry, are described, which include a short description of common oral disease, plasma kill bacteria in planktonic culture, on Petri dish, in simulated root canal, and in teeth root canal. Besides, the safety of APNP-Js in the applications of dentistry is discussed, and the first prototype of plasma for root canal treatment is sketched. Third, the applications of APNP-Js in tooth bleaching and in surface treatment of dental implants are reviewed. Finally, a short conclusion is drawn, and the future of the applications of APNP-Js in dentistry is proposed. [ABSTRACT FROM PUBLISHER]

Multipoint-to-multipoint and multipoint-to-plane electrode geometries have been investigated to enhance corona discharge modes in atmospheric pressure weakly ionized plasma. This paper presents a new geometry approach by a protrusion array over the grounded screen along with a high-voltage (HV) needle array to obtain higher coulombic discharge. It has been observed that needle-to-grounded-screen-protrusion configuration enhances the discharge modes, especially the back corona is enhanced significantly near the protrusions in Ar/C2H2 plasma. A corona mode map has been developed to depict the optimal discharge zones at various HV gaps. Similar investigations were performed in Ar/O2 plasma to study the nature of the current pulses and discharge modes. [ABSTRACT FROM PUBLISHER]

One type of atmospheric plasma jet relay driven by a 40-kHz power supply and its representative characteristics have been proposed in this paper. The plasma jet relay succeeds in the same gas stem or inside another guided dielectric tube. The first plasma jet can be capable of dividing into many small plasma jets at the end of metal wires and the filial generations can easily merge together to form longer volume discharges. The experiment indicates that the filamentary discharge starts from the formation of one snake-like discharge passage first and the followed snakes give birth from the previous snake discharge body. Taking into account the advantage of easily production methods and available to extend its discharge volume, the proposed plasma jet relay device can be modulated for many potential applications. [ABSTRACT FROM PUBLISHER]

In this paper, organic electroluminescence fluoropolymer film devices, i.e., organic light-emitting diodes (OLEDs) comprising polychlorotrifluoroethylene (PCTFE) films treated by an atmospheric-pressure nonthermal plasma (NTP) graft-polymerization process, are investigated. PCTFE films can provide a long lifetime for OLEDs because of their excellent gas barrier properties; however, they are difficult to laminate, owing to low adhesiveness. The surfaces of PCTFE films are treated by an atmospheric-pressure NTP-graft-polymerization process to improve their adhesiveness, and then, indium tin oxide and a luminous layer are deposited on the treated PCTFE films. As a result, OLEDs comprising PCTFE films are successfully demonstrated. [ABSTRACT FROM AUTHOR]

This paper tests various design and operation parameters in atmospheric-pressure helium plasma jets generated with a pin electrode to provide a plasma environment well suited for material processing or biomedical applications. The effects of the pin electrode materials (Cu, W, and Al), the position, and the width of a ground ring electrode on the characteristics of the jets are studied. The inner quartz tube encompassing the pin electrode and two types of the outer quartz tubes (straight or tapered cylinder shape) are employed, and their effects are investigated. The electrical characteristics of the plasma jets are measured by current–voltage measurements and analyzed by the equivalent circuit model. The optical characteristics of the discharges are obtained by optical emission spectroscopy to identify various excited plasma species produced in the plasma jets. Optical emission spectra are also obtained at different positions along the coaxial direction. A variety of choices in design parameters and operation parameters are undertaken to determine optimal conditions and elucidate the properties of the plasma jets. [ABSTRACT FROM PUBLISHER]

Polypropylene nonwoven materials have foundenormous usefulness in many applications. In this paper, the cyclonic plasma processing at atmospheric pressure was used to determine the surface treatment effect. The change of hydrophilicity was determined by contact angle analysis. The nonwoven polypropylene (NWPP) surface became greatly hydrophilic when exposed to the cyclonic plasma at atmospheric-pressure. A major effect in the surface free energy of material surface due to crosslinking via activated species of inert gases effect was observed. The variations in the chemical structure and surface morphology of the NWPP were confirmed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscope detections. The XPS detection reveals considerably more surface elemental composition of oxygen atoms for cyclonic plasma-modified NWPP. [ABSTRACT FROM PUBLISHER]

