High-voltage Nanosecond Pulses Research Articles

High voltage nanosecond pulse generator based on diode opening switch and magnetic switch.

Low-temperature plasma technology is widely used in various industrial fields, which require the plasma to be of large volume, diffuse, and stable. Furthermore, previous studies have shown that better plasma performance has been obtained by using generators with a high voltage, a high repetition rate, a fast rise time, and a short pulse duration. In this paper, a novel topology is proposed for such generators, which is based on magnetic switches and diode opening switches. A prototype is developed, and its output characteristics are investigated by varying essential parameters, such as the load resistance and the power supply voltage. The experimental results show that it can generate pulses with a voltage of 30.6 kV, a rise time of 7.1ns, a pulse duration of 8.2ns, and a maximum repetition rate of 12 kHz on a 300 Ω resistive load. The prototype has been successfully used to drive uniform plasma in ambient air. In the proposed topology, a diode is added to make the magnetic cores independent of each other, significantly simplifying the design calculation. It may help develop nanosecond solid-state generators.

Comparison of Nano-second and Millisecond Pulse Generators for Biological applications of Electroporation

A phenomenon that transiently increases the permeability of the cells is known as electroporation. It is the basis for number of the applications in biomedical domains. It is essential to consider requirement of high precision and the overall size of electroporator. The recent decades have seen the development of solid-state power electronic modules. The modules enable generation of high voltage millisecond and nano-second pulses with options to reduce the overall size of the equipment. The selective modules are verified with experimental models and available for commercial usage. While the other modules are still undergoing optimization processes. The generator generates pulses for varying performances. Hence, this paper presents knowledge for different nanosecond and millisecond pulse generating circuits for electroporation purposes. The performance parameters like the width of the pulse, its amplitude are compared for different circuit topologies. The performance analysis of different topologies and their impact on the performance of the electroporation at the cell biology level are considered in this paper.

Highly-energy efficient oxidation of MWCNT with nanosecond pulsed dielectric barrier discharge plasma

Carbon nanotubes constitute a unique class of materials with intriguing properties related to their structure. In most cases, their effective use requires a change in their surface chemistry. The most common functionalization is oxidation, introducing oxygen-based groups onto the outer tube walls. As reported herein, such functionalization can be achieved conveniently by means of cold plasma (CP) discharge driven by high voltage nanosecond pulses (NSP), which offers a rapid, controllable, non-wet and less destructive process compared to the chemical treatment method (e.g. with nitric acid). It is notable that compared to other plasma discharge types (e.g. AC-driven), the energy efficiency of the NSP is seriously increased showing the potential for industrial grade processing. MWCNT were treated under various CP operational parameters and thoroughly characterized in terms of surface elemental composition, morphological and physicochemical properties. Despite the validation of the successful modification, a correlation is made between the CP treatment time and pulse voltage with the final degree and type of functionalization, as well as the overall properties of the materials. The combinatorial interpretation of the obtained characterization data allowed a deeper understanding of the functionalization mechanism and showed the possibility to control the amount and type of functionality to suit the application.

Highly energy-efficient degradation of antibiotics in soil: Extensive cold plasma discharges generation in soil pores driven by high voltage nanopulses

Cold atmospheric plasma (CAP) is a green and promising soil remediation approach with significant advantages in terms of energy consumption, removal efficiency and treatment time. The most critical factor for exploiting CAP is the accomplishment of very low remediation cost, while in parallel, the limited penetration of plasma species at soil layers holds back its wider implementation. In this study, we developed a novel dielectric barrier discharge plasma reactor driven by high voltage nanosecond pulses (NSP) able to generate micro-discharges within the interconnected soil pores facilitating the effective transport of reactive species within soil layers. Key-role parameters were investigated such as pulse voltage and pulse frequency, soil thickness and air flow rate. The effectiveness of the method was identified against different types of soil (sandy soil and loam soil), both under high and low ciprofloxacin concentration in soil, while soil moisture impact on degradation efficiency was also explored. An energy efficiency of 21.2 mg of pollutant/kJ was accomplished, which is the highest ever reported for CAP-based soil remediation. The most stable intermediate degradants of ciprofloxacin, and the associated degradation pathways were identified in a kinetic point of view, while the elimination of the toxic intermediates after treatment was ensured. The present effort provides a new highly energy efficient perspective for future development of a CAP-based soil remediation technology as it maximizes the transfer and penetration of plasma species in soil layers under very low estimated remediation cost (~0.4-1.2 €/tn of soil).

