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Recent studies have found that the surface flashover strength of oil-impregnated insulation paper can be improved by the modification of nanoparticles. To reveal the working mechanism, this paper presents an experimental study on the effects of TiO2 nanoparticles on streamer propagation process at the surface of oil-based nanofluid-impregnated insulation paper under lightning impulse voltage. The results show that the surface flashover voltage of nanofluid-impregnated insulation paper is significantly increased by 34.6%. Streamer characteristics including shape and length at the surface of oil-impregnated insulation paper were investigated using the schlieren technique. It is indicated that streamer characteristics are dramatically changed by the addition of TiO2 nanoparticles. For nanofluid-impregnated insulation paper, streamers with more but much shorter branches tend to develop into adjacent nanofluid rather than clinging to the paper compared to that for pure oil-impregnated paper. The reason responsible for the shape dissimilarity lies in the change of electrical force due to the permittivity difference between oil and paper. Furthermore, more shallow traps introduced by nanoparticles contribute to the faster surface charge dissipation of nanofluid-impregnated paper, reducing the charge accumulation at the streamer head and suppressing the electric field distortion. Thus, it is hard for streamers to develop at the surface of nanofluid-impregnated paper, resulting in an increase of surface flashover strength. [ABSTRACT FROM AUTHOR]

The objective of this paper is to study the influence of microscopic electric field enhancement caused by microprotrusions on microparticle impact phenomena based on fractal modeling. In this paper, microprotrusions with a radius of 5~\mu \textm and heights 0, 1, 2, 5, and 10~\mu \textm are considered, according to the height–width ratios 0, 0.2, 0.4, 1, and 2, respectively. The microparticles and contacts are assumed to be made of copper. The radius of the microparticle is assumed to be 0.1~\mu \textm and the applied voltage is 60 kV. First, microprotrusions with different height–width ratios are modeled based on fractal theory. Then, the microscopic electric field distortions caused by microprotrusions on the contact surface are simulated based on fractal models of microprotrusions. The impact velocities of microparticles under different cases are calculated based on basic microparticle theories. Finally, the microparticle impact phenomena are simulated using the smoothed particle hydrodynamics method under the microscopic electric field caused by microprotrusions on the contact surface. The results show that the microscopic electric field enhancement caused by microprotrusions will have a significant influence on impact velocities, the characteristics of secondary particles, and the craters produced on the target contact surface. The results of this paper may provide some useful information to further understand the vacuum breakdown initiated by microparticles. [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]

This paper describes the time evolution of ball plasmoids generated by millisecond atmospheric discharge in contact with water. The aim of this paper was to clarify an initiation and a formation mechanism of an atmospheric ball plasmoid. The use of a higher frame rate of filming and shorter exposition time, in comparison with past experiments, allows us to observe the fast processes that occur during a plasmoid evolution. We assert that an initial electrical breakdown in a cathode ceramic tube filled by a conductive liquid is essential for further plasmoid formation. It generates a shock wave resulting in a blast of conductive liquid. The resulting expansion of water vapor and bubbles with an addition of weekly ionized plasma serves as a main source of matter for plasmoid formation. We also note that an electrical arc generated after the breakdown transforms to a plasma jet. This jet accelerates plasma to the plasmoid. [ABSTRACT FROM AUTHOR]

In this paper, we present the theoretical results of a self-consistent kinetic simulation, clarifying the influence of runaway electron flows on a delay time of the switching stage of a nanosecond discharge. The simulation is based on an accurate numerical solution of the Boltzmann kinetic equation, with model collision integrals that take into account elastic and ionization collisions of the electrons with neutral atoms. As an example, the breakdown of a cylindrical gap is investigated with respect to the variations of the voltage rise time value. The current and voltage time profiles, power spectrum, and current of high-energy electrons, as well as the electron distribution function, are calculated accordingly. Our numerical solution agrees with the existent experimental data. [ABSTRACT FROM AUTHOR]

