High-voltage Nanosecond Pulses Research Articles

XPS study of sulfide minerals surface oxidation under high-voltage nanosecond pulses

Surface modification of natural metal sulfides (pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, and molybdenite) treated by high-power electromagnetic pulses (HPEMPtreatment) has been studied by X-ray photoelectron spectroscopy as a function of HPEMP treatment duration. Two principal common steps and some differences in the surface evolution process were identified. The initial surface modification step was observed at low treatment doses (up to N ~ 103 pulses). Formation or accumulation in the surface layer of metal-deficient sulfide phase, oxides and hydroxides, elemental/polysulfide sulfur and/or metastable sulfur (thiosulfate, sulfite) was observed at this step. The second step (N ≥ 3·103 pulses) is characterized by thermal loss of elemental sulfur.Differences in the modification process, it was found that the chemical transformations of sulfur in the surface layer of pyrite, arsenopyrite, chalcopyrite include accumulation/formation of S0 (Sn2−) at the first transformation stage (up to N ~ 103 pulses) followed by its removal. In the case of sphalerite and galena, the surface sulfur transformation had a different pattern. It included formation/accumulation at the first stage of metastable sulfur species (thiosulfate, sulfite) converted at an increase treatment duration to the initial state (sulfide or disulfide).

Multistage converter of high-voltage subnanosecond pulses based on nonlinear transmission lines

This paper presents new experimental data that enable the observed processes in nonlinear ferrite lines to be related with the theoretical positions of the spin waves of the magnetization precession under the conditions of a high-power microwave. Such an approach has not been considered in earlier discussions on the subject and can contribute to the theory of the generation of oscillations in a gyromagnetic ferrite medium. These new aspects were used to design a new type of generator. The specific feature is the presence of regularity in the ferrite lines in the generation mode of microwave oscillations. The repeating regularity enabled the implementation of multistage pulse shape converters capable of operating in two modes and providing extreme parameters of the output pulses. Two variants of multistage converters of nanosecond high-voltage pulse shapes with a duration of ∼4 ns at a half-height and with an amplitude of −500 kV were designed and tested. The assembly of the converters and the driving generator are described in the stationary setup. In the first case, the rise time shortened to ∼45 ps, and the amplitude increased to −850 kV due to the sharpening of a pulse and the formation of a shock wave by the cascade of three nonlinear transmission lines. A record rate for the increase of the leading peak voltage of ∼15.5 MV/ns was reached. In the second case, the new approach for the generation of a sequence of subnanosecond pulses was presented and tested, and each pulse of the previous stage was modulated by the next stage doubling the number of pulses while conserving a deeper modulation. As a result, at the top of the incident pulse, a sequence of subnanosecond peaks with a large modulation depth (∼70%) was formed when the maximum voltage amplitude reached −700 kV. The results of the emission of such pulses are also presented.

First results on transient plasma-based remediation of nanoscale particulate matter in restaurant smoke emissions

Recent studies have shown that nanoscale particulate matter produced in commercial charbroiling processes represents a serious health hazard and has been linked to various forms of cancer and cardiopulmonary disease. In this study, we propose a highly effective method for treating restaurant smoke emissions using a transient pulsed plasma reactor produced by nanosecond high voltage pulses. We measure the size and relative mass distributions of particulate matter (PM) produced in commercial charbroiling processes (e.g., cooking of hamburger meat) both with and without the plasma treatment. Here, the plasma discharge is produced in a 3” diameter cylindrical reactor with a 5–10 ns high voltage (17 kV) pulse generator. The distribution of untreated nanoparticle sizes is peaked around 125–150 nm in diameter, as measured using a scanning mobility particle sizer (SMPS) spectrometer. With plasma treatment, we observe up to a 55-fold reduction in relative particle mass and a significant reduction in the nanoparticle size distribution using this method. The effectiveness of the nanoscale PM remediation increases with both the pulse repetition rate and pulse voltage, demonstrating the scalability of this approach for treating particulate matter at higher flow rates and larger diameter reactors.

