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Recent studies have found that the surface flashover strength of oil-impregnated insulation paper can be improved by the modification of nanoparticles. To reveal the working mechanism, this paper presents an experimental study on the effects of TiO2 nanoparticles on streamer propagation process at the surface of oil-based nanofluid-impregnated insulation paper under lightning impulse voltage. The results show that the surface flashover voltage of nanofluid-impregnated insulation paper is significantly increased by 34.6%. Streamer characteristics including shape and length at the surface of oil-impregnated insulation paper were investigated using the schlieren technique. It is indicated that streamer characteristics are dramatically changed by the addition of TiO2 nanoparticles. For nanofluid-impregnated insulation paper, streamers with more but much shorter branches tend to develop into adjacent nanofluid rather than clinging to the paper compared to that for pure oil-impregnated paper. The reason responsible for the shape dissimilarity lies in the change of electrical force due to the permittivity difference between oil and paper. Furthermore, more shallow traps introduced by nanoparticles contribute to the faster surface charge dissipation of nanofluid-impregnated paper, reducing the charge accumulation at the streamer head and suppressing the electric field distortion. Thus, it is hard for streamers to develop at the surface of nanofluid-impregnated paper, resulting in an increase of surface flashover strength. [ABSTRACT FROM AUTHOR]

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 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]

In this paper, a new configuration of dielectric-barrier discharge (DBD) reactor with three electrodes was manufactured and used to produce ozone. Designed flatly, this reactor is capable of establishing three different discharge modes from type of the volume and surface discharges, without modifying its internal structure. The aim of presenting this paper is to experimentally analyze the three discharge modes and their combination using a second channel to produce ozone. The two reactor channels are identical in terms of dimensions, material, and manufacturing process. Two frequency-adjustable pulse generators of the same electrical characteristics and two high-voltage transformers were used in the course of the experiments. The applied sinusoidal voltage is from 0 to 12 kVp-p. The frequency range was determined and fixed for all three discharge modes for the highest ozone concentration at a fluctuation rate of 1 L/min. Effects of increasing the applied voltage on the obtained concentration from the three different discharge modes were experimentally analyzed. Using the provided inlets–outlets, the effect of flowing gas through the length and width of the discharge area on ozone concentration was investigated, and appropriate flow directions were determined for the flowing gas under either of the three discharge modes. Experimentally results have been done for this three discharge modes as well as hybrid modes. The maximum ozone production rate achieved up to 14.52 g/h in the series combination of two different volume discharge. At 96% oxygen purity, ozone production yield, in two modes volume discharge VaDBD and surface discharge SDBD, have been improved up to 529.87 g/kWh. However, the total input power of the entire system is 120.2 W. [ABSTRACT FROM AUTHOR]

The collision frequencies between electrons and air molecules are important parameters when analyzing electrical breakdown. Different values for the collision frequency in atmospheric air have been reported in academic literature; the current analysis method for breakdown in waveguides and filters considers an electric field-independent term. However, some authors have remarked the importance of an electric field dependence of the collision frequency. In this paper, the collision frequency of electrons, accelerated by the presence of an electric field, against air molecules is obtained. The collision frequency is calculated from experimental data, for breakdown voltages at dc in positive polarity in a wide atmospheric pressure range using a plane–plane plates configuration. As waveguide filters are currently designed with a 3-dB tolerance below the electrical breakdown thresholds, this paper analyses the current methods for these breakdown threshold calculations, and proposes a novel correction factor for the collision frequency in order to approximate the analytic calculations to experimental results. [ABSTRACT FROM AUTHOR]

Photoelectric characteristics are an important reference for high-voltage discharges and are closely related to the excited mode of the high-voltage source. In this paper, we built a large-scale volume dielectric barrier discharge (DBD) system, which is composed of multilayer parallel-plate DBD electrodes and is excited by a high-voltage source in the power density modulation (PDM) mode. Subsequently, we analyzed the applied energy equation and evaluated the DBD systems photoelectric characteristics. The results show that the energy values of different applied voltage cycles during a PDM period exhibit significant differences. However, the average energy in a PDM period is approximately constant. Moreover, the equivalent capacitance of the DBD cell is a function of both the applied voltage and energy density. For the DBD cell, with the increase in both the applied voltage and energy loaded on the DBD cell, the total equivalent capacitance ($C$) is approximately constant, the dielectric capacitance ($C_{\mathrm{ d}}$) increases exponentially and decreases linearly, while the discharge gap capacitance ($C_{\mathrm{ g}}$) decreases and increases in the same cases. In addition, the relative intensities of the discharge emission increase and the energy efficiency ratios of the relative photoquantum yield of active species decline with the increase in both the applied voltage and energy density loaded on the DBD cell. The experimental results have been analyzed by evaluating the influence of the electrical parameters, and the underlying physical principles have been discussed. This paper clearly demonstrates that the photoelectric characteristics of the DBD reactor are significantly influenced by both the applied voltage and energy density, thus providing helpful insights into the energy evaluation and application of high-voltage discharges. [ABSTRACT FROM AUTHOR]

