High-voltage Nanosecond Pulses Research Articles

Stepwise development of atmospheric pressure plasma jet driven by bursts of high-voltage nanosecond pulses at multi-tens MHz

This study employs the bursts of high-voltage nanosecond pulses at multi-tens MHz to drive the helium atmospheric pressure plasma jet. Such bursts are obtained by modulating a high-voltage nanosecond pulse based on the wave reflections in a coaxial cable. The development processes and mechanisms of the plasma jet are analyzed in detail based on the discharge waveforms, discharge images, gas temperature, electron density, and axial electric field. Because the time interval between adjacent pulses is much shorter than the characteristic plasma decay time, the discharge channel driven by the first pulse still has high residual electron density and conductivity when the second pulse arrives. The first discharge channel serves as an extension of the high-voltage electrode. In this case, the second discharge starts at the end of the first discharge channel and continues to propagate forward. Driven by the bursts of high-voltage nanosecond pulses, the stepwise propagation of a guided streamer along the plasma jet is observed. The characteristic of the stepwise development of the guided streamer is stable and repeatable under the same condition and does not change at different helium flow rates if the flow is laminar. Reducing the cable length results in a higher equivalent pulse frequency in the bursts and significantly increases the plasma jet length. However, an excessively high frequency will cause a rise in gas temperature and pressure fluctuation in helium flow, resulting in a reduction in the length of the laminar region and an unstable discharge.

Electric discharge initiation in water with gas bubbles: A time scale approach

High voltage nanosecond pulse driven electric discharges in de-ionized water with an argon bubble suspended between two electrodes were experimentally investigated. Two electrode configurations were used to temporally resolve the time scales of the discharge from the applied voltage rise time (7 ns), through the end of the first pulse (∼30 ns), and longer (>50 ns). We found that, in positive and negative applied voltage polarities, discharge initiates in the water at the tip of the anode. The discharge in the water rapidly extends (∼104 m/s) to the apex of the bubble and light emitted from inside the bubble begins to form. The steep rate of rise of the applied voltage (dV/dt<4 kV/ns) and the short time for the development of discharge in the water suggest that cavitation is a likely mechanism for discharge initiation and propagation in water. In addition, the short duration of the applied voltage pulse results in only a partial Townsend discharge inside the bubble.

Plasma-enhanced electrostatic precipitation of diesel exhaust particulates using nanosecond high voltage pulse discharge for mobile source emission control

This study reports enhancement in the electrostatic precipitation (ESP) of diesel engine exhaust particulates using high voltage nanosecond pulse discharge in conjunction with a negative direct current (DC) bias voltage. The high voltage (20 kV) nanosecond pulses produce ion densities that are several orders of magnitude higher than those in the corona produced by a standard DC-only ESP. This plasma-enhanced electrostatic precipitator (PE-ESP) demonstrated 95 % remediation of PM and consumes less than 1 % of the engine power (i.e., 37 kW diesel engine at 75 % load). While the DC-only ESP remediation increases linearly with applied voltage, the plasma-enhanced ESP remains approximately constant over the applied range of negative DC biases. Numerical simulations of the PE-ESP process agree with the DC-only experimental results and enable us to verify the charge-based mechanism of enhancement provided by the nanosecond high voltage pulse plasma. Two different reactor configurations with different flow rates yielded the same remediation values despite one having half the flow rate of the other. This indicates that the reactor can be made even smaller without sacrificing performance. Here, this study finds that the plasma enhancement enables high remediation values at low DC voltages and smaller ESP reactors to be made with high remediation.

Decomposition of hexane and benzene by dielectric barrier discharge plasma and reaction temperature: Comparison of performance of DC nano-second pulsed power supply and AC high voltage power supply

The VOC decomposition performance of a dielectric barrier discharge plasma powered by a DC nano-second pulsed power system was compared with that of an AC high voltage power system. Benzene and hexane were selected as a representative aromatic VOC and a chain-structured VOC, respectively, and the decomposition of each VOC was conducted at the same applied voltage in both systems. The energy of electrons released from the plasma was analyzed, and the ozone production ability was evaluated under a constant applied voltage at different temperatures. Compared with AC high voltage system, the DC nano-second pulsed power system had about 32 times, 26 times, and 30 times better performances for ozone production yield, benzene decomposition yield, and hexane decomposition yield, respectively. For benzene decomposition, the ring cleavage reaction was constant at all reaction temperatures. On the other hand, the mineralization of hexane was largely improved by higher temperatures, because the dehydrogenation reaction was accelerated. Consequently, benzene decomposition was easier than hexane decomposition at the same energy.

