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This work investigated the interface reactions between water and ionic wind from a positive d.c. corona discharge in nitrogen. The effects of drift ions and active neutral species were investigated on their production of hydrogen peroxide in water. Both positive drift ions and active neutral species were found to produce hydrogen peroxide in water. 1 mol positive drift ions can produce 0.13 mol hydrogen peroxide under atmospheric pressure; a reduced gas pressure increased the production of hydrogen peroxide, with 1 mol ions producing 0.29 mol hydrogen peroxide at 100 torr. The gas pressure has little effect on the production of hydrogen peroxide by active neutral species. The drift positive ions acted as ion anode on water surface, reacting with water to produce hydrogen, oxygen, and hydrogen peroxide. The adsorbed form of OH and O produced at the interface can synergistically work to react with the OH scavengers in water. Both HO2 and H2O2 from the discharge were transported to water to produce the liquid phase hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Characterization of a corona-stabilized switch in the single-shot regime, including triggering range, delay times, and jitter, is reported over the pressure range 0–3 bar gauge, as a continuation of work from similar characterization with this switch filled with SF6 with different gap spacings. When filled with mixtures of 1,3,3,3-tetrafluoropropene (HFO-1234ze) and N2, the breakdown voltage can be increased by up to ~306% and ~191% under negative and positive polarities, respectively, of that using 100% N2. These results were achieved with gas mixtures consisting of 80% N2 and 20% HFO-1234ze, by pressure. The maximum negative polarity triggering range was 13.6 kV, comparable to that achieved previously using SF6. The measured delay time and calculated jitter were generally found to increase with increasing pressure, and with increasing percentage (from 5% to 20%) of HFO-1234ze in the gas mixtures. von Laue statistical analysis of time-to-breakdown data showed that both the formative time and statistical time increased with increasing pressure, and with increasing percentage of HFO-1234ze in the gas mixtures. The formative time under negative polarity was significantly longer than that for positive polarity. The results indicate that HFO-1234ze may be considered as a suitable candidate to replace SF6 for switching applications, although there are some operational observations that require further investigation. [ABSTRACT FROM AUTHOR]

A statistical analysis has been undertaken to determine the statistical and formative times associated with breakdowns along a polymer-oil interface under impulse conditions. Early analysis was based on an assumption that the breakdown data followed the von Laue Distribution. However, it was found that in the Laue plots there were deviations from the expected straight line behavior at short times to breakdown, which may be due to a normal distribution in values of the formative times. In addition, the plots showed multiple straight line sections, which suggested that changes were occurring to the breakdown processes during the experimental run, or that more than one mechanism of breakdown was occurring. Values of the statistical time ts and the formative time tf were determined from the data by making choices on the straight line section to be considered, and ignoring the effects of the normal distribution on the derived values of ts and tf. The present paper is focused on further development of this statistical method, including a rigorous analysis of the experimental data, taking into account the effect that a normal distribution of the formative times has on the derived values of ts and tf. Optimal fits in terms of three parameters: ts, tf, and ?f (the standard deviation of the formative time) have been derived using Kolmogorov-Smirnov statistics to quantify the quality of fit. The quality of these fits and the applicability of this approach is discussed. [ABSTRACT FROM AUTHOR]

Impulsive underwater discharges have been investigated for many decades, yet the complex pre-breakdown processes that underpin their development are not fully understood. Higher pre-breakdown energy losses may lead to significant reduction in the magnitude and intensity of the pressure waves generated by expanding post-breakdown plasma channels. Thus, it is important to characterize these losses for different discharge types and to identify approaches to their reduction. The present paper analyses thermal pre-breakdown processes in the case of free path and wire-guided discharges in water: fast joule heating of a small volume of water at the high-voltage electrode and joule heating and the melting of the wire, respectively. The energy required for joule heating of the water and metallic wire have been obtained from thermal models, analysed and compared with the experimental pre-breakdown energy losses. Pressure impulses generated by free path and by wire-guided underwater discharges have also been investigated. It was shown that wire-guided discharges support the formation of longer plasma channels better than free path underwater discharges for the same energy available per discharge. This results in stronger pressure impulses developed by underwater wire-guided discharges. It has been shown that the pressure magnitude in the case of both discharge types is inversely proportional to the observation distance which is a characteristic of a spherical acoustic wave. [ABSTRACT FROM AUTHOR]

