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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]

One of the critical components of high energy density pulsed power systems used to generate short high-voltage and high-power impulses is gas-filled plasma closing switch (PCS). In recent years, significant research efforts have been aimed at finding environmentally friendly gases which can be used in the PCSs, and several gases including dry air, nitrogen, carbon dioxide, argon, and their mixtures have been considered as potentially suitable working fluids in such switches. However, the lack of knowledge of the breakdown characteristics of complex switching topologies filled with these gases limits their practical applications. Therefore, further investigation of the breakdown performance of PCSs is required, in order to establish their applicability for practical use in high-voltage pulsed power systems. This paper reports on the investigation of the breakdown characteristics of a triggered PCS topology with corona discharge electrodes. The self-breakdown voltage of the switch, variation in the self-breakdown voltage, time to breakdown, and jitter have been obtained for the switch filled with “zero grade” air, N2, CO2, and an Ar/O2 mixture up to a pressure of 10 bar (abs). It was shown that the switch can provide a stable breakdown performance with jitter as low as ~1 ns. [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]

In this paper, the spatially resolved spectrum of the nitrogen second positive system ($\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$) has been measured in a nanosecond pulsed streamer corona N2 discharge with a wire-plate electrode structure. The spatial distributions of emission intensity of N2 ($\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) at different pulse peak voltages, pulse repetition rates, and gas components are used to explore the distribution and variation of the high electron density (higher than 11.03 eV) with the reaction radiation rate analysis. It is found that the high electron density increases with increasing both the peak voltage and pulsed repetition rate but decreases with increasing the oxygen contents. The spatial distribution of the emission intensity of N2 ($\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) is normalized to the value of the emission intensity at the wire electrode at different experimental conditions. The results show that the normalized distribution of the spatially resolved spectral intensity of N2 ($\text{C}^{3}\Pi _{\mathrm {u}} \to \text {B}^{3}\Pi _{\mathrm {g}}$ , 0–0) is independent of pulsed peak voltage, pulsed repetition rate, and gas component, which indicate that the normalized distributions of the high-energy electron density in the gap space at different experimental conditions are similar. These experimental results are significant to understand the discharge characters of pulsed streamer corona discharge and establish the molecule reaction dynamics model of pulsed streamer corona discharge. [ABSTRACT FROM AUTHOR]

Recently, cyanobacteria blooms (or water blooms) occurred on the surface of water bodies frequently and extensively due to eutrophia of the water. That has posed more and more serious environmental problems worldwide. In this paper, the effects of pulsed streamerlike discharge on M. aeruginosa cells are reported, which are one genus of cyanobacteria and ease to form water blooms. A stainless needle with a diameter of 30 μm was employed as a point discharge electrode, which is 15-cm apart from the cylinder cathode, and a 2-μs 160-kV pulse was applied. A pulsed streamerlike discharge was obtained in the water filled with cyanobacteria cells (named as sample water in this paper). From the experimental result, it can be found that the discharge collapsed the intracellular-structure gas vesicles in the M. aeruginosa cells, and the colonies of the cells sank to the bottom of the discharge chamber and rotten gradually. [ABSTRACT FROM AUTHOR]

This paper reports on the study of physical processes in a high-current vacuum arc shunted by semiconductor elements. The switching dynamics between a vacuum circuit breaker (VCB) and an assembly of several semiconductor elements connected in parallel to the VCB is investigated. The breaking capacity of a VCB-thyristor system is analyzed. It is found that at the instant of current switching, the arc can operate at a rather low voltage of 8–10 V. It is shown that there exists a certain limiting mode close to the conditions for current switching. In this mode, at least two cathode spots are observed. [ABSTRACT FROM PUBLISHER]

There has been considerable interest in nonthermal atmospheric pressure discharges due to their widely used industrial applications. A repetitively pulsed (RP) discharge ignited in microchannels between two nonequally broad planar electrodes is studied in this paper. The discharge current attains several 10^\mathrm -5 A orders of magnitude, and the ion concentration produced in interelectrode space by RP discharge is estimated to be about 10^17/\textm^3 . The duration of each time of RP discharge is several 10^\mathrm -8 s and the repetition frequency exceeds a few tenths of kilohertz. The repetition frequency of RP discharge depends on the $RC$ product, applied voltage, and the environmental humidity. The experiments of charging aerosol particles by RP discharges have shown that for particles with diameters of 34.8 and 103 nm, the charging efficiency can attain 14.8% and 35%, respectively. [ABSTRACT FROM AUTHOR]

