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Deposition of transparent oxide films at atmosphere pressure onto polymeric substrates at room temperature is a technique gaining rapid acceptance. These films can be used for numerous applications such as antiscratch and water permeation barrier coatings. In this paper, a \sim 1.4 - \mu \text{m} SiOx layer has been deposited on polypropylene-coated paper at atmosphere pressure with a filamentary dielectric barrier discharge (DBD). The DBD linear discharge was driven by a 30-kHz power supply. Scanning electron microscope, X-ray photoelectron spectroscopy, and attenuated total reflection-Fourier transform infrared spectroscopy were used to characterize the deposited film. The deposited thin film decreased water permeation through the paper by \sim 15$ %. [ABSTRACT FROM PUBLISHER]

This paper presents the development and description of research aimed at investigation of nanosecond surface microdischarge plasma effect on biomaterials. The technique is based on application of a simple discharge device. The device is assembled on a standard microscope slide from inexpensive materials. An optical microscope equipped with a digital camera is used for visualization of the studied samples and microdischarges. Many images of the microdischarges on the biological objects are presented in this paper. Spatial resolution of the images allows studying the discharges along the cellular structure of the tissue. [ABSTRACT FROM PUBLISHER]

This paper presents the results of studies of dust formations in a radio frequency (RF) discharge plasma. In particular, the behavior of dust clouds in various types of traps was investigated. The experiments were carried out in argon plasma with the following discharge parameters: gas pressure of 0.02–0.6 Torr and discharge power of 1–50 W. Two types of the ring were used as a trap—“closed” and “nonclosed.” It was found that by changing the discharge parameters and using a different type of trap, it is possible to control the capture region of dust formations, and therefore, manipulate the extraction of dust particles by mass (size, in the case of monodispersity of particles). It has been observed that at a lower gas pressure the dust cloud is less affected by the traps; moreover, the wider the edge opening of “nonclosed” ring trap, the more efficient the process of extracting dust particles. The results of this paper can be useful for practical application in the processes of separation and extraction of dust particles from a plasma crystal, the study of particle interactions, and the manipulation of individual particles, etc. [ABSTRACT FROM AUTHOR]

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

The 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]

Bar-plate configuration has a vital function in the intensive study of corona discharge mechanism. To study the discharge characteristics of the steady current stage in this configuration, this paper proposes a hybrid numerical algorithm composed by the finite-element method and the finite-volume method. The former solves Poisson’s equation and calculates the value of onset field intensity. The latter solves the current continuity equation, in which a time-varying charge item is added. This charge item can increase the stability of the hybrid algorithm. This paper also proposes a new selection strategy for the initial charge and inception voltage on the bar electrode surface. Based on this algorithm, corona current under different electrode radii, gap distances, and applied voltages was calculated. In this way, the distribution characteristics of an electric field intensity and space charge density along the whole gap in the model can be obtained through the experiment. To verify the validity of the algorithm, the related experiment is carried out in the laboratory. The simulation results have a good consistency with the experimental results, verifying the validity of the algorithm proposed in this paper. [ABSTRACT FROM AUTHOR]

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

The working temperature of an LED chip has a great influence on its photoelectric properties. It is urgently necessary to develop an adaptive cooling device for LEDs’ heat management. This paper proposes a “multi-needle-to-mesh” ionic wind generator for enhanced heat transfer in high-power LEDs (HPLED). Experiments were conducted to evaluate the cooling performance of HPLEDs under multiple working conditions. The electric field intensity (EFI) distribution, the charge density, and the dynamic pressure of ionic wind were measured. We also investigated the thermal resistance, the mean heat transfer coefficient, and the output luminous flux of HPLEDs. The results indicate that the EFI distribution is inhomogeneous and there was a reduction in EFI from the needle tip to the collecting electrode of up to 90%. Furthermore, the density of discharges was proportional to the overvoltage but inversely proportional to the square of the discharge gap. The ionic wind velocity was proportional to the overvoltage but inversely proportional to the discharge gap. An approximately 34% reduction of thermal resistance was observed as well. The final reducing rate of HPLED output luminous flux was 9.3%under the action of ionic wind. [ABSTRACT FROM AUTHOR]