Parameterized Nanosecond Pulse Realization Through Parametrical Modulation of Timing Sequence of Switches in Marx Circuit

The characteristics of gas discharge are closely related to the features of high-voltage pulses, especially to the rising and falling time of pulse. A parameterized pulse control method based on improved Marx generator is proposed to obtain parameterized nanosecond high-voltage pulses to match different discharge circumstances. Different parameters of nanosecond pulses are realized in real time by parametrical modulating timing sequences of switches in an improved Marx generator. Experimental results indicate that the ability of generating pulses is with 0–20 kV amplitude, 0–1 ms width (flat top), 50–500 ns or faster rising/falling time, below 5% overshoot, and a maximum 5 kHz repetitive frequency at 20 kV on a matched 0–100 pF capacitance load. The shape of pulse waveform including triangular, rectangular, or the combination of the two kinds of pulse waveform can be achieved. The discharge characteristics in the dielectric barrier discharge device driven by the parameterized pulse, especially changing the rising time of pulse, are investigated. The uniform discharge is observed, and the discharge intensity is doubled while reducing the rising time of pulse from 500 to 50 ns, and the intensity of the N2 spectrum increased to 2.5 times.

Effects of excitation voltage pulse shape on the characteristics of atmospheric-pressure nanosecond discharges

The characteristics of atmospheric-pressure microdischarges excited by nanosecond high-voltage pulses are investigated in helium-nitrogen mixtures, as a function of the parameters of the excitation voltage pulses. In particular, cases of single-pulse excitation as well as unipolar and bipolar double-pulse excitation are studied, at different pulse durations, voltage amplitudes, and delay times (for the case of double-pulse excitation). Our investigations are carried out with a particle-simulation code that also comprises the treatment of the VUV resonance radiation in the plasma. The simulations allow gaining insight into the plasma dynamics during and after the excitation pulse, the development and the decay of charged particle density profiles and fluxes. We find a strong dependence of the electron density of the plasma (measured at the end of the excitation pulse) on the electrical input energy into the plasma and a weak influence of the shape of the excitation pulse at the same input energy.

Change in the Functional Chemical Composition of the Surface and Technological Properties of Natural Quartz under the Influence of High-Voltage Nanosecond Pulses

FTIR, Hammett indicator adsorption, microhardness testing, and other physicochemical means of analysis (electrokinetic potential, contact angle of wetting, floatability) are used to study the mechanism of structural–chemical transformations of the surface, the change in physicochemial, mechanical, and technological properties of natural quartz under the influence of high-voltage nanosecond pulses. The impact of pulse energy causes softening, an increase in electron donor ability, and a reduction in the acceptor ability of the quartz surface. This lowers the sorption activity of the mineral with respect to oxyhydryl (carboxylic) flotation collecting agents (sodium oleate).

Mechanism of the Change in the Structural, Chemical, and Technological Properties of Eudialyte upon Combined Energy Effects

The mechanism of change in the structural, chemical, physicochemical, and technological properties of Lavozero-deposit eudialyte, caused by the effect of high-voltage nanosecond pulses and combined (sequential) electropulse and acid treatment of mineral samples, is studied by means of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, electrophoretic light scattering (zeta-potential), confocal laser scanning microscopy, microhardness testing, etc. The results show it is possible in principle to use pulsed energy and combined physical and physicochemical effects to improve the effectiveness of disintegration and softening, and to alter the hydrophobicity, sorption activity, and technological properties of eudialyte-group rock-forming minerals.

An MMC-based modular unipolar/bipolar high-voltage nanosecond pulse generator with adjustable rise/fall time

The rise/fall time of a high-voltage nanosecond pulse affects the application effect of the pulse; therefore, it is of great significance to study the adjustment of the rise/fall time. In this paper, a new type of generator topology based on a half-bridge modular multilevel converter (HB-MMC) is proposed that uses MOSFETs as solid-state switches to produce a unipolar/bipolar high-voltage nanosecond pulse with an adjustable rise/fall time. The proposed topology consists of 2 arms, each of which contains several HB-MMC submodules. The capacitors of each arm are charged with a positive voltage and negative voltage in parallel. By controlling the discharging sequence of the two arms, a unipolar or bipolar pulse can be generated. For each arm, by setting the switching sequence of the MOSFETs, the number of capacitors inserted into the discharging circuit can be controlled to allow a multilevel pulse to be generated. The rise/fall time of the output pulse can be adjusted by changing the number of levels and the duration of each level. Detailed illustrations of the proposed configuration and its operational concept are presented. Experimental results for a scaled-down prototype are presented to validate the concept.