The temperature dependence of the Kerr constant for water has been determined over the range 19 °C–45 °C at a wavelength of 658 nm. This paper presents the experimental arrangement used for this purpose and the data obtained, for which a polynomial fit is provided. A formula is also suggested to help estimate the variation of the Kerr constant for water with both temperature and wavelength. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the influence of environmental conditions on a nanosecond pulsed dielectric barrier discharge (NP-DBD). A test chamber where pressure and temperature can be changed to match with realistic altitude conditions has been used. Electrical and optical characterizations of the NP-DBD are proposed for pressure and temperature changes in range related to flow control applications. In particular, the influence of low pressure is investigated. The results indicate that a reduction in pressure leads to a more diffuse plasma layer to a more diffuse plasma layer and an enhanced propagation. The energy dissipated by the discharge increases with a reducing pressure. Regardless of the pressure level, the heat released by the NP-DBD leads to the formation of a pressure wave propagating at sound speed. A good correlation was found between the extension of the plasma layer and the planar part of the produced pressure wave. Similar electrical characterization has been conducted when the temperature is reduced, while the pressure is maintained at an atmospheric level. It was shown that temperature has the minor effect on the discharge characteristics, but lower is the temperature and lower is the deposited energy. In a final part, the influence of the altitude is investigated by studying the combined effects of pressure and temperature. It results that the pressure variation dominates the temperature influence. As a result, higher energy deposition is reported when the altitude is increased. The effect of changes in the pressure and temperature is interpreted as an effect of changes in the gas density. It is concluded that the gas density, $N$ , is an important parameter for studying DBD under the altitude conditions. Indeed, quantities such as the plasma extent and the deposited energy scale with N^{-0.5} . However, the gas density does not consider changes in the dielectric permittivity, which restricts the use of the gas density matching method to altitudes with moderate ambient temperature. [ABSTRACT FROM PUBLISHER]

In this paper, a new method of generation of an electrical discharge in water using plate electrodes is proposed. The electrical discharge in plate-to-plate configuration cannot be easily generated because of a low uniform electrical field. A nitrogen bubble is injected into one of the electrodes to create a favorable condition for electrical breakdown. The generated electrical discharge is studied using a high-speed framing camera. Two interesting effects have been observed. First, the discharge is preferentially initiated on the cathode. Second, the positive streamer reveals nontypical morphology. The physical mechanisms of discharge initiation and positive streamer propagation are discussed. [ABSTRACT FROM PUBLISHER]

In this paper, the influence of the additional impact of electrostatic field on dusty and buffer plasma parameters is investigated. It is shown that the addition of a light gas to heavy one and the additional impact of a constant field on the radio frequency discharge lead to changes in the spatial characteristics of the buffer plasma and the location of the plasma-dust structure in the interelectrode space. [ABSTRACT FROM PUBLISHER]

A 700-kA gas switch with graphite electrodes for pulsed power supply module has been developed. This paper describes the design, construction, and testing of the high-current gas switch and its trigger system. The two-electrode gas switch is selected, which suffers high peak and fast rise time currents. The trigger generator based on resonant charging of a pulse transformer is constructed to trigger the gas spark. An electrodynamic force model of switch electrodes is established. The electrodynamic force of connecting wires is also calculated. By comparison of the mechanical strengths of polyformaldehyde, epoxy, and fiber-reinforced plastic (FRP) rods, where FRP rods are selected as switch rods, the experimental results show that the mechanical strength of the switch increases by 200%. Extensive electric testing has proven the operating parameters of the switch and its trigger system. The experimental results show that the measured discharge current waveform is demonstrated to be over a 700-kA peak current and a 500- \mu \texts pulsewidth. The transfer charge per shot is more than 500 C. [ABSTRACT FROM PUBLISHER]

Multipoint-to-multipoint and multipoint-to-plane electrode geometries have been investigated to enhance corona discharge modes in atmospheric pressure weakly ionized plasma. This paper presents a new geometry approach by a protrusion array over the grounded screen along with a high-voltage (HV) needle array to obtain higher coulombic discharge. It has been observed that needle-to-grounded-screen-protrusion configuration enhances the discharge modes, especially the back corona is enhanced significantly near the protrusions in Ar/C2H2 plasma. A corona mode map has been developed to depict the optimal discharge zones at various HV gaps. Similar investigations were performed in Ar/O2 plasma to study the nature of the current pulses and discharge modes. [ABSTRACT FROM PUBLISHER]

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]

This paper proposes a mathematical model for electrical discharge plasmas between moving electrodes under ac condition, which happens in ac switching apparatuses. The modeling work is started by converting the problem to a conventional RL network that treats the arcing phenomenon as a black box and proposing a transient differential equation to represent the breaking arc process. A resistance–time relation model developed from the classic Mayr model is then proposed. A conceptual unit-arc approach is used to deal with the issue of variable arc length as the contacts move. Experimental data from ac contactor tests are used to approximate the resistance–time function by a nonlinear curve fitting. The model is solved computationally and compared with the experimental data. It is that the model adequately describes the breaking arc phenomenon. [ABSTRACT FROM PUBLISHER]

Experiments on high-current arcs carried out in an ultrahigh vacuum chamber are presented in this paper. For contact separation the lower electrode is moved by a mechanical-pneumatic device simulating the conditions of a vacuum circuit breaker. The arc behavior of the Cu–Cr test electrodes after the electrode separation without application of external magnetic field is observed by a high-speed video camera. Besides the usual electrical measurements, the emission in the gap along the electrode axis is investigated by spatially resolved optical emission spectroscopy. Differences are found in the intensity distribution of atomic and ionic lines along the gap. [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]

In this paper, experimental observations of propagation of negative streamers in distilled water (conductivity of 1.7 \mu \textS\cdot \mathrm cm^-1 ) in a needle-plane electrode geometry (gap of 6 mm) are described. The spatially resolved pressure field surrounding the tip of streamer channel in the given moment was determined by Mach–Zehnder interferometer with second harmonic of Nd:YAG laser as a source. The high-voltage needle electrode was brought on the potential of 23 kV and that remained practically unchanged during streamers propagation, while a significant noise with amplitude of several amperes was visible on the waveform of discharge current. Analysis of captured interferograms shows that propagation of negative streamers is not uniform: an active (propagating) streamer produces continuous moving pressure field (similar to that of moving object) with maximum amplitude greater than 40 MPa on the streamer tips and an inactive streamer nearly stops propagating being surrounded by a nearly spherical pressure wave moving away from the streamer’s tip. The inactive state can last even longer than 200 ns. [ABSTRACT FROM PUBLISHER]