This paper investigates the potential use of dielectric laser accelerators (DLAs) for nuclear security applications. For the first time, the LSP code is used to look at this application. LSP is a fast running, parallelized particle-in-cell code that includes space charge effects. The focus of this paper is to ascertain the order of magnitude, amount of charge, that can be driven through the accelerator. From these results, a recommendation on the potential of DLAs for nuclear security applications is given. [ABSTRACT FROM AUTHOR]

This paper will describe the influence of mesh geometry on the homogeneity of discharges, power, and efficiency of ozone generation. Homogeneous discharges increase the efficiency of the generation of ozone. Geometry of mesh electrodes affects the power and type of discharges, concentration, and efficiency of the ozone generation. The analysis of selected results indicates the need for the use of mesh electrodes with a small cross section at least $0.1\times0.1$ mm2 mesh to obtain a homogeneous discharge. The mechanism by which the geometry of mesh electrodes on the homogeneity of discharge is illustrated in this paper. Homogeneous discharges increase the efficiency of the generation of ozone that reduces the cost of ozone production. The results of the experimental studies show an increase in the average efficiency of 60% of the ozone generation and a 20% reduction in the demand for power with the constant concentration of ozone, justifies the problem. [ABSTRACT FROM AUTHOR]

In order to investigate the characteristics of Trichel pulse in negative corona discharge, a corona discharge measurement system, and a simulation model are proposed. Pulse parameters fit by double exponential function are discussed in this paper. Effects of the magnitude, interval, crest time, and fall time of the pulse on the parameters are discussed for different applied voltages and radii of curvature of the needle electrode. Fitting functions under different conditions are also given in this paper. [ABSTRACT FROM PUBLISHER]

Nonequilibrium plasma is an effective and one of versatile advanced oxidation process due to the formation of reactive species such as hydroxyl radicals, oxygen atom, and hydroperoxyl radicals. In pulsed discharge, free electrons gain energy from an imposed electric field and lose this energy through collisions with neutral gas/liquid molecules. The transfer of energy to the molecules leads to the formation of a variety of new species including atoms, free radicals, and ions. These products are all active chemically, and in our case, we measure the amount of hydroxyl radicals generated in the reactor and also the amount of escaped ozone generated in the reactor and decolorized indigo reagent in a graduated cylinder (GC). In this paper, we used oxygen and argon gases in various flow rate and mixed ratios to feed a gaseous phase in a water spraying droplet reactor. The experimental results indicated that the oxygen and O2/Ar mixture flow rates in spraying reactor have an effect on both hydroxyl radical generation and decolorization of indigo reagent solution. Argon gas discharge has less effect on hydroxyl radical production compared to the oxygen gas discharge with the same flow rates and no effect on the decolorization of indigo reagent solution in GC. We obtained remarkable results on both hydroxyl radical generation rate and decolorization efficiency of indigo reagent solution when we discharged with the mixture of O2/Ar “especially when the ratio has more oxygen than argon gas.” Hence, the presence of oxygen in the water spray plasma discharge is very important as it influence the generation of reactive species such as O atoms and ozone in the gas and liquid phase, which can react directly with organic contaminants and also contribute to more production of hydroxyl radicals in the aqueous phase. [ABSTRACT FROM AUTHOR]

The characteristics, breakdown probability, and statistical distribution of breakdown time delay under different du/dt in hundreds of nanoseconds pulse for millimeter gaps have been investigated by employing the statistical experimental method in this paper. The experimental results indicate that both the breakdown time delay and jitter are essentially decreased as the slope of the pulse voltage- du/dt is increased for 1-, 2-, and 4-mm gaps; in particular, increasing the value of du/dt is useful to obtain the smaller relative deviation of breakdown time delay under the same breakdown electric field. The breakdown probabilities for different gaps have been analyzed and a method of utilizing the Gaussian distribution function has been proposed which can be used for evaluating the statistical distribution of breakdown time delay. When the experimental condition is 100% breakdown probability, the breakdown time delay follows a Gaussian distribution. However, it is unsuitable for the fitting of breakdown time delay utilizing a Gaussian function for 2- and 4-mm gaps from the cumulative probability distributions of breakdown time delay because of the lower du/dt values and breakdown probabilities. [ABSTRACT FROM AUTHOR]

Hybrid energy storage device for electromagnetic launch has the characteristics of high energy density and high power density. The device will release a lot of heat in both charging and discharging processes, which will have a direct impact on the stability of the whole system. Through the analysis of the structural feature and the principle of discharging, this paper compares the effect of air-cooling and water-cooling method for the high temperature rise problem in the process of repeated large rate discharging. In order to effectively reduce the temperature and evaluate the thermal management effect, an experimental platform for electromagnetic launch is built. This paper takes kilovolt level discharging and charging experiments on the platform with air-cooling devices, and the temperature rise is within the upper limit. The simulation analysis of the two kinds of cooling methods during discharging process is taken. And the experiment and simulation result can ensure the safe and continuous operation of electromagnetic launch, with practical engineering significance. [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]

