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A low-cost and simple-arranged paper-based microplasma array device made by tape and Xerox paper was presented. Uniform array of discharge can be sustained in Ar, He, and ambient air atmosphere. Stable discharge can be sustained for at least 55 min when plasma is ignited in Ar ambient, based on the examination of time-resolved optical emission spectra. Throughout the conditions investigated, the power consumed by the device was well below 0.3 W. We also demonstrated that stable and uniform discharge can be generated when the device was bent to a radius of curvature of 2.5 mm. [ABSTRACT FROM PUBLISHER]

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]

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, we report on the propagation behavior of the atmospheric-pressure and brush-shaped He/O2 plasma plumes generated by a specially designed plasma device. The measurements show that the frequency of applied voltage $(f)$ and the O2 fraction and flow rate of the feed gas significantly affect the discharge propagation of the atmospheric-pressure plasma plume in ambient air. The uniformity of the brush-shaped plasma plume is greatly improved at a relatively high $f$ or He/O2 flow rate. Addition of a trace amount of O2 into the He gas can also contribute to the formation of uniform and brush-shaped plasma plumes in ambient air. This paper confirms that the plasma device composed of well-aligned and micrometer-thick fibers can be utilized to generate large-scale plasma plumes for potential applications. The propagation of the He/O2 plasma plume in ambient air results from the applied electric field across the small gas spacing of a barrier discharge electrode configuration, where the He atoms are easily ionized or excited for generating the brush-shaped plasma. [ABSTRACT FROM PUBLISHER]

The reactions have been accompanied ultraviolet (UV) radiation and electron impact with discharge plasmas in water–gas mixture, which can generate oxides, such as ozone (O3), hydrogen peroxide (H2O2), and nitrogen oxides (NOx). In this paper, two nonthermal plasma processing systems were established by means of a dielectric barrier discharge (DBD) arrays in water mist spray and an atmospheric pressure plasma jet (APPJ) immersed water. The yield characteristics of oxides (O3, NOx, and H2O2) in treated water were compared between the APPJ and DBD system under different applied voltages and energy densities. The results show that the relative intensity of UV from both the APPJ and DBD in water–gas mixture are stronger than the ones in air. The concentrations of O3 and NOx in treated water increased with increasing treatment time by using of both the APPJ and the DBD. Meanwhile, the APPJ-treated water is more acid than the DBD-treated one. However, it does not exist H2O2 in APPJ-treated water, rather it is enhanced in DBD-treated water with increasing discharge time. Moreover, the yields of produced oxides in water with discharge in water–gas mixture increased with increasing energy density, and decreased with decreasing applied voltage. This paper clearly demonstrates the close coupling of the yields of oxides and applied voltage, and thus is helpful in the study of the mechanism and application of discharge in water–gas mixture. [ABSTRACT FROM PUBLISHER]

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]

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]

Atmospheric-pressure plasma jets (APPJs) are widely used in biomedical treatment, surface modification, and sterilization, among others because of their advantages of simple structure, strong chemical activities, nonthermal effects, and convenient handling. In this paper, a nanosecond-pulse power generator based on Marx circuit is proposed. The apparatus consists of a nanosecond-pulse generator with crowbar switch and a needle-ring structure electrode. The nanosecond-pulse generator is modularly designed with ten stages; MOSFETs are used as the main switch and crowbar switch on each stage. A field-programmable gate array is used to generate two-channel trigger pulse signals to control the turn-on or turn-off of switches. The generator can produce repetitive pulses with output voltages of up to 8 kV, pulsewidth of 100–1000 ns, rise time of less than 30 ns, and pulse repetition frequencies of 1 Hz to 1 kHz. The designed nanosecond-pulse generator and the needle-ring structure electrode are used to produce argon plasma jets into open air, and the experiments show that the nanosecond-pulse generator can sustain stable APPJs. This paper lays a foundation for the further exploration of the biomedical effects of APPJs. [ABSTRACT FROM PUBLISHER]

