Nanosecond Discharge In Air Research Articles

Electrical and optical characteristics of a nanosecond pulsed electrical discharge in air in contact with a water droplet for various electrical conductivities

Abstract Interactions between pulsed electrical discharges and liquid dielectric materials is a growing research field with interests in fundamental discharge physics as well as in applications. Herein, we present an experimental study on the dynamics of nanosecond discharges in air with the presence of a water droplet with various electrical conductivities (EC) and at different applied voltages (Va). The discharges are characterized optically, by employing time-resolved ICCD imaging and optical emission spectroscopy, as well as electrically, by acquiring the current-voltage waveforms for every discharge. The results show that three modes of discharges can be obtained: i) streamer discharge between the cathode and the droplet, ii) streamer discharge between the cathode and the droplet as well as between the anode and the droplet, and iii) spark discharge that connects the two electrodes and propagates over the droplet. We find that the probability to obtain one of the three discharge modes is strongly related to the droplet’s EC as well as to Va. Although the ignition of the streamer is relatively insensitive to EC, its transition to a spark can be finely controlled by the droplet’s EC. The time-resolved ICCD images show that the discharge initiates in the gap between the cathode and the droplet, followed by ignition between the anode/ground electrode and the droplet. Then, an extinction phase is observed before the ignition of a secondary streamer, and depending on the conditions, the discharge may transition to a spark, i.e. a channel with high emission intensity. We find that the duration of each stage of discharge propagation as well as the corresponding emission (path and intensity) are sensitive to droplet’s EC. Finally, emissions from streamers (primary and secondary) as well as from sparks are analyzed using optical spectroscopy. We find that the emission from the streamers is dominated by the second positive system of N2, and that the droplet’s EC does not significantly influence the emission spectra nor the estimated rotational temperature of N2.

Polystyrene (PS) Degradation Induced by Nanosecond Electric Discharge in Air in Contact with PS/Water

Water pollution with microplastics has become a significant concern. Conventional treatment methods have proven ineffective, and alternatives are being explored. Herein, we assess the degradation efficiency of polystyrene (PS) by measuring its nanosecond discharge in air in contact with water. Its discharge is characterized during processing, and a transition from streamer-like to spark-like discharge occurs due to the increased electrical conductivity of water. Experiments are conducted at different frequencies, and the highest degradation is achieved at 10 kHz; an 83% polystyrene weight loss is recorded after 5 min of processing. The optical spectra of the discharge show no evidence of C-species, and an FTIR analysis of the processed polystyrene reveals no structural modifications. An NMR analysis shows the presence of ethylbenzene in water. Finally, a mechanism of PS degradation is proposed.

Ignition of Carbon Black during Nanosecond Diffuse and Spark Discharges in Air at Atmospheric Pressure

Many scientific teams are currently studying the effects of plasma generated by nanosecond diffuse discharges on the surfaces of various materials in order to modify their properties. To achieve this, uniform plasma is required to act on the target being treated, which is often an electrode in a discharge system. Previously, the surface treatment uniformity of flat electrodes during a nanosecond discharge in a point-to-plane gap was studied by applying a carbon black layer, and a discharge mode was identified in which there was no erosion on the treated electrode. In this study, it was established that during a nanosecond discharge in air at atmospheric pressure in a non-uniform electric field, carbon black deposited on the surface of a flat anode can ignite. The conditions and dynamics of carbon black ignition during the nanosecond discharge were determined. It was observed that the carbon black is ignited on the surface and continues to combust in the gap in the form of flame plumes for tens of milliseconds. It was also found that the combustion of carbon black can occur in both diffuse and spark discharges.

Thin Luminous Tracks of Particles Released from Electrodes with A Small Radius of Curvature in Pulsed Nanosecond Discharges in Air and Argon

Features of the nanosecond discharge development in a non-uniform electric field are studied experimentally. High spatial resolution imaging showed that thin luminous tracks of great length with a cross-section of a few microns are observed against the background of discharge glow in air and argon. It has been established that the detected tracks are adjacent to brightly luminous white spots on the electrodes or in the vicinity of these spots, and are associated with the flight of small particles. It is shown that the tracks have various shapes and change from pulse to pulse. The particle tracks may look like curvy or straight lines. In some photos, they can change their direction of movement to the opposite. It was found that the particle’s track abruptly breaks and a bright flash is visible at the break point. The color of the tracks differs from that of the spark leaders, while the bands of the second positive nitrogen system dominate in the plasma emission spectra during the existence of a diffuse discharge. Areas of blue light are visible near the electrodes as well. The development of glow and thin luminous tracks in the gap during its breakdown is revealed using an ICCD camera. Physical reasons for the observed phenomena are discussed.

Interaction of a Pulsed Nanosecond Discharge in Air in Contact with a Suspension of Crystalline Nanocellulose (CNC)

Interaction of a Pulsed Nanosecond Discharge in Air in Contact with a Suspension of Crystalline Nanocellulose (CNC)

Spatial and temporal dynamics of single nanosecond discharges in air with water droplets

Discharges generated in water or water-containing media have great potential for various technological applications. However, a fundamental understanding of plasma–liquid interactions, particularly the ignition and propagation of a discharge in a gap containing liquid droplets, is lacking. This study investigates the electrical characteristics and the spatial-temporal dynamics of nanosecond discharges in air containing one or two millimetric droplets of deionized water. Analysis of the effects of voltage amplitude (V a) and pulse width on the discharge mode shows that at low V a, the discharges are run in streamer mode; however, at high V a, a streamer-to-spark transition is observed. Although the droplet size (diameter between 2 and 4 mm) does not significantly influence the discharge dynamics, its position with respect to the gap (on- or off-axis) has a strong effect. Time-resolved imaging of three droplet configurations (one on-axis droplet, one off-axis droplet, and two on-axis droplets) was used to unveil the ignition and propagation dynamics of streamers and sparks at nanosecond time scale. The findings are of interest and contribute to a better understanding of` the plasma–droplet interactions, which is crucial for the development and optimization of plasma-based applications.