To enhance the heat dissipation of high-power light-emitting diodes (LEDs), corona wind based on corona discharge was promoted. In this paper, we aimed at reinforcing the intensity of corona wind by modifying the needle electrode with graphene solution. To explore the differences in the graphene-coated electrode and the original bare electrode on the electrical characteristics, the intensity of corona wind, and LED heat dissipation, a corona wind cooling system and a thermal test system were built for the experimental study. The results showed that the graphene-coated electrode system could produce corona wind at a lower voltage. In addition, the discharge current of the graphene-coated electrode system is higher than that of the bare electrode system under the same discharge voltage. The graphene-coated electrode system can induce a faster corona wind and the highest speed is about 3.4 m/s, showing that it is more efficient than the bare electrode system in corona wind production. Moreover, the temperature drop of LEDs for the graphene-coated system is greater, which means that the corona wind cooling system can reduce the junction temperature of the LED chips effectively. Ultimately, as the discharge power increases, the average convective heat transfer coefficient increases. Indeed, the result of this paper can be used for the wide variety of the graphene-coated corona wind generator application as a promising technology for the LED heat management. [ABSTRACT FROM AUTHOR]

In this paper, an array wire-to-wire surface dielectric barrier discharge (DBD) structure is used to generate large-scale plasma by bipolar nanosecond pulse power in atmospheric air. The quantity of electrodes can be adjusted from 1 to 10 for varying discharge area. The applied voltage and discharge current are measured, the discharge images are captured, and optical emission spectra (OES) are collected. The discharge power, discharge area, and OES intensity for a single group of/and whole structure are calculated. The vibrational and rotational temperatures are simulated by the OES of N2 (C-B, $\Delta \nu =-2$), and the effects of the quantity of electrodes on discharge current, discharge power, discharge area, OES intensity, and vibrational and rotational temperatures are investigated. The results show that the discharge current has two main peaks during single applied pulse voltage, and decays in a fluctuant type. As the quantity of electrodes increases, the peak value of discharge current increases and the decaying time from peak value to zero around becomes longer. The discharge power, discharge area, and OES intensity have increasing tendencies, and those of the single group of wires decrease. In addition, when the quantity of electrodes increases, the vibrational temperature increases first and then decreases, and the rotational temperature varies in a fluctuant type. [ABSTRACT FROM AUTHOR]

In this paper, we report a qualitative model of operation and energy release in pulsed dielectric barrier discharges (DBDs). We demonstrate that pulsed DBDs operate according to the “maximum power principle” and explain the relevant physical processes. Compared to experimental data, the proposed model allows an accurate estimation of the discharge pulse energy as a function of dielectric properties, electrode size, and pulse parameters (shape and voltage amplitude). [ABSTRACT FROM AUTHOR]

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

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]

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]

DC arc evolution is a complicated and rapid time-dependent process. To better demonstrate the mechanism of the dc arc without external interference factors, a test circuit was built for the entire process of arc generation, maintenance, and extinction. Two different adjustment models were adopted. The macroscopic performance and characteristics of the arc were analyzed. The discharging and extinguishing conditions were measured and compared to the results of a burning candle located under a rod–rod air gap. This paper shows that the dc arc’s color changes from blue to purple and then yellow, finally forming a flame as the current increases. The macroscopic performance can be divided into eight periods in the first adjustment model, while only three periods are included in the second model. The arc discharging condition only depends on the applied high voltage, but the extinguishing condition may depend on either the limiting current or the drop-down voltage. Dynamic volt–ampere characteristics appear only if adjusted by the first model. The arc-root voltage is constant to 0.32 kV. The degradation of the ground electrode is far worse than that of the high-voltage electrode. This paper can be regarded as the first-step research for further studies on large-current dc arcs in arcing horns used in dc transmission grounding lines. [ABSTRACT FROM AUTHOR]