This paper demonstrates for the first time the use of microplasma to perform AND, OR, and XOR logic operations. The logic circuits are implemented similar to diode-resistor logic. Output voltages are in the range of \(5-40\) V and can be modified by varying the load resistor. The active area of the microplasma device is just \(50~\mu \) m \(\times 5~\mu \) m. The small interelectrode gap kept breakdown voltage to \(\sim 250\) V when operated in He gas at atmospheric pressure. The use of plasma as a source of free carriers is also demonstrated, with free carriers available up to 500- \(\mu \) m away from plasma. [ABSTRACT FROM PUBLISHER]

For room-temperature atmospheric pressure plasma jets (RT-APPJs), because of the gas flow, the OH density at a given position is different from the case without the gas flow. In this paper, an OH density decay model, which includes the main loss processes of OH and gas flow effect, is present. Based on the model, the simulation results have a very good agreement with the OH decay behavior measured by laser-induced fluorescence. The absolute OH density of the RT-APPJ is obtained when the best fit is achieved, which is about 2.4\times 10^13~cm^-3 at 5 mm away from the plasma jet nozzle and 1 \mus after the discharge. In addition, to control the OH density, the effect of voltage polarity, applied voltage magnitude, pulse frequency, pulsewidth on the OH density is also investigated and discussed. [ABSTRACT FROM PUBLISHER]

A novel method to produce strong and effective argon plasma jets in air is reported. By adjusting the structure and setting the location of a copper wire in the quartz tube, an intensive jet composed of two jets about 2.4 cm is produced with microwave power of 50 W. The microwave frequency is 2.45 GHz. Four twisty plasma jets about 2.0 cm for argon discharge are generated in four tubes at incident power of 120 W. A plasma ball of air discharge about 0.5 cm in radii is generated in the tube at the power of 100 W. The simulated distribution of electric field in the tube with a folded copper wire is consistent with the prediction of surface plasmon polaritons. Spectral diagnosis of the plasma jets is also discussed in this paper. [ABSTRACT FROM PUBLISHER]

Nonthermal and low-temperature plasmas has been a subject attracting great interest of scientists engaged in different fields of science and application. In this paper, a cold Ar plasma jet is generated under atmospheric pressure by using a dielectric barrier discharge configuration device equipped with a copper ring electrode and an aluminous plate grounded electrode driven by a sinusoidal excitation voltage at 10 kHz. The distance (d, for short) between the grounded electrode and the nozzle of the quartz tube is set at 10, 20, and 30 mm, respectively. The jet characteristics are investigated by electrical and optical diagnostics, including discharge images, voltage-current waveforms, Lissajous figures, and optical spectrum. The electric discharge and plasma parameters, such as discharge power, transported charges, electronic excitation temperature, etc., with different d are calculated and compared. Furthermore, the influence of the location of the grounded electrode on the characteristics of plasma jet is also studied. The experimental results show that the largest discharge power is generated with d=10~mm, while the electron density and electronic excitation temperature (EET) of plasma jet will be increasing for d=20~mm. Thus keeping reasonable distance between the grounded electrode and the nozzle of quartz tube not only can reduce the discharge power, but also improve the electron density and EET of the plasma jet, which contributes to practical application of this jet device. [ABSTRACT FROM AUTHOR]

In this paper, the raising voltage process is defined as stepping up the applied voltage, whereas the reducing voltage process means turning down the applied voltage, which follow on the termination of the raising voltage process. Discharge images, the waveforms of applied voltage and discharge current, Lissajous figures, and the optical emission spectra of the two different processes were acquired in needle-plate alternating current dielectric barrier discharge in humid nitrogen at atmospheric pressure. Conclusively, the characteristics of the discharges with the same applied voltage in the raising and reducing voltage processes are pretty different. The discharge in the reducing voltage process is more intense and the power consumption is about three times than that in the raising voltage process at the same applied voltage. Analysis shows that the phenomena would be interpreted by the effect of the space charges in the discharge gap, and worth taking more efforts in the practical applications. [ABSTRACT FROM PUBLISHER]