Due to the volume and weight of the coaxial Blumlein pulse forming line (B-PFL) with liquid energy storage medium are very large and energy storage density is relatively small, a new solid-state coaxial B-PFL is designed for the pulsed power technology in this paper. There are three conductor cylinders in the pulse forming line (PFL): inner cylinder, middle cylinder, and outer cylinder. Ferroelectric ceramics is selected as the energy storage medium which is between the middle cylinder and inner cylinder, and middle cylinder and outer cylinder. The impedance, electric length, parameters such as pulsewidth and its required physical length calculation formula of the PFL is deduced, based on the coaxial cable of the related parameter calculation formula. The formula for determination of relative suitable radius size is obtained. The simulation of electric field of PFL is implemented in the simulation software Ansoft Maxwell, and the results show that the design of the coaxial B-PFL is feasibility. The pulse forming principle has carried on the detailed validation in the simulation software PSPICE, and the results show that the design scheme of PFL is feasible. The application of the PFL can largely reduce the volume and weight of the pulsed power device, and it has a good application prospect. [ABSTRACT FROM AUTHOR]

In this paper, the design and development of magnetron injection gun (MIG) for 170 GHz, 1-MW gyrotron have been presented. The triode-type MIG at 80-kV beam voltage and 40-A beam current has been designed and developed. A gun-collector test module for 170-GHz gyrotron has been developed and vacuum processed at 400 °C with continuous 48 h operation. The cathode activation and high-voltage breakdown testing have also been carried out up to desired rating. The simulation result of MIG by EGUN has been validated with 2-D-code TRAK. [ABSTRACT FROM AUTHOR]

This paper investigated the dependence of electrostatic field strength for spacecraft materials on voltage ramp rate, by applying an increasing incremental electrostatic field until electrostatic breakdown occurred. Tests on Kapton E found that at ramp rates two or three orders of magnitude lower than the maximum recommended rate, the electrostatic breakdown field, F\mathrm {ESD} was lower by a factor of two or more. This suggests that the tabulated values of F\mathrm {ESD} , which have been used by the spacecraft charging community, could substantially overestimate F\mathrm {ESD} in common slowly evolving spacecraft situations. This paper expanded these ramp rate tests to include a wider range of ramp rates and additional materials. By contrast, Kapton HN and biaxially oriented polypropylene (BOPP) data were found to be consistent with a single mean value F\mathrm {ESD} , rather than the proposed mean field and incremental voltage step ramp rate models. [ABSTRACT FROM PUBLISHER]

This paper investigates very short duration (<1 ms) flashes caused by rapid discharge arcs from isolated, charged, insulating epoxy “glue dots” to an underlying grounded substrate while under electron bombardment. The possibility that a given arc might stimulate arcs in adjacent “glue dots” was investigated through coincidence correlation analysis, as was the dependence of such correlations with “glue dot” separation. Most arcs were found to be random localized events, which occurred only when accumulated charge produced an electric field large enough for electrostatic breakdown to occur. However, for 40-keV incident beams, significant temporal and spatial correlation were observed. It is hypothesised that at higher energies more samples are charged close to the breakdown field at any given time and that a discharge in one “glue dot” might cause a sudden electric field spike in neighboring “glue dots,” which could trigger premature arcing. Such stimulated arc rates might reasonably be expected to scale with electric field intensity. A power law fit to the arc data found a power of −1.06 ± 0.09, consistent with a field falling off inversely with separation distance for charges spreading out across a 2-D conducting surface. [ABSTRACT FROM PUBLISHER]

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]

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

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

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

Recent circuit driven electromagnetic particle in cell simulation of the United Nations University-International Centre for Theoretical Physics plasma focus device revealed regular oscillations in both the voltage and current profiles. The simulated voltage waveform agreed well with the experimental profile, where similar unaccounted oscillations were also observed. In this paper, the oscillations are attributed to the plasma inductance, whose value was calculated by circuit analysis and agreed reasonably well with the computed experimental value. A circuit simulation of the prebreakdown and postbreakdown phases, with the plasma inductance incorporated, reproduced with sufficiency accuracy the electromagnetic particle in cell generated waveforms and consequently confirmed our finding. [ABSTRACT FROM AUTHOR]

The numerical modeling of electrical discharges occurring in atmospheric air has been in continuous development during the past decades in different fields, such as high-voltage techniques and lightning protection. Different methodologies have been proposed to represent the physical phenomena taking place at a single full discharge event, departing both from experimental and theoretical approaches. The implementation of these methodologies in numerical routines combined with the use of numerical methods to determine the electric potential distribution permits the creation of models whose predictions closely agree with the real case situations, where electrode arrangements might have nonsymmetric geometries. In this paper, we present an improved version of a simulation methodology for representing electrical discharges in long air gaps. This simulation methodology includes new elements like: 1) the 3-D leader channel tortuosity based on laboratory experimental measurements and 2) two new methods for the estimation of the electric charge contained in the so-called leader-corona region based on the electrostatic potential of fictitious potential rings representing the active region in front of the leader tip. Results from the simulation were compared with experimental records and a reasonably good agreement is found between them. [ABSTRACT FROM AUTHOR]