In this paper, a new circuit model is proposed to simulate plasma-induced damage (PID). It includes the two sheaths of the plasma, the blocking capacitor, and the RF power source coupled with the victim device. As a result, this model accounts for both the ac behavior of the plasma and the local voltage imbalance induced by differences in shading factors. The advantage of this approach, compared with the previous works, is that it can yield the waveform impinged by the plasma on the transistor gate, which is known to influence the amount of reliability degradation experienced by the device. Finally, this model is also utilized to elucidate the impact of a parasitic capacitance connected to the transistor gate on the extent of the PID inflicted on the victim device. [ABSTRACT FROM AUTHOR]

Air-borne micrometer and submicrometer particles produced by anthropogenic sources contaminate atmospheric air, especially in large cities where both population and industrial activities are higher leading to a reduced air quality. Recent research has pointed out particles less than 2.5 \mum in diameter (PM2.5) as a potential health hazard. To address this issue, stricter legislation has been put into force to reduce PM2.5 emissions. This paper is focused on the development of an impulsive microelectrostatic precipitation technology for charging and removal of fine air-borne particles in an economically feasible way. In this paper, a compact coaxial precipitator has been developed for possible indoor air cleaning applications. High-voltage impulses together with dc voltage have been used for energization of the reactor as it has been shown to enhance the precipitation efficiency. This precipitation system has been used for removal of fumes and fine air-borne particles from ambient air. In addition to the experimental part, analytical work has been conducted to optimize the electrostatic precipitation process and to reduce its power consumption. [ABSTRACT FROM PUBLISHER]

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]

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

We present a new technique for the design and test of coaxial switched oscillators (SWOs). In this paper (Part I of a two-part paper), we concentrate on the electrostatic design of coaxial SWOs. We introduce a new design for the electrodes, which have been conceived as conformal surfaces in a geometrically convenient curvilinear space where Laplace equation is solvable. Analytical solution of the electrostatic fields is presented, discussed, and validated using numerical simulation. A prototype of an SWO based on this design is built and validated using experimental data. [ABSTRACT FROM AUTHOR]

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

The results of an experimental study of the generation of runaway electrons (REs) during the formation of a negative streamer in an 8.5-mm-long point-to-plane gap filled with air are presented. Negative nanosecond voltage pulses (18 kV, $\tau _{0.5}\approx 10$ ns, and $\tau _{0.2-0.9} \approx 4$ ns) were applied across the gap. In this paper, we attempted to determine when REs are generated relative to the appearance of the streamer. In our previous studies of a positive streamer, we have shown that the formation of the streamer is accompanied by a dynamic displacement current (DDC) caused by the redistribution of electric field strength in the gap. This current can be easily measured with a collector placed behind a grounded grid electrode. The collector is typically used to measure the current of REs at negative polarity. In this paper, we were able to measure together and separately the DDC caused by a negative streamer and the RE beam current. This allowed us to accurately determine the moment of generation of REs. [ABSTRACT FROM AUTHOR]

Ferrite spiral delay lines intended for synchronization of high-voltage generators. The results of output pulses’ time stability are presented. All testes were carried out in both single- and two-channel systems. Adjustable precise synchronization of two nanosecond high-voltage generators (−150-kV, 5-ns full-width at half-maximum) are analyzed in this paper. The trigger high-voltage pulse was split into two channels to switch on identical double forming lines of each generator through controlled high-pressure spark gaps (nitrogen 60 atm). Designed coaxial ferrite spiral lines with an external bias field were installed in both synchronized channels. Adjustment of the bias field not only sharpens the trigger pulse but also varies its front delay and, respectively, the start of the driven generators. The maximum delay of one channel relative to the other was 1.5 ns. The minimum standard time deviation (relative jitter) of two nanosecond high-voltage generators was determined at the level of 55 ps. [ABSTRACT FROM AUTHOR]

