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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]

Surrounding air pollution is one of the important warnings to human health. It is necessary to detect hazardous pollutant gases in the air. The gas sensor is the candidate for such detection. Progress of smart and flexible sensors has been receiving growing curiosity in recent years because of their enormous sensing applications. Such smart and flexible sensors can be manufactured by depositing conducting materials, such as conducting polymer, carbon nanotube (CNT), graphene oxide, and metallic nanoparticles, onto nonconducting polymeric flexible substrates, such as paper, plastic films, and textiles. Most of the flexible polymeric substrates, such as polyethylene, polyester, nylon, and polypropylene, have low surface energy and poor wettability, which weakens the adhesion between conducting material and flexible substrate. Plasma surface modification is a novel technique to enhance surface properties to produce stable composites. This review focuses on various types of plasmas for surface modification and their effects on the surface after plasma treatment to improve the grafting and adhesion of the sensing layer with the substrate. The aim of this article is to systematically overview the development of plasma-enhanced smart and flexible gas sensors to date and to envisage their future progress. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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

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

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

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

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]

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]

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]

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

This paper investigated the effect of accumulated charges and fluid dynamics on the helium plasma jet array behavior. The plasma jet array was composed of three individual plasma jets in a parallel arrangement. The dynamic evolution and the hydrodynamic interaction of plasma jets were observed under for adjacent jet-to-jet distances, pulse frequencies, and pulsewidths. The results showed that variation of the above parameters exerted an influence on the distribution of accumulated charges and gas flow, and thus controlled the outside and middle jet lengths. With a small pulse frequency and pulsewidth, the higher air fraction in the middle jet trajectory prevented its propagation and resulted in a shorter middle jet length. The increase of the pulse frequency or pulsewidth induced higher charge accumulation, and thus the deflection of the outside jets was more significant. At the same time, the gas flow channel showed a similar divergence and changed the air participation in the jet array, which explained a shorter middle jet length under a higher pulse frequency or pulsewidth. The results obtained in this work helped to understand the plasma jet interaction mechanism in the plasma jet array and to develop a uniform large-area discharge plasma. [ABSTRACT FROM AUTHOR]

For safe handling and transport, the exterior surfaces of a container used to collect microorganisms should be disinfected. Though conventional methods are highly reliable, they could damage the container or destroy the contents, rendering the collection of microorganisms pointless. In this paper, a pulsed subatmospheric pressure microsecond spark discharge plasma jet, referred to as a pin-to-hole discharge (PHD), was used as a source of ultraviolet (UV) radiation and reactive oxygen and nitrogen species (RONS) for the sterilization of inoculated surfaces with limited thermal impact. A device was created to generate an overlapped region of treatment on a cylindrical body from an array of these PHDs. The surface was inoculated with vegetative bacteria (Escherichia coli), sporulated bacteria (Bacillus atrophaeus), or a simulated dirt and spore solution and then treated with the plasma array. Gas composition effects on the bacterial load reduction were explored, and the combination of RONS from air was found to be an improvement of the effects from pure oxygen. Increasing treatment time caused an increase in bacterial load reduction, regardless of the distance or gas composition. Treatment of simulated soil inoculation showed suppressed sterilization results which asserted the fact that addition of UV radiation from the discharges improved bacterial inactivation from PHDs. The radial array of pulsed subatmospheric pressure microsecond spark discharges was shown to reduce the bacterial load on the inoculated surface by 5-log within 20 min of treatment from a discharge in air. [ABSTRACT FROM AUTHOR]

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

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]

