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

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

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]

In this paper, the capacitances of the two-stage bushing that is installed in the 1-MV test bed for neutral beam injectors in the future fusion reactors are calculated by modeling the bushing in a 3-D electrostatic code. One of the modeling results is the stored energy in the bushing, which corresponds to 1/2 CV2. After evaluating the bushing capacitance, a MATLAB/Simulink model is presented to model the possible breakdown in the bushing and between the electrodes in the 1-MV test bed. When a breakdown occurs between anode and cathode, an overcurrent is drawing that can cause damage in the electrode surfaces while an overvoltage takes place when the breakdown happens between the bushing stages. Such damage has been observed experimentally in the past. This paper also presents some of the possible protection against the breakdown in the 1-MV test bed to dissipate the stored energy in order to protect the electrode surfaces and the bushing. The suggested protections presented in this paper are damping resistors, surge arrester individually, and both of them. Also, a coil can be added to the DR either in series or in parallel. [ABSTRACT FROM AUTHOR]

The past measurements of the plasma density and potential profiles near the exit of the keeper electrode in a hollow cathode device suggested that turbulent ion acoustic fluctuations and ionization instability in the cathode plume significantly increased the energy of the ions that flow from this region. The lifetime of keeper electrode is limited by sputtering or ion bombardment of the Molybdenum surface exposed to the discharge plasma. Increases in the cathode gas flow reduce the amplitude of the fluctuations and the number and energy of the energetic ions, which decreases the erosion rate of the keeper electrodes. However, as the cathode gas flow is raised for a given discharge current, the performance of a 5-kW Annular-Geometry Ion Engine (AGI-Engine) declines. There is a strong relationship between the performance and the lifetime of the ion thruster. To validate whether the 20-A hollow cathode satisfied China’s communication satellite platform’s application requirement for North-South station keeping, this paper analyzed the effect of the cathode gas flow on the performance and the lifetime of the AGI-Engine. Different from the previous methods, this paper first tracked the movement of energetic ions generated in the plume of the hollow cathode, predicted erosion rates, found where they hit the keeper electrode, and then determined the amount of material that they sputtered. A review of past experimental results was presented first. Next, based on the existing experimental data, theoretical analysis and numerical calculations were performed to determine the optimum gas flow range and the performance curve of the 20-A hollow cathode. The results showed that the primary erosion mechanism of the keeper electrode was caused by impact from Charge Exchange Xenon (CEX) ions, which caused the cathode orifice to be widened and attenuated over time. However, heavy double xenon ($\text{X}_{\text{e}}^{++}$) ions, which struck the keeper electrode more severely than CEX ions, were the most crucial factor that limited the lifetime of the 20-A hollow cathode due to their high energy and large mass. [ABSTRACT FROM AUTHOR]

Studies have been taken into the breakdown voltage jitter of corona-stabilized switch at high repetition rate up to several kHz. It is thought that the gas recovery affect the jitter of breakdown voltage directly at high repetition rate, because the gas switch will breakdown at a low voltage if the gas cannot fully recover. The breakdown voltage jitter is called voltage jitter in the following paper. However, based on the experimental results, the voltage jitter still exists at low repetition rate, even at single-shot mode. This is not explained by the previous studies. In this paper, voltage jitter below 100 Hz of a corona-stabilized switch is investigated experimentally. A corona-stabilized switch is introduced, using a cylindrical electrode as the cathode and a plane electrode as the anode. The gas used between the electrodes is SF6. A negative pulse with a maximum width of 30~\mu \texts is used to charge this switch. The tested factors include gas pressure, gap space, repetition rate, and switch geometry. Experimental results show that voltage jitter is mainly affected by the gas pressure and switch geometry. It is seen that voltage jitter decreases as gas pressure increases and a suitable cathode geometry presents a low voltage jitter. Critical volume is a region close to the highly stressed electrode, where the presence of an electron will lead to an electron avalanche which attains a critical size and hence leads to a stabilizing corona. Critical volume is introduced to explain the experimental results. It is found that less voltage jitter can be achieved with a smaller and more concentrated critical volume, as well as efficient corona stabilization. The results indicate that voltage jitter may be reduced by optimize the critical volume at low repetition rate. [ABSTRACT FROM PUBLISHER]