Understanding the mechanisms for the supply of reactive oxygen species (ROS) into a target through a thin liquid layer by cold plasma jets is essential in biomedical applications. In this paper, impacts of gas flow rate on ROS supply into the liquid bottom were investigated using a KI-starch reagent that can be employed as an ROS indicator even in liquids. ROS distribution visualized on the regent at the liquid bottom was discussed from the stand point of liquid flows induced by the plasma jet irradiation. In the cases of lower gas flow rates, ROS were dominantly transported into the liquid bottom by the plasma-induced linear flow going in the depth direction, and were radially distributed at the bottom. On the other hand, in the cases of higher gas flow rates, ROS were dominantly transported by the supplied-gas-induced vortex flow spreading in the radial direction, and doughnut-shaped ROS distribution patterns were observed at the liquid bottom. The ROS supply into a target through a liquid layer markedly depended on the magnitude relationship between two flows; the vortex flow and the linear flow. [ABSTRACT FROM PUBLISHER]

Even though atmospheric-pressure plasma jet (APPJ) has been shown highly effective in many biomedical applications because of reactive oxygen/nitrogen species (RONS) generated in the discharge, free jet region, and at the interfacial region with the treated surface. However, most of the studies characterized APPJ only in either discharge or free jet region. In this paper, we measured optical emissions of RONS in free jet and plasma/surface interfacial regions of a helium-based dielectric barrier discharge APPJ. The results show that the emissions caused by RONS (nitric oxide, hydroxyl radical, and atomic oxygen) are enhanced 3–5 times at plasma/surface interfacial region as compared with those of free jet region. Some typical sterilization experiments using the current helium-based APPJ show that this helium-based APPJ effectively kills the oral bacteria (S. mutans) in 15 s, which was caused by the cell wall disruption. We believe that measuring the properties at plasma/surface interfacial region is more important than in the free jet region in characterizing APPJ for most realistic applications. [ABSTRACT FROM AUTHOR]

The aerosol-assisted atmospheric-pressure planar dielectric-barrier-discharge-type plasma deposition (AA-APPD) system can polymerize monomers and immobilize biomolecules simultaneously. In this paper, we used this technology to deposit biocomposite thin films of polyethylene (PE) along with lysozyme (Lyz) under different aerosol solution temperatures and at different coating positions in the discharge region. In addition, we compared the deposition efficacy of two kinds of Lyz solution using deionized (DI)-water and phosphate-buffered saline (PBS) as solvents, respectively. The results show that deposition rate of thin films increases with increasing solution temperature at most coating positions. In addition, coatings from Lyz-PBS perform higher deposition rates, but with weaker Lyz viability as compared with that of Lyz DI-water. Finally, we also verified that this DBD-type AA-APPD system can not only successfully deposit Lyz in PE thin film, but also maintain Lyz viability after plasma process under different solution temperatures and positions. [ABSTRACT FROM AUTHOR]

An atmospheric-pressure helium plasma jet has been widely used for biological applications; due to the nature, this plasma jet is cold and can be generated in the atmosphere. In this paper, we examined whether the atmospheric-pressure helium plasma jet enables the transfer of proteins without protein transduction domain (PTD) into cells. To examine the effect of plasma exposure on the protein transduction to cells, we observed the His-green fluorescent protein (GFP)-added cells after plasma exposure. A large number of GFP-positive cells were observed in the samples after plasma exposure although few GFP-positive cells were observed in control. These data suggested that plasma exposure induced protein transduction. To examine the major causes of increase in the GFP-positive cells after plasma exposure, we observed the His-GFP-added cells after various stimulations. A denatured medium of cell culture by plasma exposure induced protein transduction as well as plasma exposure sample. These data suggested that plasma exposure induced protein transduction by the denatured medium after plasma exposure. These findings suggest that the plasma jet may become a useful tool for protein transduction to cells in that the construction step of PTD fusion protein is not necessary. Furthermore, the plasma jet enables the proteins to transfer into cells without changing the nature of the protein by unnecessary PTD. [ABSTRACT FROM PUBLISHER]