The prebreakdown current flowing in a lasertriggered vacuum switch (LTVS), investigated in this paper, is below the threshold voltage, where the switch becomes conducting. The laser irradiates in a short time the sintered KCl and Ti target of the vacuum switch and produces an initial plasma. The prebreakdown currents are measured in two different electrode geometries (planar and multirod) at both polarities and analyzed with respect to the ion and electron interactions with the electrodes. It is found that the peak value of the prebreakdown current increases with the applied voltage across the LTVS until 60 to 80 V, where it turns instantly into the conducting state. The multirod and planar LTVSs show different prebreakdown currents at different polarities, which is related to the condition of becoming conducting. [ABSTRACT FROM AUTHOR]

To understand the flashover of roof insulators in high-speed airflows, the breakdown characteristics and mechanisms of a short needle–plate air gap are investigated. An interesting and important phenomenon is found based on an artificial wind tunnel: the breakdown voltage first increases and then decreases. An experiential formula is established to describe the relationship among the airflow velocity, gap distance, and breakdown voltage. A good consistency with the experimental results is obtained. Furthermore, the breakdown mechanisms of the air gap in high-speed airflows are proposed, and the phenomenon is explained and verified according to the theories of gas discharge and fluid dynamics. The airflow blowing effect, which includes the deflection effect and blown away effect, and the airflow density effect are proposed as two dominant factors that affect the breakdown process of the air gap in high-speed airflows. The variation trend of the breakdown voltage with the airflow velocity is predicted. Two extreme points are expected during the variation process; i.e., the breakdown voltage has a maximum and a minimum, to which more attention should be paid. This paper is helpful for the safety operation of roof insulators on the high-speed train. [ABSTRACT FROM PUBLISHER]

In certain high-power RF devices, such as isolators and circulators, a static magnetic field is present in parallel with the oscillating RF electric field. This parallel magnetic field imposes electron Larmor motion, which restricts the trajectories of electrons accelerated by the RF field. In open geometries, magnetic confinement reduces electron losses in the multipactor region and can reduce the breakdown threshold. In this paper, the effect of magnetic confinement on multipactor breakdown threshold was measured experimentally using a stripline fixture with an externally applied uniform magnetic field. Multipactor threshold power was reduced from the unmagnetized case by as much as 3 dB at magnetic fields of about 0.5 kG. Multipactor gap aspect ratio has a significant impact on the degree of threshold reduction. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers (VCBs) are widely used in the medium voltage class. In VCBs, late breakdowns sometimes occur after the circuit current has been interrupted, and these late breakdowns are thought to be triggered by microparticles. In this paper, the motion of the microparticles and the breakdown triggered by the microparticles are observed under the application of dc voltage. It turns out that the motion of microparticles can be grouped into three patterns: attaching to electrodes, bouncing at electrodes, and bouncing up and down between electrodes. Some microparticles gain positive/negative charge during the flight as the acceleration changes despite application of dc voltage. The microparticles are positively charged by the secondary electron emission under the bombardment of field emission electrons from the cathode, while they are negatively charged by absorbing field emission electrons. The patterns of breakdowns triggered by the microparticles can be grouped into six patterns according to the motion of the microparticles before/after the breakdown and the location of light emission. The occurrence frequencies of each breakdown pattern are also measured with changing the microparticle size. It can be said that contamination of the gap with big and attaching microparticles should be avoided in order to prevent degradation of the withstanding voltage of the gap. [ABSTRACT FROM AUTHOR]