One of the most important features of atmospheric-pressure nonequilibrium plasmas (APNPs) is its capability of generating high concentration of reactive species while keeping low gas temperature. To generate such plasma, alternative current (ac) voltage and pulsed dc voltage have been used separately. In this paper, the combination of ac voltage and pulsed dc voltage is used to generate APNPs for the first time. The plasma characteristics, including the power deposited to the plasma, the gas temperature, the emission spectra, and the O atom concentration of the plasma for different phase shifts of the two power supplies, are investigated. It is found that when the pulsed dc voltage is added on the negative ac half period at the phase shift of about 90°, the average power deposited to the plasma, the gas temperature, and the optical emission spectrum of O atom all reach their maxima. On the other hand, the ground state O atom concentration has two peaks; one of the peaks also appears when the phase shift is about 90°. When the pulsed dc voltage is applied on the positive half period at the phase shift of 270°, the O concentration reaches another peak and the peak value is higher than that when the ac or the pulsed dc power supply works alone. Furthermore, at the phase shift of 270°, the gas temperature of the plasma and the total power deposited to the plasma are all lower than the case when the ac or the pulsed dc power supply works independently. Thus, it is more energy efficient to adjust the phase shift to 270° for applications such as plasma medicine where the gas temperature of the plasma at or close to room temperature is strictly required. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on polymer insulating material has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on the charge accumulation behavior between a pair of finger-shaped electrodes on epoxy/Al2O3 nanocomposites under dc voltage superimposed by repetitive pulses. The charge distribution was measured by means of an electrostatic voltmeter, from which the average charge density could be calculated. Effects of dc voltage, nanofiller content, and pulse voltage on charge accumulation behavior were investigated. Obtained results showed that with the increase in the filler content from 0 wt% to 5 wt%, the average charge density increased initially then appeared to decrease. The superposition of repetitive pulses on dc voltage led to a remarkable growth in charge accumulation as compared with that when only dc voltage was applied. It is suggested that the charges are originated from local gaseous ionization and/or electrode injection, which is determined by the combined voltage. The charge density is dependent upon the surface trap, which is affected by nanofiller content. The superposition of repetitive pulse is considered as a possible reason to encourage local gaseous ionization that results in enhanced accumulation of surface charge. [ABSTRACT FROM AUTHOR]

Modeling the dynamics of charged dust particles, confined in a glass box placed on the lower electrode of a Gaseous Electronics Conference cell, requires that the interactions between the charged dust, plasma, and boundaries need to be accounted for in a self-consistent manner. The charged lower electrode affects the plasma conditions throughout the glass box, altering the electron and ion densities and temperatures within the plasma sheath. These plasma characteristics determine the charge collected on the walls of the surrounding glass box, the electric potential within the glass box, the dust charge, and ultimately the dynamics of the dust. This paper describes the steps taken to build a simple model of the relationship between the plasma conditions and the potential within the box as well as the expected dust charge near the center of the box. The calculated potential and dust charge are used to construct acceleration maps for the dust, which are compared to experimentally measured acceleration of the dust within the box. [ABSTRACT FROM AUTHOR]

The multigap gas switch has been widely used in liner transformer drivers (LTDs), but there is still room for improvement on its self-breakdown and triggering characteristics. In this paper, based on the circuit model of the six-gap gas switch, the gap voltage distribution during the charging and triggering process is analyzed, and the optimization on self-breakdown and triggering characteristics by mounting resistors and capacitors in parallel with switch gaps are theoretically and experimentally investigated. The results indicate that compared with the original switch, when the self-breakdown voltage is about ±90 kV, the standard deviation is reduced from 7.5 to less than 3 kV; for a charging voltage of ±80 kV and by operating at 60% working coefficient, when the negative trigger voltage is 75 kV, the jitter of the switch is reduced from 6.1 to 1.4 ns. [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]

Paschen’s law gives the inception voltage for an electrical discharge as a function of the product of gas pressure and the gap distance between the two infinite planar electrodes. It is known that the deviations from Paschen’s law occur when the temperature is increased. Historically, two theoretical corrections, the Peek and Dumbar corrections, are proposed to predict the deviation from Paschen’s law by increasing the temperature. To carry out an experimental investigation on the deviation from Paschen’s law by increasing the temperature, a customized system was designed, which can operate at temperatures up to 400 °C and at pressure up to 1 MPa, calculated at room temperature, with an interelectrode distance between $100~\mu \text{m}$ and 6.6 mm and an error on the interelectrode distance measurement of $20~\mu \text{m}$. In this paper, first, the results from the experimental investigation on the deviation from Paschen’s law at temperature up to 400 °C are presented. The results are then compared with theoretical corrections, and finally, a theory to explain the results is proposed and 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]

The dynamics of the Trichel current pulses in a dc negative corona in SF6 at atmospheric pressure in a coaxial electrode configuration has been simulated using a self-consistent 1-D model. The aim of this paper was to clarify the role of the plasma charged particles on the ignition and development of the corona Trichel current pulses during the rise time of the applied voltage. The results showed that, during this time, the corona current consists of three sequential pulses with different amplitudes and the first pulse amplitude is larger than the others. It is found that, during the time of the first current pulse, the accumulation of the positive ions near the negative electrode has a main influence on the behavior of the radial electric field distribution and hence on the slow motion of the negative ions toward the ground electrode. This slow motion of the negative ions could play the key role on the next current pulse appearing. [ABSTRACT FROM AUTHOR]