Pulsed microdischarges produced by dielectric barrier discharges (DBDs) in a submillimeter gap were investigated under 200 cycles of sinusoidal ac voltage at 5 kHz in this paper. The impulsive current in the external circuit was accurately measured by an oscilloscope with a bandwidth of 2.5 GHz and a maximum sampling rate of 40 GS/s to calculate the filamentary current in the discharge gap. The amplitude, pulse duration, and transferred charge of a single filamentary current and the microdischarge energy acquired over the 200 voltage cycles were statistically analyzed for different discharge gaps and gas pressures. The microdischarge parameters and ozone generation efficiencies for different conditions were compared. The ozone production efficiency was found to increase with increasing pressure from 1 to 2 bar absolute, and the gap length from 0.2 to 0.5 mm. The maximum ozone production efficiency achieved in the paper was 217 g/kWh, with a gap length of 0.5 mm, an absolute pressure of 2.0 bar, and an applied voltage of 5.5 kV at 5 kHz. [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]

The uniform gas discharge has long been pursued for realizing or improving some practical applications but is difficult to achieve due to the fact that nonuniform discharges are much easier to be generated in most cases. Usually, achieving uniform gas discharge requires sophisticated devices, and the operation is complicated and time-consuming. In this paper, we introduce simple and flexible multimethods for realizing uniform discharge from patterned structures under dielectric-barrier discharge (DBD) systems by varying experimental controlling parameters, and these methods can be employed in combination. The effects of driving frequency, voltage, duty ratio, and magnetic/electric field on glow DBD structure are investigated. It is found that a uniform glow DBD is obtained when frequency, voltage, and duty ratio are either very high or very low and also by the introduction of strong magnetic/electric field. The underlying physics of these methods is consistent as the elimination of a focusing effect of space electrons. It is concluded that the key of achieving uniform discharge is to uniformize the distribution of space charges. [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]

The de-excitation of nitrogen excited states after spark gap discharge was investigated with time-resolved optical emission spectroscopy method. Recombination of ionized particles was experimentally proved less than several tens microseconds. After the recombination process, it was shown that atomic nitrogen in ground state [N(4S)] and molecular nitrogen in first excited state [N2($\text{A}^{3} {\Sigma }_{u}^{+}$)] was long-lived particles (metastable state) after gas discharge. Characteristics of decay for N(4S) and [N2($\text{A}^{3} {\Sigma }_{u}^{+}$)] were studied, and their lifetime and decay of density were estimated in this paper. Peculiar unexponential decay of N2($\text{A}^{3} {\Sigma }_{u}^{+}$) showed there was reproduction process of N2($\text{A}^{3} {\Sigma }_{u}^{+}$) after gas discharge. N(4S) could be the source for reproduction process under their mechanism of three-body recombination. Low ionization energy and high ionization collision cross section of N2($\text{A}^{3} {\Sigma }_{u}^{+}$) make it a possible factor limiting the switch recovery. The de-excitation of metastable states opens novel perspectives for understanding the recovery of gas switch. [ABSTRACT FROM AUTHOR]

Microparticles from electrode erosion would lead field distortion, microdischarge, or impact damage, which are convinced to be mainly responsible for degradation of insulation performance in switches. To investigate the splashing characteristics of microparticles from electrode erosion, this paper performs the discharge experiments between two cylinder electrodes, made of copper, molybdenum, or tungsten-copper. A statistical method based on laser confocal microscopy is introduced to visualize the distribution of microparticles on the electrode surface. Experimental results indicate that the number of microparticles increases and the acceleration tendency gets mild as the discharge shots accumulate. The Cu surface would lead more production of the $> 2~\mu \text{m}$ microparticles than other two materials after hundreds of shots, which would provide an explanation for its relative poor reliability and insulation performance. The electrode surface has formed two distinct zones for distribution of these microparticles: inner zone and outer zone after hundreds of discharge shots. Estimation of inner zone radius and splashing angles of microparticles indicates that the larger the microparticles are, the smaller the angle they would be splashed out with. Finally, the evolution of arc column in the first quarter discharge cycle is captured by a high-speed camera and its relation with the concentration of microparticles is discussed. [ABSTRACT FROM AUTHOR]

The influence of the electric parameters, applied voltage, and pulse repetition rate on the energy efficiency for hydroxyl radical production from pulsed discharge inside of a bubble is investigated in this paper, as a possible application for waste water treatment. To evaluate the energy efficiency, indigo carmine, a common dye, is used as a chemical probe of hydroxyl radicals. Argon is injected into water through a vertically positioned glass tube, into which high-voltage wire electrode is placed to generate plasmas at low applied voltage. The energy efficiency increases with the decreasing pulse repetition rate and output voltage with the same indigo carmine concentration. The results show that the energy efficiency for the hydroxyl radical production increases with the decreasing amount of energy input into the solution per unit time because of the decrease in the recombination reaction of the hydroxyl radicals in the solution. The impedance between the electrodes decreases with the increasing output voltage, which increases the ohmic losses in the solution but does not contribute to the production of hydroxyl radicals. [ABSTRACT FROM AUTHOR]