Strategies of Power Measurement and Energy Coupling Enhancement in Nanosecond Pulsed Coaxial Dielectric Barrier Discharges

Dielectric barrier discharges (DBDs) driven by nanosecond high-voltage pulses can be quite different from those driven by alternating current (ac) sources, on both electrical characteristics and plasma microparameters. In this article, the power measurement strategy in nanosecond pulsed coaxial DBDs is optimized. The effect of different experimental parameters on energy deposition and reduced electric field in plasma is investigated. First, the results measured using the instantaneous power (from the production of voltage and current) method and that using the v- q trace (Lissajous curve) method are compared and the source of divergence is analyzed. By comparing monitor capacitors with different materials and capacitances, it is demonstrated that the high-frequency response of the monitor capacitor is essential and the capacitance value can be adjusted according to the applied voltage, taking both the dynamic range of oscilloscope and the signal-to-noise ratio into consideration. Second, the influence of morphology of ground electrode, voltage rising time, and pulse width on energy deposition per-pulse and reduced electric field, obtained from the nitrogen spectral line-ratio, is studied. It is found that the copper foil promotes the discharge energy coupling per-pulse compared with the copper grid, while the reduced electric field obtained from the nitrogen line-ratio with the copper foil is weaker. A shorter rising time will also enhance the energy coupling per-pulse, as well as the reduced electric field.

Enhanced Plasma Generation from Metal Nanostructures via Photoexcited Hot Electrons

We report hot electron-enhanced plasma generation by irradiating metal nanostructures with laser light. Here, a high-voltage nanosecond pulse is discharged across two electrodes interspersed with m...

Novel combination of high voltage nanopulses and in-soil generated plasma micro-discharges applied for the highly efficient degradation of trifluralin

Cold plasma is considered a highly competitive advanced oxidation process for the removal of organic pollutants from soil. Herein, we describe for the first time the combination of in-soil generated plasma micro-discharges with the advantageous high voltage nanosecond pulses (NSP) towards the high-efficient degradation of trifluralin in soil. We performed a detailed parametric analysis (pulse frequency, pulse voltage, soil thickness, soil type, energy efficiency) to determine the optimum operational conditions. High trifluralin degradation was achieved even at the higher soil thickness, indicating that the production of plasma discharges directly inside the soil pores enhanced the mass transfer of plasma reactive oxygen and nitrogen species (RONS) in soil. The energy efficiency achieved was outstanding, being up to 2–3 orders of magnitude higher than those reported for other plasma systems. We identified the intermediate degradants and proposed the most dominant degradation pathways whereas a thorough exhaust gases analysis, optical emission spectroscopy (OES) and active species inhibition by using trapping agents revealed the main RONS involved. This effort constitutes a significant advancement in the "green" credentials and application of plasma-induced degradation of pollutants as it describes for the first time the removal of the highly harmful and toxic pesticide trifluralin from soil and provides a novel perspective towards the future development of cold plasma-based soil remediation technologies.

Demonstration of Dynamics of Nanosecond Discharge in Liquid Water Using Four-Channel Time-Resolved ICCD Microscopy

The microscopic physical mechanisms of micro-discharges produced in liquid waters by nanosecond high-voltage pulses are quite complex phenomena, and relevant coherent experimentally supported theoretical descriptions are yet to be provided. In this study, by combining a long-distance microscope with a four-channel image splitter fitted with four synchronised intensified charge-coupled device detectors, we obtained and analysed sequences of microscopic discharge images acquired with sub-nanosecond temporal resolution during a single event. We tracked luminous filaments either through monochromatic images at two specific wavelengths (532 and 656 nm) or through broadband integrated UV–vis–near infrared (NIR) discharge emission. An analysis of the sequences of images capturing discharge filaments in subsequent time windows facilitated the tracking of movement of the luminous fronts during their expansion. The velocity of expansion progressively decreased from the maximum of ~2.3 × 105 m/s observed close to the anode pin until the propagation stopped due to the drop in the anode potential. We demonstrate the basic features characterising the development of the luminous discharge filaments. Our study provides an important insight into the dynamics of micro-discharges during the primary and successive reflected high-voltage pulses in de-ionised water.

