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Deposition of transparent oxide films at atmosphere pressure onto polymeric substrates at room temperature is a technique gaining rapid acceptance. These films can be used for numerous applications such as antiscratch and water permeation barrier coatings. In this paper, a \sim 1.4 - \mu \text{m} SiOx layer has been deposited on polypropylene-coated paper at atmosphere pressure with a filamentary dielectric barrier discharge (DBD). The DBD linear discharge was driven by a 30-kHz power supply. Scanning electron microscope, X-ray photoelectron spectroscopy, and attenuated total reflection-Fourier transform infrared spectroscopy were used to characterize the deposited film. The deposited thin film decreased water permeation through the paper by \sim 15$ %. [ABSTRACT FROM PUBLISHER]

In this paper, a complete flux scheme (CFS) has been implemented in 1-D fluid model for simulating the pulsed dielectric barrier discharge (DBD) in pure argon at atmospheric pressure. The characteristic quantities of the pulsed DBD have been systematically calculated by using the CFS and presented in comparison with those by using the exponential difference scheme (EDS). This paper shows the following results. There is the two-pulse discharge mode in the present simulation. The two discharge currents obtained using the CFS and EDS converge to the same result in good agreement with the experiment as spatial step length decreases, but the CFS has a fast convergence performance compared to the EDS. With a small grid number, the numerical scheme has an evident effect on the characteristic quantities in the time region corresponding to the first discharge pulse. This paper suggests that in the pulsed DBD, the usage of the CFS with a properly small grid number can give more accurate result and also presents a high calculation efficiency. [ABSTRACT FROM AUTHOR]

In this paper, atmospheric-pressure air and oxygen corona plasma jets under water surface have been used to generate plasma-activated water (PAW) to inactivate colletotrichum gloeosporioides (C. gloeosporioides) suspension. The atmospheric-pressure plasma jets in the water were characterized by measuring: 1) the electrical and optical properties for evaluating the plasma efficiency and 2) the physicochemical properties of PAW, including pH value, oxidation-reduction potential value, and the concentration of hydrogen peroxide, nitrite, and ozone. The aim of this paper is to investigate the effects of long-lived reactive oxygen and nitrogen species (RONS) and environmental factor (acidity) in PAW on fungicidal property. The results of antifungal activity show that the inactivation rate of C. gloeosporioides is higher using air-PAW than oxygen-PAW, and increases with increasing reaction time when preparation time of PAW is fixed as 30 min. This correlates well with measurements of the aqueous-phase long-lived RONS concentration such as nitrate and ozone, suggesting these species play crucial roles in the inactivation process. [ABSTRACT FROM AUTHOR]

This paper was prepared in response to the growing interest in the numerical simulation of the gliding arc (GA) discharge. Our approach is rather simple 2-D modeling of the GA, in the plane that is parallel to the gas flow and perpendicular to the discharge current. We used Fluent software with a subroutine that calculates electric conductivity of argon plasma and local heat release due to the electric current of predetermined value. Electric conductivity of argon was calculated as function of the reduced electric field and gas temperature. Our results show that this approach can give very useful information about the gas-discharge interaction, which is very important to capture the discharge behavior. Presence of discharge inside the gas flow significantly disturbs both of them. Gas-discharge slip velocity exists at least at the beginning of GA development cycle even if there is no mechanism of the discharge deceleration. Just original spark formation associated with the electrode surfaces results in the appearance of this “independent” slip. In the cases of reasonably high gas velocities and discharge currents, this initial slip does not disappear during the discharge lifetime and can result in significant discharge cross-sectional elongation along the gas flow. Electric field fluctuation at any particular part of the discharge channel can be very large, and this can have the major effect on the nonequilibrium ionization and chemical processes. [ABSTRACT FROM PUBLISHER]

In this paper, the effects of aluminum nitride and alumina ceramics on the discharge mode of He/O2 mixed gas are studied and compared. It is found that when the O2 volume fraction is in the range of 0.2%–1%, dielectric barrier discharge (DBD) with Al2O3 is always in the unstable filamentary mode, and homogeneous and filamentary modes are observed in DBD with AlN. Under the homogeneous discharge mode, there is only one current pulse each half-voltage cycle, and the intensified charge-coupled device discharge image shows that it is glow discharge. The relative permittivity and surface charge decay characteristics of AlN and Al2O3 are measured. The experimental results show that the relative permittivity of AlN is lower than that of Al2O3, but its surface charge decay is obviously slower than that of Al2O3. The derived electron trap density from the surface charge decay of AlN ceramic is higher than that of Al2O3, which shows AlN has a strong charge capacity and can emit more electrons in the second half cycle of the discharge. The higher secondary electron emission coefficient can make the discharge ignition voltage lower and the formation of stable homogeneous discharge easier. This paper provides a new control method for expanding homogeneous discharge in He/O2 mixed gas. [ABSTRACT FROM AUTHOR]