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

Plasma in a pinch column, as produced by a plasma-focus discharge at the deuterium filling and the current intensity reaching 1 MA, was investigated at the total neutron yield reaching about 1010 per discharge. The use was made of neutron diagnostics, laser interferometry, soft X-ray measurements, optical emission spectroscopy, magnetic probes, as well as electron and ion measurements with the temporal, spatial, and energetic resolutions. The detailed studies showed the ordered toroidal, helical, and plasmoidal structures which could contain currents with poloidal and toroidal components and their associated magnetic fields. Their spontaneous transformations were explained by changes in a topology of magnetic field lines due to magnetic reconnections. A nonthermal acceleration of fast electrons and ions (producing hard X-rays and fusion neutrons, respectively) corresponded to: 1) the formation of plasmoids in the pinch column and 2) a decay of pinch constrictions and secondary plasmoids during the evolution of instabilities. A filamentary structure of the current flow could explain the high energy density and fast transformations of the magnetic energy into kinetic energy of electron and ion beams (reaching energy of hundreds of kiloelectronvolt). This paper summarizes the results obtained with the PF-1000 facility in 2009–2017, and describes the internal transformations in a dense plasma column during the evolution of MHD instabilities. [ABSTRACT FROM AUTHOR]

Gas flow is an unavoidable factor to influence partial discharge (PD) behavior of insulators, e.g., in the cases of strong wind and high-speed train. In this paper, the surface charge distribution of PD sequences was obtained by the PD measurement system based on Pockels effect in different gas flows. Both phase-resolved PD (PRPD) and pulse sequence analysis method (dV–dV pattern) were employed to study the PDs behavior. We found that the air flow could homogenize the distribution of surface charge spots and influence the inception voltage, discharge number, as well as average discharge current. The discharge number increased with the airflow velocity until reaching its maximum at the threshold of 4 L/min. Although in nitrogen, with increasing the nitrogen flow velocity, the surface charge distribution became more uniform and the discharge number decreased together with its corresponding PDs pattern varying at the same time. This difference of PD behaviors in air and nitrogen was attributed to the presence of oxygen molecules in gas. [ABSTRACT FROM AUTHOR]

The increased usage of diesel fuel of late has led the researchers to pay more attention toward abatement of increased emission of oxides of nitrogen (NOx) in the engine exhaust. The focus is, therefore, lies in providing a technique that is economical, feasible, and long lasting. The combination of electric discharge plasma with adsorbent/catalyst derived out of solid waste can be one such possible technique. In this paper, waste foundry sand from foundry industry and red mud or bauxite residue from aluminum industry have been used. Diesel engine exhaust under dry condition was exposed to an oxidizing discharge plasma environment. The plasma-treated exhaust was subjected to either adsorption over waste foundry sand or catalysis over red mud. Studies were carried out in the laboratory environment with 20% loading of diesel generator. The oxidizing plasma environment was either with direct plasma or with indirect plasma in which case ozone injection into the exhaust was accomplished. The ozone-adsorbent cascading system has resulted in about 87% NOx reduction in the dry exhaust case. The effect of O3:NO ratio was discussed from the point of NO/NO2. [ABSTRACT FROM AUTHOR]

The surface flashover usually occurs on the interface between the insulator and vacuum in a pulsed power system and high-voltage device. In this paper, we studied the improvement of insulator performance in vacuum by covering the transformer oil on different insulator surface regions. We calculated the electrical field distribution to evaluate the influence of oil coating and carried out the surface flashover experiments by oil coating on different regions. The calculated results of the electric field showed that the electrical field magnitude was reduced by coating oil layer and the maximum field located at the electrode triple junction of metal, oil, and insulator. The experiment results showed that the insulator performances with a coating on cathode or anode region were lower than that with the whole surface coating but still higher than that with no coating. Then, the flashover process with a coating on different regions was also discussed. We speculated that the oil layer could restrict the development of secondary electrons and the release of desorbed gas, so the insulator performance could be increased by coating the oil layer on the entire surface, cathode region, and anode region. The insulator performance with cathode region coating and anode region coating was lower than that with entire surface coating due to the electrons avalanche easily moving from cathode to anode. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of effect of high-power UV-radiation plasma, generated by electric discharges, on germination rate of Altaic flax seeds (Linum altaicum). It was found that UV-radiation scarifies flax seeds by means of cracks formation in the seeds’ coat. The cracks shorten moisture penetration time to a seed bud thus twice increasing the germination rate. It is found that the germination rate function has the three-stage character; the velocity-growth function has the view of three pulses, which separates the seeds into three subgroups. Division of the group into subgroups is stipulated by the probabilistic nature of the cracks formation. The number of subgroups is equal to the number of layers +1. We calculated average times of natural moisture penetration through the flax seed coat layers: $T_{s} =11.8$ h through the spermoderm and $T_{e} =17.7$ h through the endosperm. It is possible that scarification of the flax seed coats can shorten the germination time for these times. We also noted that some seeds could die due to the effect of high-power UV radiation. So, it is necessary to find more sparing regimes of the seeds UV irradiation. [ABSTRACT FROM AUTHOR]