Electrostatic discharges (ESDs) on solar cells are a possible cause of dramatic consequences such as secondary arcs responsible for definitive power losses. To cope with these significant implications, different approaches are followed such as design rules reducing voltage between the adjacent cells, conductive layers, or grouting to try to reduce discharges triggering. However, ESDs on solar cells cannot be completely avoided and having a good knowledge of their characteristics is essential for prevention, prediction, and modeling. In this paper, we describe how the plasma emitted during an ESD on a solar cell can be analyzed with dynamic tools such as triple probes and time-resolved optical spectroscopy. These techniques are used to obtain the results on plasma density and electron temperature that can be compared with outputs from ESD and flashover propagation models. While time-resolved optical spectroscopy is used on a single point (the point where optical fiber is focused on), triple probe is also used for spatial measurements. With this technique, electron density is measured at several distances from the discharge point providing both temporal and spatial information. In a second time, the optical signature measured by optical spectroscopy is correlated with scanning electron microscope observations showing the existence of two kinds of triple points at cell’s edge. These two kinds of discharges have different optical signatures showing either elements from the active junction or from the substrate and rear electrode. These discharges are also distinguished by microscopic observations and images of cell’s edges confirm the previous results. These results show the importance of the silver back electrode and also of the eventual presence of covering glue on the position of the discharge. They provide information for models but let us also imagine the possible mitigation methods. [ABSTRACT FROM PUBLISHER]

The transverse magnetic field (TMF) contact has the advantages of small loop resistance, simple structure, and strong breaking ability. In order to make the arc mode more stable and reduce the metal droplets splashed in the radial direction, this paper proposed an improved cup-shaped TMF contact. The simulation of the magnetic field showed that this contact structure could effectively enhance the axial magnetic flux intensity, especially in the small gap distance. Therefore, the arc could keep in a more diffuse mode in the ignition and expansion stages. The experimental results showed that the improved cup-shaped TMF contact had more stable arc mode and less arc droplets compared with the traditional cup-shaped TMF contact. The arc characteristics of the improved TMF contact meet our anticipated goals. Based on these experimental results, a further research for contact parameters optimization is still in work. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge (DBD) is a promising technology for ozone generation. In this paper, each electrode consists of tungsten rod and quartz glass. To improve the discharging efficiency, the air of the used quartz tube was evacuated. Moreover, to evaluate the performance of ozone formation, the electrical characteristics of volume DBD (VDBD) (two electrodes) and coupled VDBD (three electrodes and seven electrodes) are investigated. Under the condition of the same electric field using the COMSOL Software, the density of the current pulses is shifted to the right in the current waveforms. The results of ozone production show that a dynamic balance between ozone formation and ozone decomposes is complex at high frequency and high flow rate. The highest energy yield is 1650 g/kWh at a specific input energy of 0.6545 J/L. [ABSTRACT FROM AUTHOR]

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

Preionization for atmospheric pressure discharge plasma has been employed in several pulse gas lasers, while dielectric barrier discharge has often been utilized for ozone generators. A single ozone-generating device combining both preionization discharge and dielectric barrier discharge is investigated in this paper. The preionizing electrode configuration consisted of a wire-dielectric-plate with a 1.5-mm-thick aluminum oxide (Al2O3) barrier with relative permittivity \varepsilon \mathit {r} of about 10. Wire electrodes (0.8-mm diameter) and plate electrodes were all made of stainless steel. A barrier discharge was generated by applying a pulse voltage between the plate electrode and the wire electrodes across the dielectric, which was served as a preionizer. The main discharge was produced immediately after preionization by applying a high-voltage pulse between the wire-plate electrodes with a gap distance of 10 mm. This paper examines the temporal and spatial evolution of the discharge with and without preionization. Results from a high-speed framing camera indicate that preionization increases the volume of the main discharge, resulting in a streamer-like discharge system with preionization, which is an effective method for ozone generation. [ABSTRACT FROM PUBLISHER]