Electron generation and multiplication at the initial stage of nanosecond breakdown in water

Electrical breakdown of liquid dielectrics under nanosecond pulsed high voltage has been investigated extensively in the last decade. Prior studies have focused on either experimental characterization of the breakdown process and discharge plasma or formulation/verification of the electrostrictive cavitation mechanism of the breakdown initiation. There remain knowledge gaps toward a clear physical picture of how the first plasma is generated in a region saturated by nanoscale cavities created by electrostrictive forces in inhomogeneous fields at the nanosecond timescale. Initial plasma results from the multiplication of primary electrons that gain energy collisionlessly in the cavities to cause collisional ionization of water molecules on the cavity walls. This paper quantitatively discusses the possible sources of primary electrons that seed the plasma discharge. Electron detachment from hydroxide is shown to be the most probable and sustainable electron source. Using numerical modeling, this study demonstrates the plausibility of an electron multiplication mechanism involving two neighboring cavities. The drift of hydrated electrons from one cavity to the next is the rate-limiting step and sets the minimum electric field requirement. This work will inform subsequent experimental studies and have implications in various applications such as plasma sources in biomedical applications, cavitation study, and insulation of pulsed power equipment.

An Investigation Into High-Voltage Spiral Generators Utilizing Thyristor Input Switches

High-voltage nanosecond pulses are widely used in scientific research, but their wider adoption in industry requires compact, cost-effective, and easy to use generators to be developed. This article presents the modeling and experimental investigations into one method of producing such pulses-a spiral generator with a solid-state-thyristor-based input switch. It includes how the pulses are formed within the spiral, why a high-speed input switch is required, and how the geometry of the spiral dictates its output characteristics and the effects of different loads. Using thyristors, often connected in series to increase the operating voltage of the spiral, enables the spiral generators to have low jitter, high repetition rate, and long lifetime. Modeling of the circuit used a combination of telegraph equations to account for the wave propagation along the spiral and a lumped circuit exchanging charge between the spiral and the input switch and load. The model is verified by the detailed experimental results with the relative error being <; 10% in most cases. The output voltage pulse was often observed to have an initial peak of much lower magnitude than the subsequent peak(s)-which can only be fully explained by considering wave propagation effects. Lower input switch inductance, shorter switching time, larger mean diameter of the spiral, and increasing the width of the copper tape that makes up the spiral can all increase the voltage multiplication efficiency. Although increasing the number of turns that makes up the spiral can increase the output voltage, it can also lower the multiplication efficiency. By understanding the effects of different geometries, the spiral can be optimized to drive different loads-three applications of such spiral generators are then presented-pulses with 10 kV amplitude and 10 kHz repetition rate for driving dielectric barrier discharge plasma, pulses with amplitude of 10 kV and 10 kV/ns rising rate for triggering of advanced solid-state switches, and pulses with -50 kV amplitude and 50 ns rising time for triggering high-current gas switches through field distortion.

High voltage nanosecond pulse generator based on avalanche transistor Marx bank circuit and linear transformer driver.

Avalanche transistor Marx bank circuits (MBCs) are widely used in high voltage repetitive nanosecond pulse generators, but problems exist with respect to increasing the output voltage due to the limited pulsed current. Accordingly, a novel topology based on an avalanche transistor MBC combined with a linear transformer driver is proposed, the latter of which exhibits advantageous stress distribution and modular structure. A four-module prototype with four units in each module is developed in the laboratory. The output characteristics are investigated by varying important parameters such as the main capacitance, the number of conducting units, the number of cascaded modules, and the trigger signal time delay. The test results verify the validity of the proposed topology. For a 50 Ω resistive load, the prototype can generate pulses with an amplitude of 10.9 kV, a rise time of 3.3ns, and a voltage superposition efficiency of 89%. The topology proposed in this paper may help to provide a method to further improve the output performance of avalanche transistor MBCs.

Effects of pulse rise time and repetition frequency on nanosecond pulsed plasma ignition for combustion

Transient plasma ignition (TPI) employs highly non-equilibrium plasmas driven by nanosecond high-voltage pulses for combustion ignition. The effects of rise time and pulse repetition frequency (PRF) on combustion ignition are evaluated when transient plasmas, powered by 10-ns, kilovolt pulses, are employed to initiate combustion of lean, stoichiometric, or rich methane-dry air mixtures at atmospheric pressure. It was found that the plasmas driven by high voltage pulses with a faster rise time and PRF between 6–10 kHz enhanced combustion with higher peak pressure and/or shorter ignition delay. A mode transition in the plasma, corresponding to the combustion initiation, was observed based on voltage and current waveforms of four consecutive pulsed plasmas driven by a pulse burst at kilohertz PRFs. Although benefits in combustion ignition from a shorter rise time and optimal PRF were observed for all three equivalence mixture ratios, the highest peak pressure and shortest ignition delay were associated with the stoichiometric mixtures. In addition, the gas temperature of the transient plasma was measured by determining the rotational temperature of the 2nd positive system of nitrogen to be ∼1000 K for the first pulse and increased up to 2000 K after the application of the 4th pulse in a four-pulse burst TPI.