The objective of this paper is to compare the state of cathode surface of different axial magnetic field (AMF) contact systems (CSs) during arcing and after arc extinction. The arcs were ignited by opening of electrodes and were fed by sine half-wave current pulses with a duration of 10 ms. Investigations were performed in the range of arc currents up to the levels of guaranteed failure. The measurements were done by a high-speed Phantom M310 video camera. The cathode surface state during arcing was studied using a set of neutral density filters. It was discovered that melting of a part of the cathode surface during arc burning takes place in high-current vacuum arcs. A changing relief in the form of hillocks and hollows forms on the melted surface. We found out that there are two components in droplet erosion of the cathode, when its surface is partially melted: in addition to droplets formed directly in the cathode spot (which can be called droplets of the first type), the liquid part of the surface also emits droplets (which can be called droplets of the second type) significantly different in their sizes and velocities. The formation mechanisms of droplets of the first and the second type are different. The cathode surface temperature distribution immediately after current zero was obtained by comparing the results of cathode surface filming to the results of calibrated band-lamp filming in identical conditions. Reflection of anode radiation from cathode surface was analyzed by mathematical simulation. The filming was carried out using an interference filter. We found that the distribution of the cathode surface temperature is substantially nonuniform. The axial region is the most heated. We conclude that in all investigated CSs with the same amplitude value of the current, the temperature of the most heated parts of the cathode surface is significantly lower than the temperature of the most heated parts of the anode surface. Analysis of obtained results shows that switching failure can be provoked by the cathode and by the anode processes depending on CS design. [ABSTRACT FROM AUTHOR]

The aim of this paper is to compare the state of anode surface of different AMF contact systems during arcing and after arc extinction. Arcs were ignited by opening of electrodes and were fed by sine half-wave current pulses with durations of 10 ms. CuCr electrodes were used. We performed investigations in the range of arc currents from successfully interrupted ones up to the levels of guaranteed failure (limiting interrupted current) if the transient recovery voltage was applied. The measurements were implemented by a high-speed Phantom M310 video camera equipped with a Carl Zeiss 100/2 macro lens. We studied the anode surface state during the arcing using the set of neutral density filters. We found that at currents close to the limiting interrupted current, most of the anode surface melts. Liquid metal is squeezed out of the axial area and an annular crest is formed. The crest splashes out and breaks into separate jets. The jets are broken up into fragments, from which droplets separate. The anode surface temperature distribution just after current zero was obtained by comparison of the results of anode surface filming and the results of calibrated band-lamp filming in identical conditions. We carried out the filming using an interference filter (775 nm). The effect of reflection from electrodes was evaluated using mathematical simulation. The temperature distribution of the anode surface is highly non-uniform. The temperature of the most heated fragments of the anode surface increases with increasing current and reaches 2000 K with the limiting interrupted current. However, the size of these fragments is small, substantially less than the length of the interelectrode gap. They cannot create the vapor concentration in the entire gap up to the opposite electrode sufficient to provide the Townsend breakdown of the gap when the transient recovery voltage is applied. The analysis of the obtained results suggests that droplets, and hence, the phenomena on the surface that lead to their appearance play an important role in the breakdown process in the investigated contact systems at extreme currents. [ABSTRACT FROM AUTHOR]

This paper presents results of a numerical simulation of the explosion of a surface microprotrusion exposed to a radio frequency electromagnetic field. The integral of specific current action has been estimated for an RF and a dc electric field causing a microprotrusion explosion. It has been shown that in both cases, the microexplosion and the subsequent crater formation occur in much the same way. The results obtained support the hypothesis that a dc vacuum breakdown and a breakdown initiated by an RF wave incident on a metal surface proceed by the same mechanism. [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]

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]

In this paper, the evolution and transition mechanisms of typical nonlinear phenomena in an atmospheric pressure helium dielectric barrier discharge (DBD) are investigated from the perspective of transient evolution properties through fluid modeling. By gradually up-regulating the interelectrode gap width, the discharge (steady state) evolves from symmetric single-period (SP1), through asymmetric single-period (AP1), into Period-2 (P2) state. Similar evolution trace can also be obtained when increasing the driving frequency. Right after the initial breakdown, the discharge goes through several transient periods featuring unstable asymmetric current pulses before the establishment of steady-state discharge. As the bifurcation parameter increases in excess of the critical value, the discrepancy between the seed electron level of positive and negative discharges accumulates over the transient periods, switching the discharge into AP1 state. After then, a further elevation in the gas gap width (or driving frequency) leads to the generation of a “moderate intensity” positive pulse. With the “moderate intensity” positive pulse and a stronger positive pulse emerging alternatively in the temporal waveform sequence, the discharge evolves into P2 state. Finally, based on the transient evolution mechanisms, a preliminary state-controlling method regarding the use of a first-peak-leveled applied voltage is proposed, which may shed light on the modification of nonlinear states in some practical DBD application scenarios. [ABSTRACT FROM AUTHOR]