This paper reports on analysis of two different types successive underwater shock waves generated by a device incorporating a compact shock-wave generator with a magnetic pulsed compression circuit. To generate shock waves, underwater pulsed electric discharges in high-impedance saline water were used. The saline water made possible underwater shock waves propagation in tissue with low reflection between the solution and tissue boundary, owing to their similar acoustic impedances. A cylindrical electrode holder and a semiellipsoidal shock-wave focusing reflector/generator were used in this paper. The diameter of the compact shock-wave reflector was 20 mm. Two kinds of successive underwater shock waves, one generated by electric discharge plasma expansion and the other by bubble collapse, were observed. The shock waves were studied by time-resolve high-speed visualization and direct pressure measurement using a fiber optic probe hydrophone pressure transducer. The former method elucidated propagation of underwater shock waves and behavior and collapse of the bubble near the electrodes, while the later measured two kinds of underwater shock waves pressures at different voltage amplitudes using the cylindrical electrode holder and the shock focusing generator. This paper clearly shows the importance of the secondary shock waves, their control, and damping, for effective and safe medical application of shock waves. [ABSTRACT FROM PUBLISHER]

This paper presents an electromagnetic simulation method for spark-gap switched pulse generators (SGSPGs). Electromagnetic simulation programs can be useful for designing nanosecond or subnanosecond SGSPGs; however, these programs do not support simulation models of spark-gap switches. This paper describes a simulation method that determines electric field at an observation point in the SGSPG by replacing the spark-gap switch with a step voltage source. In this simulation, the discharge properties of the spark-gap switches, including the breakdown voltage and rise time, are determined using the results of the studies on electrical breakdown. A 1-ns single pulse-forming line was fabricated to validate the proposed method. The simulated waveform was in good agreement with the measured waveform. [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]

This paper explores the effects of tube shape and pin electrode diameter on the plume generation and electrical characteristics in atmospheric pressure helium plasma jets generated from a centered-pin electrode inside a dielectric tube. The quartz-covered (or bare) pin electrode and different shapes of the dielectric tube (straight cylinder or conical shape) are employed and their effects are investigated. Optical emission spectra are obtained at different positions along the coaxial direction to determine the axial distributions of the electron excitation temperature for the straight cylinder and conical jets. The rotational temperatures for the both jets are also compared. [ABSTRACT FROM PUBLISHER]

The conventional ways of processing natural gas into more efficient and economical fuels usually have either low conversion rate or low energy efficiency. In this paper, a new approach of methane liquefaction is proposed. Instead of direct treatment of only natural gas, plasma-activated methane is reacting with liquid fuel. In this way, methane molecules are directly incorporated into liquid fuel to achieve liquefaction. Nanosecond-pulsed dielectric barrier discharge and atmospheric pressure glow discharge are used here to ensure no local heating in gas bubbles. Effects of both discharges on methane reaction with liquid fuel are investigated, and mass and chemical changes in liquid are observed. Preliminary results show fixation of methane in liquid fuel. [ABSTRACT FROM PUBLISHER]

In this paper, operational limitations (the extinguishing of the stable glow discharge) and instabilities [glow-to-arc transition (GAT)] of microwave-induced microplasmas enclosed in microcavities operated at low gas pressures were investigated by experiments, in comparison with unenclosed microplasmas. For enclosed microplasmas, when gas pressure decreased, GAT occasionally occurred, whereas GAT was never detected for unenclosed microplasmas, because the gas temperatures of enclosed microplasmas were higher than those of unenclosed ones. For enclosed microplasmas operated at low gas pressures, an increase in the microcavity dimension is a valid method to avoid GAT. Extinguishing pressure of stable glow-discharge microplasma ( p\mathrm { {ext}}) for microwave-induced microplasma enclosed in a microcavity microplasma was lower than that for microwave-induced microplasma generator without the PDMS cavity (UEC) microplasmas. The increase in input power decreased p\mathrm { {ext}} for UEC microplasmas but showed a slight influence on p\mathrm { {ext}} for EC microplasmas. This paper shed some light on understanding of the enclosed microplasmas operated at low gas pressures. [ABSTRACT FROM AUTHOR]