This paper puts forward a repetitive high-voltage pulse modulator, consisting of a step-up pulse transformer to decrease the number of needed semiconductor switches, and a bipolar Marx generator to reduce the turns ratio of PT, leakage inductance, and distributed capacitance, and also to improve the pulse shape. An equivalent circuit of the proposed modulator considering parasitic elements is established. Based on the equivalent circuit, circuit operation is analyzed in detail. In order to verify the theory analysis and circuit operation, simulations are conducted. In addition, a laboratory prototype is implemented. The simulations and experimental results of resistive load and dielectric-barrier discharges load turn out matched quite well with the theory analysis, demonstrating that the prototype can operate with a voltage amplitude in the range of 0–25 kV, a repetition rate of 0.1–5-kHz stably. [ABSTRACT FROM AUTHOR]

This paper is related to the study of the formation conditions and dynamics of self-sustained plasma-beam discharge at high energy density in the plasma of multiply ionized atoms. The efficiency of energy input into the discharge is shown by using a high-current pulsed plasma diode of low pressure. Based on the original calculation method, the dynamics of active voltage and active power inputted into the discharge are given. In such a system, the level of inputted active power can reach the value of 100 MW at the initial stored energy of 140 J. It is pointed out that the main mechanism of energy input into the discharge is a double electric layer of the space charge that is formed in the discharge gap. The intense electron beam accelerates in the double layer and heats the plasma to a high temperature in a short period of time. By controlling the arrangement of double-layer formation, one can input the energy locally into a certain discharge region. The distinctive features of the double-layer formation near the high-voltage electrode with a limited working surface for the even and odd half periods of the discharge current are indicated. The distribution of space potential in the discharge gap confirms that the double-layer formation is the result of not only the current instability but also the discharge transition to a new form of the self-sustained electric discharge in gas environment. [ABSTRACT FROM AUTHOR]

High-power electric arc heaters are the only viable test equipments for heating air to high temperatures (2000–10 000 K) in a few minutes for experimental ground studies of hypersonic flight vehicle thermal protection systems. With the expansion of the exploration of outer space and the rapid development of hypersonic vehicles, more powerful arc heaters are urgently required to meet the demands of the aerospace industry. However, the design of high-power arc heaters faces many technical obstacles such as the need for high structural strength, the need for high-efficiency heat-transfer for cooling, the problem of high internal temperature flow, and the electromagnetic plasma coupling problem. To address these problems, this paper has discussed an optimization scheme, in order to improve the reliability and security of a high-power arc heater in extreme conditions, and at the same time improve the thermal efficiency of the arc heater, and extend the service life of an arc heater. [ABSTRACT FROM AUTHOR]

High-voltage, nanosecond, high-repetitive-frequency, and portable pulse generators are always required in many fields. Avalanche transistor-based Marx circuits have been widely studied to generate pulses satisfying the above requirements. However, the basic topology of an avalanche transistor-based circuit, configuration of circuit parameters, and optimal working performance (including output impedance matching) were still scarcely discussed. In this paper, the detailed process of analyzing and designing a compact Marx generator using avalanche transistors was described. Based on the conventional principles of avalanche transistors and Marx circuit, a list of useful and interesting conclusions was discovered by experiment. An example with specific parameter requirements was utilized for the clearness of illustration. The 12~cm\times 4 cm Marx circuit could finally generate pulses with a 2.5-kV amplitude, 6.0-ns width, 10-kHz repetitive frequency, lower than a 100-ps jitter and $\sim 125$ -kW maximum peak output power on a matched 50- $\Omega $ resistive load. The pulse amplitude could be adjusted from 1.5 to 2.5 kV and the pulse width could also be broadened. This paper may help to provide a reference to similar methods of producing high-voltage, nanosecond, and high-repetitive-frequency pulses. [ABSTRACT FROM PUBLISHER]

Streamer discharges provide efficient means for chemical change in a variety of applications, some of which are ozone generation, water purification, and hydrogen and syngas production. Better understanding of the streamer growth process, and simple physical characteristics, such as size and geometry, could lead to an increase in product yield for these plasma-based applications. This report focuses in particular on the size and geometry of streamers formed in liquid, with an underlying goal to generate hydrogen gas and syngas via plasma-induced hydrocarbon reformation. The examination of size and geometry was performed with a measurement of the streamer length and area, and a fractal analysis, respectively. The fractal analysis used a box counting method to quantify the geometry of the streamer with a metric of complexity called the fractal dimension. This technique was explored for its possible use in characterizing streamers in regards to volume and surface area as such direct measurements can be difficult to obtain. The streamers discussed in this paper were induced under different operating conditions and liquid parameters, namely electrical conductivity of the liquid, voltage polarity, and carbon chain length of the liquid. [ABSTRACT FROM AUTHOR]