This paper presents the application of a theoretically developed method, which when applied to a pulsed irradiance signal can provide information about the underlying chemical kinetics and reaction dynamics. The theoretical development uses a combination of state-space, Laplace transform, least-square, and correlation techniques to determine chemical kinetic and reaction dynamic terms from a pulsed discharge. The waveform irradiance signals come from a space-based optical radiometer. Four pulsed radiometry irradiance waveforms are examined where the reaction order, rate constant, and reaction rates are investigated. The application of the theory and the commensurate results demonstrate that irradiance signals obtained under similar circumstances come from distinct pulsed discharge conditions. [ABSTRACT FROM AUTHOR]

The atmospheric-pressure plasma jets and their applications discussed here are a topic of great interest in the fields of science and technology. As is referred to in this paper, the plasma generated in a laboratory setting is described as the dielectric barrier discharge like. The atmospheric-pressure plasma jets of argon (Ar) and neon (Ne) are generated using an ac-power supply with a frequency of 24 kHz and a voltage of 12 kV at room temperature. For the first time in the world in this context, the vibrational spectra Fourier Transform Infrared of coumarin molecule (abbreviated here as 1CMN) dissolved in ethanol and methanol are analyzed after the atmospheric-pressure plasma treatment (APPT) of argon and neon. Plasma jet spectroscopy is used to investigate FT-IR spectra of coumarin before and after APPT process, which takes only 3 min. Also, the changes of structure and the interaction of the plasma and the molecule (coumarin) dissolved in solvents are examined, and the vibration modes of the 1CMN molecule before and after APPT are investigated. Thus, the final structure of the molecule can be explained with respect to the vibrational characteristics of the 1CMN molecule, and the photochemistry of this compound is studied under the conditions of this experiment. [ABSTRACT FROM PUBLISHER]

The three-electrode plasma reactor for the treatment of polluted gases combines a dielectric-barrier discharge with a remote third electrode, designed to enhance streamer propagation in a relatively large region. In this paper, experimental studies of the electrical magnitudes of the discharge for different electrode bias voltage configurations are presented. Also, the Laplacian electric field distribution in the interelectrode gap is calculated for each configuration. The degradation efficiency of NO in an N2 atmosphere for the different configurations is also reported. It is found that the discharge is generated only for that electrode bias configuration for which the external electric field promotes the streamer propagation across the electrode gap. Also, for a triggered discharge, the reactor efficiency for the removal of NO changes with the different electrode bias configurations. This result can be explained in terms of the electric field intensity. The configuration with higher external electric field improves the number of streamers propagating in the interelectrode gap so that more reactive species generated in the streamers are effectively entrained in the gas flow to be treated. [ABSTRACT FROM AUTHOR]

In this paper, we want to develop and characterize a round argon-based nonthermal atmospheric-pressure plasma jet (APPJ) with an application of sterilization. We measured the basic properties of APPJ by an alcohol thermometer, an optical emission spectrometer (OES), a high-voltage probe and a Rogowski coil. The plasma jet temperature at the tube exit is lower than 37 °C, which will not induce damage to living tissue. The plasma absorbed power is about 2.7 W. The OES data indicate that this APPJ has a relatively high intensity of hydroxyl radicals (OH) in postdischarge region. Furthermore, we applied this device to inactivate the bacteria (E. coli and B. subtilis) and endospore (B. subtilis endospore). In addition, the trace amount of oxygen addition (0.04%) into working gas can not only enhance the OH radicals but also speed up the killing of bacteria and endospore. The results of D value and scanning electron microscope images show its great potential for the use of general sterilization in the future. [ABSTRACT FROM PUBLISHER]