This paper describes the development of a small field-distortion spark gap switch. Comprehensive experimental studies made with the switch revealed its self-breakdown characteristics, voltage operating range, time delay and jitter, repetition frequency, and finally the electrode erosion processes and duration of its service lifetime. A series of design improvements were required to be implemented in the switch design. For example, to reduce the structural inductance of the switch and to improve its working characteristics, the main electrode was designed as a circular track structure. Similarly, to increase the operation stability and reduce the self-breakdown probability, the trigger electrode was designed as a disk-like structure. Moreover, to balance the gas pressure in the discharge region and increase the stability during closure, a circular hole was added at the center of the trigger electrode. The compact switch has a small size of only 150 mm $\times42$ mm, a weight of 1.5 kg, and can be successfully operated at a voltage over 110 kV, at a repetition rate between 1 and 50 Hz and having a jitter of less than 4 ns. It was experimentally demonstrated that during normal operation conditions, the switch lifetime exceeds 100 000 shots. [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]

Working performances of laser-triggered vacuum switch (LTVS) mainly rely on the interactions of laser with target materials. Influences from target configuration, which is one of key factors in the interactions, are neglected so far. The trigger performances of LTVS with different target configurations are studied in this paper. Relevant influence factors about target configurations are discussed briefly based on theoretical analysis about the trigger process. The test prototype is established based on detachable vacuum chamber. The trigger characteristics of LTVS with different target structures, target depths, and laser focal positions are compared. The relationships between target configurations and trigger performances of LTVS are analyzed and discussed. The preferred targets in LTVS are suggested while considering its lifetime. The test results prove that the conical target shows the best trigger performances compared to other targets. Due to the enlarged laser irradiated area and shortened plasma moving distance, the delay time of LTVS reduces with the decrease in conical target angle and the increase in target depth, while the delay time is controlled within 32 ns. Benefited from laser reflection and plasma collision, the trigger performances of conical targets can be enhanced by focusing laser on the target side surface. In particular, the 90° conical target with 1.5 mm depth is suggested to be employed in LTVS products. [ABSTRACT FROM AUTHOR]

In vacuum circuit breakers, restrikes and nonsustained disruptive discharges are sometimes observed even up to several seconds after current interruption. These late breakdowns are triggered by a sudden increase in the field emission level and/or microparticle collision with the electrode during the application of recovery voltage. In this paper, we identify the late breakdowns triggered by the microparticles that emerged from the silver-tungsten carbide electrodes after current interruption. The combined use of a high-speed video camera and a pulse laser enabled us to conduct shadowgraph photography with a 150-ns time resolution, 10- $\mu \text{m}$ spatial resolution, and $\mu \text{s}$ framing rate for capturing the microparticle motion under the recovery voltage after current interruption. In this highly resolved photography, we observed many microparticles flying between the electrodes after current interruption. In our series of observations, we found two types of microparticle-inducing late breakdowns: those induced by small, fast microparticles whose diameter and velocity were approximately 20– $40~\mu \text{m}$ and 15 m/s, and those induced by large, slow microparticles whose diameter and velocity were approximately $100~\mu \text{m}$ and 1 m/s, respectively. Some of the large slow microparticles caused the sequential late breakdowns during the up-and-down motion between the electrodes. All the particle-induced late breakdowns occurred at the time of particle collision with the negative electrode defined by the polarity of the recovery voltage. The velocity of the large, slow microparticles was approximately 1 m/s, and these microparticles did not evaporate. Furthermore, the gradual decrease in the particle size was not observed in the continual occurrence of late breakdowns. We also observed many breakdowns caused by unknown factors. The electrode surfaces were also observed by using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The microstructures and metal compositions on the electrode surfaces varied drastically with the observation positions. [ABSTRACT FROM AUTHOR]

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]

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]

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 presents and discusses the experimental data obtained in the investigation of a short-arc high-pressure xenon discharge in dc and pulse-periodic operation modes. In the case of the dc discharge, the main focus of attention is the cathode material (thorium) evaporation into the plasma. Spectroscopic measurements show that this process strongly influences the plasma characteristics and first of all the plasma optical emission. Due to low ionization energy, thorium atoms decrease the plasma temperature at the cathode, which is confirmed by experimentally obtained spectra with an unexpectedly low optical emission temperature. The fact cannot be interpreted without the assumption of cathode material evaporation: in a homogeneous short-arc gas discharge with a conical cathode, the emission temperature at the cathode should not be low because the strength of the electric field is obviously maximal near the cathode tip. The findings are important for modeling discharges of such kind. For the pulse-periodic discharge, two effects are described: a decrease in the anode temperature and an increase in the light efficiency of about 35% in some discharge conditions. These can be used for the development of more powerful and effective xenon light sources. [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]

