High-voltage Nanosecond Pulses Research Articles

A Nanosecond High-Voltage Pulse Generator Based on Artificial Double Forming Lines

The results of experimental studies of a compact high-voltage pulse generator are presented. The generator is based on two artificial double forming lines in a collapsed circuit, which are switched by gas spark gaps; it also contains a peaking gas spark gap, transmission lines filled with a liquid dielectric, and a load equivalent. The characteristics of this generator were studied in the charging-voltage range of up to 100 kV. When the voltage pulse duration from the forming line was 100 ns, current pulses with an amplitude of 18 kA and a rise time of ~18 ns were obtained across an ohmic load.

Different approaches of measuring high-voltage nanosecond pulses and power delivery in plasma systems

In the presented study, we consider several methods to measure high-voltage, nanosecond-duration electrical pulses, and their implementation for understanding the applied voltage, current, incident, reflected, and power at a load. We examine different probes for the most common transmission line types used in high-voltage pulser’s output, present their strengths and weaknesses, and give recommendations for their use. Special attention was given to the back current shunt and its properties. This method allows scientists and researchers to directly observe the voltage profile in real-time and may find broader use in pulsed power and plasma applications.

Plasma-enhanced NOx remediation using nanosecond pulsed discharges in a water aerosol matrix

We report nitrogen oxides remediation using a transient pulsed plasma discharge in a water aerosol gas matrix using nanosecond high voltage pulses. While there have been many studies showing highly efficient conversion of NO to NO2 using plasma-driven processes, the total removal of NOx (i.e., NO plus NO2) is severely limited by the backreaction of NO2 to NO, which is also driven by the highly reactive radical species in the plasma. By injecting water aerosol into the gas matrix, we are able to selectively drive a plasma-based reaction which minimizes the backreaction of NO2 to NO. Here, the synergistic effect of the water aerosol and plasma discharge enables enhanced NOx removal by creating OH radicals which, in turn, drive NO2 to HNO3, which is highly soluble in water. In the presence of water aerosol, the plasma discharge results in a 100% reduction in NO and a 98% reduction in total NOx. Spectroscopic evidence of the short-lived, highly reactive OH radical is obtained through plasma emission spectroscopy and the vibrational signatures of the NO2− and NO3− intermediates are observed using SERS-enhanced Raman spectroscopy. We show that the NOx remediation increases with plasma power density demonstrating the scalability of this general approach.

Biogas combustion with various oxidizers in a nanosecond DBD microplasma burner

This study concerns the effect of non-thermal plasma discharges on simulated biogas (mixture of CH4 with 80–20 vol% CO2) combustion at atmospheric pressure in synthetic air or synthetic air enriched by oxygen. The plasma-assisted, premixed combustion was performed in a porous-plate burner with dielectric barrier discharge microplasmas driven by nanosecond high-voltage pulses at 3 kHz and 10 kHz repetition rates in the burner holes. The characteristics of the plasma-assisted flames and the role of reactive oxygen species in the plasma-assisted combustion process supplying various oxidizers were determined using a spatial flame chemiluminescence scanning technique acquiring OH*, C2* and CH* emission intensities. From the obtained results, the pathways of combustion enhancement by the plasma were established.During plasma-assisted combustion, the biogas flame stability has improved. The highest plasma impact on the flame stability was observed for the biogas mixture (CH4-60%/CO2-40%). The flame lift-off for a stoichiometric mixture was reduced by 54% with the discharge at 10 kHz repetition rate, but a decrease of fuel–air ratio φ resulted in reduced effect of plasma and the lift-off was reduced only by 38–10% with 10 kHz discharge and by 22–7% with 3 kHz discharge. The experiments with oxygen-enriched synthetic air showed that the oxygen addition increases the flammability limit of biogas mixtures (CH4 with 50–20 vol% in CO2), and allowed to burn mixtures which were not able to combust under normal conditions. However, the plasma-assisted combustion with oxygen enrichment showed a lower effect on the combustion enhancement than without. During experiments of plasma-assisted combustion, the plasma impact on NOX emissions was also determined, showing that NOX concentrations increased with increasing plasma power.