In this paper, we compare the helium-based atmospheric pressure plasma jets (APPJs) with power-ground (PG) and power-floating (PF) configurations by using optical analysis. We find that the PG jet traps plasma between two electrodes (discharge region); thus, the hydroxyl radical intensity is significantly strong in discharge region; however, the plasma intensity in downstream region is relatively weak as compared with that of PF configuration. In contrast, using the APPJ with PF configuration, the hydroxyl radical and nitric oxide are approximately two and three times stronger, respectively, in the downstream region, even though the gas temperature and power consumption are lower. The PF jet successfully eradicates S. mutans and decreases water contact angle by ~40 within 15-s treatment, which demonstrates higher efficient than that of PG jet, and shows highly potential for dental filling demand. [ABSTRACT FROM PUBLISHER]

In this paper, a planar nitrogen-based atmospheric-pressure dielectric barrier discharge (DBD) jet with enhanced UV emission and radical generation, and much lower power consumption and gas temperature using shorter electrodes as compared with a previously developed DBD jet is presented. The highest UV intensity (five times larger) and radical generation (two times larger) in the DBD jet region are found to occur when the electrode length is 1 cm. Corresponding jet gas temperature and power consumption are 31 °C and 39 W, respectively. The 1-cm DBD jet was used to treat polylactide film for enhancing its hydrophilic properties. The results show that a contact angle of 28.4° could be obtained with a residence time of 4 s. The resulting 1-cm DBD jet may provide an efficient surface treatment tool for delicate industrial and biomedical devices/materials. [ABSTRACT FROM PUBLISHER]

To apply plasma technologies for large-scaled and advanced agriculture, the indirect use of plasma is one of the possible ways to overcome the disadvantage of direct plasma application. The recent problems we face in agriculture are due to soil worm damages and residual chemicals that are used for the extermination of the soil worms or for the acceleration of plant growth. Here, we propose soil treatment using ozone, generated by a surface barrier discharge, performing the roles of both pesticides and fertilizers. To investigate the efficacy of ozone for the extermination of soil worms, this paper researched the influence of ozone on nematodes (C. elegans). Furthermore, to evaluate the effectiveness of ozone for plant growth, the growth of radishes planted in the ozone-treated ridge in an actual greenhouse was observed. [ABSTRACT FROM AUTHOR]

Irradiation of atmospheric plasma jets to liquid targets induces a stream of reactive oxygen or nitrogen radicals from the liquid surface to the bottom under limited conditions, including frequency of applied voltage, gas flow rate, and so on. Pressure waves can be considered to be one of possible forces that concern with the stream inside liquid targets, because we succeeded to detect pressure waves generated by plasma jets in air with a fibered optical wave microphone. The fibered optical wave microphone works based on Fraunhofer diffraction of laser for phase objects, having superior sensitivity compared with other conventional optical methods for the detection of refractive index changes. In this paper, the fibered optical wave microphone measurement was done in air to investigate the frequency properties of the generation of pressure waves from plasma jets. In addition, the detection of pressure waves inside distilled water was attempted. [ABSTRACT FROM AUTHOR]

In the field of microfluidics, it is possible to facilitate liquid transport through microsized holes with large slip lengths by lowering the friction at the interface between the flow and the inner surface of the holes. In this paper, we discuss the use of nonequilibrium atmospheric-pressure plasma to modify the surface wettability of microsized holes in glass substrates that are similar to those used as flow channels in glass microfiltration devices. In our experiments, liquid transport flows were driven by internal Laplace pressure differences based on the surface tensions of droplets placed on the front and back sides of the tested substrates. [ABSTRACT FROM AUTHOR]

