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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]

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]

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, 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]

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]

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]

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]

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 deals with the realization of a diffuse dielectric barrier discharge in air at atmospheric pressure using a high-voltage pulse generator operating in a single-pulse mode and at frequencies of tens of hertz. This paper is focused on the effects of the series resistor and dielectric materials. It is shown that the parameters of the external circuit strongly influence the discharge mode. [ABSTRACT FROM PUBLISHER]

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]

The bare conductor in switchgear constitutes complicated air gaps, and their AC withstand characteristic will obviously affect switchgear insulation performance. In this paper, AC withstand tests of various types of air gap were carried out. The air gap samples were rod-plane air gap and 4 typical types of air gap from the bus chamber of 40.5 kV metal-enclosed switchgear. The samples were tested in climate chamber where high altitude environment was simulated. And correction of withstand voltage for switchgear air gaps at low air pressure were conducted. Test results indicate that, the withstand characteristic of 4 typical types of air gap in switchgear are different from that of rod-plane air gap. The relationship between withstand voltage Uw and air gap distance d is nonlinear. The influencing characteristic exponent n of air pressure on Uw is related with air gap type. Linearity value m and air pressure index n are independent to some degree. An equation was proposed to express the relationship of Uw with air gap distance d and altitude H, and this equation can be used to calculate the safety distance of air gaps in switchgear under low air pressure situations. The results are significant for the design and selection of switch devices. [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]

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]

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]

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]

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 ultrawideband (UWB) system has been a subject of research in the last few decades due to its utility in various high-power electromagnetic applications. Effectiveness of the UWB system, for the targeted performance, is expressed mainly in terms of the intensity and the frequency spectrum of the radiated field. If the system is simultaneously meant for high-energy output with good pulse repetition rate and jitter then the performance of the source of the UWB system, i.e., the pulsed power system, and in particular, the switch becomes extremely important. This paper presents the work carried out on such a UWB system with focus on the experimental investigations performed on a 50 kV pulsed power system. The switch of the pulsed power system is designed to use various dielectric gases, such as dry Air, N 2, SF6, and a mixture of these gases as the switching media at varying pressures which are above and below atmospheric pressure levels. For gas pressures above the atmospheric pressure level, the relationship between the switch breakdown voltage and the gas pressure as well as between the rise time and the gas pressure have been studied. Rise time performances of the switch for various pure gaseous media have been estimated. Jitter and shot life performance of the switch for N2 and SF6 as the switching media have also been studied. Effect of shot life on the switch jitter has been evaluated for N2 filled switch for a shot life of 10.8 × 106 shots. In case of switch filled with subatmospheric pressure SF6 gas, the rise time as a function of pressure has been characterized up to a voltage level of 45 kV. The Paschen's curve for the subatmospheric pressure levels is also derived from the results. [ABSTRACT FROM AUTHOR]

A cold Ar atmospheric pressure plasma jet generated using a DBD configuration device equipped with two powered electrodes as well as a grounded ring electrode driven by a sinusoidal excitation voltage at 38 kHz is presented in this paper. In this paper, properties of the jet discharge are studied by electrical diagnostics, including applied voltage, conducting current, and average absorbed power. Moreover, the optical emission spectroscopy is used to measure the plasma parameters, of which the electronic excitation temperature is determined by the Boltzmann's plot method using ten characteristic lines of Ar from 3p^54p \rightarrow 3p^54s and 3p^55p \rightarrow 3p^54s transitions whereas the gas temperature is obtained by using a fiber thermometer (FISO FOT-L-SD). It has been found that the conducting current, average absorbed power, the excitation temperature, and gas temperature increase with the applied voltage. On the other hand, these parameters are inversely proportional to the argon gas flow rate. What is more is that the production of oxygen radical (produced by the collisions between oxygen molecule from atmosphere and high-energy particles in plasma effluent) at a gas flow rate of 2 slm is investigated by means of optical actinometry, which is found to increase with the applied voltage. [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]

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]

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]

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]

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]

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]

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]