Over the past 25 years, the dust acoustic wave has been a subject of intense study and the impact that thermal effects have on the dispersion relation has been a subject of investigation. Recently, a theory of dust correlations and the effect that these correlations have on the propagation of compressional modes has been developed that incorporates the effects of the confinement of the dust cloud in a finite volume within the larger plasma volume. This paper applies this model to a systemic study of the dispersion relation over a wide range of experimental conditions in a radio frequency (RF) discharge plasma. It is found the dust thermal pressure is larger than the dust electrostatic pressure and that both pressures are the square of the dust charge calculated using the orbit-motion-limited (OML) theory. It is also observed that the dust temperature and thermal pressure decreases with increasing neutral gas pressure. [ABSTRACT FROM AUTHOR]

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

Numerical experiments are carried out on a low-energy (2.2 kJ) Mather-type Egyptian Atomic Energy Authority-Plasma Focus (EAEA-PF1) to investigate the optimum combination of all electrode system dimensions and gas pressure for maximum argon soft X-ray (SXR) yield, $Y_{\mathrm {SXR}}$ , using Lee Model RADPF5.15. This paper aims to finalize the first step prior to building an automated method of optimization that could be applied when a low-energy dense plasma focus is designed or need to be reconfigured, for this purpose, and to assist further research efforts in this field. The second part of the study deals with the investigation of the role of changing outer electrode radius “b” and the outer to inner radii ratio “c” on plasma focus (PF) parameters such as ion density, pinch duration, and column length and how are these, consequently, related to the maximum SXR yield. It is shown that lower radius ratio values (typically less than 2) are favored over higher ones, for argon SXR yield, and unlike most of the low-energy PF devices that are designed for this purpose. It is also shown that inductance and pinch current are only affected by the dimension of inner electrode radius, while the ion density, pinch duration, and focus volume are also affected by the change of outer electrode radius. [ABSTRACT FROM AUTHOR]

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

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

Atmospheric-pressure plasma jet (APPJ) array could effectively enlarge the treatment area for the requirement of application efficiency. The downstream uniformity of jet array is the determinant for the even processing effect. In this paper, a three-jet 1-D APPJ array with the electrode structure of needle–ring is constructed, and the position of needle electrode (high-voltage electrode) is adjusted to investigate the influence of electrode arrangement on the downstream uniformity of the 1-D APPJ array. The results show that the relative difference of the positions of the middle and side needle electrodes ${d}$ has great influence on the downstream uniformity. When the distances of the middle and side needle electrodes to the tube nozzles ${a}$ and ${b}$ are both fixed at 40 mm ($d= 0$ mm), the middle plume is suppressed. With increasing the distance of the side needle electrodes to the tube nozzles ${b}$ to make $d=1$ , 2, and 3 mm, the middle plume is prolonged and the lengths of all plumes are almost equal at $d=2$ mm. With the intensified charge-coupled device (ICCD) image measurement, it is found that the desirable synchronicity of bullets propagation is obtained at $d = 2$ mm. The electrical field distributions of different d are simulated, which can be seen that the high electric fields of the side jets can suppress the propagation of middle jet and at $d= 2$ mm, the three jets have similar maximum values of the electrical field strength along the direction of needle electrode resulting in similar plume lengths in the APPJ array. [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]