In this paper, the interaction between Ar flow channel and atmospheric pressure plasma jet (APPJ) is investigated quantitatively by combining 3-D species transport simulation and optical schlieren observation together. The turbulence model, gravity force, and electrostatic force model are included into the Ar flow channel simulation. It is found that, with the increment of the Ar flow rate, the plasma plume reaches the maximum length at 3.5 L/min and then decreases sharply, which is corresponding to the Ar flow status. The simulations of the Ar flow channel show good agreement with the captured schlieren images. At small flow rates, the Ar flow channel bends downward due to the gravity. Under laminar flow, the high Ar mole fraction region near the axis of the Ar flow channel increases with the flow rate. However, the Ar flow presents as twist and radial diffusion, and the Ar mole fraction decreases rapidly when the Ar flow transits into turbulence, which leads the length of the Ar plasma plume to decrease sharply correspondingly. The plasma plume bestows the Ar flow channel a forward momentum, which decreases the curvature of bending downward and reinforces the twist and instability of the Ar flow channel under turbulence flow. By coupling the optical emission spectra and flow channel investigation together, it is revealed that Ar APPJ propagates along the core of the conelike flow channel. The Ar mole fractions at the head of the plasma plume are about 0.985 and 0.45 under laminar and turbulence flow, respectively. [ABSTRACT FROM PUBLISHER]

It is well accepted that increasing the frequency and reducing the electrode gap are effective ways to enhance the discharge stability in atmospheric radio-frequency (rf) discharges. In this paper, we explore a 1-D fluid model to investigate the discharge characteristics when the \alpha-\gamma mode transition occurs. The differential equation satisfied at the \alpha-\gamma mode transition point is given based on the governing equations. From the theoretical analysis and computational data, with an increase in the electrode gap, the power density coupled to the plasmas decreases, and the critical electron density modestly increases at the transition point; the electron temperature both in the sheath and bulk plasma decreases as the sheath shrinks. On the other side, as the frequency is raised, just at the mode transition point, the applied voltage reduces, and the plasma density increases almost exponentially with a higher electron temperature in the sheath. From the view point of application, the discharge driven by a high frequency at a narrow gap is desirable to produce a stable and high-density atmospheric plasma with a large power density coupled. [ABSTRACT FROM PUBLISHER]

Plasma processing of carbon fibers (CFs) is aimed to provide better contact and adhesion between individual plies without decrease in the CF mechanical resistance. This paper deals with surface modification of CFs by an atmospheric pressure dielectric barrier discharge (DBD) for enhancing the adhesion between the CF and the polymeric matrix. The scanning electron microscopy of the treated samples revealed many small particles distributed over entire surface of the fiber. These particles are product of the fiber surface etching during the DBD treatment that removes the epoxy layer covering as-received samples. The alteration of the CF surface morphology was also confirmed by the Atomic force microscopy (AFM), which indicated that the CF roughness increased as a result of the plasma treatment. The analysis of the surface chemical composition provided by X-ray photoelectron spectroscopy showed that oxygen and nitrogen atoms are incorporated onto the surface. The polar oxygen groups formed on the surface lead to the increasing of the CF surface energy. The results of interlaminar shear strength test (short beam) of CFs/polypropylene composites demonstrated a greater shear resistance of the composites made with CFs treated by DBD than the one with untreated fibers. Both the increase in surface roughness and the surface oxidation contribute for the enhancement of CF adhesion properties. [ABSTRACT FROM PUBLISHER]

Finding a solution for air species contamination of atmospheric pressure plasmas in plasma medical treatment is a major task for the new field of plasma medicine. Several approaches use complex climate chambers to control the surrounding atmosphere. In this paper, ambient species are excluded in plasma–human-skin-cell treatment by ensheathing the plasma jet effluent with a shielding gas. Not only does this gas curtain protect the plasma jet effluent from inflow of air species but it also, more importantly, allows controlling the effluent reactive species composition by adjusting the mixture of the shielding gas. In the present investigations, the mixture of nitrogen to oxygen within the gas curtain around an argon atmospheric pressure plasma jet (kinpen) is varied. The resulting reactive plasma components produced in the jet effluent are thus either oxygen or nitrogen dominated. With this gas curtain, the effect of reactive oxygen species (ROS) and reactive nitrogen species (RNS) on the cell viability of indirectly plasma-treated HaCaT skin cells is studied. This human keratinocyte cell line is an established standard for a skin model system. The cell viability is determined by a fluorometric assay, where metabolically active cells transform nonfluorescent resazurin to the highly fluorescent resorufin. Plasma jet and gas curtain are characterized by numerical flow simulation as well as by optical emission spectroscopy. The generation of nitrite within the used standard cell culture medium serves as a measure for generated RNS. Measurements with the leukodye dichlorodihydrofluorescein diacetate show that, despite a variation of the shielding gas mixture, the total amount of generated reactive oxygen plus nitrogen species is constant. It is shown that a plasma dominated by RNS disrupts cellular growth less than a ROS-dominated plasma. [ABSTRACT FROM PUBLISHER]