Influence of DSRD Operation Cycle on the Output Pulse Parameters

Drift step recovery diodes (DSRDs) are semiconductor opening switches designed for the forming of high-voltage nanosecond pulses. DSRD-based circuit includes inductive energy storage and works as a high-efficient compression stage of the tens to hundreds of nanoseconds input pulse down to nanosecond or subnanosecond range output pulse. Despite the well-investigated physical principles, a lot of published DSRD simulations, and practical DSRD-based pulsers, the fundamental research aimed at optimization of DSRD circuit has not been conducted yet. The present letter shows the result of extensive experiments elucidating the maximum voltage rise rate, pulse compression ratio, energy losses, and prepulse amplitude in DSRD circuits. The explicit definitions of DSRD pulse parameters, which are vital for the optimization process, are suggested for the first time. It is demonstrated that optimizations of different parameters contradict each other, and there is no universal optimal solution. The compromise should be found for each application using the recommendations presented in the letter.

Comparative Studies of High-Voltage Diode-Dynistor Generators of High-Power Nanosecond Pulses

The results of comparative studies of two compact generators of nanosecond high-voltage pulses are presented. Both generators include an opening switch in the form of a block of drift step-recovery diodes (DSRDs) and a closing switch in the form of a block of shock-ionized dynistors (SIDs). The generators are designed according to two different schemes, but they have similar parameters of the output pulses on a load of <inline-formula> <tex-math notation="LaTeX">$50~\Omega $ </tex-math></inline-formula>: the amplitude of the output voltage is &#x007E; 30 kV, its rise time is &#x007E; 3 ns, and the output energy is &#x007E; 0.4 J. It is shown that it is possible to increase the output voltage and output energy of the generators.

Periodical discharge regime transitions under long-term repetitive nanosecond pulses

Intuitively, the nanosecond repetitively pulsed (NRP) corona and spark regimes are sustained successively after onsets due to the high background electron density and/or the surplus heat. In this paper, the NRP discharge unexpectedly swings among different regimes (corona → glow → spark → corona → …) in one pulse train, which is characterized by the periodical spark quench and reestablishment. We have investigated discharge regime instabilities by applying long-term repetitive high-voltage nanosecond pulses of ∼15 ns duration to needle–needle and needle–plane gaps in atmospheric-pressure N2 and N2–O2 mixtures. Pulse-sequence resolved electrical and optical diagnostics have been implemented to capture transition processes. The initial corona gradually grows into glow and then spark ‘pulse-by-pulse’, however, the spark regime was interrupted after a certain number of voltage pulses until the next reestablishment. Narrow pulse width impedes the discharge instability growth within one pulse, and a certain number of voltage pulses are required for the discharge regime transition. The addition of O2 dramatically boosts the duration length of spark regime. A lower output impedance of the power supply induces a higher deposited energy into a spark, however, not necessarily leads to a longer spark regime duration, although both the energy storage and the average electric field strength are approximate. Polarity effects, conventionally diminished in pulse-periodic discharges, are still evident during the discharge regime transition. The periodical discharge regime transition is qualitatively explained based on the plasma–source coupling and the evolution trajectory along the power transfer curve. Feedback mechanisms and residual-conductivity related screening effect in NRP spark discharges are analyzed based on a simplified 0D simulation. The periodical feature is probably caused by the insufficient average deposited energy per unit distance per one pulse cycle. In-depth understandings of ‘non-binary’ regimes (neither corona nor spark) and memory effect mechanisms of NRP discharges could be reached.

