Nanosecond Discharge Research Articles

Velocity of initial propagation of positive nanosecond discharge in liquid water: dependence on high voltage amplitude and water conductivity

This study deals with the effect of water conductivity and high voltage pulse amplitude on the initial velocity of nanosecond discharge in liquid water. As variable parameters, we used water solutions with three different conductivities (2 μS cm−1, 100 μS cm−1, 500 μS cm−1), and positive high voltage pulses with four different amplitudes (80 kV, 91 kV, 100 kV, 113 kV). The discharge reactor consists of metallic electrodes in a point–to–plane geometry, both immersed in liquid water. The discharge was generated by a commercial nanosecond pulse power generator with positive HV pulses of ∼6 ns pulse duration (FWHM) and ∼2.5 ns rise time. ICCD time-resolved imaging microscopy with high temporal resolution (∼ns) was utilized as a suitable diagnostic tool for the discharge dynamic propagation. It can be concluded that the discharge visual characteristics and behaviour are not significantly influenced by water conductivity and the length of the filaments increases with the increasing voltage amplitude and reaches the maximum value of ∼1.8 mm for 90 kV. The initial propagation velocity also depends on the voltage amplitude and increases with the voltage. The effect of water conductivity on the propagation velocity is negligible. As far as we know, this paper is the first to bring insight into the topic of the effect of water conductivity on the nanosecond discharge propagation in liquid water.

Progress on laser induced fluorescence in a collisional environment: the case of OH molecules in ns pulsed discharges

A nanosecond discharge imposes severe challenges to the application of laser induced fluorescence (LIF), due to the nature of its variable and hot collisional environment. In this paper, we review these difficulties, the current knowledge on collision processes and the concept of collision energy transfer LIF (CET-LIF). The application of CET-LIF to nanosecond discharges for CO2 dissociation shows results that make this challenge worth pursuing.

Features of High Current Nanosecond Discharge in Mixture of High Pressure CuInSe<sub>2 </sub> Chalkopyrite Vapor and Argon

The features of an over-voltage high-current nanosecond discharge in argon of high pressure (р=202 kPa) ignited between the electrodes of CuInSe₂ compound are presented. In the sputtering of massive chalcopyrite electrodes, the CuInSe₂ pair gets into the discharge plasma. Main products of dissociation of chalcopyrite molecules in the over-voltage nanosecond discharge are established. They were in excited and ionized states and in the spectra of plasma radiation they were predominantly represented by atoms and single charged ions of copper and indium. It is proposed to use the spectral lines of copper and indium to control the process of thin films of chalcopyrite deposition in a real time. Using gas-discharge method thin films of chalcopyrite are synthesized on quartz substrates. These films effectively absorb the radiation falling on their surface in the spectral range of 200-800 nm. This property opens the prospects for their application in photovoltaic devices.

Development of high-voltage nanosecond discharge in strongly non-uniform gas

The results of the experimental and numerical study of a high-voltage nanosecond discharge developing through a shock wave in air and combustible mixtures were presented for various neutral density jumps across the wave. The discharge uniformity was investigated using ICCD camera images in a shock tube. The results demonstrated that the discharge plasma became more uniform when the ionization wave moved from a high-density region to a low-density region. The radiation intensity emitted by the plasma in the low-density region was higher than that emitted by the plasma in the high-density plasma. The results of a zero-dimensional simulation in the case of quasi-uniform plasma agree well with the measured ratios of the intensities radiated by the plasmas before and after the shock front. A two-dimensional simulation of the development of a steamer intersecting the shock wave showed that the streamer characteristics change drastically during the transition from the high-density region to the low-density region. Streamer penetration into the low-density region was accompanied by the formation of primary and secondary ionization waves.

Characteristics of High-Current Pulse Discharge in Air with Ectonic Mechanism of Copper Vapor Injection into a Discharge Gap

The characteristics of bipolar high-current nanosecond discharge in the air between the copper electrodes is described. With an inter-electrode gap of 1–2 mm and the air pressure of 0.05–3.0 atm the conditions for obtaining a homogeneous volume discharge in the inhomogeneous electric field, associated with the generation of a beam of a runaway electron and concomitant X-ray radiation, are realized. It is shown that this discharge is a simple point source of radiation in the spectral range of 200–230 nm on the transitions of singly charged copper ions. The results of the optimization of the UV-emitter depending on the pump conditions and parameters of the discharge medium are provided. It is found that under the influence of a discharge, a deposition of thin nanostructured membranes made of electrodes erosion products and products of dissociation of air molecules is possible.