In this paper, the optical emission spectroscopy (OES) of plasma pencil generated at atmospheric pressure with pulsed voltage was studied. Single-electrode and two-electrode configurations to approximate the conditions during various material treatment have been compared. By means of time-resolved OES, particle behavior during pulse duration, particularly atomic and molecular components represented by Ar lines and OH band, has been studied. The axial distribution of the rotational and the electron temperature showed that the presence of conductive material in plasma jet increased the rotational and electron temperature and even influenced the particle behavior inside the plasma nozzle. Furthermore, it was found that rotational temperature can be easily controlled by the duty cycle. [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 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]

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]

In this paper, an innovative coaxial-type dielectric barrier discharge plasma generator is proposed to produce the large-volume and visibly uniform cold argon plasmas at atmospheric pressure by enhancing the local intensity and uniformity of the electric field simultaneously with the aid of a cylindrical screwlike inner electrode configuration. The experimental measurements show that the discharges transit from the initial stage after breakdown to the stable stage through a transitional stage and finally reach an unstable discharge stage with the increase of the applied voltage. The estimated values of the electron temperature and the number density of the gas discharge plasmas in the electrode region vary in a small range, i.e., 8.0–8.9 eV and (\4.6–\6.4) \times \10^11\ \cm^-3, with increasing the applied voltage. Moreover, the plasma streams are quite uniform in the radial direction with a low gas temperature (\sim300 K) and an abundance of chemically reactive species in the stable discharge stage, which will be potentially a useful tool for the treatment of the heat-sensitive materials. [ABSTRACT FROM PUBLISHER]

In this paper, the formation of the avalanche, primary streamer, secondary streamer, neutral gas heating effects, striations, as well as the radial expansion of the discharge from the symmetry axis toward the boundaries in a constant voltage atmospheric pressure air-dielectric barrier discharge configuration are analyzed. A voltage of 11.2 kV is applied between two metallic parallel plates which are placed at a distance of 4 mm apart. Two rectangular blocks of dielectric medium of 1 mm thickness, each with a relative permittivity of 8, are attached to the cathode and anode metallic electrodes, leaving the remaining 2-mm air gap for the atmospheric air discharge to develop. A single electron is released at the cathode as an initial condition and the development of the barrier discharge with its associated heating effects is analyzed. It has been shown that the discharge exhibits phenomena of radial expansion toward the outer boundaries, forming patterns of striations/filaments along the discharge and temperature rising of ambient air to 490 ^\circ\K amounting to 63% increase above the ambient temperature. A secondary streamer has been observed traveling from the anode toward the cathode, after the primary streamer hits the cathode, and the primary and secondary streamer speeds were found to exhibit similar propagation speeds within the range 0.5 \times 10^5 - 5 \times 10^5\ \ms^-1. The secondary streamer was found to be associated with electron charge densities of the order of 0.5 \times 10^18 - 1.5 \times 10^18\ \m^-3, net charge densities of 1 \times 10^18\ \m^-3 and radial and axial electric fields of 0.5 \times 10^6\ \Vm^-1. [ABSTRACT FROM PUBLISHER]

The main process in oil refinery technologies is the cracking of the heavy fraction of oil into light and valuable hydrocarbons. Dielectric barrier discharge (DBD) reactors, working at atmospheric pressure and low temperature, is one of the newest methods for cracking hydrocarbons, which has been successfully used to crack low-carbon-containing molecules. Therefore, in this paper, the cracking of n-hexadecane as a heavy hydrocarbon fed by using the cylindrical DBD reactor (nonthermal plasma) has been investigated. We studied the effects of gas type, applied voltage, and gas flow rate quantitatively and qualitatively by using gas chromatography with flame ionization detector and mass spectrometry detector. Results showed that methane has better effects on both conversion and cracking percentage in comparison with air. Also, it has been shown that increasing the applied voltage and working gas flow rate enhances the conversion and the cracking percentages. The highest conversion percentage obtained was 9.26% when the applied voltage and methane flow rate were 12 kV and 50 sccm. In this condition, the cracking percentage obtained was 84.34% of the products. [ABSTRACT FROM PUBLISHER]