Prefire is the unexpected breakdown of gas switch at triggered mode and have to be limited at extremely low level in fast linear transformer driver (FLTD). In this paper, the dispersion of breakdown voltage as well as prefire characteristics of high pressure gas spark switches under typical working conditions of FLTD was investigated and reported. Tested switches included a three-electrode field-distortion gas switch (TFGS) and a six-stage multichannel gas switch (SMGS), which had compact structure and low inductance. The results showed that the self-breakdown voltage of both TFGS and SMGS obeyed three parameter well-bull distribution and the dispersion of Ub at ±90 kV could reach 4% of TFGS and 14% of SMGS, respectively. The dispersion of Ub was remarkably influenced by the floating potential of middle electrode. By grounding the triggering electrode via a kilohm resistor, the dispersion of Ub decreased to 2% in TFGS and 6.5% in SMGS, respectively. When a voltage equalization method by cascade resistors was introduced, the dispersion of Ub in SMGS dramatically decreased to 4.4%. In repetitive operation at triggered mode, the prefire rate of TFGS reached 0.9% at $\gamma = 80{\%}$ working coefficient and decreases with the decrease of $\gamma $ , being 0.3% at $\gamma = 72{\%}$ and 0.2% at $\gamma = 65{\%}$ , respectively. The prefire rate of SMGS was much higher, reaching 1.7% at $\gamma = 72{\%}$ and 0.7% at $\gamma = 65{\%}$ , and decreased to 0.6% and 0.3%, respectively, after applying the equalizing resistors. Generally, the prefire rate of SMGS was somewhat higher than that of TFGS with the same working coefficient and the floating potential limiting was imperative for prefire inhibition. [ABSTRACT FROM AUTHOR]

Due to its low-loss and high dielectric strength, polypropylene is widely used as electrical insulation material in pulse capacitors. In order to study its breakdown characteristics for nanosecond voltage pulses, an experimental setup was designed to generate voltage pulses with a 10%–90% rise time of 38 ns and a full width at half maximum of about 90 ns. Tests of the three polypropylene films with thicknesses of 12, 15, and $18~\mu \text{m}$ were performed. In addition, hundreds of nanoseconds pulse and dc voltage were also applied for comparison. The experimental results reveal that most of the breakdown occurs during the front edge of the pulse for tens of nanoseconds pulse, and the breakdown strengths of the three kinds of polypropylene films are almost identical for different applied voltages, which show a weak correlation between the thickness of the dielectric and the breakdown field. The expected breakdown strength of tens of nanoseconds pulse defined in this paper is not significantly higher than the mean value of the hundreds of nanoseconds pulse and the dc condition, suggesting that the breakdown of a thin polypropylene film is mainly determined by the electrical field but not the voltage-time cumulative effect. All these observations strengthen the conclusion that the breakdown of a thin polypropylene film is an intrinsic phenomenon. [ABSTRACT FROM AUTHOR]

In this paper, the experimental results of the behavior of an X-pinch plasma conducted in a small capacitive generator of low impedance and inductance are reported. The generator produces currents of the order of 120 kA in times about 500 ns, when a charging voltage of 24 kV, and wires as load are used. W, Al, and Cu X-pinches of different diameters were tested. The experimental observations show a similar global dynamic to those observed in experiments of higher current and shorter quarter period, with an intense emission of energetics X-rays (>5 keV) generated by plasma dynamics in the cross point of wires. The fast plasma dynamic is evidenced from the strong change of frequency in the current-derivative signal, which is correlated with the X-ray signals observed from the radiation detectors. From the time-integrated pinhole images and time-integrated aperture images, filtered with different aluminum foils of different thicknesses, an estimated X-ray source size of $70~\pm ~20~\mu \text{m}$ with energies above 7 keV is obtained. [ABSTRACT FROM AUTHOR]

Repetitive high-voltage square pulses are of great importance for producing long-pulse electron beams and high-power microwaves. One of possible technologies for the generation of such pulses is a Marx generator using pulse forming network (PFN) stages, often combined with a pulse sharpening technique to reduce the rise time to a few nanoseconds (peaking stage). This paper presents an innovative design, named the “zigzag design,” for the optimization of the compactness and of the rise time of 400-kV–85-ns PFN-Marx. Thanks to this design, the 16 stages of this generator, which delivers an open circuit output voltage of 720 kV, fit in a 650-mm length. For a slightly overmatched load ($Z_{\mathrm {load}} = 100 ~\Omega$), the output voltage reaches 400 kV with a rise time as less as 5 ns. The inductance reduction associated with the innovative zigzag design, which allows this sharp rise time with no need for a peaking stage, is described. The 85-ns plateau duration of the pulse is given by the PFN construction of each stage, which is based on six ceramic capacitors (2.1 nF–45 kV) connected within a strip line. The 16 PFN stages are housed in a 360-mm diameter gas pressurized vessel. Burst mode operation for a duration of 10 s at a pulse repetition frequency of 100 Hz is reported, for a resistive load and for the electron beam diode of a X-band relativistic backward-wave oscillator (BWO). To reach further compactness, the BWO system is integrated on side of the generator vessel and a U-shaped gas pressurized line connects both systems through a compact conical vacuum insulator. [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]