Studying Nanosecond Discharge in Argon at Atmospheric Pressure with Preionization

The influence of initial conditions on specific features of the formation and development of a cathode-directed ionization wave between two flat electrodes in argon at atmospheric pressure was studied at nanosecond time resolution using a high-speed photoelectron monitor and numerical simulations based on the two-dimensional axisymmetric diffusion–drift model.

Nanosecond discharge in atmospheric pressure air with ectonic introduction of iron and copper vapor in plasma and its application in nanotechnology

Introduction: Nanosecond discharges in high-pressure gases between metal electrodes are promising for applications in selective UV lamps. The most investigated working media of such lamps are copper and iron vapors in the air, which are excited by a high-voltage discharge of subnanosecond duration. The use of various metal electrodes in one discharge gap and discharge excitation pulses with an amplitude of 20–40 kV and a duration of 50–100 ns is little studied, which is important for controlling the spectral characteristics of the lamp and producing complex oxide nanostructures based on two different metals. Also important is the use of such discharges for the synthesis of nanostructures of transition metal oxides in assisting the deposition process with hard UV radiation, which allows to improve some of their characteristics. Purpose: The aim of the work is to study the electrical and emission characteristics of a bipolar overstressed nanosecond discharge between stainless steel and copper electrodes in atmospheric pressure and to synthesize and study the optical characteristics of thin films deposited on a glass substrate from the sputtered products of metal electrodes in an air plasma. Methods : We used an optical spectroscopic method for studying the discharge plasma. Results : The results of a study of the electrical characteristics of overstressed nanosecond discharge in air at atmospheric pressure between stainless steel electrodes and copper and stainless electrodes found that it is a source of UV radiation from atoms and iron and copper ions in the spectral range 200-300 nm. The peak value of the electric power of the discharge is ~ 4 MW, and the energy contribution to the plasma per pulse was ~ 0.1 J. The developed point source of UV radiation based on the discharge between the copper and stainless electrode is promising for applications in medicine and sanitation. It has been established that under the assistantance by UV-radiation the developed “point” source in the nanostructures of iron oxides, enlightenment bands appear in the visible region of the spectrum. Conclusion: Experiments revealed the suitability of this discharge for use in a selective UV lamp on iron and copper vapor and deposition of nanostructured films based on iron oxides while assisting the process of deposition by UV radiation.

Application of a hybrid model for the numerical study of the generation of runaway electrons and the formation of high-pressure gas discharge

The paper analyses the details of the application of the hybrid model for calculation of the formation of high-pressure gas discharge in conditions where the transition of electrons into runaway mode is possible. In hybrid model, PIC MC method is used only for calculation of runaway electrons, and the standard hydrodynamic approach is used for calculation of plasma electrons. Using such model can significantly reduce computing resources. The results of calculation of kinetics of electrons emitted from a micro-spike on the cathode during the formation of the cathode layer of nanosecond and sub-nanosecond high-pressure gas discharge are presented. The conditions of transition of electrons into runaway mode at this stage and their influence on the further formation of the gas discharge are analyzed.

Optical characteristics of overstressed nanosecond discharge in atmospheric pressure air between chalcopyrite electrodes

The results of the investigation of the optical characteristics of a high-current nanosecond discharge in atmospheric pressure air between chalcopyrite electrodes (CuInSe2 and CuSbSe2 compounds) in conditions of overstressed discharge gap are presented. When using electrodes with a relatively large radius of curvature of the working part (3 mm) and a special system for isolating a part of the surface of the electrodes, a relatively uniform nanosecond discharge was obtained in millimeter intervals. Electrical and optical (spectral and temporal) discharge characteristics were investigated. Based on the solution of the Boltzmann equation for the electron energy distribution function, the parameters of the air plasma with small additions of the vapor of easily ionized impurity, in the form of copper vapor, were simulated.

Low-energy ions source of plane geometry on the basis of plasma-beam discharge with a slot cathode

In this paper, we present the results of experimental studies of the process of “plasma sheet” creating based on a ribbon electron beam formed in a nanosecond discharge with a slot cathode. The slot cathode and the flat anode are made of aluminium and placed at a distance of 0.5 cm from each other. An emission window of 0.5×5 cm closed off with a fine-grained tungsten grid is made in the anode. The magnitude of the accelerating voltage varied within the range of 1-1.5 kV at gas (neon) pressures in the chamber of less than 0.5 Torr. The ribbon electron beam formed in such a system is transported and received with a collector placed at a distance of 3 cm from the locking anode. Concurrently, a plasma sheet with an area of 5×3 cm and a thickness of about 0.5 cm is formed. Experimental studies of the conditions for the plasma sheet formation were performed depending on the gas pressure, the amplitude of the accelerating voltage pulses at the anode and the voltage at the collector.