This paper describes the time evolution of ball plasmoids generated by millisecond atmospheric discharge in contact with water. The aim of this paper was to clarify an initiation and a formation mechanism of an atmospheric ball plasmoid. The use of a higher frame rate of filming and shorter exposition time, in comparison with past experiments, allows us to observe the fast processes that occur during a plasmoid evolution. We assert that an initial electrical breakdown in a cathode ceramic tube filled by a conductive liquid is essential for further plasmoid formation. It generates a shock wave resulting in a blast of conductive liquid. The resulting expansion of water vapor and bubbles with an addition of weekly ionized plasma serves as a main source of matter for plasmoid formation. We also note that an electrical arc generated after the breakdown transforms to a plasma jet. This jet accelerates plasma to the plasmoid. [ABSTRACT FROM AUTHOR]

To enhance the heat dissipation of high-power light-emitting diodes (LEDs), corona wind based on corona discharge was promoted. In this paper, we aimed at reinforcing the intensity of corona wind by modifying the needle electrode with graphene solution. To explore the differences in the graphene-coated electrode and the original bare electrode on the electrical characteristics, the intensity of corona wind, and LED heat dissipation, a corona wind cooling system and a thermal test system were built for the experimental study. The results showed that the graphene-coated electrode system could produce corona wind at a lower voltage. In addition, the discharge current of the graphene-coated electrode system is higher than that of the bare electrode system under the same discharge voltage. The graphene-coated electrode system can induce a faster corona wind and the highest speed is about 3.4 m/s, showing that it is more efficient than the bare electrode system in corona wind production. Moreover, the temperature drop of LEDs for the graphene-coated system is greater, which means that the corona wind cooling system can reduce the junction temperature of the LED chips effectively. Ultimately, as the discharge power increases, the average convective heat transfer coefficient increases. Indeed, the result of this paper can be used for the wide variety of the graphene-coated corona wind generator application as a promising technology for the LED heat management. [ABSTRACT FROM AUTHOR]

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]

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]

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]

In this paper, an investigation of the control of electron energy in the atmospheric-pressure helium plasma jet produced by a needle–plane discharge system has been performed by means of the numerical simulation based on a 2-D self-consistent fluid model. Due to the consideration of practical application of the cold atmospheric-pressure plasma jet (CAPPJ) in the fields of biomedicine, in this paper, the mean electron energy (MEE) nearby the cathode plane is accounted for. The parameter dependences of the MEE have been systematically calculated. The considered parameters include the voltage amplitude and rising time $t_{r}$ of the applied voltage pulse as well as needle electrode radius. The voltage amplitude is changed in the range from 3 to 19 kV, and $t_{r}$ is from 1 to 200 ns. The spatial electric field has also been analyzed in detail because of its dominant role in controlling electron energy. In addition, the effect of electron energy on the production of the reactive species OH, O3, and H2O2 has also been investigated when considering the addition of humid air to the working gas helium. This paper gives the following significant results. For a given $t_{r}$ , the MEE increases almost linearly with increasing voltage amplitude. The effect of voltage amplitude on the MEE becomes much more evident for smaller $t_{r}$ and is obviously weak for the $t_{r}$ with a few hundreds of nanoseconds. Fixing the voltage amplitude, the MEE decreases with the increase in $t_{r}$. The dependence of the MEE on $t_{r}$ is evident for a high voltage amplitude and the reverse is true for the lower voltage amplitudes. As a whole, the higher voltage amplitude and smaller rising time $t_{r}$ or their synergism should be considered for obtaining high electron energy. Especially, an MEE of about 10 eV can be obtained, which covers the energy thresholds inducing all the processes of dissociative electron attachment to water molecule and thus is of essential importance for the production of the reactive species such as OH, H2O2, and O3 in the interactions of plasmas with the aqueous solution embedded in biofilms or tissues. The needle electrodes with different radii result in a minor variation of the MEE under the fixed voltage amplitude and $t_{r}$. Therefore, changing the radius of the needle electrode is not an effective solution to the control of electron energy in the CAPPJ. Furthermore, the parameter dependence of the spatial electric field is similar to that of the MEE, which reveals the dominant role played by the spatial electric field in controlling electron energy in CAPPJs. Considering the addition of humid air to the working gas helium, with the increase in electron energy, the averaged densities of OH and O3 increase, but that of H2O2 decreases. [ABSTRACT FROM AUTHOR]