Recently, the plasma medicine received a lot of attention in the plasma and biology community. Most of the plasma treatment targets are living tissues and cells immersed in liquids (such as blood or culture media). Reactive species generated by plasma in the gas phase are transported into the liquid and possibly converted to different types of reactive species, so that they can affect tissues or cells. In this paper, we presented a numerical investigation of the interaction between the plasma and the cells immersed in the culture media. The space and time evolution of dissolved reactive species [reactive oxygen species (O2−, OH, H2O2, HO2, and O3) and reactive nitrogen species (O2NO−, NO, NO2−, NO3−, and O2NOH)] are studied by the mass balance model in liquid. The reaction mechanism and the effective transportation range of dissolved reactive species are analyzed. The pH of the liquid has significant effects on the concentration of O2−, HO2, O2NO−, and O2NOH in the culture media. The increasing concentration and the higher permittivity through the cell membrane of HO2 and O2NOH at acidic pH are consistent with higher bacterial inactivation efficiency of plasma treatment in acidic pH environment. The cellular and the subcellular concentration of HO2, O2NO−, and O2NOH are studied by the conservation equations in a spherically symmetric concentration field. The plasma treatment increased the cellular concentration of O2NO− over ten times. The HO2 generated by plasma aqueous species was the only way for superoxide to penetrate cell membrane and damage cytosolic fumarase B. The cellular plasma reactive species are also sensitive to the pH of culture media. [ABSTRACT FROM AUTHOR]

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]

Energy and conversion efficiencies of the carbon dioxide (CO2) dissociation process at atmospheric-pressure conditions are investigated using a direct-coupled continuous microwave plasma system (MPS). Gas chromatography and mass spectrometer measurements were performed on the gas mixture postplasma treatment, over a range of specific energy inputs (SEIs) (0.06–0.6 eV mol ^-1) , in order to determine species mass fractions of CO2, carbon monoxide, and oxygen. In this region of SEI, energy efficiency is maximized at the cost of conversion efficiency. The corresponding maximum observed quantities for conversion efficiency and energy conversion efficiency (ECE) occurred at conditions close to the end of the test range and are, respectively, 9% and 0.0048 L min ^-1\textW^-1 . The maximum throughput of CO2 converted was 0.59 L min ^-1 , at an SEI of 0.1 eV mol ^-1 and an ECE of 0.004 L min ^-1\textW^-1 . Optical emission spectroscopy was used to approximate the rotational and vibrational temperatures of the plasma system to be in the range of 7000–8000 K. This paper suggests that an MPS is the most energy efficient method in dissociating CO2 under atmospheric pressure and, therefore, most suitable to be used in a CO2 recycling setup, which can further increase conversion rates. [ABSTRACT FROM PUBLISHER]

In this paper, we present the inactivation study of bacteria suspended in water by atmospheric pressure nonthermal plasma generated by pulsed dielectric barrier discharges (PDBD) in a wire-cylinder reactor. The experiments were carried out with Gram-positive Bacillus subtilis bacteria at an initial concentration of $1 \times 10^{6}\,\,\text {cells}\cdot \text {mL}^{-1}$. Bacterial inactivation was analyzed comparing two different types of treatments: bacteria in contact with distilled water previously exposed to plasma (indirect plasma treatment) and bacterial suspension in direct contact with plasma (direct plasma treatment). Plate count, microscopy, and spectrophotometry methods were used to study the bactericidal action of the PDBD. The obtained results indicated that both treatments eliminate bacteria, where direct plasma treatment led to a faster biodecontamination with a 4.87 – log10 reduction in 10 min than 2.36 – log10 reduction achieved with indirect plasma treatment. Microscopic observations reveal that treated bacteria were damaged suggesting the disruption of their cell walls during the direct plasma treatment. [ABSTRACT FROM AUTHOR]

Spatial bullet velocity distribution of an atmospheric-pressure plasma jet (APPJ) in the N2 and O2 mixture gas were investigated by varying the gas mixing ratio. The bullet propagation from the discharge tube exit was observed by an ICCD and the bullet velocity had three phases as the acceleration, the constant velocity, and the deceleration phases. These velocity phases were analyzed using the simple and analytical fluid model. The density of neutrals and the transport parameters of electron were obtained from CFD-ACE+ and BOLSIG+. It can be envisaged that each of three propagation phases are influenced closely by the Penning ionization effect of helium metastable on N2 and O2 ionization, the induced electric field in an APPJ discharge tube, and the formation of negative oxygen molecules, respectively. It is expected that this paper explains the effects of grounded or floated target under the jet on bullet and vice versa. [ABSTRACT FROM PUBLISHER]