In this paper, the functional aging of gas-filled surge arresters (GFSAs) is addressed. Aging is determined by the features of the lifetime. Statistical samples of the random variables of breakdown time and breakdown voltage have been recorded. Experiments on the model of a GFSA were carried out in controlled laboratory conditions. The parameters of the experiment were: 1) gas type; 2) gas pressure; 3) interelectrode distance; 4) electrode material; and 5) treatment method of the electrode surface. The results indicate that the GFSA shows slower functional aging provided that: 1) the operating point is to the right of the Paschen minimum in the area of breakdown initiation with streamers mechanism; 2) the pressure is lower, i.e., at a constant pd value (product of pressure and interelectrode distance); 3) the electrode material has a higher melting point and thermal conductivity; and 4) the electrodes have a built-in topography. In addition, it was established that aging of the GFSA does not depend on the noble gas type. Finally, the production of a GFSA with optimal characteristics in terms of functional stability is proposed. [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]

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

Radio frequency (RF) breakdown can result in pulse shortening and severely limits the performance of high-power microwave (HPM) generators. In this paper, the initial stage of RF breakdown in HPM generators with a strong external guiding magnetic field has been carefully analyzed. It is thought that the initial breakdown process involves electron emission induced by an intense local field, electron acceleration in the electric field, and electron bombardment on the structure’s surfaces. Strong external guiding magnetic fields play a key role in the RF breakdown process of HPM generators. They concentrate the impact energy and make it more destructive. To suppress RF breakdown, feasible solutions include lowering the local field strength, decreasing the energy of the field-emitted electrons obtained from the RF field, reducing the deposited energy density, and improving the material’s resistance to electron bombardment. [ABSTRACT FROM AUTHOR]

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

This paper presents the application of a theoretically developed method, which when applied to a pulsed irradiance signal can provide information about the underlying chemical kinetics and reaction dynamics. The theoretical development uses a combination of state-space, Laplace transform, least-square, and correlation techniques to determine chemical kinetic and reaction dynamic terms from a pulsed discharge. The waveform irradiance signals come from a space-based optical radiometer. Four pulsed radiometry irradiance waveforms are examined where the reaction order, rate constant, and reaction rates are investigated. The application of the theory and the commensurate results demonstrate that irradiance signals obtained under similar circumstances come from distinct pulsed discharge conditions. [ABSTRACT FROM AUTHOR]

A previous computational study of a relativistic magnetron with diffractive output at the University of New Mexico using the particle-in-cell code MAGIC achieved an efficiency of 70%. The research described in this paper aimed to achieve an experimental verification of 70% efficient operation of this design. Changes to the topology were necessary, such as the introduction of a Helmholtz-like magnetic coil pair and the use of a polished stainless steel endcap on the downstream end of the transparent cathode. These structures maintain a high degree of magnetic field uniformity in the anode–cathode gap interaction space and intercept leakage electrons that might otherwise impact the dielectric output window. The use of these structures stands in contrast to the modified magnetic fields used in the work of others to protect the window. An ethanol calorimeter and S-band waveguide detector were placed in the near-field to obtain radio frequency pulse shape and frequency and to infer peak power through a measurement of total energy radiated. A coaxial D-dot probe and self-integrating Rogowski coil were used to measure pulser voltage and total current, respectively, and showed that the tube operated at an efficiency of 63.5% until the endcap started emitting electrons, after which the efficiency was 40.4% in $\pi $ -mode. Images of radiated field pattern on a neon-bulb grid and of air breakdown outside of the 21-cm diameter output window were captured to confirm conversion of the $\pi $ -mode of operation to a TE31 circular radiated output mode. [ABSTRACT FROM PUBLISHER]