In this paper, the author develops a method of generation and characterization using an electrical model of a dielectric barrier discharge at atmospheric pressure. The principle of plasma generation is based on the resonant behavior of the secondary circuit of a modified flyback transformer, with the working frequency being 48 kHz. The plasma chamber is made of glass, and the working gas is helium with a flow rate of 0.44 L/min. The study refers to the homogeneous stage of the discharge which is characterized by a maximum power density of 6.4 \W/cm^3, electron current densities lower than 1.23 \mA/cm^2, and electron number densities in the range of 7.5 \cdot 10^8 to 2.7 \cdot 10^9\ \cm^-3, depending on the dc supply voltage. The gas temperature is slightly higher than the ambient one, with the plasma being nonaggressive with thermosensitive materials. [ABSTRACT FROM AUTHOR]

Several variations of dielectric barrier discharge (DBD) have been developed for nondamaging living-tissue sterilization and blood coagulation. This so-called floating electrode DBD (FE-DBD) has been shown by histology to not damage the treated tissue. Nevertheless, preliminary experiments show that a person who touches the FE-DBD can feel the discharge action. Some of these unpleasant sensations are related to the thermal effects of the plasma. These thermal effects and other important parameters of the discharge are strongly dependent on the electrical properties of the discharge, i.e., driving voltage and waveform shape. In this paper, we first employed sinusoidal driving waveform for medical applications. After that, in order to increase the uniformity and decrease the temperature, we employed a microsecond- pulsed waveform system with a few microsecond pulse durations. Both plasma systems have been analyzed and compared for thermal effects and temperature of the discharge in order to determine the possibilities to control the heating effect with driving waveform. [ABSTRACT FROM AUTHOR]

A nonequilibrium plasma flow produced uniformly in a tube was developed in this paper. The plasma was generated in polyvinyl chloride tube, 3 mm in inner diameter and 100 mm in length, between a wire electrode, 0.2 mm in diameter, and a grounded flat electrode located at the bottom of the tube. We investigated the spectrum, temperature, and ozone concentration of this plasma flow and its sterilization efficacy against Geobacillus stearothermophilus. The temperature in the tube showed uniformity along the wire electrode and increases as applied voltage was increased. With a wire electrode temperature of 337 K at a peak-to-peak applied voltage of 10 kVpp in the sine wave and a frequency of 6 kHz, sterilization of 105 cells was obtained. This result suggests the potential of the application of plasma flow rather than ethylene oxide for sterilization of the inner wall of tubes, such as catheters and artificial blood vessels. [ABSTRACT FROM AUTHOR]

In general, printed circuit boards (PCBs) used in power devices and system operation in low pressure environments are more susceptible to damage from surface discharges. Additionally, repetitive operation of power systems is an important factor leading to tracking failure. Whether the tracking phenomenon at low pressures is different from that at atmospheric pressure needs better understanding to ensure reliable applications. In this paper, studies of tracking failure of PCBs in a low-pressure chamber, are reported for an electrode configuration comprising a pointed end of track close to the side of a track. Test samples were made by printing these tracks onto a glass-cloth epoxy-resin laminate. Experiments were carried out using repetitive unipolar pulses to simulate voltage surges. The ambient pressure was reduced from atmospheric pressure to a very low pressure (0.6 kPa). The time to failure and the cumulative charge passing before failure were recorded as function of the pressure, temperature, pulse interval and insulation distance. The results obtained indicate that the low pressure enhances the breakdown endurance of PCBs and the breakdown phenomena at low pressure are different from those at atmospheric pressure. With the decrease of the pressure, the cumulative charge is increased but the tracking failure is delayed. At low pressures, increasing temperature has little effect on the cumulative charge, but has significant influence on the time to tracking failure. [ABSTRACT FROM AUTHOR]

This paper reports on dc pulse-powered microdischarges in air at atmospheric pressure and their potential utility in chemical sensing. For electrode gaps of 50-100 µm, microdischarges take the form of a glow discharge, an arc discharge, or a hybrid of the two. Arc microdischarges have high optical intensity but suffer from high background emission. Glow microdischarges have low background emission, but the prominent emission is confined in the UV-blue region of the spectrum. The arc-glow hybrid has characteristics that are intermediate between the two and can be tuned by circuitry to suit the chemical sensing application. A handheld system for chemical analysis using synchronized emission spectroscopy of these pulsed microdischarges is demonstrated. The system employs an exchangeable sensor chip (different for gas and liquid samples), a control circuit, and a commercially available portable spectrum analyzer coupled to a handheld computer. A pump and inert carrier gases are not utilized. The system can generate one or a series of single-shot microdischarges per chemical analysis. The gas discharge microchip, which utilizes electroplated copper electrodes on a glass substrate, has an electrode separation of 75 µm and an active area of 300 × 300 µm². The handheld system has been used to detect 17 ppm of acetone vapor in air. The liquid discharge microchip also has an electrode gap of 75 µm and an active area of 1 × 1 mm². It uses a porous cathode fabricated by micromolding and sintering glass frit slurry in a microchannel. When a microdischarge is initiated between the metal anode and the wet cathode, the liquid is sputtered into the microdischarge and emits characteristic line spectra. In this configuration, the system can detect 2 ppm of aqueous Cr without preconcentration. [ABSTRACT FROM AUTHOR]