Characteristics of high pressure nanosecond discharge in methane-containing gas mixtures

A nanosecond discharge of voltage up to 240 kV and pulse length of 10÷25 ns in mixtures of CH4 and CO2 at gas pressures up to 6 bar was investigated. For a pulse corona discharge and diffuse discharge from pointed cathodes, the dependences of the energy input in the gas on pressure, gas composition, and electrode geometry were obtained. It is demonstrated that the pulse energy of the diffuse discharge far exceeds the pulse energy of the corona discharge. The maximum specific energy input per pulse for the diffuse discharge was 0.5 J/cm3. The data obtained are necessary to determine the specific energy consumption for methane reforming and correct assessment of the efficiency of discharge technologies for processing natural gas.

The effect of fuel oxidation on electron swarm properties and nanosecond discharge characteristics in combustible mixtures

The results of the calculations of electron transport and rate coefficients in oxidized methane:O2, propane:O2 and H2:O2 mixtures were presented for different temperatures and reduced electric fields E/N from 1 to 3 × 103 Td. The calculations were made for various oxidized fuel fractions. It was shown that fuel oxidation led to a drastic decrease in the average electron energy, electron drift velocity and attachment coefficient for E/N < 60 Td. At higher reduced electric fields, the effect of fuel oxidation on the average electron energy and electron drift velocity was small, whereas the attachment coefficient increased with increasing oxidation degree. In addition, in the hydrocarbon-containing mixtures for E/N ∼ 30 Td, the electron drift velocity varied nonmonotonously with the oxidation degree increase. The critical reduced electric field at which the average rate of electron production in the mixture was equal to the average attachment rate increased with fuel oxidation due to the increased attachment rate and decreased detachment rate. The effect of intermediate species on the electron transport and rate properties in partially oxidized mixtures was small. The calculated results were used to self-consistently simulate fuel oxidation and plasma characteristics for high-voltage nanosecond repetitive discharges in combustible mixtures. Zero-dimensional simulation in a H2:O2 mixture showed that the reduced electric field at the instant when the deposited energy peaked was close to the critical values of E/N and increased with increasing oxidized fuel fraction.

Comparison of mechanisms of the plasma generation by nanosecond discharge at extremely high overvoltage

Two mechanisms of the nanosecond timescale discharge initiation in nitrogen at extremely high overvoltage are compared using a one-dimensional Particle-in-Cell Monte Carlo collisions model. In the first mechanism, the discharge is ignited by the electrons seeded initially in the vicinity of the cathode, while in the second mechanism, the discharge is initiated by the electron field emission from the cathode. It was shown that both approaches predict discharge evolution governed by the runaway electrons generating in the cathode-anode gap. The latter promotes the propagation of the fast ionization wave from the cathode to the anode. However, there are some distinctive features which are explained by different numbers of runaway electrons presented in the cathode-anode gap. In the case, when the field emission is considered, one obtains the virtual cathode formation, the generation of electrons with the anomalous energy, and the fast ionization wave velocity comparable to the speed of light.

Non-equilibrium kinetics of the ground and excited states in N2–O2 under nanosecond discharge conditions: extended scheme and comparison with available experimental observations

A numerical 0D kinetic model is developed here to simulate the detailed kinetics of the ground and excited electronic states of atmospheric gases occurring under streamer discharge conditions. The model is based on an extended kinetic scheme that involves state-to-state vibrational kinetics of the ground electronic states of N2, O2 and NO diatomics, including e–V, V–V and V–T energy transfers, and contains about 104 processes for more than 500 tracked state-specific states (including the higher excited and autoionising states of NI/OI atomic species), and also for state-non-specific species. This scheme takes into account the most important radiative processes occurring in N2 and N2–O2 mixtures that are of diagnostic interest, including the extreme ultraviolet and vacuum ultraviolet radiation produced by many excited and autoionising states of NI/OI. The dependence of the rates of electron-impact processes on the reduced electric field E/N is found by solving the Boltzmann equation for electrons in the two-term approximation using the Boltzmann equation solver Open Source library, BOLOS.We examine several test cases: pure nitrogen at 50 and 200 Torr and synthetic air at 10, 50 and 760 Torr, at a gas temperature of 300 K. The numerical results for pure nitrogen were compared with experimental results recently obtained by laser induced fluorescence for metastables. Good qualitative agreement was observed between numerical simulations and experiments at vibronic levels v = 2–5, giving important feedback on the appropriateness of the kinetic scheme. Numerical results were also used to find several general spectrometric signatures that might be helpful in the development of diagnostic procedures.