Chemical oxidation and the bactericidal capabilities of nonthermal plasma discharges can be used in different practical applications, such as biodecontamination, sterilisation of medical equipment, waste water treatment, syn-gas treatment, and others. In this paper, the oxidation and biodecontamination effects of impulsive plasma discharge, which propagate across a liquid sample/air interface (surface discharges), and through the bulk of a liquid sample (direct discharges), have been investigated. The oxidizing capability was analyzed by measuring the degree of decolorization of indigo carmine dye in water solutions. Gram-negative and gram-positive bacterias, E. coli and S. aureus, respectively, were used as model microorganisms in the investigation of the biocidal effects of plasma discharges. Surface and direct plasma discharges were generated by high-voltage impulses of both polarities, with the magnitudes of 20, 24, and 28 kV, and the chemical oxidation and biodecontamination capabilities of such discharges have been obtained and analyzed. It has been established that the defining factor in the chemical and biological effects of plasma discharges is the normalized delivered charge (dose). The results obtained in this paper show that surface discharges have greater biodecontamination capability as compared with direct transient plasma discharges. Also, it was shown that the decontamination rate of E. coli is more than double than that of S. aureus. [ABSTRACT FROM AUTHOR]

This paper investigated hydroxyl radicals and hydrogen peroxide formation under a needle-plate electrode configuration using positive-polarity dc discharges generated in air, nitrogen, and helium. The discharge mode in air and nitrogen was found to change above ultrapure water; initially, a nanosecond pulse discharge was observed, transitioning to a diffuse discharge due to the increasing conductivity of the water. The discharge in helium was a nanosecond pulse discharge and the repetition rate increased with increasing water conductivity. It was found that hydroxyl radicals contribute to 7%, 78%, and 70% of hydrogen peroxide formation when using the ultrapure water in air, nitrogen, and helium, respectively. It is suggested that hydroxyl radicals are formed by water reactions with energetic positive ions and the neutral particles, such as N2+, He+, O, H, and HO2. Part of hydrogen peroxide is directly formed from atoms and radical reactions with water in nitrogen and helium, while oxygen reactions are heavily involved for hydrogen peroxide formation in air. A fluorophotometry method, using terephthalic acid, was used to directly quantify the formation of hydroxyl radicals and compared with the tert-butanol method. [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]

This paper consists of two parts. In the first part, the emission was generated in air, and the waveform recording the spectral line at 337 nm (= prominent N2 laser line) was noted. The pulse forming network (PFN) Marx generator having a large ($50~\Omega$) internal impedance was used. The pulses of the nitrogen emission at 337.1 nm of long ($< 3~\mu \text{s}$) duration and of short (≈10 ns) duration were obtained. The photodiode registered both the spontaneous emission and the stimulated (laser) emission in the 337 ± 5 nm spectral range. The data show that the laser emission predominates in the pulses of long duration. In the second part of this paper, it is suggested that the ultraviolet (UV) radiations emitted by the sun, together with the electric fields present at high altitudes, are capable of exciting the N2 molecules to the upper excited $\text{C}^{3}\Pi _{u} $ level to yield the laser emission of long duration. On the basis of the laser energy content dissipated into the plasma, the size of the transient luminous events (TLEs) known as the elves and the sprites was evaluated. The dynamics of initially small size, highly compressed, and very hot plasma formed inside the sprite was presented. It is proposed that the TLEs named “crepuscular twilight in the sky of New York” observed on December 28, 2018; “mysterious bright flash” occurred in Russia on January 9, 2018; and maybe the Tunguska event happened in Siberia on the morning of June 30, 1908 should be included in the list of the TLEs. [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 plasma produced by a pulsed generator is an efficient tool for an airflow control. In this paper, a nanosecond pulsed generator constructed with a fast solid-state switch is designed for triggering synchronous discharges in plasma synthetic jet (PSJ) actuators connected in series. The generator delivers high-voltage pulses with a peak voltage varying from 0 to 20 kV, a rise time of 20 ns, a full-width at half-maximum of 200 ns, and a wide range of pulse-repetition rate varying from 0 to 5.5 kHz. It is proved that this generator is able to trigger synchronous discharges in three PSJ actuators in atmospheric air with a peak discharge current more than 90 A and a deposited energy per pulse of 39 mJ. A schlieren system is used to observe the airflow dynamics, which shows the high synchronization among the three PSJ actuators with a time triggering delay of about 20 ns. The synchronous operation of three PSJ actuators produces a plasma jet with a maximum velocity of 60 m/s and a precursor wave with a velocity of 350 m/s. [ABSTRACT FROM AUTHOR]