Quantitative fs-TALIF in high-pressure NRP discharges: calibration using VUV absorption spectroscopy

This work presents a femtosecond two-photon absorption laser-induced fluorescence (fs-TALIF) diagnostic for measuring ground-state atomic nitrogen in nanosecond repetitively pulsed (NRP) discharges. Absolute atom density is obtained from the TALIF signal via a novel calibration technique based on one-photon direct absorption measurements performed in a low-pressure DC discharge. The Vacuum Ultraviolet (VUV) measurements were done at the Soleil synchrotron facility using the high-resolution Fourier-transform spectrometer (minimum linewidth Δ = 0.08 cm−1). The main goal of this work was to develop a quench-free diagnostic technique, which would allow measurements at elevated pressures with high spatial and temporal resolution. Here fs-TALIF measurements of N(4S) are demonstrated in the NRP post-discharge between 1–500 μs after the nanosecond high-voltage pulse. A maximum number density of N-atoms of 5 × 1016 cm−3 was measured at 1 μs after the pulse when the discharge was operated at 1 bar in pure nitrogen. This corresponds to a dissociation fraction of ∼0.1%. The fs-TALIF technique at high laser intensity regime (>1 TW cm−2) calibrated using VUV absorption was compared with the fs-TALIF at low laser intensity regime (<100 MW cm−2) calibrated via the well-established non-saturated TALIF technique using krypton as an etalon gas. It was found that the two measurements of N(4S) in the NRP post-discharge agree within a factor of 3. Importantly, the limit of detection of the fs-TALIF at high laser intensity regime was determined to be . This is approximately one order of magnitude better than previously reported by ns-TALIF in low-pressure discharges.

Improved Auxiliary Triggering Topology for High-Power Nanosecond Pulse Generators Based on Avalanche Transistors

The avalanche transistor-based Marx circuit has great advantages in generating high-voltage nanosecond pulses. The introduction of auxiliary triggering topology (ATT) can reduce the damage probability of transistors in M × N-stage Marx bank circuits (MBCs). However, as the number of modified stages increases, the output voltage drops significantly, which makes it not achievable to adopt ATT at each stage. The transistors in nonmodified stages still have a certain failure rate when operating at a high repetition rate. Moreover, the previous ATT is only applicable in the negative polarity MBC. In this article, an improved ATT is proposed to solve the above problems. First, its operating principle is analyzed, and the feasibility of its application in both negative and positive MBCs is verified by simulations. Then, the effects of the improved ATT on M × N-stage MBCs are experimentally studied, and the results show that the improved ATT can be used in all stages of MBC without reducing the output voltage. It can also reduce the minimum operating voltage of transistors and widen the regulating range of output voltage. In addition, it can improve the synchronous conduction of parallel-connected transistors. Finally, two nanosecond pulse generators with positive and negative polarity, respectively, are developed and used to drive the atmospheric pressure plasma jet. The amplitude of output voltage can be adjusted in the range of 5-10 kV, measuring at the open end of a coaxial cable with 75 Ω impedance, and the maximum repetition rate is up to 7 kHz.

Comparative study on high-voltage nanosecond pulses and dielectric barrier discharge effects on surface morphology and physico-chemical properties of natural pyrrhotite

In this paper we used analytical electron microscopy, potentiometric titration (electrode potential), sorption and flotation measurements and other methods to study changes in the surface morphology, electrochemical, and physicochemical properties of the natural pyrrhotite exposed to nonthermal action of the repetitive nanosecond high-power electromagnetic pulses and low-temperature plasma of dielectric barrier discharge in air at atmospheric pressure. As a result of exposure to high-voltage nanosecond pulses, a sharp shift in the electrode potential of pyrrhotite to the region of negative values caused a decrease in the sorption of the anionic collector on the mineral, a decrease in the hydrophobicity of the surface and flotation of the mineral was due to an increase in the content of oxidized ferric iron on the mineral surface. Dielectric barrier discharge treatment caused the shift of the electrode potential to the region of negative values (–60 mV) in the range of pH 9.7-12, which causes the effect of a decrease in the sorption and flotation activity of pyrrhotite. The advantages of using the short-term (10-30 seconds) energy impacts for structural and chemical modification of the surface and physicochemical properties of sulfide minerals of iron are shown.