The effects of the position of the current probe on electrical measurements as well as those of typical materials on the current of a He plasma jet during the interaction of the plasma jet with surface materials were investigated using a dielectric barrier discharge reactor, in which the two electrodes were isolated from ambient air by electrical insulating oil. Here, we demonstrate accurate discharge power measurement obtained by positioning the current probe between the two electrodes rather than on the ground wire. The emission current of the plasma jet increased sharply upon the interaction with a ground-connected metal surface, because in this case, the surface functioned as a second ground electrode. Similarly, important is that the average velocity of a plasma bullet can be estimated from the phase shift of the current waveforms at different positions. The phase shift can be monitored by an oscilloscope using a cursor tool during the plasma discharge process. The average velocity of the plasma bullets in this paper ranged from 56 to 266 km/s. [ABSTRACT FROM AUTHOR]

Lightning is a common natural phenomenon and is a typical air discharge on a large spatial scale. The stepping of lightning leaders and space stems of thunderstorms are similar to those of negative discharges in the laboratory. There have been extensive experimental observations and theoretical research on positive discharge but less research on the negative form. This paper conducts an experiment on a 1-m rod–plane gap under a negative impulse voltage. To observe the thermodynamics of the negative discharge, a Mach–Zehnder interferometer combined with a high-speed video camera was set up. The Abel inverse method was used to quantify the thermal parameters for negative channels. The space stem is of great interest, and its bidirectional propagation and connection with the electrode were captured. When a space stem formed, the gas temperature within the stem ranged 320–550 K. Two negative leaders connected in space and formed one negative channel. The connection region was about 800 K while the temperature on the two sides of the negative channel reached 1500–1800 K. After a negative channel formed, it expanded, and its thermal parameter distributions tended to be uniform owing to thermal conduction and convection losses. The gas density near the discharge center was about 20%–30% of the ambient density, and the corresponding temperature was 1000–1500 K. The experiments provide deep insight into the thermodynamic properties of a negative leader discharge. [ABSTRACT FROM AUTHOR]

This paper summarizes our recent studies on a gas breakdown in microgaps with a surface protrusion on the electrode with more detailed information. The breakdown voltages are quantified when the discharge enters into the subnormal glow region with negative differential resistance, using a 2-D fluid model. The breakdown characteristics are evaluated with the effects of the protrusion geometries, such as protrusion size and aspect ratio, as well as the discharge polarity. It is found that in an atmospheric-pressure microgap, the protrusion size has a more profound effect on the breakdown voltage than its aspect ratio, which is due to the competition between the current density enhancement and the effective cathode emission area. As gas pressure varies, the surface protrusion on the electrode results in a combined Paschen’s curve, which transits from long-gap behavior at low pressure to short-gap behavior at high pressure. The key parameters on the breakdown characteristics with the surface protrusion are elucidated. [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]

In this paper, the dual-frequency atmospheric-pressure glow discharge is operated in helium with a small amount of oxygen. It is found that the plasma density increases, but the reactive atomic oxygen density decreases with high-frequency (HF) power. The plasma density also increases with low-frequency (LF) power, but it is weak as with HF power. However, the reactive atomic oxygen density increases with LF power. It shows that HF power is in favor of excited helium, but LF power is in favor of producing reactive O, N2, and OH. The discharge intensity decreases with oxygen gas admixture in working gas due to its electronegative nature. The generation rate of reactive oxygen atom has a trend of increasing first and then decreasing after 0.3% oxygen gas admixture. [ABSTRACT FROM AUTHOR]

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, we propose an innovative method for synthesizing copper nanoparticles (Cu-NPs) using underwater plasma. The proposed method using underwater plasma has advantages such as one-pot synthesis, fast reaction time, and high throughput. We obtained yields as high as 15 g of Cu-NPs powder from 25 g of copper hydroxide, for 10-min a reaction time. In addition, we confirmed that the Cu-NPs produced are spherical and range in size between 40 and 80 nm. We also verified that the synthesized Cu-NPs are almost pure Cu powder, close to 100 %, through high-resolution transmission electron microscopy and X-ray diffraction analysis. [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]

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]

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

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