A magnetohydrodynamic (MHD) thruster is a type of electric motor which does not have mechanical moving parts and directly converts electrical energy into mechanical energy. In this paper, a multiphysics numerical simulation has been performed to investigate the phenomena occurred in the channel of marine MHD thrusters. In this simulation, all electric, magnetic, and fluid flow fields have been considered 3-D. For this purpose, a marine MHD thruster model with saddle-shaped coils is selected, and its dimensions are determined. Then, this thruster is simulated numerically, and its electromagnetic and fluid flow parameters are studied. In this simulation, the effects of seawater electrolysis and end loss are taken into account. An experimental setup is established to validate the results obtained from the numerical simulation. The results reveal that the nonuniformities of the electric and magnetic fields along the channel have a great impact on the performance of the thruster. Unlike the results obtained in the previous studies, it is shown that the velocity near the electrodes is higher than that near the sidewalls arisen from the higher electromagnetic force close to the electrodes. [ABSTRACT FROM AUTHOR]

Recently, marine resources have been attracting much attention owing to their growing role in sustainable development. Growing interest in the exploration of marine resources and numerous studies on ecology and biochemistry has made the high-precision analysis of sea water necessary. In this paper, the possibility of using the atomic emission spectroscopy of microarc discharges generated in sea water for on-site contaminants detection and elemental composition analysis has been studied. We analyzed the discharge process and optical emission spectra from microarc discharges in three types of liquid, namely, artificial sea water composed of ten main components, reference solutions containing a single component each, and naturally sampled deep sea water. Microarc discharges were generated under low breakdown voltages using a compact experimental setup with a needle-to-plate electrode system immersed in each liquid in a quartz cuvette. In the spectra, the emission peaks of the main components of sea water and contaminants from the electrodes were detected, and reference solutions were used for the identification of unassigned peaks. To study the effect of electrode materials on the optical emission spectra and plasma parameters, three types of needle electrodes were used. The effect of the experimental conditions on the measured optical emission spectra was studied, and the applicability of proposed method for on-site detection of metals and elemental composition analysis was confirmed. [ABSTRACT FROM AUTHOR]

In this paper, a filamentary air plasma array is explored for attenuation of a transmitting X-band microwave (MW) beam at reduced atmospheric pressure, $P = 3$ –9 kPa. Discharge parameters such as voltage–current characteristics, gas temperature, and the plasma filament diameters are measured; the electron density and electron-molecular collision frequency are calculated. The attenuation of a 10 GHz microwave is measured for parallel and perpendicular polarizations with respect to the plasma filament direction. It was found that the maximal attenuation of an MW beam with perpendicular polarization can be as high as 25 dB at $P = 3$ kPa. The processes of plasma contraction and expansion are considered an important factor of the plasma’s impact on transmission characteristics. A simulation of the interaction between the MW and a plasma array was performed using the method of finite difference time domain. [ABSTRACT FROM AUTHOR]

This paper is focused on carbon coating of anatase type TiO2 by underwater discharge with a capillary in water carbon electrode. The discharge electrode consists of a graphite electrode covered by an alumina tube for insulation and a ground electrode. The aqueous solution used for discharging is tap water with an electric conductivity of about $120~\mu \text{S}$ /cm. The applied power for TiO2 carbon coating is about 500 W. As a result of TEM and energy dispersive spectrum measurements, a carbon layer with thickness of several nanometers was measured on the surface of TiO2. Raman analysis also confirmed that the layer is either graphite or glassy carbon. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a plasma misting system capable of inactivating Escherichia coli O157:H7 (E.coli) in a 4 ft3 (approximately 100 L) volume with potential for future use in decontaminating fresh produce. Water droplets, with an average diameter of $5~\mu \text{m}$ , are generated via ultrasonic nebulizers and carried by compressed air. These micrometer-sized droplets flowthrough a set of three cylindrical, microsecond-pulsed dielectric barrier discharges (DBDs). We observe the Coulombic fission of droplets up to a critical radius into submicrometer droplets (Sauter mean of approximately 0.3 $\mu \text{m}$), measured by a laser diffraction analyzer. E.coli, on agar plates, is inactivated by this mist in a time and flowrate-dependent manner. We hypothesize that the observed antimicrobial effect correlates with the concentration of submicrometer droplets. The observed formation of submicrometer droplets from this volumetric DBD is similar to the bursting of droplets observed with electrospray devices using corona discharges. [ABSTRACT FROM AUTHOR]