This paper presents the results of experimental and numerical studies of the behavior of metallic shaped-charge jets (SCJs) with passage of electric current through them. The possibilities of decreasing or increasing the depth of penetration of SCJs into targets are discussed. It is shown that the penetration capability of SCJs can be decreased or increased by varying the electric pulse parameters. [ABSTRACT FROM PUBLISHER]

Electrode structures have an important effect on the electric-field strength at the cathode tip in vacuum. Effectively increasing the electric-field strength at the cathode tip can contribute to increasing the density and energy of vacuum-arc discharge plasmas. In this paper, a tubular electrode is designed and employed as the anode. The electric-field distribution of the electrode was simulated using the software package Maxwell 3-D. Through a series of simulated experiments, the factors that affect the electric-field distribution were explored, including the length of the tubular anode and the relative positions of the electrodes. In addition, the effect of an insulator situated between the cathode and the anode and optimal designs for the electrode structures are discussed. The plasma parameters and thrust were measured using a Langmuir probe and a piezoelectric thin-film sensor, respectively. The experimental and simulated results indicate that optimizing the electrode structure can effectively reduce the weight of the electrodes, increase the field strength at the cathode tip, and generate higher plasma density and greater thrust. [ABSTRACT FROM PUBLISHER]

Electrode erosion is a notable issue influencing the performance and restricting the lifetime of gas switches. In the erosion process, electrode materials heated by spark channel will melt or evaporate and be driven to depart from electrode surface, contaminating the gas switch insulator, and potentially inducing flashover accidents. In this paper, sputtering spots are observed near the erosion crater in a two-electrode gas switch, which indicates the existence of molten droplet ejection. In addition, a set of polymethyl methacrylate rings are inserted in the gas switch to detect the ejection of molten droplet as well as to simulate the switch insulator for investigating the degradation of surface insulation strength. The results show that the ejection of molten droplet is along the tangent surface of electrode with a small divergent angle. After repeated discharges, the insulator surface is bombarded by the droplet ejection and forms dense cracks and embedded metal particles in a narrow band. The spatial varied droplet ejection causes a decrease in both flashover electric field and surface resistance. It also leads to different surface resistances in different regions, which can result in an uneven electric field distribution. Thus, droplet ejection increases the probability of surface flashover accidents in gas switches. [ABSTRACT FROM PUBLISHER]

With the rapid expansion of urbanization, the technology of wastewater treatment has an increasingly crucial role in the field of environmental protection science and technology. The technology of pulsed arc electrohydraulic discharge (PAED) has been studied in depth by virtue of its signally treatment effect, low power consumption, and so on. The experiments were carried out with the wastewater from cyclic activated sludge system tank. The 10-L PAED reactor with eccentric electrodes is designed as industrialization mode. The PAED power supply is 3 kJ/pulse and the discharge rate is 2 Hz. The experiments on different distances, radii, and types of water gap electrodes were carried out. Three different electrode materials (titanium, tungsten, and titanium alloy) were used in the PAED system in the experiments. The results show that the sterilization effect on Escherichia coli is the highest when the material of the water gap electrodes is tungsten and the cumulative input electrical power is 1000 Wh/ \textm^3 . Fundamental discharge characteristics linked with disinfection performance will be discussed in detail in this paper. [ABSTRACT FROM PUBLISHER]

The problem of armature transition in a rail accelerator is considered in this paper from the position of analysis of the commutation process realized by a moving armature. The needed electrical conductivity of the surface layer of the rails to avoid arc excitation has been calculated for each step of armature motion using the simple model of the transient electromagnetic process. Conductivity must be changing depending on the path of armature transportation along the rails. The efficiency of variable conductivity and multilayer structure of the rails has been demonstrated by 2-D simulation of the field and current density distribution using the finite-element software Comsol and FlexPDE6. It was concluded that the main problem of railgun (armature transition, i.e., current concentration and extra-voltage appearance near the trailing edge of the armature resulted in the local melting of both the rails and the armature) can be resolved successfully when 2-D gradient of the electrical conductivity of the rails near the contact surface is provided jointly with the reduced conductivity of the armature contact surface. [ABSTRACT FROM PUBLISHER]

Arc determines whether the vacuum switchgears can break current successfully, so it is significant to study its characteristics. In this paper, a hybrid high-speed actuator was designed, and a method of forced current zero was used to interrupt dc in a synthetic test circuit. With the different contact opening speeds, the processes of arc burning and current transferring were observed by a high-speed CMOS camera. Through the arc area obtained by an image processing technology, the influences of the opening speed on arc were researched, including the influences in the initial arc burning stage, in the forced current zero stage, and at the same electrode distance. The results indicate that with the increase of the opening speed in a certain range, the arc area in the forced current zero stage tends to be small, and the one in the initial arc burning stage spreads more quickly. Although the arc area increases with the opening speed in the initial arc burning stage, its impact on the whole dc current transferring process is slight when the contact opening speed is high. So, high opening speed is helpful to extinguish arc and transfer current. In addition, there is another discovery in the experiments. In a certain range, when the opening speed is higher, arc burns stably earlier, and the arc area is smaller in the stable burning stage. So, it is beneficial to inject the transferring current in this stage. Experimental results and analysis of the arc images prove that increasing the opening speed is useful to transfer the current successfully and recover the dielectric strength of the electrode distance. [ABSTRACT FROM PUBLISHER]