Surface potential decay on negative corona charged epoxy/Al2O3 nanocomposites irradiated with high-energy electron beam has been investigated in this paper. 2-mm-thick laminate nanocomposite samples were irradiated with electron beam at an average energy of 7.5 MeV, and the total accumulated dose was up to 500 kGy. After the irradiation, the nanocomposites were corona charged with dc voltage at −10 kV through a pair of needle to plate electrode. Surface potential of the sample was then measured by means of an electrostatic voltmeter through which trap distribution and carrier mobility were calculated. Differential scanning calorimetry curve for the each sample was measured to understand the change in chemical and physical structures induced by the irradiation. Results obtained indicated that the presence of nanofiller in the nanocomposites played a role in limiting the charge transportation both before and after the irradiation, and the charge transportation behavior was remarkably dependent upon the total irradiation dose. It is found that when irradiated with a certain total dose of electron beam, electron migration within epoxy and its nanocomposites is restricted, which should be attributed to the high-energy irradiation-induced structural change of the material. [ABSTRACT FROM AUTHOR]

This paper is based on a tutorial presented by the author as a part of the Minicourse on charged particle beams and high-powered pulsed sources given at the 2017 International Conference on Plasma Sciences at Atlantic City, NJ, USA. It is intended to provide a brief overview of the phenomenology and physics of the vacuum surface flashover process. These mechanisms will be used to motivate techniques commonly employed to improve the voltage standoff of insulators. In addition to serving as the primary limiting mechanism for vacuum insulators, vacuum surface flashover has a number of beneficial applications, primarily due to its ability to provide a simple pulsed plasma source, and a number of these applications will be discussed. [ABSTRACT FROM AUTHOR]

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]

Temperature field simulation for self-healing power capacitor makes sense to the capacitor optimization and improvement of capacitor’s rated voltage and capacity. On the basis of reasonable simplifications and assumptions for capacitor structure, a 3-D temperature field numerical simulation model for a self-healing power capacitor is formulated in Fluent 15.0. The ambient temperature is set to 55 °C, and the applied voltage is ac 400 V. The temperature distributions of the shell and core of the self-healing capacitor are obtained. The results reveal that the temperature of the core is 2 °C–3 °C higher than that of the shell. The highest temperature of the shell locates on the large side surface, and the temperature of the large side surface is higher than that of the small side surface. To validate the above simulation, a self-healing capacitor is manufactured and thermal resistance sensors are used to measure the temperature in the thermal stability test. The simulation is validated by the experiment. Finally, the influences of the ambient temperature and applied voltage on the temperature rise are investigated. This paper can be taken a reference to the self-healing capacitor operation, maintenance, and even the optimization of its internal structure and material. [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]

Pulsed electric fields have recently been the focus of considerable attention because of their potential application in biomedicine. However, their practical clinical applications are limited by poor understanding of the interaction mechanism between pulsed electric fields and cells, particularly in the process of electroporation and its effect on parameter selection. This paper established a multishelled dielectric model based on finite elements to simulate and analyze the processes involved in electroporation. In particular, the processes include the dynamic development of the pore radius and electroporation region: the distribution of recoverable, nonrecoverable, and nonelectroporation areas on the cell; and the influence of pulse parameters on varying degrees of electroporation. Results showed that membrane conductivity, pore density, transmembrane potential, and distribution of pore radii are functions of time and position on the cell. The electroporation areas were divided into recoverable, nonrecoverable, and no-electroporation pores. For 10~\mu \texts , 1.5-kV/cm pulse was observed in the regions exposed to sufficiently high transmembrane voltage (1 V), electroporation occurred, membrane conductivity and pore density (up to 10^\mathrm 16/\textm^\mathrm 2) rapidly increased with time, and electroporation areas increased gradually and were mainly distributed in the range 0°–70° (recoverable pore [0°, 35°], nonrecoverable pore [35°, 70°], and no-electroporation pore [70°, 90°]). Electric field strength was the major factor that induced electroporation, particularly in the recoverable pore, but it had minimal effect on pore expansion. However, pulse duration affects the nonrecoverable pore, such that the high-intensity wide pulse is more useful in the field of irreversible electroporation. The high-intensity short pulse can increase permeability and maintain cell viability. [ABSTRACT FROM AUTHOR]

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]