Development of a High Peak Voltage Picoseconds Avalanche Transistor Based Marx Bank Circuit

Avalanche transistor-based Marx bank circuit (MBC) is widely used to generate high voltage nanosecond pulses with high amplitude, high repetition rate, fast rise time, and low jitter. Researchers have tried to modify the circuit structure by using parallel or series avalanche transistors to increase peak power. However, in this work, the detailed process of analyzing and designing a compact Marx generator using avalanche transistors will be described. The purpose of this article is to report our experimental observations on the mechanism of operation of the MBCs. By studying the influence of amplitude and pulse width of the trigger circuit, a Gaussian pulse with a rising edge of 160 ps, full width at half maximum (FWHM) of 660 ps, and amplitude of 5000 V are obtained. The design improves the output voltage and pulse repetition frequency (PRF) effectively while reducing the use of the number of transistors. Based on the conventional principles of avalanche transistors and Marx circuit, a list of useful and interesting conclusions obtained from experiments will be reported.

Electric field measurements in a He:N2 nanosecond pulsed discharge with sub-ns time resolution

The electric field in the He:N2 nanosecond atmospheric pressure plasma jet is studied using the electric-field induced second harmonic generation technique. It is shown that the calibration obtained with a DC voltage applied to the discharge cell may lead to incorrect results in the electric field measurements. It is proposed to use nanosecond high voltage pulses at low repetition rates for the calibration instead of a DC voltage. The temporal development of the electric field in the discharge at different distances from the cathode is measured with high temporal (100 ps) and spatial (50 µm) resolution. An electric field profile structure similar to the one in streamers or ionization fronts is observed. The velocity of the propagation of the falling edge of the ionization front is determined to be 0.85 × 106 m s−1. The validity of the local field approximation, important for modeling of these kind of discharges, is confirmed for the present conditions based on time and space derivatives of the measured electric field. The temporal evolution of the electron density is obtained by the measured electrical current and the time resolved electric field measurement combined with the electron mobility calculated with BOLSIG+.

A MOSFET-based high voltage nanosecond pulse module for the gating of proximity-focused microchannel plate image-intensifier

Gate modules based on avalanche technology for photocathode gating to proximity-focused microchannel-plate image intensifier (MCPII) are often limited to short gate exposures. A nanosecond pulse module based on MOSFET devices has been demonstrated at our lab, which is capable of generating pulses of adjustable full width at half maximum (FWHM) from 3 ns to D.C. operation with 1 ns switching time and a burst repetition rate up to 4 MHz. A method of supplying gate-current pulses to the MOSFET device is adopted to increase the switching speed based on the totem pole driver. Nanosecond optical gating time of an 18-mm proximity-focused MCPII with a metallic underlay photocathode was obtained. A MCPII with standard multi-alkali photocathode was analyzed for comparison. Moreover, a photocathode-MCP model based on the Finite Integral Technique (FIT) is developed to investigate the dependence of the gating time on the sheet resistance of the photocathode.

Influence of dielectric coatings on pin-to-rod nanosecond-pulsed discharges in phosphate-buffered saline.

Plasma medicine is a rapidly expanding field that utilizes non-equilibrium plasma discharges at atmospheric conditions or in liquids for clinical applications. There is significant interest in the production of plasma in the liquid phase for wastewater treatment, agricultural applications, and medical purposes. However, little investigation has been done about the effects of dielectric coatings on submerged electrodes, which is of significant interest to limit electrical current flow in the liquid. This work investigates the effect of different dielectric coatings including aluminum oxide, parylene C, and bi-layer combinations, on plasma discharge characteristics in phosphate-buffered saline (σ = 18 mS/cm) from nanosecond high-voltage pulses. Observed results for aluminum oxide are consistent with past works, including micron-sized clusters of holes generated in the layer due to dielectric breakdown. A bi-layer combination of parylene C on top of aluminum oxide resulted in longer lifetime for electrodes, possibly due to the melting/solidification behavior of the polymer, which may have a "healing" effect. The use of a thick parylene C layer resulted in a different, "creeping", discharge regime, which is hypothesized to be similar to triple-gap discharge observed in space plasma physics and high-voltage insulators, in which the electric field is enhanced at the boundary of a conductor, dielectric, and a vacuum/fluid, resulting in discharge at this junction point. Temporally-resolved and high-spatial-resolution imaging are required for verification.