This paper presents the experimental results on the characterization of plasma produced in narrow tubes using a pulsed dielectric barrier discharge (DBD), working in helium or helium–oxygen gas mixture at atmospheric pressure, in a symmetrical configuration of external electrodes. This paper focuses on the effect induced by the total gas flow rate and gas composition on the characteristics of pulsed DBD. Using tunable diode laser absorption spectroscopy, ultraviolet absorption, and optical emission spectroscopy, complementary information on the reactive species (O, O3, N2, and N2+) present in the discharge has been obtained. It results that the excited species generated by direct electron excitation (as He and N2) follow the evolution of their precursors with increasing gas flow rate, while those created by chain reactions (as N2+, O, and O3) depend on the collective behavior of all their precursors, regardless of the fact that these are originating from the feeding gas or are coming from impurities. At specific energies, between 5 and 50 J/L, and a gas temperature of 315 ± 20 K, the atmospheric-pressure plasma is able to produce 1014−1015 m−3 of O (35S2) or (1.5− 2.8)\times 10^15~cm^-3 of O3, depending on the feeding gas composition and its flow rate. Low gas temperature and high density of reactive species could make the present DBD arrangement suitable for medical applications. [ABSTRACT FROM PUBLISHER]

Bubbles generated by a pulsed discharge in water can emit extensive pulsed acoustic waves. The bubble behavior is quite important for the electroacoustic analysis. This paper presents the high-speed photographs of the plasma-containing bubble behavior under the pulsed discharges of different polarities, including a single negative bubble, single positive bubble, and bipolar bubbles. The single bubble results show that the electrobubble energy transition rate of the positive discharge is higher than that of the negative discharge. The positive bubble has longer oscillation period and lower fundamental frequency than the negative one. For the bipolar bubbles, interaction between the two bubbles influences their own behavior, irrespectively of how long the gap distance between the electrodes is, and decreases the electrobubble energy transition efficiency and the acoustic wave amplitude as well. It is also interesting that the negative bubble oscillates twice, although its energy is much lower than that of the positive bubble, and the time of the negative bubble collapse at the end of the second period almost coincides with that of the positive bubble. Finally, the positive bubble breaks into pieces and vanishes faster than the negative bubble. [ABSTRACT FROM PUBLISHER]

In this paper, the mechanisms and characteristics of the pulsed dielectric barrier discharges in Ar and N2 at atmospheric pressure are analyzed and compared by means of numerical simulation based on the 1-D fluid model. Under different operating conditions, including gap width dg , dielectric thickness ds , and relative dielectric constant \varepsilon r , the important characteristic quantities of describing the discharge, i.e., maximum discharge current density Jm , averaged electron density \mathrmNe-\mathrm {ave} , and averaged dissipated power density P\mathrm {ave} , are observed and studied in detail. This paper gives the following significant results. In Ar, the discharge occurs after the gap voltage has reached its maximum and is in the form of two short discharge current density pulses. In N2, the discharge starts from the increase of the gap voltage and presents the smooth development in a longer time being nearly equal to the pulsewidth. For the two gases, Jm , \mathrmNe-\mathrm {ave} , and P\mathrm {ave} decrease with the increase of d\!g , and these characteristic quantities decrease with the increase of ds , or with the decrease of \varepsilon r . In addition, the discharges in Ar maintain in the atmospheric pressure glow discharge (APGD), but the discharges in N2 operate in the varying discharge modes, including the APGD, the weak APGD, and the atmospheric pressure Townsend discharge. The development of the APGD in N2 requires the smaller gap width, the thinner dielectric thickness, and the larger relative dielectric constant. [ABSTRACT FROM PUBLISHER]

In this paper, we present the final implementation of our 0–50-kV picosecond rise time 0.5–10-ns pulse generator. The pulse generator will be used in future work to generate a (sub)-nanosecond streamer plasma for air purification research. The pulse generator is a single-line pulse generator with an oil spark-gap (SG), which generates 0.5–10-ns pulses with a 200-ps rise time and can operate at repetition rates of over 1 kHz into a 50- \Omega load. It is an improvement over the first implementation of our nanosecond pulse generator that we designed and verified experimentally in previous work. In this paper, we evaluate the performance of the final design. Furthermore, we present 3-D electromagnetic simulations of the nanosecond pulse generator and show that the simulations are in good agreement with the measurements. A variation in pulse duration from 0.5 to 10 ns is possible and the output pulses are square shaped without the large plateau behind the main pulse that was present in the pulses from the first implementation of the nanosecond pulse generator. At high voltages, the pulse top becomes less flat due to a time-dependent mismatch in the spark-gap. Furthermore, investigation of electrode erosion of the oil spark-gap shows that the erosion rate of the electrodes is in the range of 200–600 \mu \mathrmcm^3 \cdot \mathrmC^-1 for the electrode that is mainly the cathode and 100–300 \mu \mathrm{cm}^{3} \cdot \mathrm{C}^{-1}$ for the electrode that is mainly the anode, respectively. This is almost an order of magnitude higher than most gas spark-gap studies show for brass electrodes. Therefore, electrode erosion in the oil spark-gap will be a limiting factor on the lifetime of the system. We designed a new electrode with a stainless steel head to increase this lifetime. [ABSTRACT FROM PUBLISHER]