The audible noise (AN) production mechanism caused by corona discharge in ultrahigh voltage transmission lines is less understood. The study on sound pressure characteristic is necessary to obtain the inherent relation between AN and corona discharge. In this paper, the experimental research on single-point direct current (dc) corona discharge was evolved and the time-domain sound pressure waveform was obtained using capacitor microphone. The experiment results show that the dc corona discharge comprises multiple subsequent discharge pulses. The discharge voltage and the electrode polarity have a direct effect on the rising time and pulsed width of the single current pulse. The waveform of sound pressure produced by single discharge is a bipolar microsecond pulse, which lags behind the current pulse in time domain. The time delay is propagation time of sound signal from the discharge spot to the measurement spot. Based on the corona discharge characteristic in dc voltage, the experiment platform for nanosecond pulsed discharge was built to obtain the relation between discharge parameter and sound parameter. The characteristics of sound pressure in different discharge conditions were analyzed. The study results indicate that the sound pressure produced by pulsed discharge is similar with that produced by corona discharge. The experiment platform for pulsed discharge can be used to research the AN production mechanism by dc corona discharge. [ABSTRACT FROM AUTHOR]

Megavolt-class-triggered switches play a key role in large-induction voltage adder accelerators. This paper introduces a 2.8-MV, low-inductance, low-jitter, electrical-triggered, gas SF6 switch. The main section is a $V/n$ switch and the pretrigger section is a trigatron switch. Based on electric field simulation, experiment, and analysis, the structure and spacing of gaps, location of trigger disk, diaphragm, and switch inductance are all discussed. The primary test indicates that the switch can be operated in the range of 0.85–2.76 MV with the pressure of the SF6 changing from 0.1 to 0.9 MPa. The self-breakdown voltage is linearly related to the logarithm of the pressure, as the gap spacing and the voltage rise time are fixed. Three working modes were observed: self-breakdown, self-triggered, and ex-triggered. In the triggered modes, the switch jitter is <3 ns and the switch inductance is usually below 150 nH. [ABSTRACT FROM AUTHOR]

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

One of the factors of the functional life of the electrodes used in pulse current discharge depends on the erosion of electrodes. There are many areas that have not been investigated and many areas that require additional study. Some studies have presented results related to the erosion of electrodes made of Cu, Cu–W, Ti, graphite, stainless steel, etc. There is little information available on the erosion of molybdenum electrodes. The erosion of electrodes is related with the electrode material (conductivity, melting point, and density) and the Coulomb charge transferred per impulse. In this paper, molybdenum (Mo) was selected as the main electrode material, considering these factors in addition to high erosion resistance due to high work function and better formability. The performance of pulse discharge devices is mainly characterized by static breakdown voltage, prebreakdown voltage, recovery time, delay time, jitter, and reliability. The degradation of these performance parameters (PPs) is related to many critical factors affecting electrode erosion, consisting of peak current, electrode material, electrode geometry, electrode surface roughness, and gas type. The degree with which the electrode-erosion factors (EEFs) affect the PPs of the pulse discharge device relatively varies and has complex interrelationships, and the relative importance weight of each EEF in order to maximize the life of the pulse discharging device is calculated using quality function deployment and analytic network process methodology. This paper presents experimental work carried out to investigate the erosion characteristics of a molybdenum electrode. Testing was performed at 10–11-kA current discharge every 35 s at a rate of 300 discharges per day with a total of 10 000 shots. The experimental results for Mo electrodes indicate approximately 60 \mu \g/C for 5000-C transfers. For 10–11-kA current transfer with Mo electrodes, we can take about 8.5 \times 10^5 shots with wear of 0.3 g without appreciable local wear. [ABSTRACT FROM AUTHOR]

There has been a significant interest in many technical applications and natural phenomena concerning two-phase mixture discharges (TPMDs). Few studies have focused on the influences of different macroparticles on TPMDs. The dielectric constant is usually considered to be the only factor affecting the discharges, but in this paper, 21 kinds of different dielectric materials were used to investigate the effects on TPMDs. By the experimental results, this paper reveals the effects of macroparticle sizes, and the dielectric constant has little influence. When the diameter of TPMs is less than about 0.01 mm, the percentage of the selection of TPMs is always smaller than 50%, the discharge path selects the air but TPM, and the breakdown voltage is higher than that in air. However, when the diameter is greater than about 0.1 mm, the conclusion is opposite. When the diameter is in the range of 0.01–0.1 mm, the TPMDs have a polarity effect. The dipole-enhanced approximation model is applied to explain the experimental phenomena. It is very important in TPMDs that the macroparticle dielectric constant, the saturation charge, and the adsorption/desorption process on the material, except the effects of TPMDs, are highly correlated with the macroparticle sizes. [ABSTRACT FROM AUTHOR]