In this paper, an Ar plasma jet is generated under atmospheric pressure using a DBD configuration device equipped with a copper-ring powered electrode as well as an aluminous plate ground electrode, which is driven by a sinusoidal excitation voltage at 10 kHz, and three types of dielectric barriers, i.e., quartz glass, epoxy, and PTFE, are employed to study the influence of the barrier materials on the characteristics of the plasma jet. The jet characteristics are studied by electrical and optical diagnostics, and the voltage–current waveforms, Lissajous figures, lighting emission images, and optical spectrum are obtained. The electric discharge parameters and plasma parameters, such as discharge power, transported charges, electronic excitation temperature, etc., are calculated and compared by using different dielectric barriers, and the mechanism of the influence of the barrier material on the jet discharge is discussed. The experimental results show that the influence of the barrier materials on the characteristics of the plasma jet is related not only to the relative dielectric constant but also to the desorption of surface electrons from them. Under the same operation conditions, more intensive jet discharge can be obtained by using PFTE as the barrier material, and the discharge power, transported charges, and electronic excitation temperature are higher than those of quartz glass and epoxy as dielectric barriers. [ABSTRACT FROM PUBLISHER]

This paper describes the investigation of an atmospheric-pressure glow discharge in air at a current of 0.05–0.3 A. Before the glow discharge is established, a preliminary nonsteady temporal stage is available in the gap. The principal process, which governs with the nonsteady-state discharge behavior, is the glow-to-spark transition phenomenon. The transition is initiated due to the explosive emission instability in the near-cathode layer of glow-type discharge that results in a microexplosion of the cathode surface and appearing of a spark cathode spot. At a low current, the spot is extinguished, so that the discharge starts burning again in one of the glow modes. After that, a new act of transition occurs and so on. The preliminary nonsteady-state stage ensures two prerequisites. First, an effective gas pressure decreases to a low value. Second, due to microexplosions, conditioning of the cathode surface is provided. Both factors facilitate establishing the normal glow discharge. [ABSTRACT FROM PUBLISHER]

Plasma bullets are ionization fronts created in atmospheric-pressure plasma jets. The propagation behavior of those bullets is, in the literature, explained by the formation of an interface between the inert gas and the ambient air created by the gas flow of the plasma jet, which guides these discharges in the formed gas channel. In this paper, we examine this ionization phenomenon in uniform gases at atmospheric pressure where this interface between two gases is not present. By changing electrical parameters and adding admixtures such as oxygen, nitrogen, and air to the gas flow, the conditions for which plasma bullets are present are investigated. Nanosecond time-resolved images have been taken with an ICCD camera to observe the propagation behavior of these discharges. It is argued that the inhomogeneous spatial concentration of metastable atoms and ions, due to the laminar gas flow and the operation frequency of the discharge in the range of a few kilohertz, is responsible for the guidance of the ionization fronts. Furthermore, conditions have been observed at where the branching of the discharge is stable and reproducible over time in the case of a helium plasma by adding admixtures of oxygen. Possible mechanisms for this phenomenon are discussed. [ABSTRACT FROM PUBLISHER]