A microplasma process for hexagonal boron nitride thin film synthesis

A process based on microplasmas generated in Ar/N2 mixtures for nanomaterial synthesis is described in this Letter. The targeted material is hexagonal boron nitride (h-BN) that is in high demand for electronic and optoelectronic applications. The synthesis of high crystalline quality h-BN films over large areas still remains a challenge. In this study, a nanosecond pulsed high voltage is applied between two electrodes separated by a dielectric layer, with the whole system being drilled by a 400 μm diameter hole (micro hollow cathode structure). This geometry allows for an efficient dissociation of N2 gas, a particularly important asset for the synthesis of nitride materials, which normally requires very high deposition temperatures (∼1300 °C). In this work, we report the growth of h-BN on 2-in. silicon substrates at temperatures below 1000 °C, with a growth rate of about 30 nm/h, using this approach. The deposited films are characterized by Raman and electron energy loss spectroscopies and transmission electron microscopy to evaluate the phase purity, the quality, the surface morphology, and the crystallinity of the material. The films exhibit a stoichiometry very close to 1 with a crystalline domain size of about 3 nm.

Nanoparticle-Enhanced Plasma Discharge Using Nanosecond High-Voltage Pulses

By discharging nanosecond high voltage (5kV) pulses across an insulating substrate containing Au, Pt, or Cu nanoparticles, a three order of magnitude (1000X) enhancement in the generation of plasma...

Decomposition process of volatile organic compounds dissolved into water by pulsed discharge inside bubble

Decomposition process of volatile organic compound dissolved into water by discharge plasma inside bubble is investigated. The experiment is conducted on decomposition of dichloromethane (DCM). Argon or oxygen gas is injected into the water through a vertically positioned glass tube, in which high-voltage wire electrode is placed to generate plasmas at low applied voltage. The nanosecond pulsed high voltage generated by an inductive energy storage system pulsed power generator is applied to the tungsten wire to generate streamer discharge. Total organic carbon decreases and chloride ion concentration increases by the discharge treatment. To clarify the decomposition process, DCM and indigo carmine (IC) mixed solution is employed as specimen. The amount of IC decomposition decreases with increasing the DCM concentration. On the other hands, the amount of DCM decomposition is almost independent of IC concentration. These results show that DCM is quickly volatilized into the bubble, which is decomposed by hydroxyl radical produced by the discharge in gas phase inside bubble.

On the low-temperature plasma discharge in methane/air diffusion flames

Interest in methane has grown recently because of its encouraging characteristics. However, methane comes with serious concerns regarding stability and flammability limitations. Some methods have been proposed to improve the ignition characteristics of methane in diffusion flame burners such as electrical fields, dielectric barrier discharge, and low-temperature plasma. In this study, an innovative single-element coaxial shear injector coupled with a high-voltage nanosecond pulse generator has been used to study the effects of low-temperature plasma (LTP) discharge on methane/air inverse diffusion flame at different plasma and flow conditions. The stability analysis focuses on the detachment conditions of the flame and how RNP discharge can delay this phenomenon, explaining the presence of an optimal operating point with the least applied energy. Comparing the lean blow-off limits for the cases with and without plasma discharge, it is shown that low-temperature plasma discharge enhances the flammability of the diffusion flame. The effect of LTP discharge on laminar flames is also discussed using chemiluminescence photography. It shows that the shape of the diffusion flame becomes more similar to premixed flame with more air entrainment and stability. Resultantly, it is shown that RNP discharge can improve the flame stability and ignition characteristics.

Tar Removal by Nanosecond Pulsed Dielectric Barrier Discharge

Plasma-catalytic reforming of simulated biomass tar composed of naphthalene, toluene, and benzene was carried out in a coaxial plasma reactor supplied with nanosecond high-voltage pulses. The effect of Rh-LaCoO3/Al2O3 and Ni/Al2O3 catalysts covering high-voltage electrode on the tar conversion efficiency was evaluated. Compared to the plasma reaction without a catalyst, the combination of plasma with the catalyst significantly enhanced the conversion of all three tar components, achieving complete conversion when an Rh-based catalyst was used. Apart from gaseous and liquid samples, char samples taken at five locations inside the reactor were also analyzed for their chemical composition. Char was not formed when the Rh-based catalyst was used. Different by-products were detected for the plasma reactor without a catalyst, with the Ni- and Rh-based catalysts. A possible reaction pathway in the plasma-catalytic process for naphthalene, as the most complex compound, was proposed through the combined analysis of liquid and solid products.