Surface discharges along oil-immersed solids used as insulators and supports in high-voltage pulsed-power equipment can lead to catastrophic system failures. To achieve reliable compact pulsed-power systems, it is important to quantify the electrical fields at which surface flashover, or other types of breakdown event, will occur for different dielectric materials. This paper reports the observed behavior of samples of polypropylene, low-density polyethylene, ultrahigh-molecular-weight polyethylene, Rexolite, and Torlon, which were subjected to impulse voltages of peak amplitude of 350 kV and a rise time of 1 \mu\s. The cylindrical samples were located between pairs of electrodes immersed in insulating oil. Breakdown events were studied under both nonuniform- and uniform-field conditions, with sample lengths being chosen so that the breakdown events occurred on the rising edge of the impulse. Ultrahigh-molecular-weight polyethylene showed the highest average breakdown field, which is 645 kV/cm, in uniform fields, and the corresponding breakdown field was reduced to \sim400 kV/cm in the nonuniform fields. Weibull plots of the various sets of results are presented, providing comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage pulsed-power machines. [ABSTRACT FROM PUBLISHER]

Comprehensive knowledge and understanding of the breakdown behavior of solid–gas interfaces are important for the development, optimization, and coordination of insulation in practical high-voltage (HV) gas-insulated systems (GISs) that are widely used in the power and pulsed power industries. However, despite significant research efforts focused on the characterization of the breakdown parameters and properties of complex gas-filled HV systems, the basic mechanisms that underpin the development of discharges in such solid–gas topologies are not fully understood. This lack of knowledge is particularly noticeable in the case of solid–gas interfaces stressed with HV impulses. This study is aimed at the experimental investigation of the breakdown behavior of solid–gas interfaces, formed between solid dielectrics and common gases: dry air, N2, and CO2 at atmospheric pressure. Four different solid-dielectric materials, PTFE, HDPE, Delrin, and Macor, with relative permittivities in the range from 2.1 to 6.3, were used in this work. The solid–gas interfaces formed by these dielectric materials and the surrounding gases were stressed with positive and negative HV impulses. The breakdown voltage and time to breakdown were obtained for all combinations of solid–gas interfaces using both positive and negative impulses, with a nominal rise time of $\sim 1.9~\mu \text{s}$. A digital camera operated in the open-shutter regime was used to obtain images of the breakdown spark channels that were classified according to their propagation paths. The results obtained in this study will help in further understanding of the breakdown behavior of solid–gas interfaces and can be used in the development and optimization of dielectric topologies for use in GISs. [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]

Gas-filled plasma closing switches (PCSs) are essential components of high energy density pulsed power systems used to generate short, high-power (tens MW to several GW) impulses. In practical applications, PCSs are required to operate in high-current (tens kA), high-voltage (10s–100s kV) regimes, to produce fast-rising ns and sub-ns HV impulses. The transient impedance of a PCS affects the rise time of the generated impulses and the power delivered to the load. Thus, the design and optimization of PCSs require detailed information on the dynamic plasma resistance. This article is focused on an investigation of the time-dependent resistance of the plasma channel(s) formed between the electrodes of a multielectrode PCS. Experimentally measured underdamped current and voltage waveforms were used to obtain the transient plasma resistance of the PCS. The PCS was filled with different gases: dry air, CO2, N2, and a 90%/10% Ar/O2 mixture, in the pressure range from 0 up to 10 bar (gauge). It was found that the plasma resistance drops rapidly from a few hundreds of ohms to a few hundreds of milliohms due to the Joule heating of the breakdown channel. The methods proposed by Braginskii and Kushner to model the transient postbreakdown resistance were used to obtain analytical plasma resistances for all of the gases. These resistances have been compared with the transient resistance obtained using a Kirchhoff analysis of the lumped-element, postbreakdown RLC circuit. Based on this comparison, the suitability of the chosen analytical methods to determine the transient breakdown resistance in gases is discussed. The obtained results will help in the optimization of the operational performance of PCSs filled with environmentally friendly, low environmental impact gases. [ABSTRACT FROM AUTHOR]

This article reports and discusses the results of impulse breakdown study of different insulating liquids under highly divergent electric field conditions. Samples of a natural ester (Envirotemp FR3), a synthetic ester (MIDEL 7131), and a naphthenic mineral oil (Shell Diala S4 ZX) at different levels of relative humidity were exposed to HV impulses with a nominal 7- $\mu \text{s}$ rise time and 150-kV peak voltage of both positive and negative polarity. A strong dependence of the breakdown voltage and time to breakdown of the investigated dielectric liquids was observed with respect to the polarity of the applied HV impulses. It was shown that the FR3 natural ester liquid has a higher dielectric strength when exposed to positive impulse than when under negative impulse stress. The opposite breakdown behavior was observed for the synthetic ester MIDEL 7131 and the naphthenic oil Shell Diala S4 ZX which exhibited lower breakdown voltage under positive energization as compared with the negative energization. The breakdown voltage and prebreakdown time obtained in the present tests of the naphthenic oil, Shell Diala S4 ZX, lie between that of the ester liquids irrespective of impulse polarity. It has been established that no statistically significant variations exist in the breakdown parameters (breakdown voltage and time to breakdown) of the studied dielectric liquids as their relative humidity is increased under either impulse polarity. The obtained results will help in coordination of practical applications of low environmental impact dielectric fluids in power and pulsed power systems and components. [ABSTRACT FROM AUTHOR]