Effects of Plasma Actuator Discharge on Lift-Enhancement and Flow Patterns of Flying Wing Aircraft

The nanosecond pulsed plasma discharge actuator is used on a flying wing aircraft. At the angles of attack rang from -4° to 28°, the impact of plasma actuator arrangement position and discharge frequency on lift-enhancement effect is tested. Oil flow visualization is used to investigate the surface flow pattern varies with angles of attack for the plasma actuator turned on and off. The result indicates that lift-enhancement can be achieved through the actuator discharges at large angles of attack on flying wing aircraft. The arrangement position and discharge frequency both have a significant impact on lift-enhancement effect. The actuator which arranged at the leading edge of the aircraft could get the best lift-enhancement effect. There exists an optimal discharge frequency, flow separation under this frequency can be effectively suppressed, which results the best lift-enhancement effect. The flow visualization test shows that the control mechanisms of the plasma actuator are to inject energy to the shear layer, thus increased the vortex strength. The vortices strengthen the mixing of the outer high-speed fluid with inner low-speed fluid, which effectively restrains the separation.

Influence of Runaway Electrons on the Formation Time of Nanosecond Discharge

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

Effects of Vibrational Excitation on Nanosecond Discharge Enhanced Methane–Air Ignition

A zero-dimensional model of nonequilibrium plasma-assisted methane–air ignition at atmospheric pressure is presented to study the effects of vibrationally excited species on ignition enhancement. It is found that the vibrationally excited species , , and especially can be generated efficiently when the reduced electric field strength is below 100 Td in a stoichiometric methane–air mixture. The results show that vibrationally excited species could not effectively enhance ignition via kinetic pathways due to their fast relaxation, but instead via thermal pathways through gas heating. Despite this, the thermal enhancement is much less effective than the kinetic effects due to plasma, indicating that the production of vibrationally excited species consumes the energy deposited in the plasma, and thus limits the production of more active particles, such as O, , and . A sensitivity analysis is conducted to further understand the detailed chemistry of the ignition enhancement involving vibrational excitation. The results show the reactions and have significant inhibitive effects on ignition enhancement in discharge conditions with a fixed plasma energy. The reactions involving the production of O and show promotive effects in enhancing ignition because they accelerate the radical production through chain branching reactions. Finally, the calculated ignition delay times at different temperatures show that the ignition enhancement by nanosecond discharge and the promotive effect of N are more significant at low temperatures.

Synthesis of nanostructured transition metal oxides by a nanosecond discharge in air with assistance of the deposition process by plasma UV-radiation

The conditions for the synthesis of zinc, copper and iron oxides nanostructures using plasma nanosecond high-current discharge in air when introducing electrodes material vapor into a plasma due ectonic mechanism and the main parameters of the plasma are investigated. It is shown that this discharge can be used for the synthesis of nanoparticles of transition metal oxides on a dielectric substrate. Optical characteristics of nanostructures are given.

Russian Physics Journal (Former Soviet Physics Journal) and its Contribution to the Development of High-Current Pulse Electronics and Electrophysics

This article assesses the impact that the journal has had on the research and development in high-current pulse electronics and electrophysics, gas electronics, physics of gas lasers, relativistic microwave electronics, plasma electronics, etc. All these fields of research involve achievements in three areas of science and technology, namely, the creation of high-power nanosecond pulse generators; fundamental studies of nanosecond high-current discharges in gases, which have led to the discovery of the phenomenon of multielectron initiation of discharges, and studies of pulsed vacuum discharges, which have resulted in the discovery of explosive electron emission. The author began his research activities in these areas in 1958 at Tomsk Polytechnic Institute and continued them at the Institute of High Current Electronics of the Siberian Branch of the USSR Academy of Sciences, which was opened in 1977. A number of articles published in the journal were devoted to priority issues such as the studies of nanosecond discharges in gases, in vacuum, and in water; the description of the properties of explosive electron emission; the invention of metal-dielectric cathodes with ferroelectrics, and the proposal of gas compression in devices based on electrically exploded cylindrical conductors.

Development of nanosecond discharges in atmospheric pressure air: two competing mechanisms of precursor electrons production

In this paper, we present the results from the computational study of the two competing mechanisms of precursor electrons production—conventional photoionization and preionization by fast electrons from the cathode. To discriminate between the two mechanisms we simulate a negative streamer evolution under conditions when photoionization is zero/non-zero and/or fast electrons are present/absent. In the absence of all factors producing the precursor electrons the streamer eventually stalls. We show that the effect of fast electrons on streamer evolution is similar to that of the photoionization but it is more stochastic by nature. The domination of one or another of the mechanisms considered depends on the pulse duration and voltage amplitude (other conditions being equal).