Multilayer dielectric barrier discharge (DBD) can efficiently enlarge the volume of homogeneous plasma and its interactional surface area with materials in vertical space, which seems attractive to the industry application. In this paper, a new plasma generator of DBD structure which has multilayers of dielectric barrier boards excited by repetitive submicrosecond pulsed power (0 to -100 kV, 130 Hz-1 kHz, pulsewidth 230 ns, and rise time 120 ns) is introduced, and homogeneous plasma has been obtained in atmospheric pressure air. Experiments on high-speed photography with an exposure time of 5 ns have been carried out to the discharge with three layers of dielectric barrier boards with each gap width of 2 mm. It demonstrates that luminance of the discharge distributes uniformly throughout the upper and the lower gaps. Also, the result of the time evolution image of a three-layer DBD is discussed in this paper, which shows that the two layers of luminous intensity keep good consistency with each other, and this indicates that breakdown of each gap layer happens at the same time in a multilayer DBD. A preliminary processing experiment for polytetrafluoroethylene film has been carried out by adopting homogeneous triplelayer DBD plasma. By testing the water contact angle of the polymer surface before and after the treatment, it was found that hydrophilism of the surface and efficiency of treatment could be effectively improved by the processing of each layer of discharge plasma. [ABSTRACT FROM AUTHOR]

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 explores the effects of tube shape and pin electrode diameter on the plume generation and electrical characteristics in atmospheric pressure helium plasma jets generated from a centered-pin electrode inside a dielectric tube. The quartz-covered (or bare) pin electrode and different shapes of the dielectric tube (straight cylinder or conical shape) are employed and their effects are investigated. Optical emission spectra are obtained at different positions along the coaxial direction to determine the axial distributions of the electron excitation temperature for the straight cylinder and conical jets. The rotational temperatures for the both jets are also compared. [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]

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]

The dielectric-barrier discharges (DBDs) under airflow have been widely used in the fields of airflow control, plasma-assisted combustion, and surface modification. Our previous work demonstrates that the discharge intensity under airflows could be adjusted by a discharge configuration with upstream and downstream electrodes. In this paper, a further investigation of discharges under airflows is processed with a multicathode DBD configuration. With the injection of airflows to the discharge region, the first upstream region produces a decrement of discharge intensity, while the following downstream region always provides greater discharge intensity than that of the adjacent upstream discharge region. An optimal discharge configuration is found by appropriately selecting the distances between the cathodes, wherein the last downstream region can produce maximum discharge intensity. The mechanisms are analyzed by considering the transport effect of airflows and the lifetime of charged and metastable particles. The charged and metastable particles are transported to the downstream region, and these particles always act as the responsible seeds to enhance the downstream discharges. In addition, due to the limited lifetime of charged and metastable particles, the enhancement effect may be weakened under long transport distances. Finally, potential applications for multicathode DBDs are also provided. [ABSTRACT FROM AUTHOR]

The characterization of an atmospheric pressure microwave argon plasma in the form of a plasma sheet and the results of its use in the investigation of the wettability modification of polyethylene (PE) surfaces are presented in this paper. The spectroscopic investigations performed indicate a plasma temperature at the level of 750–1100 K and an electron density at the level of 2.9– $5.4\times 10^{14}$ cm−3. The following PE-type specially prepared materials were subjected to the plasma treatment process: PE (pure low-density PE), PE + UV (PE with a UV stabilizer), PE − UV + M (with a UV stabilizer and a montmorillonite), PE + S (PE with soot), and PE − F (PE with a UV stabilizer, a montmorillonite, and soot). The experimental investigations prove the high potential of the presented method for the PE surface activation in industrial applications. The atomic force microscopy scanning of samples was performed before and after the plasma treatment. The aging of the adhesion enhancement effect indicates that the water contact angle is related to the surface energy changes. [ABSTRACT FROM AUTHOR]