This paper presents an experimental and numerical study of the dynamics and structure of an atmospheric-pressure helium discharge with nitrogen admixture propagating through a thin dielectric tube surrounded by two ring electrodes. The experimental unfiltered optical emission of the discharge has been compared to the computed emission of the second positive system of nitrogen and shows very good agreement. In all studied cases, the discharge ignition occurs inside the tube at the outer edges of the high-voltage electrode ring, and the discharge propagates outward of both sides of the high-voltage ring with a rather homogeneous discharge front structure. When the discharge approaches the grounded ring, the emission is enhanced and moves from the symmetry axis to the tube surface. In both simulation and experiment, an initial front propagation velocity of about 3 \times 10^6\ \cm/s is observed as the plasma traverses the first part of the electrode gap. This velocity increases in the later part of the electrode gap as the plasma approaches the grounded ring, and the observed velocity in the experiment is slightly higher than that in the simulation. In experiments, when the admixture is decreased, the discharge constricts close to the tube axis during its propagation between the electrode rings before moving to the tube surface close to the grounded ring. In simulations, as a first step, we have considered that, in reducing the amount of nitrogen admixture, the efficiency of photoionization decreases significantly. This allows the formation of an electron depleted volume close to the grounded electrode ring, which then constrains the discharge to propagate close to the tube axis, in agreement with experiments. [ABSTRACT FROM PUBLISHER]

Plasmas have been frequently employed to modify material surface properties; however, many of these processes are not suitable for treating sensitive materials and biological objects that cannot withstand vacuum and/or high temperature. Atmospheric-pressure plasma jets (APPJs) using inert gases can be easily adapted for this purpose since they exhibit high plasma stability, efficient reaction chemistry, and low temperature. In this paper, an APPJ with simple configuration was designed and applied for surface treatment of polycarbonate (PC) films. Optical emission spectroscopy was used to identify the excited plasma species presented inside the device and in the plasma plume. Material characterization was carried out by water contact angle measurements and atomic force microscopy. The interaction of the plasma jet with the PC samples resulted in a rougher surface and enhanced wettability. [ABSTRACT FROM PUBLISHER]

Gliding discharges can generate nonthermal plasma at atmospheric pressure. Therefore, they are widely used in plasma-assisted ignition and combustion. In this paper, the gliding discharge sustained by a resonant ac power supply was obtained with a pin-to-pin electrode geometry, and the characteristics of such discharge were investigated through its voltage–current and discharge images. Inceptive, nonstable, and stable stages involved in this gliding discharge were studied. Experimental results showed that the discharge was first ignited by a spark with a current peak of tens of amperes and soon turned into a stable stage, where the discharge respectively behaved in repetitive spark mode with a current peak of several amperes in a small gap and glowlike mode with a current peak of several microamperes in a relatively large gap spacing. Under a certain situation, a nonstable discharge was observed, which changed from a spark discharge to a glowlike discharge after some time. In addition, both the discharge stability and the breakdown voltage were influenced by the air flow. The discharge became unstable when the air flow exceeded 3 L/min. [ABSTRACT FROM PUBLISHER]

The influence of ambient air species is an ever-present problem for atmospheric pressure plasma jet applications. In particular, applications where the plasma-induced effects are extremely sensitive to specific types of ambient species (oxygen, nitrogen, humidity)—as, for example, in plasma medicine—require concepts to exclude or to control ambient species flux into the jet effluent that go beyond an environmental control via process chambers or even vacuum systems. In this paper, we demonstrate how to eliminate ambient species influence on effluent chemistry by ensheathing the effluent. With a designed shielding gas composition, we control the species flowing into the jet effluent and thus control the effluent chemistry. The proposed approach can be applied to the majority of possible jet plasma sources. Flow simulations as well as VUV-absorption spectroscopy measurements prove the gas curtain to be effective in shielding the jet gas from ambient species and show that a control of reactive species within the jet effluent is possible. On the example of plasma treatment of a NaCl solution, we demonstrate that, by adjusting the shielding gas composition, the generation of nitrite and nitrate in the solution can be finely controlled. [ABSTRACT FROM PUBLISHER]

Recently, we have reported a microwave plasma jet at atmosphere in argon, capable of generating filamentary streamer discharges within the entire quartz tube, while several bifurcations yield at the end of the copper wire immediately in the quartz tube when incident power reaches 20 W. However, the ionization process for the discharges is still not very well clarified. This paper shows a numerical study of the proposed plasma jet by means of the 2D3V particle in cell with Monte Carlo collision method. The detailed information about the distributions of plasmas and electromagnetic fields is obtained by sampling the simulated results at different time steps. The simulation results suggest that the production of the proposed plasma jet is attributed to the seed plasmas triggered by the enhanced electric field of surface plasmon polaritons and its interaction with plasmas. [ABSTRACT FROM PUBLISHER]