We present 1-D simulations of atmospheric-pressure RF-excited plasma with two concentric spherical electrodes and the inner electrode powered. The gap distance between the inner and outer electrodes is 1 mm. The gas used is helium with a small amount of nitrogen as an impurity. The coupled continuity equations and electron energy equation are solved with Poisson's equation using the finite element method. In this paper, we particularly focus on the influence of a blocking capacitor, nitrogen concentration, and secondary electrons. In the presence of a blocking capacitor, the self-bias voltage alters sign from negative to positive as the power increases. Reduction of relative nitrogen concentration from 10-3 to 10-8 leads to significant changes in the gas-phase chemistry as well as species flux impacting the outer electrode. Secondary electrons turned out to play a minor role in the transition from the corona to glow modes. We also show that the directed ion kinetic energy distribution to the outer electrode largely depends on the discharge mode. [ABSTRACT FROM AUTHOR]

Fluctuations in atmospheric pressure arc plasma devices play important role in plasma processing applications. A full knowledge and control over such fluctuations can effectively lengthen lifetime and drastically improve performance and reliability. Dynamical analyses of associated experimental fluctuating signals established existence of chaotic dynamics in such devices. However, the origin of such fluctuations remained unexplained so far and no theoretical investigation is carried out to explore underlying physics behind such phenomena. This work addresses development of a general theory for such fluctuations in atmospheric pressure arc plasma devices in terms of various nondimensional parameters using basic governing equations and presents the result of application of the theory to various important experiments reported in literature. Various aspects of dynamic behavior have been investigated through the study of coefficients appearing in the nonlinear amplitude equation. It has been shown that the theory supports arc current and gas flow rate as the major externally available controlling parameters in agreement with experiment. Theory exhibits period doubling route to chaos under variation of control parameter as observed experimentally. System includes catastrophic behavior for some operating range. The whole work is divided into two parts. This paper presents part-I: Development of theory for such fluctuations using basic equations of the dynamics and study of system behavior. [ABSTRACT FROM AUTHOR]

Negative self-bias is well known at the powered small-sized electrode in low-pressure capacitive-coupled discharge plasmas. In this paper, however, the self-bias at the powered electrode observed in an RF atmospheric-pressure microplasma demonstrates either a positive or negative sign depending on the supplied power and interelectrode gap. [ABSTRACT FROM PUBLISHER]

In this paper, we present some results of a plasma source developed at the Plasma Laboratory of the University of Brasilia for sterilization studies at atmospheric pressure. This source was primarily conceived to produce a corona-type discharge to be used on pollutant control experiments. We used ordinary air as the precursor gas. Our apparatus consists of two coaxial cylindrical tubes with different radii connected to a high-voltage power source. We used G. stearothermophilus spores as the biological indicators. We counted the viable spores after the exposure to the plasma with the pour plate technique. Finally, we studied the biocide mechanisms of the plasma and related the inactivation of the microorganisms to plasma-induced chemical and physical processes. [ABSTRACT FROM PUBLISHER]

Abstract-In this paper, an atmospheric plasma jet with long flame has been developed. The plasma jet is covered with a cylindrical glass container, where the inner volume is purged by the working gas. The flame of N2 plasma jet has been elongated to about 200 mm, while the conventional plasma jet has a flame of only 10-20-mm length. It has been confirmed that the long-flame plasma jet can modify polymer film with a work distance of over 200 mm. This plasma-jet device could be applicable for treating and cleaning objects having deep channels or large structures and could be used in the wider application fields. [ABSTRACT FROM AUTHOR]