The capacitively coupled radio frequency double-pipe plasma discharge jet is used for the etching process. An argon carrier gas is fed through the atmospheric-pressure plasma source; octafluorocyclobutane (C4F8) etch gas is injected into the plasma. Etchings were carried out on a crystalline silicon substrate. The etching characteristics are discussed and the etch rate tendency shows the reliance of C4F8 gas flow rate and oxygen addition. The optimum etching rate of $7.2~\mu \text{m}$ /min was obtained at a plasma power level of 100 W and C4F8 gas flow rate was 250 sccm. From surface profile detection, it displays the etch profile under this atmospheric-pressure plasma jet treatment. This plasma technique could offer a breakthrough for chamber-free dry etching processing. [ABSTRACT FROM AUTHOR]

In our previous study, internal stress was suggested as the mechanism causing the deterioration of paint adhesion through atmospheric-pressure plasma irradiation. In this paper, this mechanism is examined in detail. According to the Japanese Industrial Standards (K-5600-5-7), we evaluate the experimental results by varying some parameters. An applied voltage of 10 kV, plasma irradiation distance of 10 mm, and plasma irradiation duration of 60 s are the parameters that resulted in the peeling of the paint at a lower peeling-off load. In addition, from the simulation results, the generation and thermal input of a plasma streamer are confirmed and considered as one of the factors causing the paint to peel more readily. [ABSTRACT FROM AUTHOR]

When the pressure and temperature of a fluid exceed a critical point, the fluid enters into the supercritical (SC) region. In this region, the physical properties are believed to be in favor of a good current interruption medium. This paper focuses on the arc voltage characteristics of nitrogen arcs burning inside cylindrical tubes at different filling pressures: 1, 20, 40, and 80 bar, thus covering the SC region. Two different tube materials have been used in the experiments, alumina and polytetrafluoroethylene. Arc voltages are measured for arcs burning inside tubes of 2, 4, 8, and 15 mm inner diameters. In addition, free-burning arcs have been investigated at the same filling pressures. The arc current was 150 A at 350 Hz throughout the study. The arc voltage is found to increase with decreasing inner diameter of the tube at atmospheric pressure. At higher filling pressures (i.e., 20, 40, and 80 bar), however, such a simple relationship is not observed. The arc temperature and radius have been calculated based on the “simple theory of free-burning arcs” and the “two-zone ablation arc model.” The calculated arc radius decreases with increasing gas pressure. Furthermore, due to increased absorption of radiation at high filling pressures, ablation is found less significant for ultrahigh-pressure nitrogen arcs compared to atmospheric pressure arcs. This is in line with the observations from optical micrographs of the inner surfaces of the tubes exposed to arcs at different filling pressures. [ABSTRACT FROM AUTHOR]

The properties of corona discharge in practical applications are strongly influenced by the variation of environmental parameters. A 2-D axisymmetric hydrodynamic drift–diffusion model coupled with Poisson’s equation and three Helmholtz differential equations is established to investigate the effect of environmental temperature on negative corona discharge under the action of photoionization. This numerical model is performed by a traditional needle-to-plane configuration in dry air at atmospheric pressure. The characteristics of Trichel pulses, negative ion density, electric field, and electron density are discussed in this paper. It is found that the magnitude of Trichel pulses, first pulse duration, and pulse frequency increase with increasing the ambient temperature. Moreover, the effect of photoionization under these conditions is also investigated by simulations intensively. [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]