A new plasma-based widely tunable power limiter is introduced and experimentally investigated in this paper. The proposed limiter is composed of a high- $Q$ evanescent-mode cavity resonator loaded with a gas discharge tube in its gap area over the post. Increasing input power results in enhancing electric field over the gap, which eventually leads to microwave gas breakdown and plasma formation. The limiter loss after the breakdown depends on the electron density in the tube, which itself is a function of input power. Hence, the limiting mechanism is self-sustained. The threshold power is tunable either coarsely by selecting different tubes with various breakdown voltages or finely by dc biasing the tube. In a fabricated proof-of-concept limiter at 2.16 GHz with 22% bandwidth, preionization by an external dc bias provided 15.5 dB of limiting power tunability in the range of 370 mW–13 W, while the limiter could easily handle up to 100-W input power. The response time of this limiter is <10 ns. Thanks to the nature of capacitively coupled microwave gas discharge in the $ \alpha $ -discharge regime, the limiter performance is quite stable and no degradation was observed after a long operation under high input power. [ABSTRACT FROM PUBLISHER]

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

This paper describes the analysis following the breakdown of an ion cyclotron radio frequency (ICRF) tuner purchased from Advanced Ferrite Technology (AFT). The codes used in the analysis were CST and COMSOL. These codes use the standard gyromagnetic model for the ferrite, which gives results that are largely in error when compared with measurements at ICRF and at lower hybrid frequencies. We have measured a slab of the ferrite used in the ICRF tuner provided by AFT and from these measurements we have constructed a tabular model of the ferrite and inserted it into the COMSOL code. The results give performance that closely agrees with the performance specifications issued by AFT. We then used this modified code to correlate the simulation with the destructive evidence found in the tuner. The correlation was good between the destruction spot and the peak of the standing electric field. Pictures of the destruction and the heating in the tuner and the standing field results from the simulation are given. [ABSTRACT FROM AUTHOR]

Normally, a three-electrode spark–gap switch is controlled by the application of an external trigger impulse. In this paper, a novel self-breakdown sharpening switch based on the three-electrode spark–gap switch is proposed. However, in this paper, the trigger electrode is connected to ground through a resistor, with the prespark between the trigger and the main electrodes providing the electrons and ions that initiate conduction of the main gap. A prototype sharpening switch with a breakdown voltage of 116.0 kV \pm 1.0 kV and a breakdown time of 3.396\ \mu\s\pm 0.036 \ \mu\s is described. When compared with a conventional two-electrode spark–gap sharpening switch, the novel sharpening switch has both a more stable breakdown voltage and lower jitter, and the dc breakdown and impulse breakdown characteristics of the two types of switches are presented and compared. When the impedance of the resistor connected to the trigger electrode is high, it is demonstrated that both the value of this resistor and also the type of load have little effect on the characteristics of the novel switch. However, the breakdown voltage of the novel sharpening switch was found to be sensitive to the rise time of the input pulse from the trigger generator. The prototype sharpening switch has a lifetime at least 20 000 shots and is now in use in a major pulsed power conditioning system. [ABSTRACT FROM PUBLISHER]

This paper discusses the modeling of a peaking switch to study the reduction in rise time for the subnanosecond duration pulses. The effect of the various shapes of input pulse, inductance, and interelectrode distance on the output voltage and wave shape is discussed in this paper. The modeling has been carried out using the electromagnetic and microwave modeling software of Computer Simulation Technology. [ABSTRACT FROM PUBLISHER]

An equivalent circuit for a core snubber is established in this paper. The circuit can approximately express a parallel resistance and inductance. The resistance can be directly calculated according to the resistivity of the magnetic core and structure dimensions of the core snubber referring to Fink–Baker–Owren (FBO) method, and the eddy current factor is adjusted to one. In this paper, the shunt inductance neglected by FBO is first considered, and it can be obtained from critical characteristics of the magnetic core and structure dimensions of the core snubber. The two electrical parameters are varied with saturated zone of the inner turn of tape. Then, the simulated model of a core snubber is set up. Finally, a miniature core snubber is analyzed, and its parallel resistance and inductance are obtained from the experiment condition. The test data validate the analytic model. The method presented in this paper is proved to be useful in the design of core snubber for the Experimental Advanced Superconducting Tokamak and the International Tokamak Experimental Reactor. [ABSTRACT FROM PUBLISHER]