In this paper, a dielectric-barrier discharge (DBD) of Ar:\N2 mixtures at atmospheric pressure is studied in relation to plasma jet production. The discharge takes place in a capillary dielectric tube, and it is sustained by positive high-voltage pulses. It is herein claimed that, apart from the traditional DBD (which is developed perpendicularly to the gas flow and can produce afterglows), plasma jet propagates simultaneously parallel to the gas flow due to ionization waves guided by the dielectric tube. A quite simple electrical model is applied to simulate the proposed DBD and plasma jet coexistence. The concept of capacitive behavior of both barrier discharge and jet is taken into account. This model in combination with UV–visible optical emission spectroscopy and conventional photography supports the aforementioned statements. The dependence of the jet domination against the afterglow on the gas mixture is demonstrated, and the \N2 additive at 2.5 \%–3\% in Ar is found to be the most efficient for jet production. The model runs with the measured interelectrode voltage as input and yields the circuit total current as output. Matching between the measured current and the model output is attempted by adjusting two free parameters. This tuning of the free parameters provides reliable values for the electrical components of the model. Thus, a simple mean for realistic representation of both DBD and jet is achieved. This tool could be applied to the design of plasma jet reactors. [ABSTRACT FROM PUBLISHER]

It remains a challenge to generate the uniform and large-area cold plasma at atmospheric pressure. In this paper, we report a method to generate a reliable and homogeneous brush-shaped plasma plume running at atmospheric pressure. The plasma brush (110 mm in length and 10 mm in width) is mainly composed of well-aligned and hollow optical fibers. Current–voltage measurements indicate that the brush-shaped plasma plume consists of glowlike pulsed discharge with their pulsewidths of several microseconds. The generation of the \He/O2 glowlike discharge is further proved by the uniform distribution of O atoms along the transverse location of the plasma brush. This brush-shaped plasma plume is used for the application in the plasma inactivation of Candida albicans cells. About 97% of Candida albicans cells with a population of 10^5 spores are killed when exposed to the \O2/\He (volume ratio: 5/95) brush-shaped plasma plume for 150 s. Analysis indicates that plasma-activated species, such as O radicals, may play a crucial role in killing the resistant Candida albicans cells. [ABSTRACT FROM AUTHOR]

In this paper, the effects of operating conditions on the electrical characteristics in a dielectric barrier discharge excited by voltage pulses are systematically investigated by means of a 1-D fluid model. The operating conditions refer to barrier fashion, secondary electron emission coefficient \gamma, gap width dg, dielectric constant \varepsilonr, and dielectric thickness ds. Under different operating conditions, the important characteristic quantities of describing the pulse discharges, i.e., discharge current density Jg, breakdown voltage Vb, averaged electron density Nave, averaged dissipated power density Pave, and axial distributions of both electron density Ne and electron temperature Te, are calculated and analyzed in detail. The present work gives the following significant results. There are almost no effects of the operating condition on the characteristic quantities except for the amplitude of Jg in the first discharge if the accuracy of the model is taken into account. The peak value of Ne nearby the momentary cathode (MC) becomes larger, and large Nave can be obtained by small Pave by increasing \gamma of the MC. For small dg, the breakdown of the gap occurs earlier, and for large dg, both the small peak value of Ne and the wide area of quasi-neutral plasma bulk can be obtained. All of the parameters except for Vb in the second discharge decrease, the peak value of Ne nearby the MC gets smaller, and the Te in the cathode sheath presents lower, when decreasing \varepsilonr or increasing ds. [ABSTRACT FROM AUTHOR]