Voltage-induced modulation in the charge state of Si-vacancy defects in diamond using high voltage nanosecond pulses

Silicon-vacancy defects have been identified as a promising optical transition for quantum communications, quantum control, and quantum information processing. In the work presented here, we demonstrate a voltage-controlled mechanism by which the photoluminescent (PL) emission from silicon-vacancy (Si-V) defects in diamond can be modulated. In particular, we can selectively produce emission from the negatively charged state of this defect (i.e., Si-V−), which exhibits narrow (Γ = 4 nm) emission at 738 nm at low laser power. This approach uses high voltage (2–5 kV) nanosecond pulses applied across top and bottom electrodes on a 0.5 mm thick diamond substrate. In the absence of high voltage pulses, we observe no emission at 738 nm. This feature increases monotonically with peak pulse voltage, pulse repetition rate (i.e., frequency), and incident laser intensity. We observe saturation of the PL intensity for pulse voltages above 3.2 kV and frequency above 100 Hz. Based on electrostatic simulations, we estimated the local electric field intensity near the tip of the Cu electrode to be 2.8 ×106 V/cm at these voltages. However, as a function of laser power, we observe a linear dependence of PL intensity without saturation. These saturating and non-saturating behaviors provide important insight into the voltage-induced charging mechanisms and kinetics associated with this process.

Plasma Discharge across Metal Nanoparticle Surfaces and Plasma-Driven CO2 Reduction to CO and Higher Order Hydrocarbons

: By discharging nanosecond high voltage pulses (up to 25kV) across an insulating substrate coated with metal nanoparticles (Au or Pt), significantly enhanced plasma generation is observed through local field enhancement on the surface of the nanoparticles. The structural integrity of metal nanoparticles can be maintained due to the low-temperature nature of this transient plasma. Electrostatic simulations based on high-resolution transmission electron microscope (HETEM) image of the nanoparticles demonstrate a 3-fold enhancement of the electric field near the nanoparticle surfaces. Since field emission of electrons, which initiates plasma generation, depends exponentially on electric field, this 3-fold increase in the local electric field can significantly enhance plasma generation at a given applied external voltage. Similar enhancement was also observed by discharging in a methane environment, revealing a 50X enhancement in methane upconversion to C2 and higher order hydrocarbons, presenting the exciting possibility of converting a notorious greenhouse gas into an energy dense hydrocarbon fuel. Under laser irradiation, we observe a 200-fold enhancement in the plasma emission intensity, indicating the important role that hot electrons play in the electron emission process. In addition to gas phase plasma discharge, we also demonstrate CO2 reduction to CO and higher order hydrocarbons by discharging nanosecond high votlage pulses in CO2-saturated water, as revealed by C2 Swan band emission, cryogenic NMR spectroscopy and liquid ion chromatography, which indicate clear peaks corresponding to formic acid, methanol, and acetic acid.

Plasma-enhanced electrostatic precipitation of diesel exhaust using high voltage nanosecond pulse discharge

We have demonstrated nearly 80% remediation of diesel particulates from an 18 kW (i.e., 24.4 HP) diesel engine with just 1.6% of the engine power using a transient pulsed plasma in conjunction with an applied DC bias voltage. This result was achieved using a high voltage (~10 kV) DC bias together with nanosecond high voltage pulses (~20 kV) in what we refer to as a plasma-enhanced electrostatic precipitator (PE-ESP). Here, the remediation takes place in a two-step process in which the particles are first charged by the ions in the plasma and then they are swept out to the collecting electrode by the applied DC bias. The fast rise times (i.e., dV/dt≈ 1012V/sec) associated with these nanosecond pulses produce a streamer discharge with ion densities that are more than one order of magnitude higher than conventional DC coronas. These extremely high ion densities produce the enhanced electrostatic precipitation observed here. In fact, little or no remediation was observed with the DC bias only or with the nanosecond pulses only, and it is the combination of these two applied fields (pulsed and DC) that produces the robust enhancement observed here. This general approach of using nanosecond pulse discharge to produce plasma-enhanced electrostatic precipitation opens up new degrees of freedom in the design of new and more compact ESPs.

Periodic forced flow in a nanosecond pulsed cold atmospheric pressure argon plasma jet