Pseudospark-sourced electron beam with high energy can be produced by the pseudospark device. In this paper, the breakdown voltages of the hollow cathode discharge with the pseudospark geometry influenced by electrode geometry and the gas have been studied and analyzed. In the wide range of pressure and gap, the breakdown voltage increases with the increase in the pressure and the gap distance. There is a pressure threshold and a gap distance threshold, below which the discharge mode will change. The product of the pressure threshold and the gap distance threshold is about 65 Pa $\cdot$ mm. The breakdown voltage is affected by the aperture diameter and the gap distance together. When the ratio of the gap distance to the aperture diameter is greater than 4, the electric field inside the small hole is almost zero and the discharge is converted to the plate electrode discharge. When the ratio is in the range of 0.67–4, the breakdown voltage decreases with the increase in the aperture diameter. When the ratio is less than 0.67, the breakdown voltage hardly changes with the aperture diameter. [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]

The trigger lifetime of the target electrode has a great effect on the triggering characteristics of the laser-triggered vacuum switch. In this paper, the relevant experimental research shows that when the main voltage is 1 kV and the laser energy is 10 mJ, a irradiation point on the target electrode can work continuously 18 000 times. By comparing two laser energy of 10 and 3 mJ, it is found that the KCl/Ti loss ratio of the high-energy laser pulse is much larger than that of the lower energy laser pulse, which will worsen the conduction performance more rapidly, therefore, it is necessary to adjust the mixing ratio of KCl and Ti in accordance with the energy of the pulsed laser to increase the conduction reliability of the switch and the lifetime of the target electrode. In the pulsed-arc spectroscopy experiments, the laser pulse energy has little effect on the intensity of the arc spectrum, however, the intensity of the arc spectrum increases obviously with the increase of the main gap voltage of the switch and the enhancement effect of voltage on different linear lines is different, which means that the density and number of different plasmas are not increased uniformly. [ABSTRACT FROM AUTHOR]

Propylene carbonate (PC) has a good application prospect in compact pulsed power source as the energy storage medium of pulse forming line. However, its insulation strength is susceptible to impurities, temperature, pressure, and other factors. Hence, it is of great significance to study the effect of temperature on breakdown characteristics of propylene carbonate. In this paper, the effect of temperature on breakdown characteristics of PC was carried out under microsecond pulse. First, pulsed breakdown setup was built. The temperature of PC varied from −50 °C to 50 °C. Breakdown voltages were captured with a capacitive voltage divider and streamer patterns are obtained by ultrahigh-speed cameras. Second, the experimental results are obtained. The breakdown strength of PC increases with increasing temperature. It is 239 kV/cm at −50 °C and rises to 407 kV/cm at 50 °C. At low-temperature breakdown, electron current is more concentrated and breakdown voltage is more stable. Moreover, the energy release for streamer at low temperature is more concentrated, but it is more dispersed for streamer at high temperature. At last, considering the CO2 solubility in PC, PC generates more bubbles and the increase of temperature benefits the release of bubbles at low temperature, resulting in lower breakdown strength. Because of the moisture in PC, breakdown strength of PC falls slightly near 0 °C. Thus, the experimental results are explained by use of stream theory and bubble breakdown theory. PC can adapt to wide-range temperatures, effectively expanding practical applications of the PC in pulsed power source. [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]