Poly(vinylidene fluoride) (PVDF) was extensively used as the filtration material because of its stable thermal and chemical capabilities. However, hydrophobic surface of PVDF membrane induces the restriction for its manufacturing uses. In light of this, the plasma at atmospheric pressure was used for the PVDF membrane surface treatment with argon/methane gas mixture in this paper. The variation in hydrophilicity of the plasma-treated PVDF membrane was analyzed by the contact angle analysis. It shows that this plasma is operative in membrane surface modification. The argon/methane gas mixture cyclonic plasma-treated PVDF membrane also showed the enhanced filtration behavior rather than the untreated PVDF membrane. [ABSTRACT FROM PUBLISHER]

This paper presents a zero-dimension model of a capillary plasma pulse jet generator governed by wall ablation feed of plasma. Experiments are made and electrical measurements compared with model simulations. Spectral measurements are performed to validate the assumption of radiation from black body radiation with a gray factor. [ABSTRACT FROM AUTHOR]

In this paper, cold atmospheric pressure brush-shaped plasmas are reported. The brush, which is driven by a direct current (dc) power supply, is capable of generating plasmas glow up to 30-mm wide with no gas flow supplement. The plasmas can be touched by bare hand without any feeling of electrical shock or warmth. Current measurements show that the discharge in air appears periodically pulsed, while the discharge in argon actually presents either pulsed, except for their discharge mechanism placed at differently. For understanding this particular characteristic, a 2-D fluid model is developed with the use of Comsol Multiphysics software, under the condition of discharge in argon treated as an example. The simulation results are in good agreement with our discharge experiment in argon, which further indicate that the space charges trapped along the whole dielectric surface in air but only confined in the hole ahead the anode needle tip in argon may be responsible for the generation of the different pulsed discharges. [ABSTRACT FROM PUBLISHER]

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

This paper deals with an experimental study of contacts ablation in interaction with an ac arc discharge (half period 10 ms). Images obtained by fast camera are correlated to weight measurements to deduce the mean erosion rate for several types of materials. This paper is completed by thermography measurements to calculate the energy and the mean value of heat flux transferred by the arc to the contacts. [ABSTRACT FROM PUBLISHER]

The replacement of fossil hydrocarbons with the renewable biomass alternatives is an inevitable requirement in our transition toward a sustainable economy. However, traditional petrochemical technologies are not designed to operate using biomass raw materials. Thus, the development of new hydrocarbon processing methods is essential. This paper deals with the study of the hybrid plasma-catalytic reforming of liquid hydrocarbons. The system for the reforming of liquid hydrocarbons, which used low-power rotating gliding discharge as a plasma generator, was studied. Sunflower oil (C17H33COOH) and ethanol (C2H5OH) have been used as model oxygen-containing hydrocarbons and diesel fuel (C16H34) has been used as a model hydrocarbon without oxygen. Reforming products have been analyzed using mass spectrometry and gas chromatography, and the combustion of produced syngas was studied. The values of the reforming efficiency, the ratio between the chemical energy of the produced syngas and the electric energy spent on the plasma generation, and the efficiency of the produced syngas combustion in the standard water heaters were obtained. [ABSTRACT FROM PUBLISHER]