Plasma needle is a novel design of a plasma source at atmospheric pressure to achieve a nonthermal plasma jet. The advantage of the plasma needle is that it can be operated in open air, outside a vessel. The plasma that is generated with the plasma needle is small (about 1 mm) and nonthermal; the temperature of the neutral particles and ions are in about room temperature and suitably can be used to treat living biological cell without damaging the cell. In this paper, we report design, development, and electrical and optical emission spectroscopy characterization along with applicability in biomedical investigation of a dc plasma needle that can easily interact with living cell/human finger. Argon gas is used to operate the plasma needle, and the plasma jet is operated on water surface instead of human finger for stability during the characterization. The electrical diagnostics of the plasma needle shows that the discharge is pulse in nature. It has been observed that the increased in the applied voltage increasing the discharge frequency without affecting the discharge voltage and discharge current. The frequency of the discharge is found to increase almost linearly with increasing applied voltage. The estimated excitation temperature by using Boltzmann’s plot method from OES is found almost independent on the applied voltage. The temperature is found to increase with increasing ballast resistance at above a threshold value of the resistance, below of which, the temperature is found almost constant. The variation in separation between the tip of the plasma needle and the water surface did not show any considerable variation in temperature when the separation is higher than 5 mm. However, considerable increase in temperature is observed when the separation is decreased below 5 mm. The developed plasma needle has been also used to treated Nova Blue bacteria and water collected from drinking water dispenser of pets, and the results shows the applicability to treat microbes in localize region. [ABSTRACT FROM AUTHOR]

In this paper, a low-cost and portable plasma device is developed to generate atmospheric pressure nonthermal air plasma jet for safe and effective biomedical applications. The device mainly consists of a pen electrode, a high-frequency ac power supply, an ac/dc module, and a dc air pump, and it totally costs only U.S. $63 and has a small size of 280 mm $\times190$ mm $\times180$ mm. The appearance of two-mode discharge of half-wave and full-wave breakdown with the changing of applied voltage is identified, and the length of the plasma jet is optimized through studying on the influences of distance between two electrodes, gas flow rates, and hole diameters of the gas outflow in ground electrode. Stronger plasma with a longer jet length of 12 mm can be obtained in the full-wave breakdown discharge mode, while moderate plasma with a length of 8 mm can be obtained in the half-wave breakdown discharge mode. The discharge characteristics of the device such as the main generated active particle, voltage and current, discharge power, and operation temperature are obtained. It is shown that rich active species for biomedical application can be generated at low power of approximate 2 W and low operation temperature of approximate 40 °C. The developed device is tested for biomedical application, and the results of effective sterilization of C. albicans and blood coagulation are obtained. [ABSTRACT FROM AUTHOR]

A 2-D fluid model is developed to study the pulsed discharges with pin--plane electrode in atmospheric pressure. A positive streamer forms at the pin electrode connecting to the applied voltage and then propagates toward to the ground plane electrode (cathode). Simulation results show if the streamer head is close enough to the cathode, in front of the original streamer a new streamer forms, and simultaneously a second positive current peak is observed, suggesting that the discharge mode transforms into glow mode. Otherwise, the discharge operates at corona mode. The characteristics of the two typical discharge modes are analyzed through the spatiotemporal evolution behaviors of conduction current, electron density, electric field, and electron flux. The transition between corona and glow modes depending on the discharge parameters such as applied voltage, curvature radii, and secondary electron emission coefficients are studied in this paper. It should be noted that no matter what discharge mode is, discharge with reversed direction appears at the falling edge of voltage pulse, which is caused by space charges [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]

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. [ABSTRACT FROM PUBLISHER]

This paper reports that a plasma generator at atmospheric pressure, which is characterized by double dielectric layers and a stable dielectric-barrier discharge (DBD) excited by a sinusoidal power supply of 30 kHz, successfully generates a low-temperature argon plasma jet. The DBD has a coaxial and cylindrical configuration, with an annular gap of 2.35 mm between the inner and outer quartz tubes. The rotational (Trot) and vibrational (Tvib) temperatures of the DBD are measured by fine structure fitting of the emission bands of UV OH, N2 molecules, and the Boltzmann plot method, and in comparison with the data of jet temperature obtained by an optical fiber thermometer. The obtained experimental results suggest that Trot and jet temperature increase with the peak applied voltage (Vp) . On the other hand, they are inversely proportional to the argon gas flow rate. In addition, Tvib is found to be insensitive to Vp and gas flow rate. Furthermore, the correlation between electrical diagnosis and ultrahigh-speed photographs shows that there are two plasma jets at the positive and negative half cycles of the applied voltage. And the temporal and spatial evolution of the DBD inside the quartz nozzle and plasma jet is also elucidated. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