Charge and exciton dynamics of OLEDs under high voltage nanosecond pulse: towards injection lasing

Electrical pumping of organic semiconductor devices involves charge injection, transport, device on/off dynamics, exciton formation and annihilation processes. A comprehensive model analysing those entwined processes together is most helpful in determining the dominating loss pathways. In this paper, we report experimental and theoretical results of Super Yellow (Poly(p-phenylene vinylene) co-polymer) organic light emitting diodes operating at high current density under high voltage nanosecond pulses. We demonstrate complete exciton and charge carrier dynamics of devices, starting from charge injection to light emission, in a time scale spanning from the sub-ns to microsecond region, and compare results with optical pumping. The experimental data is accurately replicated by simulation, which provides a robust test platform for any organic materials. The universality of our model is successfully demonstrated by its application to three other laser active materials. The findings provide a tool to narrow the search for material and device designs for injection lasing.

Enhanced electrospinning: Multi-level fiber alignment by control of electrohydrodynamic jet motion for tissue engineering

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 peculiarity of the proposed technical solution is the ability to control polymer jet localization in the interelectrode space with the possibility of stabilization and retention of the jet at an arbitrary point. 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 2–4° degrees of disorientation were obtained. The study of thermal and mechanical behavior of oriented materials based on polyamide was carried out, and macromolecular orientation was established by X-ray diffraction in small and wide angles. The possibility to create material by stacking multiple layers with given fiber orientation at 65° and 90° and polymer spinning on various dielectric materials by means of the reverse polarity operating principle is demonstrated. The ability to control fiber alignment in electrospinning will expand the possibilities of high-performance production of polymeric nonwoven materials with a given architecture and unique physicochemical characteristics required for solving a whole range of medical and technological challenges of a different profile.

Fully ionized nanosecond discharges in air: the thermal spark

The formation and decay of the thermal spark generated by a single nanosecond high-voltage pulse between pin electrodes are characterized in this study. The influence of air pressure in the range 50–1000 mbar is investigated at 300 K. By performing short-gate imaging and optical emission spectroscopy (OES), we find that the thermal sparks exhibit an intense emission from excited electronic states of N+, in contrast with non-thermal sparks for which the emission is dominated by electronic transitions of N2. Spark thermalization consists of the following steps: (i) partial ionization of the plasma channel accompanied by N2 emission, (ii) creation of a fully ionized filament at the cathode characterized by N+ emission, (iii) formation of a fully ionized filament at the anode, (iv) propagation of these filaments toward the middle of the interelectrode gap, and (v) merging of the filaments. The formation of the filaments, steps (ii) and (iii), occurs at sub-nanosecond timescales. The propagation speed of the filaments is on the order of 104 m s−1 during step (iv). For the 1 bar condition, the electron number densities are measured from the Stark broadening of N+ and Hα lines, with spatial and temporal resolution. The electron temperature is also determined, from the relative emission intensity of N+ excited states, attaining a peak value of 48 000 K. In the post-discharge, the electron number density decays from 4 × 1019 to 2 × 1018 cm−3 in 100 ns. We show that this decay curve can be interpreted as the isentropic expansion of a plasma in chemical equilibrium. Comparisons with previous experiments from the literature support this conclusion. Expressions for the Van der Waals and resonant broadenings of Hα, Hβ, and several lines of O, O+, N and, N+ are derived in the appendix.

A Polarity-Adjustable Nanosecond Pulse Generator Suitable for High Impedance Load

This article presents a new method for forming nanosecond short pulse on high impedance load using the turnon and turn-off delays of dual Marx. The generator combines advantages of the traditional solid-state Marx generator's modular stacking design to easily stack high-voltage pulse, flexible pulsewidth, and compact size. It can output unipolar or bipolar pulses by controlling the driving signal of each Marx. And the delay time between bipolar pulses can be flexibly adjusted. The dual Marx of the pulse generator is designed by the same seven-stage module stack. The SiC-MOSFET with fast turn-off capability and high repetition rate is used as the main switch, which has superior performance under high-frequency conditions. Through theoretical analysis and prototype test, the generator can generate voltage amplitude ±5 kV under 2-kΩ noninductive resistance load, pulsewidth 10-30 ns continuously adjustable, and the delay time of positive and negative nanosecond pulses is 100-400 ns. This high-voltage nanosecond pulse generator has a repetition frequency of up to 1 MHz in the burst.