This paper treats over a reforming process using a warm plasma reactor for CH4 and CO2 conversion and hydrogen yield recovering. The conversion of hydrocarbon in syngas is mainly contributed by dissociation and ionization processes. Warm plasma is environment-friendly and autosustainable process; in addition, the electric discharge has low specific energy (SE) requirement and is able to retain enough high temperature to produce excited species and support subsequent chemical reactions. Such plasma discharges have significant advantages: do not require extra cooling systems, since they work with reduced electric current and high voltages, decreasing significantly electrode erosion. Consequently, reactors can be accomplished with a simpler framework and high gas treatment capacity. Plasma interaction with greenhouse gases (GHGs) leads into a molecular dissociation, mainly forming CO and H2, also known as syngas. In recent years, the syngas has become one of the alternative energy sources, which is more profitable and investigated. This mixture, normally recovered from organic material decomposition, provides energy with innovative applications in microturbines and fuel cells, in conjunction with other applications. In addition, an experimental analysis by using pulsed or resonant converter power supply is conducted; this converter enables the maximum energy transfer into plasma discharge without requiring complex electronic structures. Electric analysis was performed to determine instantaneous current, voltage, and power applied in the warm plasma torch for GHG treatment. From the analysis of power consumption, flux flow rate, and other physical chemical characteristics, SE and energy conversion efficiency are obtained. The effect of frequency in voltage–current relationship, depending on the waveform source, is described here. The input and exhaust gases were analyzed by a mass spectrometer and a gas analyzer. A comparison of these results with other results obtained in different bibliographic references is also signaled. [ABSTRACT FROM AUTHOR]

Application of the nonthermal plasma (NTP) technology for NOX removal from diesel engine exhaust has already been experimentally proved to be an efficient method at laboratory level. The NOX removal efficiency depends on various electrical and physical parameters, and very few studies have been carried out to predict it with the variation in those parameters. In this paper, an approach has been made using dimensional analysis to predict the NOX concentration with the NTP treatment, based on its dependence on various operating parameters. A relation has been obtained between NOX concentration and 11 numbers of parameters affecting NOX removal so as to form dimensionless groups. A mathematical model has been established using the experimental data and nonlinear regression technique. Experiments are conducted to validate this model with variations in the parameters voltage, flow rate, temperature, discharge gap width, and initial NOX concentration. The predicted NOX concentration values have been found to be well matched with the experimental results. The rms errors for the test data are found to be 4.64%, and in ppm, it is 9.58. [ABSTRACT FROM AUTHOR]

The numerical modeling of electrical discharges occurring in atmospheric air has been in continuous development during the past decades in different fields, such as high-voltage techniques and lightning protection. Different methodologies have been proposed to represent the physical phenomena taking place at a single full discharge event, departing both from experimental and theoretical approaches. The implementation of these methodologies in numerical routines combined with the use of numerical methods to determine the electric potential distribution permits the creation of models whose predictions closely agree with the real case situations, where electrode arrangements might have nonsymmetric geometries. In this paper, we present an improved version of a simulation methodology for representing electrical discharges in long air gaps. This simulation methodology includes new elements like: 1) the 3-D leader channel tortuosity based on laboratory experimental measurements and 2) two new methods for the estimation of the electric charge contained in the so-called leader-corona region based on the electrostatic potential of fictitious potential rings representing the active region in front of the leader tip. Results from the simulation were compared with experimental records and a reasonably good agreement is found between them. [ABSTRACT FROM AUTHOR]

Drift step recovery diodes (DSRDs) have a special place in high-power short-pulse generation. In this paper, a cascaded configuration of two DSRD-based high-power shortpulse generators with gas discharge switches was used. The highpower pulses generated in the first stage feed the second stage in order to generate shorter pulses with higher peak powers. A prototype was implemented based on this idea. In the first stage, 1.2-kV pulses were generated from a 50-V power supply. At the output of the second stage, 2.1-kV pulses with a repetition rate of more than 50 Hz were obtained. The output peak voltage was limited by the breakdown voltage of the used DSRD. Repetitive pulses with 4-ns rise time and 1.3-kW peak power were obtained. The maximum input power was 4.1 W which showed 320 times increase in the peak power. The maximum efficiency of 20% was obtained. [ABSTRACT FROM AUTHOR]

This paper gives instructions on how to build a 3-D particle-based model of a Hall microthruster. Due to nonequilibrium character induced by low electron thermalization and isotropization rates, presence of different microinstabilities and strong plasma-surface interaction, a multidimensional and kinetic description is necessary. The different modules characterizing the particle-in-cell/Monte Carlo collision cycle are described presenting the last algorithms developed. The model is applied to the study of an SPT20 configuration. Results confirm the importance of a 3-D structure of the discharge with self-organized azimuthal structures. Important deviations from Maxwellian behavior have been detected. [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]

Applicability limit of the well-known phase diagram of dusty plasmas in κ-Γ plane (κ is structural parameter and κ is parameter of Coulomb nonideality) is under discussion. Existence of extensive domains with violation of plasma thermodynamic stability conditions (i.e., with negative isothermal compressibility) was also claimed if one uses well-known nonideal equations of state by (Hamaguchi S. et al., Phys. Rev. E, 1997) and (Khrapak S. et al., Phys. Rev. E, 2014). This paper is devoted to analysis of a range of applicability for basic assumption in Hamaguchi's phase diagram, i.e., linearized (Debye) screening of macroions by microions, which leads to the Yukawa form for effective interactions between macroions. Parameters of nonlinear screening for macroions were calculated within differential Poisson--Boltzmann equation. Two effects were revealed as a result of such calculations: 1) decomposition of all microions onto two subclasses, free and bound ones, and 2) significant reduction of effective charge Z* of initial bare macroion Z under nonlinear screening by small high-density envelope of bound ions. This effect leads to a renormalization of initial Γ and κ into Γ* and κ* (Γ* < Γ, κ* < κ). The main physical assumption is phase states of complex plasma under nonlinear screening, which are still the same as on the initial phase diagram, but in κ*-Γ* plane instead of κ-Γ one. Corresponding calculated shifts of phase states are discussed and illustrated. [ABSTRACT FROM AUTHOR]