This paper proposes a magnetohydrodynamic model that does not assume local thermal equilibrium (LTE) to predict the flow field and electron temperature and species density distributions inside a direct-current nontransferred-arc steam torch with a well-type cathode at atmospheric pressure. A steady, axisymmetric flow is assumed, and the azimuthal velocity component is not neglected. A finite volume method is adopted to solve the continuity equation, the current continuity equation, the momentum equation, and the energy equation according to a $k-\varepsilon $ turbulence model. Ohm’s law is used to calculate the induced magnetic field, and Ampere’s circuital law is adopted to compute the current distribution in space. Fifty-two chemical and plasma kinetic equations are employed to describe the interactions among the 12 main species of water plasma, H2O, OH, H, O, H2, O2, HO2, H2O2, O3, H+, O+, and electrons, considered in this paper. The electron temperature is predicted from the transport equation based on the electron energy balance, whereas the transport coefficients of the plasma are obtained from the Chapman-Enskog solution of the Boltzmann equation. The thermal plasma flow of steam inside the plasma torch, which measures 503 mm in length and 9 mm in radius, is predicted to have $I=180$ A and $Q=5$ g/s. The non-LTE simulation suggests that a plasma temperature of 11600 K and flow velocity of 3.8 km/s can be achieved at the center of the torch outlet. Compared with the LTE model, the non-LTE calculation yields lower plasma temperature and higher axial velocity at the torch outlet. The calculated electron temperature principally varies between 1 and 3 eV, and energetic electrons occur not only near the electrode surfaces but also within the axial electric arc. The model predictions suggest that the thermal plasma is well approximated as LTE in the hot plasma core, which is characterized by an isothermal contour of 10 kK, and in the vicinity of the electrodes. The deviation from the LTE condition predominantly grows with the radial coordinate, and the temperature ratio approaches unity at the electrode surfaces. The dominant species components of the water plasma in the inner region ( $r< 6$ mm) at the torch outlet are monoatomic and ionic species of H and O, whereas the diatomic species and water molecule become relatively important in the outer region ( $r>6$ mm) at the torch outlet. [ABSTRACT FROM PUBLISHER]

The electrode-gap effects on the discharge characteristics have attracted increasing attention to the design of atmospheric discharge sources. In this paper, a 1-D fluid model is used to explore the discharge structures in atmospheric radio-frequency microplasmas with He/O2 mixture as working gas as well as to discuss the generation of reactive oxygen species (ROS) with the electrode gap varied. As oxygen admixtures are introduced into the helium microplasmas, the heavy anions of O− and O2− become the dominative negative species instead of electrons, and then establish the bulk plasma region together with the positive ions. Thus, even at very small gaps, a normal glow-discharge discharge structure can be formed, and a sheath-dominated discharge structure, which is usually formed in pure helium microplasmas in a small size, cannot be observed any more. The simulation results also indicate that the production of main ROS is more effective in small dimensions. [ABSTRACT FROM PUBLISHER]

This paper presents the design and experimental validations of a system of three new high-voltage (HV) pulsed-power converters for the H− sources. The system requires three pulsed voltages (50, 40, and 25 kV to ground) at 2-Hz repetition rate, for \(700~\mu \) s of usable flat-top. The solution presents ripple-free output voltages and minimal stored energy to protect the ion source from the consequences of arc events. Experimental results on the final full-scale prototype are presented. In case of short-circuit events, the maximal energy delivered to the source is in the Joule range. HV flat-top stability of 1% is experimentally achieved with a simple Proportional-Integral-Derivative regulation and preliminary tuned H− source (e.g., radio frequency control, gas injection, and so forth). The system is running since more than a year with no power converter failures and damage to the source. [ABSTRACT FROM PUBLISHER]

Agriculture in Japan is approaching a crisis for two reasons: a declining self-sufficiency rate and a decreasing number of agriculture workers. To solve these problems, plant factories have been attracting attention recently. Plant factories are facilities that aid the steady production of high-quality vegetables year round by artificially controlling the cultivation environment, allowing growers to drastically decrease production time. Despite the many advantages of plant factories, a main impediment is the reduction of initial and running costs. This paper utilizes leaf lettuce (Early impulse), which is a typical item cultivated in plant factories, as a target to improve productive efficiency of plant factories due to its relatively high price. Various pulsed electric fields (PEFs) were applied to roots of the lettuce to increase lettuce growth rate. The experimental results show PEF intensity from 0.2 to 1.0 kV/cm is positive for growth stimulation. Conversely, those over 1.0 kV/cm resulted in growth inhibition. Furthermore, roots of the samples which exhibited increased leaf weight grew more robustly than those of decreased leaf weight. In addition, analysis results showed that there was no significant difference when liquid fertilizer was applied prior to or after application of PEF. The results suggest that PEF does not affect the composition change of liquid fertilizer but directly influences the growth of leaf lettuce. [ABSTRACT FROM PUBLISHER]