The dielectric performance of gases in insulation systems used in high voltage power and pulsed power applications is a subject of intensive theoretical and experimental investigations. Transient breakdown processes in gases stressed with short, high-field impulses, have been studied for many decades. However, there are still significant gaps in the understanding of the main breakdown processes and mechanisms associated with fast transient breakdown processes in gases. This knowledge is important for the optimization of gaseous insulating systems and for the coordination of gaseous insulation in power and pulsed power apparatuses. This information is also required for the development of gas-filled components such as circuit breakers and plasma closing switches. This article is aimed at the analysis of the field-time breakdown characteristics of air, N2, CO2, and SF6, using kinetic and drift-diffusion approaches. The kinetic approach is based upon the avalanche-to-streamer transition criterion, while the fluid drift-diffusion model requires self-consistent numerical solution of the continuity equations for charged species, and the Poisson equation for the electric field. The time to breakdown as a function of the applied field was obtained for all investigated gases. The obtained analytical results agree well with the experimental data reported in the literature, which suggests that both approaches can be used for insulation coordination, and for the development of gas-insulated power and pulsed power systems and components. [ABSTRACT FROM AUTHOR]

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

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

Objective: This study investigates possible advantages in pulsed over continuous 405-nm light-emitting diode (LED) light for bacterial inactivation and energy efficiency. Background: Alternative nonantibiotic methods of disinfection and infection control have become of significant interest. Recent studies have demonstrated the application of systems using 405-nm LEDs for continuous disinfection of the clinical environment, and also for potential treatment of contaminated wounds. Methods: Liquid suspensions of 103 colony-forming units/mL populations of Staphylococcus aureus were subject to pulsed 405-nm light of different frequencies, duty cycles, and intensities and for different lengths of time. Results: Pulsed exposures with the same average irradiance of 16 mW/cm2 and varying duty cycle (25%, 50%, 75%) showed very similar performance compared with continuous exposures, with 95-98% reduction of S. aureus achieved for all duty cycles. The pulsing frequency was varied in intervals from 100 Hz to 10 kHz and appeared to have little effect on antimicrobial efficacy. However, when comparing pulsed with continuous exposure, an improvement in inactivation per unit optical energy was achieved, with results showing an increase of approximately 83% in optical efficiency. Conclusions: These results suggest that under pulsed conditions, a lower energy consumption and lower perceived brightness could be achieved, thus potentially providing improved operating conditions for medical/infection control applications without compromising antimicrobial efficacy. [ABSTRACT FROM AUTHOR]

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

Underwater spark discharges are used in multiple practical applications including plasma closing switches, water treatment, plasma channel drilling and mineral processing, waste recycling, treatment of metals, and medical lithotripsy. Spark discharges in water have been studied for several decades; however, despite significant research efforts and progress in this area, further investigation into the efficiency of plasma acoustic sources and their optimization is required in order to expand their practical application. This paper is aimed at investigation of the electrical and hydrodynamic parameters of underwater plasma-generated cavities, including plasma resistance, energy delivered into the plasma cavity, period of cavity oscillations, and characteristics of pressure impulses. Different energy levels, breakdown voltages, and gap distances were used in the present study to allow systematic analysis of these electrical and hydrodynamic parameters. Empirical scaling relations that link the maximum acoustic pressure and the period of cavity oscillations with the energization parameters and the resistance of plasma have been obtained. These empirical functions can be used for optimization of the plasma acoustic sources and for tailoring their parameters for specific practical applications. [ABSTRACT FROM AUTHOR]

In this paper, the relationship between reduced electric field and ozone efficiency was determined between $\sim 120$ and 280 Td, with an optimized efficiency of $\sim 207$ g/kWh at $\sim 123$ Td. An equivalent circuit with stray capacitance was used to analyze the filament current in the barrier discharge. The statistical distribution of the filament currents was found to change with different conditions, observing decreased mean amplitude and a narrower distribution with increased pressure and barrier thickness. Under the same reduced electric field, higher ozone efficiency was achieved at a lower current and narrower distribution. [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 an analysis of energy partition among various physical processes during the formation of an electrical arc. The experimental work was conducted to accurately determine the energy delivered into the discharge. The transient voltage and current waveforms have been measured. An analytical model was developed that allows estimation of energy partition in the discharge to be performed in order to evaluate risks associated with different energy components: thermal, kinetic acoustic, and light. Approximately 60% of the electrical energy is converted into mechanical work, subsequently contributing to the pressure rise. The results obtained will help in studies of safety considerations regarding hazards associated with plasma discharges in transient faults/sparks and during the onset of arcing faults (flash and blast hazards). [ABSTRACT FROM AUTHOR]