One of the practical usages of plasma in large-scaled agriculture is the indirect application of plasma by irradiating plasma derivative radicals. Since agricultural chemicals cause environmental problems, such as the generation of resistant bacteria and the increase of toxic residuals, we have proposed the extermination of soil worms and the acceleration of plant's growth by the ozone treatment of soil. Here, we propose soil treatment using ozone, generated by a surface barrier discharge, as both roles of pesticides and fertilizers. To investigate the effectiveness of gaseous ozone for the extermination of soil worms, this paper researched the influence of ozone on representative nematodes of C. elegans. Furthermore, to evaluate the practical effectiveness of the ozone treatment of natural nematodes living in agricultural soil, natural andosol was treated by ozone and the survival rate of nematodes was analyzed statistically using the Baermann funnel extraction. [ABSTRACT FROM AUTHOR]

The capillary-based pulsed plasma thruster (PPT) has high-energy transfer efficiency, which provides potential to improve traditional PPT performance. In this paper, the discharge characteristics of a capillary-based PPT have been investigated. First, the typical process of voltage and current waveform is recognized. It is featured with a fast voltage drop (~25 ns) and a consequent damped sine wave oscillation discharge. Then based on the circuit analysis, the equivalent plasma resistance has been calculated. The current waveform is well fit with a linearly increasing resistance model. The influence of charging voltage has also been studied. The deposited energy increases while the transfer efficiency decreases with the increasing applied voltage. The cavity dimension has effects on the equivalent circuit parameters. The results show that longer cavity and smaller diameter lead to more deposited energy and higher transfer efficiency. The influence of voltage and capillary dimension on the mass shot characteristic has been discussed. Finally, the estimated impulse bit has been calculated and the impulse bit characteristics have been discussed. These results can contribute to the further optimization of PPT. [ABSTRACT FROM PUBLISHER]

This paper is focused on investigation of the electrical, hydrodynamic, and acoustic parameters of underwater plasma discharges, stabilized with thin copper wires. The experimental current and acoustic waveforms have been obtained using different combinations of the circuit capacitance, charging voltage, and wire length. The resistances of plasma discharges have been calculated for all combinations of electrical and topological parameters, based on the constant resistance approach. Phenomenological scaling relationships that link the plasma resistance and the total energy delivered to the plasma, the period of discharge cavity oscillation and the peak magnitude of the acoustic impulse have been obtained. These relationships can be used in optimization of the acoustic output from the wire-guided discharges for different practical applications. [ABSTRACT FROM PUBLISHER]

To understand the flashover of roof insulators in high-speed airflows, the breakdown characteristics and mechanisms of a short needle–plate air gap are investigated. An interesting and important phenomenon is found based on an artificial wind tunnel: the breakdown voltage first increases and then decreases. An experiential formula is established to describe the relationship among the airflow velocity, gap distance, and breakdown voltage. A good consistency with the experimental results is obtained. Furthermore, the breakdown mechanisms of the air gap in high-speed airflows are proposed, and the phenomenon is explained and verified according to the theories of gas discharge and fluid dynamics. The airflow blowing effect, which includes the deflection effect and blown away effect, and the airflow density effect are proposed as two dominant factors that affect the breakdown process of the air gap in high-speed airflows. The variation trend of the breakdown voltage with the airflow velocity is predicted. Two extreme points are expected during the variation process; i.e., the breakdown voltage has a maximum and a minimum, to which more attention should be paid. This paper is helpful for the safety operation of roof insulators on the high-speed train. [ABSTRACT FROM PUBLISHER]

We examined the laser-induced discharge (LID) in medium-vacuum air. The time-averaged discharge energy Wd of a primary discharge prior to an arc discharge was affected by the number of initial electrons. The initial electrons were produced by the laser irradiation of electrodes. The number of electrons was proportional to the energy of the laser, Lp. Thus, it was adjusted by changing Lp. Although the experimental conditions were rather limited, i.e., air at 200-Pa pressure, we demonstrated a simple relationship, \textWd\propto \,\,\text{V}s^{2} \times \,\,\text{L}p^{s} , where Vs is the applied voltage and s is an exponent determined empirically. Note that the number of initial electrons is a function of Lp. Such a simple relationship for the behavior of LID that incorporates Wd is proposed for the first time in this paper. [ABSTRACT FROM AUTHOR]