High-power electromagnetic (HPEM) pulse can be delivered to electronic equipment in two ways. One is through the application of radiated fields, and the other is through conduction along cables and wires. In this paper, a high-voltage pulse generator using a spiral Blumlein pulse forming line (PFL) was developed for the test of HPEM effect by radiation and conduction. For the conduction test, a spiral strip Blumlein PFL filled with transformer oil is employed to generate high voltage (>300~kV) and long duration (50 ns) pulse. High-power ultrawideband pulse for the radiation test was generated by combining a TEM horn antenna with the high-voltage generator. The peak-to-peak value of electric field intensity of a radiated pulse is 53.3 kV/m at a distance of 10 m away from the antenna. The pulse generation system was used for the examination of effects of the electric fields and conducted pulses on the operation of electronic devices. [ABSTRACT FROM PUBLISHER]

Physical and electrical contact between liquid food and the metallic electrodes during the pulsed electric field process for microbial inactivation is unavoidable and causes some metallic ions to be released from the electrodes into the processed food. In this paper, the resistance to the release of metallic ions from electrodes coated with four different materials (Ag, Cr, Ni, and Ti) is compared. Ti has been found to be the most effective of these metals and is compared more extensively with widely used food-grade stainless steel. When the electrodes are made of Ti, the concentration of metal released is always found to be below the 32-ppb detection limit. [ABSTRACT FROM PUBLISHER]

With the development of pulsed-power technology, more and more applications require high-voltage and heavy-current pulse switches. Laser-triggered vacuum switch combines laser technology, vacuum switch technology, and three-electrode trigger switch technology, and has the advantages of heavy current capability, good isolation from the main circuit, and short delay time. In this paper, the 1-D thermal conduction model was developed to analyze the influence of laser energy on the velocity of initial plasma. The relationship between the ablation area and the laser energy was derived. The theoretical analysis can be verified by the relationship between the trigger delay time and laser energy and the initial plasma microcurrent curve in the experiments. [ABSTRACT FROM AUTHOR]

Power supplies have played crucial role to improve and extend plasma applications. Several dc, pulsed, and radio frequency (RF) stabilized power supplies have been developed over a wide range of frequencies and voltage waveforms. However, the influence of voltage waveform on the plasma densification, mainly due to the secondary electrons emission from the electrodes, has not been quite explored. This paper proposes an asymmetric pulsed bipolar power supply, adjustable in frequency, amplitude, pulsewidth, and number of pulses for generation of cold plasmas. Short period positive pulses, between longer negative pulses, increase greatly the secondary electron emission from the electrodes and, consequently, the plasma ionization rate. Short pulses (ns) are obtained by the phase shift between each carrier, and the high-intensity pulses are obtained by cascading the cell submodules in a half-bridge cascade topology, using a modular half-bridge converter configuration. The intensity of the positive and negative pulses can be varied independently. There is no unintended dc voltage level between the electrodes, which appear in RF plasmas. The plasma generated in this way is free of electric arc and can be kept stable within a broader range of operating parameters, mainly the voltage and the working gas pressure. [ABSTRACT FROM AUTHOR]

In this paper, the electrical and optical characteristics of an ac-excited argon streamer-like discharge operating in a gas–liquid-phase are investigated under different initial liquid electrical conductivities. The experimental results show that on one hand, there exist significant influences of the initial liquid electrical conductivities, ranging from 20 to $2000~\mu \text{S}$ /cm, on the characteristics of the two-phase discharges at the initial stage, e.g., the discharge voltage and current, the penetrating depth of the plasma plume into the liquid, the rotational and vibrational temperatures of the plasmas, and the electron number density. While on the other hand, significant temporal behaviors of the discharges, e.g., the discharge voltage and current, the plasma plume length, and the corresponding solution properties, e.g., the pH value, electrical conductivity, and the H2O2 concentration, are also observed with the extension of the operating time with other parameters being unchanged. These results are helpful for promoting the applications of the two-phase discharge plasmas in the field of environment protection. [ABSTRACT FROM AUTHOR]

Boron-doped carbon nanotubes (B-doped NTs) are predicted to behave as semiconductors over a large range of diameters and chiralities and might thus constitute a suitable class of materials for nanoelectronics technology; they could be used, for example, to enhance properties of supercapacitors as capacitance and time of charge/discharge. In this paper, we propose an electric arc to synthesize B-doped NTs, based on the erosion of graphite electrodes with nickel and yttrium as catalysts and boron as the doping element. This technique allows obtaining carbon nanotubes (NTs) doped with around 8% of boron, in a short amount of time (2 min) and under relatively low applied power (2 kW). B-doped NTs were characterized with scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Physical properties of the plasma were also studied using optical emission spectroscopy. Temperatures of around 5000 K were obtained suggesting a high concentration of $C_{2}$ molecules and then, the ideal conditions to synthesize NTs. [ABSTRACT FROM AUTHOR]

This paper is aimed to identify the mechanism that atmospheric pressure plasma jet (APPJ) damages malignant melanoma (B16-BL6 cells) cultured in vitro through the induction of oxidative stress. After being exposed to APPJ with different time durations, the reactive species of H2O2 and NO2− inside cell culture medium, together with a series of biochemical parameters including the cell viability, cell morphology, DNA damage, intracellular reactive oxygen species (ROS) and antioxidant capacity, are measured. The results reveal that there are obvious increases of H2O2 and NO2− in the plasma-irradiated medium. And the cell viability, intracellular total antioxidant capability (T-AOC), and glutathione (GSH) contents decrease with the exposure to APPJ in a time-dependent manner compared with the untreated cells, i.e., 0-s group ($p < 0.05$). Besides, the intracellular malondialdehyde (MDA), ROS contents, and the degree of cellular damage increase significantly with 30, 60, and 90 s of plasma treatment ($p < 0.05$). Furthermore, the pretreatment with N-acetyl cysteine, which is a free radical scavenger, can markedly prevent the decrease of cell viability, T-AOC, and GSH content, the increase of MDA, ROS contents, and the degree of cellular damage caused by 90-s exposure to APPJ. These research findings suggest that low-temperature plasma exerts its cytotoxic effects on melanoma cancer cells mainly through the ROS inside cells induced by reactive oxygen and nitrogen species generated in gaseous and liquid phases, which ultimately cause oxidative stress-evoked damage to cellular components. [ABSTRACT FROM AUTHOR]