In this paper, we present the evaluation of a DBD reactor that generates an energy per pulse of 65.3 mJ in order to inactivate E. coli ATCC 8739 at 10^3 , 10^6 , and 10^8 CFU/mL order concentrations and E. cloacae CDBB-B-963 at 10^3 and 10^7 CFU/mL order concentrations, in a volume of water flowing continuously. Particularly, experimentation is focused in 500 mL, under atmospheric pressure. The DBD reactor was coupled to a peristaltic pump type, a cooling jacket, containers for water in treatment and cooling fluid, and systems to monitor the experimental conditions. The implementation of the experiments was carried out at three different fluid flow rates: 2.0±0.1, 3.5±0.1, and 4.4±0.1 mL/s; in each of them the time required to carry out a cycle of treatment corresponded to 256±7, 143±2, and 113±1 s, respectively. During the DBD application, water flowed continuously at recirculation mode, promoting the continuous oxygen injection at 8.3 mL/s. In the three established fluid flow rates, the efficacy of treatment reached 100% in inactivation of E. coli bacteria at 10^3 and 10^6 order concentrations at the end of the first cycle of treatment. At 10^8 CFU/mL order concentration, complete inactivation of E. coli bacteria was achieved at the end of the fourth cycle of treatment. Meanwhile, E. cloacae bacteria showed an inactivation of 100% at the end of the first cycle of treatment at 10^3 order concentration; when the order concentration increased to 10^7 , the efficacy of the process depended on the fluid flow rate, at 3.5 ± 0.1 and 2.0 ± 0.1 mL/s survival was 0% at the end of the first cycle of treatment; nevertheless, at the highest (4.4 ± 0.1 mL/s), an additional cycle was required. [ABSTRACT FROM AUTHOR]

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

This paper presents an experimental study of the inactivation in water of two representative classes of bacteria, Gram-negative Escherichia coli and Gram-positive Bacillus subtilis, using pulsed dielectric barrier discharges (PDBDs) in a coaxial arrangement. To this purpose, an adjustable plasma source supplies 25-kV/500-Hz pulses, 30 \mu\s long, at atmospheric pressure, with total energy consumption estimated at about 100 mJ/pulse. The inactivation effect of a PDBD on these types of microorganisms has been previously studied in dependence on an oxygen gas flow mode (null, continuous, and modulate). The results have shown a significant bacterial reduction rate from 10^8 to 10^3\ \cells/mL with E. coli and from 10^7 to 10^3\ \cells/mL with B. subtilis. The inactivation effectiveness is substantially similar in both kinds of bacteria, although some data suggest a greater susceptibility of the Gram-negative E. coli to plasma exposure. Plasma diagnostics was carried out using optical emission spectroscopy whereby the OH radical and reactive oxygen species formation rates in solution were found and the level of ozone produced by the discharge was monitored. Finally, a kinetics model was developed to characterize the chemical species taking place in nonthermal plasma inactivation processes in water. [ABSTRACT FROM PUBLISHER]

The atmospheric-pressure plasma jets (APPJs) are nonthermal plasma sources studied for their high potential in many medical applications where conventional solutions failed. In this paper, we show the influence of helium APPJ on pepsin structure and function. The APPJ source is characterized using voltage–current measurements, optical emission spectroscopy, and high-speed imaging. Pepsin powder was exposed to the action of the plasma jet, and then, spectroscopic investigations were carried out to obtain information on the structural modifications. Protein function was tested using an enzymatic assay. [ABSTRACT FROM PUBLISHER]

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

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

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

In this work, the results of experiments on the dust particle synthesis process by combining two types of discharges at atmospheric pressure are presented. The experimental setup consists of two pin type copper electrodes connected to the pulsed high voltage source (spark discharge) and two copper foils wrapped around a quartz tube powered by a kilohertz high voltage sinusoidal signal [atmospheric pressure plasma jet (APP jet)]. In that case, the spark discharge serves as a precursor. It is a source of vapor and primary nanoparticles. Furthermore, these nanoparticles transported by gas flow to the region of uniform dielectric barrier discharge of the plasma jet increased in size and settled on the surface of the substrate. The results of experiments with combined discharge and with spark discharge only are compared. Particle formation and growth mechanisms were discussed. The chemical composition of the deposited particles was obtained. [ABSTRACT FROM AUTHOR]

Effects of the driving frequency on temperature in a multiphase ac arc were successfully clarified. A multiphase ac arc is one of the thermal plasmas, which is suitable for producing functional materials such as nanoparticles, in-flight glass melting, and waste treatment in terms of its large plasma volume, high-energy efficiency, and low flow velocity. The temperature and arc behavior in various driving frequencies were investigated by the observation system consisting of a high-speed video camera and bandpass filters for plasma spectroscopy. The temperature measurement was conducted on the basis of the Boltzmann plot method. The obtained results indicated that the arc behavior and its temperature field were strongly influenced by the driving frequency. An increase of the frequency led to concentrated arc region, higher arc temperature at the center of electrode region and lower arc fluctuation. The temperature and its distribution can be controlled depending on the material properties to be treated and the purpose of the process. [ABSTRACT FROM AUTHOR]