The production of large volume streamer discharges is essential to the industrial application of such discharge in water. The use of dielectric-coated electrode was found to have a great influence on the initiation of the streamer discharge as well as the formation of streamer channels. In this paper, a sphere-ring electrode configuration, in which the sphere was coated with a kind of silicon rubber, was put forward to generate multiple radial streamer discharges in tap water by applying a pulse voltage. Different from the previous methods which need very high electric strength and short pulse duration, this kind of electrode configuration can generate large volume streamer discharges in water easily at lower voltage amplitude. The effect of the pulse parameters, such as pulse amplitude and pulsewidth, on the streamer-channel length has been investigated. The influence mechanism of the coated dielectric on the streamer initiation and propagation is discussed in this paper. [ABSTRACT FROM AUTHOR]

Surface dielectric barrier discharge (SDBD), used as the plasma actuator for airflow control at atmospheric pressure, has been widely concerned over the past decades. In this work, four different electrode configurations, i.e., copper mesh, thin wire, blade, and aluminum foil, are chosen as exposed electrodes for the SDBD plasma actuator. The different effects of the four structures on the airflow acceleration behavior are experimentally investigated through the discharge current, surface potential distribution, ionic wind velocity, and mean thrust production. The result shows that the actuator with the copper mesh exposed electrode can generate the maximal induced force, while the actuator with the aluminum foil exposed electrode can generate the minimal induced force. This difference, as analyzed, is mainly due to the distinct discharge characteristics, i.e., different discharge asymmetry and surface potential, caused by the specifically designed exposed electrode configurations. This paper illustrates that the actuator with low surface potential has preferable mechanical performance. [ABSTRACT FROM PUBLISHER]

With the benefits of the high chemical selectivity and low energy cost, atmospheric rotating gliding arc (RGA) plasma is considered as a promising method in various industrial applications. In this paper, rapeseed oil is first proposed as the raw material to produce high-valued chemical products by RGA plasma. The influences of operating conditions (applied voltage, oil flow rate, and gas flow rate) on RGA discharge with rapeseed oil are focused, in terms of the basic physical properties ( $V$ – $I$ characteristics and discharge visualization) investigated using electrical diagnostics and high-speed photography. Blank experiments are conducted by supplying only pure N2 gas. The visual images presented complex arc dynamic behavior in N2 discharge, with the phenomenon of arc contact spot leap, spatial curl arc, and cracked. Intense purple light emission was observed by adding 3-mL/min oil droplets with four distinguished reaction stages. According to the electrical results, average current and power of arc increased with increasing applied voltage, while the average voltage indicated opposite variation tendency in different feedstocks. The augment of rapeseed oil flow rate decreased the average voltage and power, whereas raised the average current value in contrast. [ABSTRACT FROM PUBLISHER]

The basic structure and work mechanism of laser-triggered vacuum switch (LTVS) are introduced briefly in this paper, and the processes of primary plasma production and expansion are analyzed as well. A series of experiments has been carried out with different gap voltages, laser wavelengths, laser energies, polarity configuration modes, switch structures, focal lengths, and laser waveforms. The switch structure is modified to improve the heavy-current capability of the switch, and the gap distance is increased to improve the voltage capacity. The special design of the trigger structure can reduce the dependence on the laser energy of the switch and the time delay. A new laser waveform of LTVS multiple wave crests could further decrease the laser energy, and it is the research basis of laser trigger miniaturization and its application in the LTVS. [ABSTRACT FROM PUBLISHER]

Hydroxyl (OH) radicals generated in wire–plate pulsed corona discharge (PCD) were detected by laser-induced fluorescence (LIF). In this paper, the 2-D distribution of OH radicals and the time-resolved development of the streamers in humidified nitrogen were recorded by an intensified charge-coupled device camera. The results indicate that the OH-LIF signals could not be detected when secondary streamer was absent in PCD with low input energy. Input energy, which varies with the configuration of wire–plate reactor and applied voltage, significantly affected the spatial distribution of OH radicals. [ABSTRACT FROM PUBLISHER]

This paper considers the possibility of numerical generation of pulse breakdown voltage random variable in SF6 gas. A theoretically constructed model was tested at low, medium, and high values of \(pd\) product (pressure \(\times \) interelectrode distance), ranging from 0.1 mbar mm to 50 bar mm. Numerical generation of the statistic sample of the pulse breakdown voltage random variable was performed in homogenous and nonhomogenous fields. Variable experiment parameters were the pulse rise rates (from 1 to 400 kV/ \(\mu \) s). Obtained results indicate that the proposed theoretical–numerical model is absolutely satisfactory at high values of \(pd\) product (10–50 bar mm), which is the very region of SF6 gas application. At lower values of \(pd\) product (less than 10 bar mm), there are certain deviations between a numerically generated statistic sample of the pulse breakdown voltage random variable and the one obtained experimentally. However, this deviation is not relevant from the aspect of engineering practice. [ABSTRACT FROM PUBLISHER]