Pulsed electric fields (PEFs) can cause irreversible damage to bio-membranes and may result in inactivation of microorganisms. The aim of this paper is to investigate the PEF treatment of the yeast Saccharomyces cerevisiae, using a novel treatment cell with parallel-plane electrodes coated with a 2- \mu \textm thin TiO2 film. Two different PEF waveforms, square and exponential, with magnitudes of 67 and 80 kV/cm were used in this study. The efficacy of the PEF treatment was assessed by a comparison of the surviving treated and untreated yeast populations, and it was shown that a treatment cell with TiO2-coated electrodes can be successfully used for the PEF treatment of microorganisms: 3-log10 reduction in the yeast population was achieved with 100 impulses. The energy efficacy of the PEF process in the proposed treatment cell has been compared with the energy losses in the PEF treatment cell with uncoated, conductive electrodes. It is shown that the electrodes coated with TiO2 provide better performance compared with the traditional uncoated electrodes. [ABSTRACT FROM AUTHOR]

Pulsed electric field (PEF) treatment can be used to facilitate microbial cell lysis. The aim of this paper is to investigate this effect of PEF treatment on microalgae. The PEF system used in this paper consists of a pulse generator and treatment cell with parallel-plane metallic electrodes. The PEF treatment of microalgae, Spirulina, was conducted using 33.3- and 66.7-kV/cm electric field impulses. The efficiency of the PEF treatment for inactivation of microalgae was assessed by comparison of the growth curves of PEF-treated and untreated samples. Results showed that growth of microalgae can be stopped by the application between 100 and 500 high-field impulses with field magnitude 33.3 kV/cm. When the field is increased to a magnitude of 66.7 kV/cm, the growth of microalgae can be stopped by application of 50 impulses. Overall, this paper confirms that PEF treatments can be used for the inactivation of algae and the energy consumption of the PEF process can be reduced using suspensions with lower electrical conductivity. [ABSTRACT FROM PUBLISHER]

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]

It is shown that high-voltage corona discharges in atmospheric air have significant potential for bacterial inactivation. Neutral reactive oxygen and nitrogen species and ions generated by the corona discharges act upon the target liquid or solid surfaces and produce chemical or biological effects. The concentration of ions and reactive species including ozone generated by these discharges defines the efficiency of the corona treatment. In this paper, the chemical (oxidation) effect of direct corona discharges (where ions act upon the target surface) and indirect corona discharges (where ions are screened by a grounded metallic mesh) in atmospheric air is studied by measuring the degree of decolorization of a blue dye dissolved in water. The biological effects of the direct and indirect discharges are studied by observing the degree of bacterial inactivation of gram-negative and gram-positive microorganisms, Escherichia coli and Staphylococcus aureus, seeded on agar plates. The relationship between the ozone concentration and biological efficiency of the corona treatment is evaluated. The obtained results can be used for optimization of cleaning and inactivation treatment processes based on the use of nonthermal plasma produced under dc energization conditions. [ABSTRACT FROM AUTHOR]

Particles with dimensions less than 2.5 \mum (PM2.5) have been identified as being potentially hazardous to human health. The electrostatic precipitation process, which is mainly used in industrial applications, displays a drop in the precipitation efficiency for particles in the range 0.1–1 \mum. This paper is focused on the development of an impulsive microelectrostatic precipitation (\mu-ESP) technology for indoor air cleaning applications. Short (microsecond) high-voltage impulses are used in this technology, which allows the magnitude of the electric field that particles experience to be increased without complete spark breakdown occurring and also reduces the energy consumption compared to that of dc-energized systems. The charging process of particles in the impulsive electric field used in the reactor has been analyzed. Ambient laboratory air and air-diluted cigarette smoke, which contain a significant proportion of PM2.5 particles, were used in the precipitation tests. In order to optimize performance for the \mu-ESP process, different energization modes of the developed precipitation reactor were studied: dc energization, impulsive energization, and their combination. It has been shown that combined dc and impulsive energization of the two stage \mu-ESP reactor produces the maximum precipitation effect. In both cases, ambient laboratory air and diluted smoke, 100% precipitation efficiency has been achieved for fine (250 nm and above) particles; in the tests with diluted smoke, a fine mesh filter was incorporated in the precipitation system to achieve this level of performance. [ABSTRACT FROM AUTHOR]