This paper investigates the sterilization effects of a low-temperature cyclonic atmospheric-pressure plasma. Bacillus subtilis was exposed to the cyclonic atmospheric-pressure plasma, and the degradation of the bacterial cell was thoroughly examined with scanning electron microscopy. It was found that cyclonic atmospheric-pressure plasma is effective in the destruction of the B. subtilis cells. [ABSTRACT FROM AUTHOR]

Optical emission spectroscopic measurements were performed on atmospheric pressure electrodeless microwave plasmas produced in a 95% carbon dioxide-5% hydrogen mixture. The rotational and vibrational temperatures of the plasma were determined by measuring the C2 Swan band spectra at wavelengths in the ranges of 500-517 and 548-565 nm. The electron number density of the plasma was deduced by measuring the Stark broadening of the hydrogen Balmer-β line shape at 486.13 nm. The microwave power was fixed at 2 kW, and the flow rate was varied from 5 to 20 standard liter per minute. The difference between the rotational and vibrational temperatures was found to be negligible. The temperatures reached 6200 (±200) K and were independent of the flow rate. The electron number densities of the plasmas were estimated to be approximately 2.06 (±0.12) × 1014 cm-3. Thermodynamic-equilibrium calculations indicated that the temperature corresponding to the measured electron density was 6221 (±200) K, which is almost the same as the temperatures measured according to the C2 Swan band spectra. Therefore, the electron temperature was nearly the same as the gas temperature, and the plasma was in local thermal equilibrium. [ABSTRACT FROM PUBLISHER]

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

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

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

An atmospheric pressure argon plasma was generated using a magnetic loop antenna with a pulse modulated ultrahigh frequency signal of 850 MHz. Finite-element simulations were performed to study the patterns of gas flow and electromagnetic waves. Fast photography of the plasma jet was used to study temporal behavior of the plasma jet. Emission and mass spectrometry were used to identify active species in the plasma jet. The detected dominant species included excited argon atoms and singly charged ions of argon, nitrogen, oxygen, nitrogen oxide, and water. To study the effect of the plasma jet on biological samples, a thin onion epidermal membrane was treated with the plasma jet. The hydrophobic layer displayed hydrophilic characteristics after treatment for 1 min. [ABSTRACT FROM AUTHOR]

The current–voltage characteristics of atmospheric pressure plasma jets with various working gases (He, Ne, Ar, N2, and air) are investigated. Systems of the plasma jets are composed of a syringe needle inserted into a glass tube and are operated by a sinusoidal high-voltage through a dc–ac inverter generating several tens of kilohertz. The various electrode structures with or without the ground electrode are analyzed by using an equivalent circuit model. For the biomedical applications concerning the discharge stability and the electric safety with a low plasma-current and a low voltage operation, the suitable structures of plasma jets for each gas are suggested. For the plasma jets of inert gases (He, Ne, and Ar), the discharge triggered by an external ground electrode seems to be suitable, because the low current of a plasma plume is adjusted readily with a low voltage of 1–2 kV. For the jets of N2 and air, the nozzle of a metal ground electrode at the end of a glass tube is suggested to reduce the operation voltage below 3 kV and to acquire a low plume-current of a few milliamperes exiting the metal nozzle. [ABSTRACT FROM PUBLISHER]

Previous studies have shown that paint tends to easily peel off when irradiated with plasma. In this study, we use atmospheric pressure plasma irradiation to peel off surface paint. The variable parameters were the applied voltage and the plasma irradiation time. We were able to irradiate the painted surface with atmospheric pressure plasma for 1 min and peel off more than 80% of the paint. It was hypothesized that plasma irradiation affects the internal stress in the painting. [ABSTRACT FROM AUTHOR]