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

In this paper, an experimental investigation of pseudospark discharge behaviors was conducted under nanosecond pulsed voltages using a flexible discharge chamber. The breakdown voltages of the pseudospark discharge gap were measured for a wide range of gas pressures, anode-cathode gap distances, and cathode aperture diameters to find the match of gap distance and cathode aperture diameter at a certain gas pressure with the nanosecond pulsed voltage. According to the experimental results, an empirical relationship was obtained. The roles of the parameters in the empirical relationship during the discharge were analyzed. The breakdown characteristics were also consistent with the Paschen’s law in the pseudospark under nanosecond pulsed voltages, when the gap distance was replaced by the effective gap distance. In the end, a possible reason was put forward to explain the difference between the empirical relationships obtained under dc voltages and nanosecond pulsed voltages. [ABSTRACT FROM PUBLISHER]

In this paper, a device for accurate electrical measurements for nanosecond repetitive pulsed discharges (NRPDs) is presented. The experimental setup developed is based on an interelectrode system integrated in a transverse electromagnetic cell. This setup allows synchronizing the voltage and current measurements with a 4-GHz frequency bandwidth, corresponding to 250-ps pulse duration. A coaxial-shaped sharp metallic needle serves as a probe for current measurements. The needle probe is also the point electrode of a point-to-plane system used to generate discharges. The experimental setup was used to electrically characterize NRP corona and diffuse discharges, in negative polarity. Discharge current pulses with rise times less than 1 ns and amplitudes up to 120 mA were measured. The energy deposited by discharges was also determined. [ABSTRACT FROM PUBLISHER]

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

In this paper, the variation of the development of positive first corona space charge in long air gaps is investigated. A 1-m rod-plane air gap under different rising rates dU/dt of impulse voltages is reported. The current signals and still photographs are recorded during the first corona development. The relationship between the first corona charge Qi and the inception voltage Ui is presented. The physical mechanism of the influence of the first corona is provided. With the experiments and the single branch propagation model, a semi-empirical calcultion method for positive first corona charge under impulse in long air gaps is obtained through the calculation of the number of branches Nb. Using this method, the variations between Qi and Ui for different dU/dt and electric field distributions are calculated and compared with the reported experimental results. Reasonable agreement between the calculated and experimental results is obtained. It shows that this calculation method is suitable for predicting the positive first corona charge Qi and the discharge current at a given dU/dt and Ui. [ABSTRACT FROM PUBLISHER]

The development of a three-electrode trigatron gap with the trigger electrode inside the main electrode is discussed in this paper. Two models of the operation mechanism are proposed to explain the breakdown in the trigatron gap. In addition, a mathematical model was proposed to calculate the breakdown time based on the theoretical analysis. The influence of different parameters on the breakdown time is discussed. Some characteristics in dry air have been experimentally determined such as the influence of the air pressure and the influence of the undervoltage ratio on the spark gap operation. The experimental results show that the operating voltage range between 0.5 and 0.7 might be reasonable. Then, the experimental results and analysis demonstrate that there are three regions divided by two inflection points, and the corresponding values of the undervoltage ratio are threshold values presenting different breakdown processes. [ABSTRACT FROM PUBLISHER]

In this paper, a quartz coaxial dielectric-barrier-discharge tube operated at different gas pressures and frequencies has been studied. A sinusoidal voltage up to 2.4 kVp with frequencies 34.5 and 47.5 kHz has been applied to the discharge electrodes for the generation of microdischarges. The experimental results confirm the filamentary nature of discharges when operated at different pressures (300, 600, and 1000 mbar) and at different frequencies (34.5 and 47.5 kHz). The relative influence of the given pressures and applied voltage waveforms on the discharge parameters has been analyzed. An equivalent electrical circuit model representing the multipeak phenomenon in the discharge has been developed, which validates the characteristics of the filamentary behavior. A series of simulations has been carried out in order to obtain the internal discharge parameters including discharge impedance which is not measurable during the experimental process. A close agreement between the simulated and experimental results has been obtained. From the experimental results and equivalent electrical circuit model, the dynamic nature of equivalent capacitance has also been reported. [ABSTRACT FROM PUBLISHER]

In order to investigate the different features of the positive leader propagation in the rod–plane and inverted rod–plane gaps, the discharge experiments in a 3-m rod–plane gap and a 3-m inverted rod–plane gap were carried out under switching impulse voltage. The positive leader propagation process was recorded by using a high-speed CCD camera. Some aspects to describe the positive leader propagation characteristics of the rod–plane and inverted rod–plane gaps are obtained and compared in this paper, including the critical corona radius, the average continuous leader inception voltage, the axial leader velocity, and the final jump length. The possible reason resulting in those differences is also discussed here. [ABSTRACT FROM PUBLISHER]