A portable dc power supply based on electric double-layer capacitor (EDLC) bank was established for high-power applications. EDLC bank needs a dc–dc converter to maintain a constant output voltage and current. Especially, a low-impedance load makes the voltage of capacitors discharge faster, and their discharging time is determined by RC time constant. The proposed system is designed as a fundamental concept, and deals with some issues occurring in a large-scale system. Also, this paper provides detailed information and consideration for a real establishment. Last, we performed a full-scale experiment using basic techniques. [ABSTRACT FROM PUBLISHER]

Pulsed atmospheric discharge has been studied by using a pulsed high-voltage generator based on linear transformer driver (LTD) scheme. Taking advantage of the output flexibility of the LTD, we have studied gas discharge behavior by applying two consecutive pulses to a coaxial discharge load consisting of a wire and a pipe. The experimental results have shown that the discharge current of the second pulse is always lower than that of the first pulse for the same voltage amplitude, when the two pulses are too close to each other (<100 \mu s ). An explanation for this phenomenon has been explored by using a model that considers the effect of residual charge left by the first pulse. The findings obtained by this paper will help us understand the fundamental characteristics of pulsed atmospheric discharge. [ABSTRACT FROM PUBLISHER]

This paper reports the experimental results from the appearance of three discharge modes in a special geometry as a function of applied negative voltage pulses. The geometry is a four-gap pseudospark one with a gap distance of 4 mm, a metallic hollow cathode, and an anode. The applied pulsed voltage Up varies from −20 to −80 kV. The pulse shape is a rectangular one with a pulsewidth of 50 ns and a rise time of 4 ns. There is no breakdown at Up < 27 kV, and at Up > 27 kV, a pseudospark discharge starts, which transforms at Up > 45 kV into a surface discharge. The working gas is dry air at a constant pressure of 13 Pa. Using these parameters, electric field simulations of the triple point junctions are conducted and time-integrated pictures of the different discharge modes are presented. When the gas pressure is increased from 13 to 35 Pa, the voltage range of the pseudospark discharge mode grows from 13 to 65 kV. [ABSTRACT FROM PUBLISHER]

This paper first presents a short review of the recent experiments performed on large test fixtures, whose aim was to evaluate the flashover (FO) propagation during an electrostatic discharge. Then, the model of plasma bubble expansion is presented and compared with the results collected during the review. We will show that the model can represent qualitatively and quantitatively most of the results. The parameters of the model are mainly the ion velocity and the backscattered electron emission yield. The other experimental parameters influencing the FO propagation will be discussed. [ABSTRACT FROM PUBLISHER]

The aim of this paper is to investigate the effect of nonthermal atmospheric pressure plasma jet on human breast cancer and normal cells. High voltage, dc-pulsed power supply was used to generate low temperature helium plasma in atmospheric pressure. In this paper, cancer and normal cells were exposed to plasma during four time steps. For further exploration, Doxorubicin as common chemotherapy drug was employed to compare the efficacy of plasma treatment with convectional cancer therapy. Also, the Caspase-Glo 3/7 assay was obtained to reveal the death process of cancer and normal cells. The results of MTT and apoptosis assay showed that the plasma treatment has drastically reduced the viability of breast cancer cells, while it has no significant damage to the normal cells. In addition, after plasma treatment three different zones were formed in the plate, which will represent the detachment of cells from plate surface. Moreover, adding 5% oxygen to the helium plasma will lead to enhancement of cancer cells viability reduction. In addition, the outcome of this paper has verified that the plasma treatment successfully overcomes drug treatment in inhibition of the cancer cells viability, while decreases the adverse effect of drug treatment. [ABSTRACT FROM PUBLISHER]

In this paper, a dual-electrode gas switch triggered by ejected plasma is proposed to ensure the switch to be triggered reliably under extremely low switching coefficient. The switch has the configuration of dual electrodes, in one of which a microincentive chamber is embedded to develop ejected plasma into the switch gap, leading to the breakdown of the switch. Both the features of ejected plasma and the triggering discharge characteristics of the switch are studied with different types of gas, gas pressures, voltage polarities, gap distances, triggering pulse energies, and so on. The results show that the switch can be triggered reliably in a much wide working voltage range, as the minimum switching coefficient is low to 9% with the delay time of about 10 \mu \texts . With the decrease of gas pressure and the increase of triggering pulse energy, the height of ejected plasma increases while the delay time of the switch reduces. The polarities of charging voltage and triggering voltage both have obvious influence on the delay time of the switch, and the effect of the former is greater. Under the same gas pressure and triggering pulse energy, the delay time in SF6 is much bigger than that in N2. [ABSTRACT FROM PUBLISHER]

In this paper, we extended the recent work of Liu and Becerra to employ the position-state separation (POSS) method to simulate filamentary streamer discharges. POSS is a semi-Lagrangian method, which solves convection-dominated continuity equations without numerical flux correction. An improved interpolation strategy for POSS is here introduced to overcome the excessive numerical diffusion of the method when very small time step is used. Several benchmark tests in the literature are used to validate the improved method. Numerical experiments show that POSS is an accurate, efficient, and robust numerical method to simulate streamer discharges in arbitrary geometries when combined with finite-element method. [ABSTRACT FROM PUBLISHER]