Nanosecond Pulse Electroporator With Silicon Carbide mosfets: Development and Evaluation.

Nanosecond electroporation of cell organelles is being studied since more than a decade, but it is still not entirely understood. Unique prototype hardware equipment and challenging measuring methods may also be a contributing reason for this situation. In the scope of this paper, we improve the performance of the high-voltage nanosecond pulse generator by introducing silicon carbide (SiC) mosfets. We developed a new high-voltage diode opening switch (DOS)-nanosecond pulse generator for laboratory use for in vitro experiments in electroporation cuvettes. Analysis and comparison of the most commonly used switching technologies in pulse generators were made. The device is designed by two parallel two-stage Marx-bank circuits with SiC mosfets that generates up to 200 A in the resonant network. A driving circuit for stable simultaneous switching of SiC mosfets was developed. The developed generator can deliver from 500V to more than 6kV, approximately 8ns pulses to a 50Ω load. Even though the amplitude of the output pulse is not as high as expected, the multiplication factor [Formula: see text] is still approximately 9, which is an improvement compared to the previously published linear DOS generator. Measurement and evaluation process is described in detail. Additionally, we emphasize on the size of an error that occurs during measurements.

Experimental characterization of a ns-pulsed micro-hollow cathode discharge (MHCD) array in a N2/Ar mixture

An array of seven micro-hollow cathode discharges (MHCDs) operating in a N2/Ar mixture and ignited by a nanosecond pulsed high voltage is experimentally characterized in this work. Compared to other non-equilibrium discharges, high electron densities can be obtained with this type of microdischarge, and, thus, a high dissociation degree of the molecules is expected to be achieved. This is particularly suited for nitride deposition, which is the targeted application of this work, given that the atomic nitrogen density is a key parameter for this deposition process. The electrical diagnostics reveal that the energy deposited in the plasma during one voltage pulse increases with the Ar fraction in the gas mixture and the voltage pulse repetition frequency. A small effect of the repetition frequency is observed on the voltage and current characteristics of the discharge, while a significant increase in the amplitude of these two electrical parameters is observed with increasing Ar admixture. Consequently, a higher electron density is expected with increasing Ar fraction in the gas mixture and repetition frequency. Time-integrated optical emission spectroscopy is carried out to identify the excited emissive species in the plasma and to determine the time-averaged vibrational and rotational temperatures. For a discharge operating in pure N2, at a repetition frequency of 40 kHz, the time-averaged rotational temperature is found to be 390 K ± 40 K and the time-averaged vibrational temperature is 3580 K ± 200 K, revealing the non-equilibrium nature of the discharge. Both temperatures increase with the Ar fraction in the N2/Ar mixture, while they are almost independent of the repetition frequency. Finally, the different phases of the spatio-temporal evolution of the discharge are mapped using space-time resolved ICCD images. The spatial evolution of the discharge between two consecutive voltage pulses can be decomposed in four phases, corresponding to the different stages of the temporal evolution of the discharge voltage.

On evolution of flow structures induced by nanosecond pulse discharge inside a plasma synthetic jet actuator

Detailed phase-lock schlieren measurement was conducted to study the physical evolution process of the structures inside the plasma synthetic jet actuator driven by a high voltage nanosecond pulse. One strong blast wave and heat source core are generated immediately after the arcing discharge. Within the cavity, as the blast wave is reflected by the cavity walls and interacts with the heat source core, the pressure of the gas inside the cavity is increased rapidly and a series of diffractive wave comes out from the orifice of the cavity, followed by a train of vortex rings and a high speed jet.

Development of a High-Power Burst Pulse Generator Based on the Sequential Operation of Magnetic Switches

Nanosecond and subnanosecond high-voltage pulses have used in new biological applications, such as cancer treatment using an ultrashort pulsed high electric field. For this treatment, the use of high-power pulsed electromagnetic wave has been proposed to obtain the required high electric field. This paper focuses on the design of a compact high-power pulsed electromagnetic wave generator using a nanosecond pulsed power generator for cancer treatment. We developed a pulsed power generator that continuously outputs multiple pulses via a nonlinear transmission line (NLTL) using magnetic switches. The NLTL comprises a ladder of capacitors and saturable inductors. The NLTL generates a pulse train by delaying the propagation of the pulse using the magnetic switch of each ladder. The frequency of repetition of the burst pulse is 13.8 MHz. The peak output voltage is 7 kV at the maximum input voltage of 28 kV. The number of pulses in the pulse train can be varied by the number of units of the magnetic switch.