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]

To influence the weather is a long-treasured dream of mankind. Current cloud seeding technology mostly relies on chemicals such as silver iodide and hygroscopic salts, which may have negative impacts on environment and human health. Here, we present a new method for triggering macroscopic water precipitation in air. Experiments demonstrated that high-voltage generated corona discharge was able to induce rain and snow formation in atmospheric pressure air. The effect was confirmed by precipitation experiments performed in a 1- and 15 000-m3 cloud chamber, where the absolute water content was close to the actual values in natural cumulonimbus clouds. With the presence of electrical charges, the collision efficiency between the water droplets was increased by over one order of magnitude, accelerating the coalescence process and possibly leading to the rain and snow formation otherwise impossible to form. The electric-based technology presented in this paper provides an effective, inexpensive, and environmental friendly tool for triggering water precipitation, and may open up new opportunities for producing water precipitation in large open space. [ABSTRACT FROM AUTHOR]

The quench protection switch (QPS) is an indispensable component ensuring the safety of the magnet coils of a superconducting Tokamak when a quench happens. In this paper, the second commutation process of a QPS based on artificial current zero is investigated. In this process, the current, which has already transferred from the bypass switch to the main circuit breaker, is forced to commutate from the vacuum circuit breaker (VCB) to the discharge resistor by the countercurrent. An LC oscillating circuit is applied to generate oscillating current to simulate the direct current near its peak which is about 20 kA. The countercurrent with frequencies of 500 and 1000 Hz is provided by a commutation branch. The equivalence of the experimental interrupting process compared with the practical situation is analyzed. Two kinds of vacuum interrupters of the VCB are used in experiments. One kind is equipped with contacts generating transverse magnetic field, and axial magnetic field contacts are used in another one. The experimental results indicate that the initial process of the vacuum arc before injecting the countercurrent has crucial impacts on the interruption performance. The countercurrent with the frequency of 500 Hz is easier to interrupt the current than the case of 1000 Hz. [ABSTRACT FROM AUTHOR]

As the demand for advanced microelectronic devices of small form factor and high power density has increased, the capability of the miniaturized mechanical solutions for effective cooling has become critical. Electrohydrodynamic (EHD) air blowers have great potential as alternative cooling solutions over the traditional mechanical systems to meet the thermal management requirements with flexible design and considerable flow production for effective heat removal. In this paper, a numerical analysis and optimization of wire-to-plane EHD air blowers are performed based on 2-D developed models validated against previous data. For a range of blower heights from 2 to 10 mm, the location and length of the collecting plane located at the blower walls apart from the emitter wire electrode are investigated and optimized based on pumping efficiency using the ranges of fixed operating powers and voltages. Simple relations for each optimization method are presented to determine the optimal blower configuration. Results of flow rate and static pressure obtained by each optimized blower show good agreement with those predicted by EHD scaling laws previously presented. [ABSTRACT FROM PUBLISHER]

Results from a smoothed-particle hydrodynamics (SPH) method of modeling electrode ablation in pulsed power systems are presented. The model follows numerous previous studies on electrode erosion in which the primary mechanism is conductive heat transfer. Total eroded mass as a function of peak current, frequency, and circuit damping were compared to theoretical and experimental data. The results indicate an average of a 16% deviation of the SPH code from the analytical prediction; however, most of the SPH data points qualitatively fall close to or within experimental ranges. The results indicate the potential of the SPH code to effectively model fusion propulsion reactor components for use in space travel. [ABSTRACT FROM PUBLISHER]

In this paper, linear and spanwise-segmented plasma actuator implementations as well as base airfoil with no plasma cases are presented. These approaches are used to control the flow around a NACA0015 airfoil. The experiments were conducted in a wind tunnel at Reynolds number of 3.6×104. The plasma actuators mounted on the leading edge of the airfoil at chord position of 0.1 (x/C). The electrical parameters used for the plasma generating device are set to constant values of 6-kVpp applied voltage and 3.5-kHz excitation frequency. It is observed that the use of spanwise-segmented plasma actuators converts the 2-D flow structure around the airfoil into 3-D forcing flow structure. The change of the wake region width of the airfoil is visualized by using the smoke-wire method. The flow visualization is performed at attack angles of 0°, 5°, 10°, and 15°. In addition, necessary measurements are also made to determine drag and lift forces. A comparative study on the drag and lift forces for the NACA0015 airfoil is performed. As a part of the conclusions, linear and spanwise-segmented plasma actuator implementations as well as base airfoil with no plasma cases are compared and related results on flow control are presented. [ABSTRACT FROM PUBLISHER]