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

In our previous research, a high-voltage vacuum closing switch has been proposed to synchronize the output pulses delivered from multiple parallel plasma opening switch modules to the load in a scheme of power conditioning of a generator of high-power nanosecond pulses. However, the breakdown voltage for each stage of the closing switch has to be increased to 150-300 kV to make the whole concept feasible. This paper considers experimental research of the electric breakdown of 1-mm vacuum gaps formed between the plane cathode and the sharp high-voltage anode to achieve higher breakdown voltages. Two electrode arrangements described in this paper include a point-to-plane system at 5 kA and a multichannel disk-shaped switch at 50 kA. Both systems were studied at voltages up to 170 kV, current densities up to 5 kA · cm-2, and submicrosecond pulse durations. A concept of a new closing switch capable of operating at 3 MV, 50 ns, and 0.3 MA using multiple sharp-anode vacuum gaps stacked in series is proposed on the basis of the research results. [ABSTRACT FROM AUTHOR]

Pulsed power technology has possibility to be able to provide a new method for tissue ablation. Applying a pulsed high electric field with nanosecond duration time onto a cancer cell can induce apoptosis into that. In this method, a frequency component of the electric field applied to the cell is an important factor. This paper focuses on the investigation of frequency characteristics of a difference of a cell death caused by applying the pulsed high electric field. The budding yeast that is a eukaryotic cell has been used as a model organism of a human cell. Difference of the cell death of the yeast for frequencies of the pulsed electric field by using molecular probes, propidium iodide, Annexin-V, and FLICA has been investigated. The frequency of the pulsed electric field was changed from 200 kHz to 70 MHz. The low frequencies, 200 kHz and 3.5 MHz, under 45 MHz yielded both necrosis and apoptosis in the cells. The electric field of frequency of 200 kHz with an intensity of 30 kV/cm only induced necrosis by breakdown in most cells. At the frequencies of 200 kHz with 16 kV/cm and 3.5 MHz, both apoptosis and necrosis occurred. The apoptotic pathway at 3.5 MHz went via caspase. At the frequency of 70 MHz, only apoptosis, not necrosis, was induced in the cells. However, the apoptosis via caspase was not dominant for the cell death. A signal for the cell death passed through other pathway of apoptosis, which was different from that of 3.5 MHz. At 45 MHz, the cell death did not occur. 45 MHz is the boundary where necrosis occurs, and the apoptotic pathway is different. [ABSTRACT FROM PUBLISHER]

Surface flashover has already become a limiting factor in pulsed power systems, and a thorough understanding of its mechanism is fundamental to improve it. Since optical diagnostic methods can provide more information for understanding the flashover mechanism than electrical ones, in this paper the light emitted during surface flashover along polytetrafluoroethene (PTFE) was diagnosed by a spectrograph together with an intensified charge-coupled device, and the spectrum of laser-induced breakdown of PTFE was also recorded as a comparison. The results show that the spectrum of laser-induced breakdown is composed of line spectra emitted by material elements. While many band spectra emerge in the spectrum of surface flashover besides the former line spectra, which implies that the source of flashover plasma includes desorbed surface gases as well as vaporized insulator material. This result also reveals a more detailed picture of the flashover process. [ABSTRACT FROM PUBLISHER]

Anode surface temperature after current zero has a great impact on the interruption capacity of a vacuum interrupter. The objective of this paper is to theoretically investigate the relation between breakdown voltages and anode surface temperature after current zero. A heat conduction model was adopted to describe the temperature development of the anode, taking account of phase transition and evaporation. The breakdown voltages in certain metal vapor densities were obtained by the Particle-in-Cell/Monte Carlo collision (PIC-MCC) method. Finally, the Paschen curve for copper vapor was obtained using the PIC–MCC method and verified by the theoretical model. Moreover, the minimum breakdown voltage, 30 V, was obtained at a density of 1.3\times 10^22/\textm^3 with a gap of 10 mm, which corresponded to a surface temperature of 1983 K. In order to ensure a successful interruption, anode surface temperature should not be higher than 1983 K at current zero, and the melting time should be kept as short as possible. [ABSTRACT FROM PUBLISHER]

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]

A 2-D two-temperature model has been developed to simulate the heating of a microprotrusion on a metal surface exposed to a radio frequency (~10 GHz) electromagnetic field. The numerical simulation using this model includes a self-consistent calculation of the electric field at the microprotrusion surface and the field emission characteristics of the microprotrusion using the particle-in-cell method, a calculation of the current density distribution in the microprotrusion, and a calculation of the lattice and electron temperatures with the use of the heat equation taking into account the Joule and Nottingham effects, and also the finite rate of the heat exchange between the electrons and the lattice. The microprotrusion heating time has been calculated in relation to the electric field enhancement factor and to the electron–phonon interaction parameters. [ABSTRACT FROM AUTHOR]