A Step Forward in Tissue Engineering Design: Control on Multi-Scale Fiber Alignment by Electrospinning

This paper proposes a novel electrospinning method for controllable fiber alignment and deposition on a dielectric substrate by the electric field manipulation using nanosecond rise time high-voltage pulse generators. A preliminary numerical simulation shows electric field distribution in proposed geometry with a syringe and two cylindrical collectors. Samples of oriented materials based on a polyamide 6/66 copolymer with a low degree of disorientation 2-4° were obtained. The study of thermal and mechanical behavior of oriented materials based on polyamide was carried out, and for the first time for electrospun fibers the microscale orientation effects of polymer crystallites were found by X-ray diffraction in small and wide angles. Orientation occurs in the developed materials both at macro and micro levels. The possibility to create material by stacking multiple layers with given fiber orientation at 65° and 90° and spinning on various dielectric materials due to the reverse polarity operating principle is demonstrated. The ability to control fiber alignment in electrospinning will expand the possibilities of high-performance polymer nonwoven materials production with a given architecture and unique physicochemical characteristics for solving a whole range of medical and technological challenges of a different profile.

Subnanosecond breakdown of a point-to-plane gap at negative and positive polarities

The influence of the polarity of high-voltage nanosecond pulses on the prebreakdown stage duration at the subnanosecond breakdown of a 1-cm point-to-plane gap filled with air (13-800 kPa) has been experimentally studied. Furthermore, the influence of the shape of the plane electrode surface on the one has been studied too. Waveforms of voltage and current pulses were analyzed. It was found that when a streamer appears near the pointed electrode, a dynamic displacement current flows due to the redistribution of electric field strength in the gap. This allowed us to establish the instant of appearance of the streamer relative to the instant of applying the voltage across the gap. It was established that the positive streamer appears later than the negative one at low air pressure. As a result, the inversion of the polarity effect is observed. An increase in air pressure, as well as the use of a plane electrode, on the surface of which there are sharp protrusions, reduce this time gap. It disappears at air pressure of 400-800 kPa. The processes taking place in the gap are discussed.

Volume added surface barrier discharge plasma excited by bipolar nanosecond pulse power in atmospheric air: optical emission spectra influenced by gap distance

In this paper, volume barrier discharge with different gap distances is added on the discharge border of high-voltage electrode of annular surface barrier discharge for generating volume added surface barrier discharge (V-SBD) excited by bipolar nanosecond high-voltage pulse power in atmospheric air. The excited V-SBDs consist of surface barrier discharge (d = 0 mm) and volume added surface barrier discharges (d = 2 mm and 3 mm). The optical emission spectra are recorded for calculating emission intensities of N2 (C3Πu → B3Πg) and (B2 → X2 ), and simulating rotational and vibrational temperatures. The influences of gap distance of V-SBD on emission intensity and plasma temperature are also investigated and analyzed. The results show that d = 0 mm structure can excite the largest emission intensity of N2 (C3Πu → B3Πg), while the existence of volume barrier discharge can delay the occurrence of the peak value of the emission intensity ratio of (B2 → X2 )/N2 (C3Πu → B3Πg) during the rising period of the applied voltage pulse and weaken it during the end period. The increasing factor of emission intensity is effected by the pulse repetition rate. The d = 3 mm structure has the highest threshold voltage while it can maintain more emission intensity of N2 (C3Πu → B3Πg) than that of d = 2 mm structure. The structure of d = 2 mm can maintain more increasing factor than that of the d = 3 mm structure with varying pulse repetition rate. Besides, the rotational temperatures of three V-SBD structures are slightly affected when the gap distance and pulse repetition rate vary. The vibrational temperatures have decaying tendencies of all three structures with the increasing pulse repetition rate.