Given its nonthermal property and other advantages, irreversible electroporation (IRE) has quickly translated into clinical applications. An increasing number of clinical cases using IRE have also revealed crucial issues. The uneven distribution of the electric field caused by the heterogeneity of biological tissues has not been completely and effectively addressed to date. The use of high-frequency monopolar pulse bursts (HFMPBs) is expected to solve this problem. The high-frequency content of the HFMPB is used to ensure the uniform distribution of the electric field in the tissue. A temperature increase similar to that of the conventional pulse method does not cause thermal damage and results in a killing effect similar to that of the conventional technique. Meanwhile, the subpulse has a pulse duration of 1– 100~\mu \texts , which remains unexplored and may induce new cell responses. This paper analyzes the HFMPB based on the frequency domain and infers that the cell death pathways under this pulse induce necrosis and other processes, such as apoptosis. The phosphatidylserine externalization rate had a peak value at a different inner frequency of HFMPB when the electric field was 1 kV/cm for melanoma cells. This new type of pulse is expected to solve the problem of the uneven distribution of the electric field without altering the cell killing effect. If this effect is also verified in tissue ablation, these new types of pulses will promote the clinical application of IRE. [ABSTRACT FROM AUTHOR]

Nowadays, most of solid-state circuits are fabricated through the application of the 2-D electrode manufacturing technology (printed circuit). In this paper, solid-state pulse-forming modules using 2-D electrode manufacturing technology are presented to produce long pulse duration while less space volume is being occupied. First, on a glass–ceramic (dielectric constant 225) substrate with the dimension of 250~\text mm \times 95~\text mm \times 4 mm, as meander line is the usual delay-line circuit in printed circuit boards, the meander pulse-forming line is used to deliver a high-voltage pulse with pulse duration longer than 120 ns by simulation and test validation. Furthermore, we also discuss the double parallel meander-line and the “V” shaped meander-line in this section. Second, with the same substrate, the LC pulse-forming module is used to generate the high-power pulse with good square pulse quality. By changing the inductance L, this module can be adjusted to deliver pulses with different durations. Third, planar concentric ring PFL is proposed with simulation analysis. In simulation, the planar concentric ring PFL is designed using an attractive storage medium—Barium Titanate (BaTiO3 base- ceramics (dielectric constant ~1000). At last, a compact PFL based on the structure of multilayer ceramic capacitor is introduced, and can generate a quasi-square pulse in simulation. These various types of solid-state pulse-forming modules may be the potential component in the compact pulsed power systems to generate high-voltage, long-duration pulses. [ABSTRACT FROM AUTHOR]

Reducing the working coefficient of gas switch can effectively lower the prefires probability. This paper discusses in detail the discharge characteristics of a three-electrode plasma-jet triggered gas switch (PJTGS), especially at low working coefficients. The triggered discharge process of the PJTGS is analyzed. Plasma jets are observed and discussed with respect to trigger voltage, trigger energy, and gas pressure. In addition, the switch jitters at different conditions are investigated, including ground resistor, charging voltage, trigger energy, trigger voltage, and working coefficient. The results indicate that the height of the plasma jet increases with the increase of trigger voltage and energy, and decreases with the increase of gas pressure. At working coefficients higher than 75%, trigger voltage of +80 kV, and ground resistor of 100 \(\Omega \) , reliable subnanosecond jitters can be obtained with the charging voltages of ±25, ±30, ±40, and ±50 kV. When the working coefficients are between 50% and 28.1%, the switch jitters range from 1.6 to 3.5 ns. Even at the working coefficient of 28.1%, the PJTGS can still be triggered reliably with a switch jitter of 3.5 ns. [ABSTRACT FROM AUTHOR]

This paper presents experimental studies of a surface discharge of an aerodynamic actuator produced by a high-voltage pulse with a nanosecond rise time and a millisecond decrease time. Time-resolved imaging of the plasma and interferometric imaging of the shock wave generated by a unique nanosecond ramp were performed. Interferometry enabled shock fronts to be visualized with a 1 \(\mu \) s time resolution and to experimentally deduce for the first time the associated overpressure values. The interaction of the shock wave with the ionic wind generated during consecutive millisecond-scale voltage decay is also reported from phase-averaged laser Doppler velocimetry measurements. The observed phenomena were correlated with time-resolved images of the plasma developing at the dielectric surface during discharge phases. [ABSTRACT FROM AUTHOR]

This paper is concerned with the development and testing of a compact flat format multichannel electrically triggered rail spark gap. It is tested for multichannel discharge under atmosphere for high reliability. Multichannel discharge rail spark gaps can be developed using laser trigger or fast rising trigger voltage pulse (>5~kV/ns). The extra volume and weight added by laser or fast triggering circuits limit the use in pulse power applications. An electrically multitriggered low-inductance spark gap is developed. It is used as a multichannel low-inductance discharging element in a fast rising high-current generation system. The trigger of such rail gap is realized using the set of round copper pins similar to single trigger pin in a field distortion spark gap. In parenthesis, five different trigger pins are located in main trigger plate and these are isolated with high impedance. Therefore, five different trigger signals are generated with time difference of tens of nanoseconds. The major material erosion at five points of both stainless steel main electrodes confirms the multichanneling discharge. The main gap spacing in this switch is 4 mm and the trigger is located close to the ground electrode for reducing the delay time and jitter in delay time. This paper shows the trigger circuit design, main gap voltage, and trigger voltage effect on the closing of the spark gap and picture of electrodes after use. [ABSTRACT FROM AUTHOR]