Synthesis of isolated carbon nanowalls via high-voltage nanosecond pulses in conjunction with CH4/H2 plasma enhanced chemical vapor deposition

Carbon nanowalls (CNWs) are vertically standing, interconnecting flake- or wall-like collections of graphene sheets. In the present work, this material was synthesized by applying precisely controlled high-voltage nanosecond pulses to a substrate using an inductor energy storage circuit in a radical-injection plasma-enhanced chemical vapor deposition system, employing a CH4/H2 plasma. The resulting interconnected networks had a low density of CNWs with large average wall-to-wall distances. During the application of short-period pulses, the entire substrate surface was uniformly activated, thus enhancing the adsorption of carbon precursors and preventing CNW nucleation. As a result, an amorphous carbon film covered the surface of the substrate and a low CNW density was obtained with average wall-to-wall distances greater than 700 nm. On the basis of these results, the growth mechanism of CNWs was modeled.

Self-Triggering High-Frequency Nanosecond Pulse Generator

With the increasingly extensive and in-depth applications of all solid-state high-voltage nanosecond pulse generators in the defense and industrial fields, the development of traditional pulse generators faces many key issues, such as high-voltage drive isolation, compact design, and reduced weight. Hence, a novel circuit topology for a self-triggered high-frequency nanosecond pulse generator is proposed. Through high potential energy-gaining technology of the interstage capacitance, this generator does not need a complicated metal–oxide–semiconductor field-effect transistor isolation drive circuit, and there are also no switching dynamic and static voltage equalization problems. This kind of generator is very suitable for compact assembly with only a single external gate driver. High voltage output can be realized by quantizing multilevel module stacking according to actual needs. At the same time, the generator has a high repetition rate and long life. The characteristic parameters of the 20-stage superposition experimental prototype are as follows: an output voltage amplitude of 15.3 kV with a rising time of approximately 45 ns, a repetition rate of 10 kHz in the pulse train, and a pulsewidth of 200–1000 ns.

Temperature-dependent behavior of nitrogen fixation in nanopulsed dielectric barrier discharge operated at different humidity levels and oxygen contents

This study thoroughly analyzed the gas-temperature dependence of nitrogen fixation in a dielectric barrier discharge powered by a nanosecond pulsed high voltage. The correlation between temperature (in the range of 300–600 K) and the humidity effects (H2O = 0.1% vol.–12.5% vol.) was systematically investigated at different oxygen contents (O2 = 5% vol.–40% vol.) in nitrogen. The nitrogen-content products were accurately evaluated by measuring them in the gas phase and that trapped in water, using Fourier transform infrared spectroscopy and ion chromatography, respectively. An examination of the current–voltage characteristics and optical emission spectroscopy indicated that temperature (within the tested range) had minor effects on the discharge characteristics, where the excitation processes slightly decreased while the dissociation and the ionization increased marginally. This eventually led to a constant amount of fixed nitrogen with temperature at a given gas mixture. However, a higher oxygen content promoted nitrogen fixation by increasing and accelerating the oxidation of fixed nitrogen to higher oxidation states. On the other hand, the temperature significantly affected the selectivity of the nitrogen-content products owing to its effect on the reaction rates of their formation and its significant influence on ozone decomposition. Operating the dielectric barrier discharge (DBD) at low temperatures favored the production of high-oxidation states of nitrogen that led to the formation of nitrate with free nitrite in water, which would be useful for agriculture. The results also indicated that operating the DBD at high temperatures is useful for obtaining high selectivity of NO, which can be useful for biological applications.

A High Voltage Diode-Transistor Generator of Nanosecond High Voltage Pulses

A small generator of high-power high voltage nanosecond pulses with a 12 V power source is considered. At a load of 75 Ω, it provides the generation of pulses with an amplitude of ~17 kV, a front of ~4 ns, and an energy of ~15 mJ. The maximum pulse repetition rate is 15 kHz. The generator contains an inductive energy storage device and a capacitive storage device with an operating voltage of 1 kV. The formation of high voltage pulses is carried out by a high voltage current chopper in the form of a block of drift diodes with a sharp recovery. The conditions for the effective operation of the diodes are provided by a block of parallel-connected IGBT transistors with an operating voltage of 1.2 kV. The possibility of using a generator for multispark ignition of the spark plug of an internal combustion engine is shown.