Development and characterization of a wire-plate air bubbling plasma for wastewater treatment using nanosecond pulsed high voltage

This study developed a prototype of a wire-plate air bubbling plasma reactor that can be easily scaled up for wastewater treatment. The electrical characteristics, including the discharge current and average power consumed, of the developed reactor were deeply investigated at different operating parameters and solution conductivities. The performance of the reactor was examined on the basis of energy efficiency and methylene blue (MB) decoloration efficiency. Moreover, the removal of the total organic carbon and the changes of the physicochemical properties of solution, including pH, conductivity, and temperature, were evaluated. The analysis of current discharge and average power consumed showed that the discharge mode in the present reactor is a filamentary streamer. Interestingly, the solution conductivity had no effect on the average power consumed at low applied voltages, due to confinement of the discharge in a small area surrounding the discharge electrode in the gas phase. However, at relatively high voltages, the effect of conductivity on the average power consumed was noticeable, yet it had no effect on the decoloration efficiency at the same average power. The present reactor showed a high energy-efficiency value of 42 g/kWh at 50% decoloration of 30 mg/l MB solution, but it dropped to 14 g/kWh at 97% decoloration. A first-order kinetics model described well the decoloration reaction rates and the overall rate constant correlated linearly to the average power.

Electrostrictive Mechanism of Liquid Breakdown in Strongly Nonhomogeneous Field under the Action of Nanosecond Voltage Pulse

Electrostriction mechanism of breakdown in polar liquid caused by high-voltage nanosecond pulse is studied. Nonstationary motion of liquid in the pin-to-plane system exposed to a pulse with peak voltage of 30 kV and 6-ns duration is numerically analyzed. Cavities in which the breakdown can be initiated are formed in the vicinity of the tip electrode. Dimensions of such cavities are estimated, and the conditions for formation are formulated. Profiles of voltage and current pulses are measured for breakdown in water and air. The velocity of breakdown development in air is determined using the time delay of the pulse measured by the shunt of discharge current at several interelectrode distances. The proposed method has limitations in the measurement of breakdown in water due to the effect of displacement current that exceeds the discharge current.

Intensification of Eudialyte Concentrate Leaching by Nanosecond High-Voltage Pulses

The mechanism of weakening and directional change in structural and chemical properties of eudialyte under nonthermal exposure to nanosecond high-voltage electromagnetic pulses and nitric-acid leaching is studied. The methods of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy and microhardness measurement are used. The rational mode of high-energy pulsed treatment is determined. After such mode treatment, the acid leaching of eudialyte concentrate results in recovery of zirconium and total rare earth elements higher by 1.7 and 1.4 times as against reference standards.

Effect of High-Voltage Nanosecond Pulses on the Physicochemical and Technological Properties of Rare-Metal Minerals

The mechanism of the structural and chemical state modification of columbite, tantalite and zircon surface under the effect of high-voltage nanosecond pulses is investigated using a set of precision physical and chemical methods (e.g., XPS, FTIR, SEM–EDX, potentiometric titration, electrophoretic light scattering, AFM–Kelvin force probe microscopy, and microhardness). An effective mode of preliminarily treating rare-metal minerals with high-voltage nanosecond pulses to produce directional changes in their physicochemical, electrical, mechanical, and technical properties is validated that increases mineral flotation and sorption activity and greatly improves the flotation technological characteristics of columbite and zircon.

The effect of the pulse repetition rate on the fast ionization wave discharge

The effect of the pulse repetition rate (PRR) on the generation of high energy electrons in a fast ionization wave (FIW) discharge is investigated by both experiment and modelling. The FIW discharge is driven by nanosecond high voltage pulses and is generated in helium with a pressure of 30 mbar. The axial electric field (Ez), as the driven force of high energy electron generation, is strongly influenced by PRR. Both the measurement and the model show that, during the breakdown, the peak value of Ez decreases with the PRR, while after the breakdown, the value of Ez increases with the PRR. The electron energy distribution function (EEDF) is calculated with a model similar to Boeuf and Pitchford (1995 Phys. Rev. E 51 1376). It is found that, with a low value of PRR, the EEDF during the breakdown is strongly non-Maxwellian with an elevated high energy tail, while the EEDF after the breakdown is also non-Maxwellian but with a much depleted population of high energy electrons. However, with a high value of PRR, the EEDF is Maxwellian-like without much temporal variation both during and after the breakdown. With the calculated EEDF, the temporal evolution of the population of helium excited species given by the model is in good agreement with the measured optical emission, which also depends critically on the shape of the EEDF.