This paper is devoted to the study of the argon flow modification in a cold atmospheric pressure plasma jet driven by nanosecond high voltage (HV) pulses, from single to multiple HV shots applications. A schlieren optical bench has been designed in order to visualize the argon flow downstream expansion in quiescent air, for moderate flow rates below 1 standard liter per minute. A coupled approach is used between charge coupled device (CCD) schlieren imaging and intensified CCD (ICCD) plasma plume imaging, both time-resolved. It is shown that the application of only one HV pulse (i.e. single HV shot) is enough to disturb the flow. The disturbed flow exhibits ripple propagation, on a timescale similar to the flow velocity. When operating in double HV shots, the second ionization wave can be used as a probe, to instantly visualize the flow structure any time after the first HV pulse application. For some flow rates, the ripple can increase in amplitude up to the point when it strongly deforms, or even stops, the plasma plume expansion, after which it is entrained by the flow and the plasma plume retrieves its full usual expansion. When a series of HV pulses are applied, the maximal disturbance of the flow is achieved for a certain pulse repetition frequency (PRF), specific of each flow rate. It is associated with ripples alternation in the plasma plume, in a 3D helical-like arrangement. For greater PRF, the ripples progressively vanish, and the flow is clearly less disturbed. Once the ripples have vanished, increasing further the PRF does not change the plasma plume and flow structures. We suggest that the repetitive plasma ignition mechanically forces the flow inside the capillary with consequences on the global flow structure, similarly to a forced backward-facing step flow with actuator.

Experimental Study of the Mechanism of the Formation of Microdefects in Rocks when Exposed to High-Voltage Nanosecond Pulses

Experimental Study of the Mechanism of the Formation of Microdefects in Rocks when Exposed to High-Voltage Nanosecond Pulses

Effect of High-Voltage Nanosecond Pulses and Dielectric Barrier Discharges on the Structural State and Physicochemical Properties of Ilmenite Surfaces

Effect of High-Voltage Nanosecond Pulses and Dielectric Barrier Discharges on the Structural State and Physicochemical Properties of Ilmenite Surfaces

A hybrid plasma de-icing actuator by using SiC hydrophobic coating-based quartz glass as barrier dielectric

Aircraft icing poses a major threat to flight safety, and plasma anti-/de-icing becomes a new approach in the field of anti-/de-icing in recent years. In this paper, a surface dielectric barrier discharge (SDBD) plasma actuator with SiC hydrophobic coating-based quartz glass is designed and fabricated. Actuated by nanosecond high voltage pulse, its de-icing characteristics are explored experimentally and compared with the uncoated actuator. The results show that under the same actuation parameters, the discharge current peaks and the power consumption of SDBD are reduced with hydrophobic coating, which can be further verified by surface temperature distribution. Intensified CCD camera images indicate that after the adding of SiC coating, the discharge propagation process of SDBD does not change significantly. For both coated/uncoated actuators, two discharges occur during the voltage rise and fall phases respectively, while no discharge occurs during the pulse width phase, but the coated actuator exhibits slightly longer plasma dissipation time. Static de-icing results reveal that the instantaneous energy utilization rate of the coated actuator at 60 s of de-icing process is about 54% higher than that of the uncoated actuator, which can be explained by two aspects: one is to weaken the adverse effects of melted water on the discharge plasma to a maximum extent, and the other is to reduce the contact area between the ice accretion and the hydrophobic surface.

Modeling of fast ionization waves in pure nitrogen at moderate pressure

The fast ionization wave (FIW) discharges in pure nitrogen in a capillary tube at 27 mbar, initiated by positive polarity, high-voltage nanosecond pulses, are numerically studied by coupled two-dimensional plasma fluid modeling. The 2D fluid code based on local mean energy approximation is validated and used, an extended three-exponential Helmholtz photoionization model is proposed for pure nitrogen. The development and structure of the nitrogen FIW is analyzed, the electric field and current are calculated compared with experimental measurements. The evolution of radial distribution of electrons and N2(C 3Π u ) during the FIW development stage and in the afterglow are analyzed, the radial profiles of electron density show a ‘hollow’ structure in the FIW development stage, the temporal-spatial evolution of N2(C 3Π u ) is dominated by the competition between the pooling reaction of and the quenching by electrons. The role of photoionization on the nitrogen FIW radial morphology is discussed, the equivalent background electron density of photoionization in nitrogen discharge is suggested to be (4–6) × 1013 m−3. Spatial distribution of specific energy deposition (SED), fast gas heating (FGH) energy and temperature rise are obtained, heating efficiency varies with electric field E/N and SED and tends to be 10% at high SED. The dominating reactions responsible for FGH and their fractional contribution in space and time are analyzed, in the near axis region, pooling reactions of and N2(B 3Π g ) contribute up to 80% FGH energy, electron impact dissociation of molecular nitrogen contributes about 10%, while e- recombination and quenching of N(2 D) atoms by N2 molecules contribute rest.

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.