In this paper, an atmospheric pressure low-temperature plasma pencil generated in helium and helium/oxygen gas mixtures was characterized in detail for its discharge characteristics, plasma power, reactive plasma species produced, plasma density, and plasma temperatures using electrical and optical emission spectroscopy (OES) diagnostics, and its efficacy for biomedical application. A visible plasma plume length of approximately 27 mm was generated using a 60-kHz ac HV power supply. The OES results showed the most intensive plasma emission lines of OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=0) at 308 nm and OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=1) at 287 nm, O I transition 3p^5P\to 3s^5S^0 at 777.41 nm, O I transition 3p^3P\to 3s^3S^0 at 844.6 nm, and N2(C\-B) second positive system with electronic transition C^3\Piu{\to}B^3\Pig in the range 300–450 nm. The effects of controlled oxygen content on the plasma pencil and on various helium plasma emissions and electrical properties are studied. A spatial distribution of reactive plasma species produced by the plasma pencil is presented. The electron density of plasma jet was estimated to be in the order of 2.1\times 10^14~cm^-3 using Stark broadening line profile of the hydrogen alpha emission. The temperatures of afterglow plasma pencil were evaluated using OH rotational temperatures, and the results demonstrate temperatures of 316 and 362 K for pure He and He/ O2 gas mixtures (0.1% O2 ), respectively. Preliminary results on inactivation of Streptococcus pneumoniae on a solid surface and in liquid suspension were carried out using the plasma pencil for biomedical applications. [ABSTRACT FROM PUBLISHER]

Atmospheric pressure plasma jets (APPJs) have attracted considerable interests due to their low-temperature and easily controlled features. In order to cover a larger area for broader applications, spatially extended atmospheric plasma arrays are designed and constructed by a number of packed plasma jets. Despite their outstanding stability and flexibility, it remains a challenge for the jets to form large-scale uniformity on downstream substrates due to complex electrical and hydrodynamic interactions. In this paper, we use a 2-D temporally evolving code coupling electric, flow, and temperature fields, as well as chemical reactions to study synergistic effects of the multi-fields coupling on discharge and propagation characteristics of the jet array based on a USim software framework. The influence of gas flow and a substrate downstream on the plasma jets dynamics and uniformity are investigated by the model. Also, essential strategies for uniformity modulation are acquired. Results show that the balanced evolution of the ionization process and the effective merging of discharge channels could be realized by modulating the gas flow field. Therefore, a homogeneous distribution of plasma downstream can be obtained by adjusting the gas flow field properly, which provides a new efficient way for the uniformity control in the field of plasma processing. [ABSTRACT FROM AUTHOR]

Presents the table of contents for this issue of the periodical. [ABSTRACT FROM PUBLISHER]

Unintended atmospheric pressure dc arc is very common and harmful in many power applications. There is still no effective detection method for series dc arcs. In this paper, the initial features of current and electromagnetic signal of series dc arc are investigated on an arc generation platform. It is found that the current varies abruptly at the starting moment of the arc, and then a series of stochastic pulses can be observed. Corresponding to the current pulses, electromagnetic pulses are also measured by antenna simultaneously. Based on the abrupt current variation and unique pulse-time pattern features of the series dc arc, a fault detection algorithm is proposed. The proposed algorithm is proved to be robust and effective. [ABSTRACT FROM PUBLISHER]

In this paper, we study the discharge modes of pulsed dielectric barrier discharge (DBD) in atmospheric nitrogen by means of a 1-D self-consistent fluid model. The results show that different from the atmospheric nitrogen discharges driven by sinusoidal voltages, which usually operate in Townsend discharge mode, the pulsed atmospheric nitrogen discharges can be generated in glow mode over a wide parameter range. Base on the numerical data, the discharge mode seriously depends on the voltage changing rate ( $dV/dt$ ) at the rising and falling phases, and with the decrease of the voltage changing rate, the discharge can transfer from glow mode to Townsend mode. In the glow discharge mode, the numerical data show the density of N2+ is much larger than that of N4+, indicating the direct ionization of N2 by electron impact is the primary ionization mechanism, however, the Penning ionizations between two metastable molecules play a dominate role in the Townsend discharge mode, resulting in the concentrations of N4+ ion much higher than that of N2+ ion. [ABSTRACT FROM AUTHOR]