Pulsed discharge plasma in supercritical fluids (SCFs) has attracted a great deal of attention in the field of plasma application for chemical processing. Characteristics of electrical breakdown are one of the important concerns for dielectric reliability of a plasma reactor with SCFs. In this paper, the pulsed breakdown voltages of quasi-uniform gaps were measured by changing the \CO2 medium from gas to supercritical phase at a given temperature, and Weibull statistical analysis was applied to the measured breakdown voltages. The area effect on breakdown voltage, which is known to give an equivalent effective constant to Weibull shape parameter m, was examined with three sphere-to-sphere gaps. The experimental results indicate that the dispersion in the pulsed breakdown voltage in pressurized carbon dioxide obeys Weibull distribution, and the Weibull shape parameter m depends on the state of the \CO2 medium. The dependence of m on the medium density that was obtained from direct analysis of breakdown voltages for a given electrode system indicated a similar tendency to that of the effective constant by area effect analysis. [ABSTRACT FROM AUTHOR]

In this paper, we observe the lifetime characteristics of a single-sustainer-driven ac plasma display panel (PDP) based on the variation of luminance which is one of the important points to be considered for a practical application. It was found that the application of bipolar sustain pulse waveforms for the sustain discharge deteriorated the long-term lifetime characteristics in single-sustainer driving compared to conventional monopolar pulse driving. This phenomenon was investigated through 3-D discharge cell simulation. In the sustain operation using the bipolar sustain pulses, it was found that more amount of ion energy was transferred to the surface of the phosphor layer. Moreover, the temporal variation of the luminance in the PDP is assumed to be related to the phosphor deterioration resulting from the ion bombardment or the redeposition of the sputtered Mg particles from the protecting layer. In order to decrease the deterioration of the phosphor layer, we modified the address electrode potential to be floated during the sustain discharge. The calculated ion energy to the phosphor surface decreased with the modified waveforms in the discharge cell simulation. Furthermore, the same effect was observed in the conventional monopolar pulse driving, which led the improvement of lifetime characteristics. The effect of the modified waveforms was also verified through experiments in the test panel. [ABSTRACT FROM AUTHOR]

As the temperature of the panel increases in AC-PDPs, the minimum driving voltage increases. Thus, the driving voltage margin is not sufficient at high temperature. In this paper, we have investigated the mechanism of a misdischarge which is generated due to the decrement of the driving voltage margin at high temperature. The main factor of the high-temperature misdischarge is the increased electron emission ability from the MgO surface. We have confirmed that the wall charge loss in the address period is the largest among the driving periods. We have verified that the wall charge loss at high temperature depends on not only the voltage difference but also the time when the voltage difference is applied. Therefore, the wall charge loss is influenced by the number of sustain discharges in the previous subfield and address load. Finally, we have improved the driving voltage margin at high temperature using a narrow scan time and a high scan voltage in a 50-in panel with HD resolution. [ABSTRACT FROM PUBLISHER]

This paper presents a semi-empirical model for a wire–wire corona reactor driven by a capacitive storage solid-state pulse generator. The reactor electrode system is configured as a checker mesh of potential and grounded threaded electrodes, and the pulse generator is based on a modern magnetic pulse compression topology. This presentation considers the effect of the geometrical parameters of the reactor (the total length of the high-voltage electrode surrounded by its grounded counterparts and the gap between the high-voltage and grounded electrodes) on the operation of the atmospheric pressure streamer plasma system. The model analyzes the discharge processes in the reactor by distinguishing between four phases, each being represented by an equivalent circuit: before the streamer generation, during the primary streamer propagation, after the primary streamers have crossed the interelectrode gaps, and after the plasma conductivity quenching. The new reactor model is realized on the PSpice platform, and the simulations are done using an improved pulse modulator model. The simulation results are compared with the experimental data, showing the model validity. Based on the simulated model, a better matching between the wire-to-wire reactor load to the pulse generator may be achieved. [ABSTRACT FROM PUBLISHER]

This paper presents a model of the typical dielectric barrier plasma discharge at atmospheric pressure, structured as an equivalent electric circuit whose elements are identified with, and deducted from, the main influential variables of the process, namely, the applied gas, the geometry of the reactor, the breakdown parameters, as well as the power supply associated to the dielectric barrier discharge cell. Considering a parallel-plate reactor and a high-voltage sinusoidal power supply, an electrical comprehensive Simulink/MATLAB model has been developed in order to reveal the interaction between these two elements. The main components of this discharge model are as follows: 1) a double dielectric capacitance; 2) a voltage-controlled current source; and 3) a gas capacitance associated to the ionized gas. A sinusoidal voltage of up to 15 kV peak to peak at frequencies of 12.5 and 47 kHz has been applied to the discharge electrodes. The electrical model is based on the power law proposed by Roth, which defines the V --I behavior during the discharge startup. A series of simulations has been carried out in order to estimate the total current and voltage consumed during each discharge and to identify those parameters which are not measurable during the process. Finally, both the experimental and simulated voltage and current results in helium, argon, and nitrogen, as well as their Q--V graphics, are shown, and a comparison between them is discussed. [ABSTRACT FROM AUTHOR]