Boosting the Energy Efficiency of a Nanosecond Pulsed Corona Plasma System With a Multiple-Wire Plasma Reactor

Transient plasma generated by high-voltage nanosecond pulses in a pulsed corona configuration has proven to be an efficient medium for e.g., air purification applications. In this article, we present a study on boosting the energy efficiency of such a system by using a special type of plasma reactor: the multiple-wire plasma reactor. The basic principle of such a reactor is that it has a lower transmission-line impedance than a normal wire-cylinder reactor while at the same time still producing the required high electric fields necessary for plasma generation. The lower impedance of the reactor results in a smaller impedance mismatch between the high-voltage pulse source and the reactor, thereby minimizing pulse reflections on the source-reactor interface, increasing the energy efficiency of the system. We calculate the impedance of the multiple-wire reactor and assess both the electrical energy efficiency as well as the chemical efficiency of the plasma by measuring electrical energies and ozone concentrations generated by the plasma when energized by a fast solid-state nanosecond pulse source (with 7-ns rise time pulses of up to 20kV) for a range of multiple-wire plasma reactor parameters. We show that with the multiple-wire reactor we can almost double the energy efficiency of the reactor (from 45% to 85%), reduce the voltage stress in the system by 29%–31% and increase the system efficiency by 95%–98% when using a multiple-wire electrode geometry (as compared to a single-wire system).

A Compact Series-Connected SiC MOSFETs Module and Its Application in High Voltage Nanosecond Pulse Generator

Nanosecond pulse discharge plasma has many prospects in industrial applications, and high-voltage repetitive nanosecond pulse generators with compact design and light weight have become one of the key issues limiting its development in some applications. This paper presents a high voltage series-connected silicon carbide (SiC) metal-oxide -semiconductor field effect transistor ( MOSFET s) module which can be served as the main switch in a repetitive high-voltage nanosecond pulse generator. This kind of series-connected MOSFET s module with only single external gate driver requiring very few components is very suitable for compact assembly. By analyzing the working principle, three topologies of series-connected MOSFET s module are proposed. The switching behaviors of the three different topologies with four SiC MOSFET s series-connected are compared experimentally. The variation of switching characteristics of series-connection SiC MOSFET s module with different numbers of devices are investigated. The layout is also optimized to shorten pulse front time and improve output pulse quality. Furthermore, a 10 kV SiC MOSFET s module with a turn- on transition time ∼10 ns is developed. The double pulse test result demonstrates excellent switching performances. Finally, a compact and high-voltage pulse generator composed of three 10 kV SiC MOSFET s module is tailored, with a typical rise time ∼40 ns and peak voltage of ∼30 kV.

Semiconductor generator of high voltage nanosecond pulses for plasma technologies

A generator of nanosecond pulses is discussed in the paper. The main output parameters of the generator are as follows: the maximum output voltage amplitude is 20 kV, the output current strength is 300 A, the maximum frequency is 3 kHz, the output pulse rise time is 4 ns, the output pulse energy is 25 mJ. The generator is based on a current interrupter, which is an assembly of drift step recovery diodes (DSRD). Effective operation of the DSRD is provided by assemblies of IGBT-transistors connected in series, the operating voltage of each assembly is 4 kV. It is shown that the generator can be effectively used for purification of air from organic pollutants and for ignition of car spark-plugs.

Investigation of the Electrode Erosion in Pin-to-Liquid Discharges and Its Influence on Reactive Oxygen and Nitrogen Species in Plasma-Activated Water

Although the erosion of high-voltage electrodes was extensively studied in in-liquid electrical discharges, to the best of our knowledge, the erosion produced by discharges generated above water has been barely explored. This work studies the erosion of three pin electrode materials (hafnium, copper, stainless steel) in two gas atmospheres (oxygen, air). They are powered by repetitive high-voltage nanosecond pulses, producing pulsed streamer discharges above water. The electrode material does not affect the energy deposited per pulse. The surfaces of all three electrodes erode, releasing metal particles into the water. Stainless steel is the material with least erosion, in both gas atmospheres. Overall, copper in air shows the highest erosion. We also examine how the metals released into the water affect three long-lived reactive oxygen and nitrogen species (RONS), H2O2, NO2− and NO3−, during four weeks post-discharge. After treatment with air plasma, NO2− and NO3− are measured in the treated water, but H2O2 is not detected. NO2− is almost completely converted into NO3− after two weeks. H2O2 is measured for samples prepared with an oxygen plasma. Neither the RONS nor the conductivity of plasma-treated water are significantly affected by the use of different electrode materials.