The influence of gas pressure and electrical parameters on low-pressure plasma has been investigated in this paper. A fast intensified charge-coupled device (ICCD) imaging is utilized to examine the dynamics of plasma bullet and plasma plume length at different pressure and plasma parameters. The experimental results reveal that the gas pressure has great influence on both the length of the plasma and on the propagation velocity of the plasma bullet. By increasing the gas pressure from 15 to 15 000 Pa, both the length of the plasma jet and the velocity of the plasma bullet first increase and then decrease. The maximum value of plasma plume occurred at 100 Pa, in which the propagation velocity gets the maximum value of 5\times 10^6 m/s. Further increasing the gas pressure to 15 000 Pa results in decrease in both the plasma length and bullet velocity. Relative to voltage, the frequency of the applied pulse voltage has a different impact on the plasma propagation at different gas pressures. While a higher voltage induces a longer plasma plume and a faster propagation velocity at both 30 and 2000 Pa, increasing the frequency has little influence on plasma at 30 Pa but reduces the plasma length and propagation velocity observably at 2000 Pa. In addition, an exotic plasma plume structure is observed by ICCD. A possible hypothesis is discussed here to explain this phenomenon. These experiments may lead to a more precise control of the low-pressure plasma, warranted for advanced materials technologies. [ABSTRACT FROM AUTHOR]

The atmospheric pressure plasma jet (APPJ) has become one of the hot research issues in plasma science and technology. In this paper, a cold Ar APPJ is generated using a dielectric barrier discharge configuration device equipped with an inverted tapered tube (ITT). Its characteristics are investigated by optical and electrical diagnostics, including discharge images, voltage–current waveforms, and optical emission spectra (OESs). The parameters, such as discharge power, gas temperature, and electronic excitation temperature (EET), are calculated and analyzed. All the above characteristics and parameters are compared with those of Ar APPJ generated with a conventional straight tube (CST). Furthermore, by numerical simulation, the flow field distribution of the ITT and CST is obtained and compared. The results show that the use of the ITT can raise Ar flow velocity, improve the distribution of Ar mole fraction, and Ar flow field. Moreover, the discharge power for the ITT is lower than that for the CST, so are the gas temperature and EET. The difference between theOESs is less obvious. Finally, the plasma plume develops along the inner surface of the CST with bits of apparent filamentary discharge, but along the central axis of the ITT and manifested as a stable and homogeneous discharge, which might be more promising for material processing and biomedical application in some cases. [ABSTRACT FROM AUTHOR]

The parallel operation of array microhollow cathode (MHC) discharges is studied to generate high density of electrons owing to its multichannel MHC discharges. To ignite all the holes synchronously in one pulse, a pretrigger device is introduced, which is composed of three layers (two electrode layers and a dielectric layer). With the pretrigger process, some initial electrons can be injected into the holes, which makes array MHCs easier to ignite and improves the behavior of parallel operation. In this paper, the array MHC discharges with pretrigger in one pulse mode are presented and the influence on the parallel operation of the pretrigger process is studied. At last, the simulation result is given to have a better understanding of the pretrigger mechanism. [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]

In this paper, the evolution and transition mechanisms of typical nonlinear phenomena in an atmospheric pressure helium dielectric barrier discharge (DBD) are investigated from the perspective of transient evolution properties through fluid modeling. By gradually up-regulating the interelectrode gap width, the discharge (steady state) evolves from symmetric single-period (SP1), through asymmetric single-period (AP1), into Period-2 (P2) state. Similar evolution trace can also be obtained when increasing the driving frequency. Right after the initial breakdown, the discharge goes through several transient periods featuring unstable asymmetric current pulses before the establishment of steady-state discharge. As the bifurcation parameter increases in excess of the critical value, the discrepancy between the seed electron level of positive and negative discharges accumulates over the transient periods, switching the discharge into AP1 state. After then, a further elevation in the gas gap width (or driving frequency) leads to the generation of a “moderate intensity” positive pulse. With the “moderate intensity” positive pulse and a stronger positive pulse emerging alternatively in the temporal waveform sequence, the discharge evolves into P2 state. Finally, based on the transient evolution mechanisms, a preliminary state-controlling method regarding the use of a first-peak-leveled applied voltage is proposed, which may shed light on the modification of nonlinear states in some practical DBD application scenarios. [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]

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]

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]

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 dg , dielectric thickness ds , and relative dielectric constant \varepsilon r , the important characteristic quantities of describing the discharge, i.e., maximum discharge current density Jm , averaged electron density \mathrmNe-\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, Jm , \mathrmNe-\mathrm {ave} , and P\mathrm {ave} decrease with the increase of d\!g , and these characteristic quantities decrease with the increase of ds , 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. [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]

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

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]