The diffusion of transient magnetic fields through the walls of a hollow conductive shell is an important phenomenon of interest throughout a variety of pulsed power applications. Basic solutions do exist for cylindrical geometries in the limiting case that the skin depth is much larger than the wall thickness; however, in many pulsed applications, the transient skin depth is often similar to the conductor thickness. As the underlying thin-wall assumption begins to breakdown, the production of complex eddy current distributions in the conductor walls results in deviation from these simplified analytical solutions of the diffused field. Precise calculation of these current distributions is essential for many applications including inductive shielding and magnetic field diagnostics near conductors. Electromagnetic simulations using the finite-element method provide a more accurate picture of the diffusion process in this regime. A high magnetic field testbed facilitates measurement of the diffused fields in order to verify simulation accuracy. The effect of material conductivity, wall thickness, and conductor geometry on the diffusion process is examined. [ABSTRACT FROM AUTHOR]

Many approaches exist for energy storage and delivery to the load, including high-power relativistic applications. One of the best solutions for the driver of high-power relativistic applications is the Marx generator. This paper describes the design, fabrication, and experimental validation of a Marx generator consisting of capacitors, spark-gap switches, and resistors. It is designed as an eight-stage Marx circuit to reach an output voltage level as low as −500 kV, and it is directly connected to the Blumlein pulse-forming line (PFL) to achieve more than 100 ns of the full-width at half-maximum. Experiments are performed with a solution load in a manner similar to having a coaxial structure in a high vacuum with a pressure of below 0.5\, \times \, 10^-5 torr, to prevent breakdown and measure the amplitude of the negative high-voltage pulse waveform. The solution load is designed to capture the short-pulse output of the PFL with a rise time of less than 25 ns and a voltage level of approximately −500 kV. The experimental results show that the output pulse can be used as a source to generate an intense relativistic electron beam at the gun for high-power relativistic applications. [ABSTRACT FROM PUBLISHER]

This paper presents a two-stage hybrid plasma catalyst system for toluene decomposition in dry air. It consists of a dielectric barrier discharge reactor and a homemade Co–Mn catalyst bed reactor. At room temperature and under a bed gas hourly space velocity of up to 32 233 h ^\mathrm -1 , the decomposition efficiency is about 92.4% when plasma specific energy density is around 100 J/L. With increasing the catalyst bed temperature to about 350 K, almost 100% of the toluene and the plasma generated O3 are decomposed simultaneously. The Fourier transform infrared spectra show that the major reaction byproducts are CO2. By means of X-ray powder diffraction, X-ray photoelectron spectroscopy, and N2 physisorption diagnostics, we conclude that both Co3Mn3O4 and the lattice oxygen species play an important role in simultaneous toluene decomposition and ozone utilization. [ABSTRACT FROM PUBLISHER]

In pulsed power systems, metallized film capacitors facilitate the operation of the film with a relatively small margin to its dc breakdown strength. Electrical conduction in metallized biaxially oriented polypropylene (BOPP) film may result in the leakage in high energy density capacitors and thus the reduction of the energy efficiency. This paper investigates the mechanism of the electric field and temperature dependence of electrical conduction in the BOPP film capacitor. A proposed model for the electrical conductivity takes into consideration both the Poole–Frenkel effect and field-enhanced carrier mobility. Experiments are performed to measure the electrical conductivity of the BOPP film at different electric fields and temperatures. [ABSTRACT FROM PUBLISHER]

Corona discharge refers to the phenomenon when the electric field near a conductor is strong enough to ionize the dielectric surrounding it but not strong enough to cause an electrical breakdown or arcing between conductors or other components. This phenomenon is unwanted and dangerous in high-voltage systems; however, a controlled corona discharge may be used to ionize a fluid and induce motion by directly converting the electrical energy into kinetic energy. Phenomena that involve the direct conversion of electrical energy into kinetic energy are known as electrohydrodynamic (EHD) and have a variety of possible applications today. This paper contains a literature review of the research regarding the EHD effects associated with corona discharges, from the first observation of the phenomenon to the most recent advancements on its mathematical modeling, as well as the advancements on specific applications, such as thrust, heat transfer improvement, boundary layer enhancement, drying, fluid pumping, and cooling. [ABSTRACT FROM PUBLISHER]