Comparison of Electrical Breakdowns Produced by a Nanosecond High-Voltage Pulse Applied to Metallic and Composite Material Electrodes

In this article, the effect of electrode material on the electrical breakdown, produced by a 500-ns duration high-voltage pulse in dry air at atmospheric pressure, is investigated. The configuration chosen is a pin-to-plane geometry with a gap distance of 2 mm. Both polarities of the high-voltage pulse have been investigated for three different pin electrodes. The reference pin is a copper wire of 50 mm length, while the two other pins are made of a highly resistive composite material of 240 Ω/m, with two different lengths of 50 and 500 mm. The plane electrode is a tungsten plate of 3 cm diameter. The discharges obtained for the highly resistive wires (HRWs) can be categorized as resistive barrier discharges. Both electrical and optical characteristics of the discharges are presented and discussed. The current, voltage, and energy deposition are first analyzed. Then, the time-resolved phase-locked images of the discharges are presented, showing the propagation of the discharge filaments in the gap. The experimental results demonstrate a strong influence of the electrode material on the discharge characteristics, regardless of the polarity of the applied voltage. The main finding is that, for the same applied high-voltage pulse, the use of highly resistive materials significantly reduces the energy deposition into the discharge and the light emission from the discharge.

The dynamics of discharge propagation and x-ray generation in nanosecond pulsed fast ionisation wave in 5 mbar nitrogen

In this work, the propagation of fast ionisation wave (FIW) discharges driven by negative nanosecond high-voltage (HV) pulses and the x-ray spectrum from the FIW discharges are investigated. The measurement using a capacitive probe shows that the peak axial electric field () at each position rises with the increase of the applied voltage amplitude (Umax), resulting in an increase of the FIW velocity (VFIW). The influence of the pre-ionisation on the FIW propagation is estimated from the relationship between VFIW and The pre-ionisation effect appears to be enhanced with the increase of Umax and it is suspected to be due to the presence of more high energy electrons. This is supported by the measured x-ray spectrum, showing a higher count rate and a more elevated high energy tail with a larger Umax. The spatially resolved measurement of the x-ray spectrum shows that, with the increase of the distance away from the HV electrode (as the cathode), the lower energy part (< ∼15 keV) of the x-ray spectrum keeps decaying, while its high energy tail (> ∼25 keV) rises at first and then decays. Based on the spatially resolved x-ray spectrum, it is inferred that, as high energy electrons move away from the HV electrode, the peak of their energy distribution is shifted toward a higher value, while their total number decreases. Further analysis implies that the electrons emitted from the cathode obtain a large percent of the applied potential in the vicinity of the cathode and become runaway electrons. The electrons with a high initial energy travel freely in the discharge region, due to a decreasing electron collisional cross section with its energy.

An overvoltage driver with inductive adder pulse for fast switching of series-connected MOSFETs module

A novel overvoltage driver is proposed to speed up the turn-on transition of series-connected MOSFETs module which serves as the main switch in high voltage pulse generator. In order to realize the overvoltage driver, a nanosecond pulse with the amplitude of hundreds of volts is superposed on a square driving signal by linear transformer driver scheme. The results show that, comparing to the commercial high current driver, the turn-on time of a 10kV MOSFETs module including ten devices with the proposed driving scheme can be shortened from ∼25ns to ∼7ns. The proposed overvoltage driver can be used to conveniently modulate the rise time and pulse width of high voltage nanosecond pulse generator constructed by MOSFETs. In addition, it is demonstrated that there is almost no influence of the overvoltage driver on the gate-source characteristics of device by analyzing the variation of C-f curves of input capacitances.