Microplasma can be found in many applications. The technology is also used for surface treatment of polymers. The process of surface treatment by microplasma is environmental friendly, and it could be realized at low cost due to the relatively low discharge voltage (around 1 kV) even under atmospheric pressure and the small size of the power supply and reactor. This paper presents the surface treatment by microplasma of polyethylene naphthalate (PEN) film using Ar gas and mixtures of Ar with \N2 and \O2. The microplasma process was analyzed by the emission spectroscopy method. An experimental Marx generator with MOSFET switches was used as a pulsed high-voltage power supply. The emission spectra were measured by an intensified charge coupled device camera, a spectrometer, and a photomultiplier tube. Surface wettability of the PEN film was confirmed by measuring the contact angle before and after the microplasma surface treatment. It was observed that the contact angle of the PEN film decreased, especially with the \O2/\Ar mixture. The analysis using an X-ray photoelectron spectrometer showed the decrease of C1s, which correspond to the C-H bond. The emission spectrum of the microplasma discharge in the \N2/\Ar mixture showed Ar peaks, OH peaks, \N2 second positive band system peaks (\N2 SPS), \N2 first positive band system peaks ( \N2 FPS), and decrease in the peak intensities of ArI and OH for microplasma discharge in the \O2/\Ar mixture. The lifetime emission signals for the \N2 SPS for the microplasma discharge in 0.25% \N2 in Ar were around 1 \mu\s. The calculation of the microplasma rotational and electron temperatures shows low rotational and high electron temperatures. [ABSTRACT FROM AUTHOR]

It remains a challenge to generate cold air plasma at atmospheric pressure. In this paper, a room-temperature atmospheric-pressure air plasma plume is generated by a dc power supply. Current–voltage measurements show that the discharge actually appears periodically with a frequency of about 25 kHz. The discharge current has a pulsewidth that is less than 100 ns while its peak value reaches about 17 mA. There is no risk of glow-arc transition. The plasma can be touched by a bare hand without any feeling of electrical shock or warmth. The maximum length of the plasma is about 2 cm. The whole device, including the power supply, is less than 1 kg. The preliminary inactivation experiment results show that the plasma can effectively kill Enterococcus faecalis, one of the main types of bacterium causing the failure of root canal treatment. [ABSTRACT FROM AUTHOR]

In this paper, the deposition and characterization of plasma-polymerized polystyrene (pp-PS) using PECVD under atmospheric pressure on a variety of substrates was investigated. An atmospheric RF plasma torch and an HF dielectric-barrier- discharge (DBD) system were used to deposit thin pp-PS coatings on PTFE, HDPE, stainless steel, glass, and silicon wafer. The styrene vapor was carried by Ar or He. The pp-PS films were characterized by Fourier transform infrared spectroscopy (FTIR) (infrared reflection absorption spectroscopy), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA), static secondary ion mass spectroscopy (SSIMS), and optical microscopy, and the plasma phase was studied by optical-emission spectroscopy. The major features that characterize PS are present in the FTIR, SSIMS, and XPS spectra of our films, although some differences are observed between pp-PS and their conventionally polymerized counterparts: oxygenation, branching, degree of cross-linking, and unsaturation. According to the WCA and XPS results, the films deposited by the RF plasma torch (placed in a Plexiglass chamber) are more oxygenated than those deposited by DBD, which is operated under a much more controlled atmosphere. A comparison of the chemical structure of the deposited coatings (branching, cross-linking) as a function of the nature of the earner gas was established by FTIR: pp-PS synthesized in the presence of Ar (for both processes) exhibit more branching and a higher degree of cross-linking than pp-PS synthesized with He as the main plasma gas. The optical microscopy points out a diversity of structures that depend on the nature of the substrate and the plasma parameters. [ABSTRACT FROM AUTHOR]

This paper describes a procedure for experimental determination of metastable and resonant populations along a surface wave argon plasma column at atmospheric pressure. As modeling work progresses extensively, an experimental database is necessary to confirm these models. Obtained results, within the range of values reported in literature, indicate that densities of metastable and resonant levels grow along the plasma column for positions near the energy coupler device, where the energy of the surface wave which creates discharge is the highest. This behavior is also found for electron density and temperature; however, it is not the same for gradient. Therefore, at atmospheric pressure, populations of 4s levels are not only controlled by collision with electrons from ground state, but the dissociative recombination mechanism is also important, in agreement with results found by other authors using collisional-radiative models. [ABSTRACT FROM AUTHOR]