Characteristics and Plasma Parameters of the Overstressed Nanosecond Discharge in Air between an Aluminum Electrode and a Chalcopyrite Electrode (СuInSe2)

Characteristics and Plasma Parameters of the Overstressed Nanosecond Discharge in Air between an Aluminum Electrode and a Chalcopyrite Electrode (СuInSe2)

Electrophysical Characteristics of Gas-Discharge Synthesis of Thin Films On The Basis Of a Superion Conductor (Ag2s) In Air

The electrophysical characteristics of an overvoltage nanosecond discharge in air at atmospheric pressure between electrodes made of a superionic conductor, Ag2S, are presented. In the process of microexplosions of inhomogeneities on the working surfaces of electrodes in a strong electric field, vapors of the Ag2S compound and its dissociation products in plasma are introduced into the interelectrode space. This creates the prerequisites for the synthesis of thin structured films that have the properties of superionic conductors and can be deposited on a dielectric substrate placed near the discharge gap. The spatial and electrical characteristics of an overvoltage nanosecond discharge, the Raman scattering spectra of the synthesized films and their surfaces are studied.

Conditions For "Cold" Gas-Discharge Synthesis of Zinc Oxide And Silver Sulfide Nanostructures Under Automatic Assisting With Ultraviolet Radiation

The characteristics and parameters of the plasma of an overvoltage nanosecond discharge in oxygen, which was ignited between zinc electrodes in oxygen, are presented. Zinc vapors were introduced into the discharge due to microexplosions of natural inhomogeneities on the surfaces of zinc electrodes in a strong electric field. This creates the prerequisites for the synthesis of thin nanostructured zinc oxide films, which can be deposited on a rigid dielectric substrate placed near the electrode system. The results of a study of the optical characteristics of an overvoltage nanosecond discharge with a discharge gap of d=2mm are presented. The identification of the plasma radiation spectra made it possible to establish the main excited plasma products that form the plasma UV radiation spectrum and simultaneously act as a pulsed source of clusters and small particles of zinc oxide. The characteristics of an overvoltage nanosecond discharge in air between polycrystalline electrodes made of a supericonic conductor Ag2 S are presented. In the process of microexplosions of inhomogeneities on the working surfaces of electrodes in a strong electric field, vapors of the Ag2 S compound and its dissociation products in plasma are introduced into the interelectrode space. This creates prerequisites for the synthesis of thin structured films that have the properties of superionic conductors and can be deposited on a dielectric substrate placed near the discharge gap. The spatial, electrical, and spectral characteristics of the discharge, the Raman scattering spectra of the synthesized films, and the homogeneity of their surface are studied.

Measurement of the duration of runaway current pulses using measuring equipment with bandwidths up to 50 GHz

The duration of current pulses of runaway electrons generated during the formation of a nanosecond discharge in air in a sharply inhomogeneous electric field was measured using measuring equipment with a bandwidth of 50 GHz. The influence of the gas pressure and the shape of a cathode on the duration of the RE current pulses is investigated. Current pulses with full width at half maximum of 16–28 ps were recorded, depending on the conditions.

Water Treatment with the Cold Plasma of a Diffuse Nanosecond Discharge in Air at Atmospheric Pressure

The treatment of wastewater with the atmospheric cold plasma is a promising method to purify it by means of neutralizing various toxic components. The degradation of an aqueous methylene blue solution used as a model dye was studied. The surface treatment of the solution was carried out with cold plasma of a diffuse nanosecond discharge in air at atmospheric pressure. It has been found that the efficiency of removing pollutants increased when the treatment time increases from 5 to 20 min. Optical UV-IR spectroscopy was used to determine the transmittance of aqueous solutions before and after treatment. Experimental results showed that the transmittance of the aqueous methylene blue solution after 20 min treatment with the diffuse discharge plasma increased by several times. The discharge formation under these conditions has also been studied by analyzing the waveforms of the current and voltage. It has been established that regardless of the presence of a cuvette on the flat grounded electrode, a large-diameter streamer is formed in the discharge gap. If there is a cuvette filled with the solution on the grounded electrode, a breakdown is initiated over the dielectric surface after the streamer reaches the dielectric. In this case, the plasma channel is closed on the grounded flat electrode.

Study into Synchronous Flows of Bactericidal Ultraviolet Radiation and Transition Oxides Metals (Zn, Cu, Fe) in a Pulsed Gas Discharge Overvoltage Reactor Nanosecond Discharge in the Air

The characteristics of an overstressed, high-current nanosecond discharge in atmospheric air between zinc, copper, and iron electrodes are given with a distance between the electrodes of 1–3 mm. It is established that this discharge is a point source of ultraviolet radiation in the spectral range of 200–300 nm and a nanoparticle stream of zinc, copper, and iron oxides. The optimization results of the UV emitter depending on the pumping conditions and parameters of the discharge medium, as well as the optical characteristics of the film nanostructures of transition metal oxides deposited on the surface of a glass substrate, are presented.

Runaway Electrons Emitted by Electron Avalanches in Nanosecond Discharges in Air

Nanosecond electric discharges in atmospheric air at high overvoltages are considered. Plasma channels and diffuse plasma glow simultaneously exist in these discharges. Channels are created by subnanosecond streamers formed in the cathode region. Diffuse glow is caused by runaway electrons emitted by electron avalanche heads. The necessary electric field enhancement is created due to the plasma configuration in the avalanche head and body.

Очистка воды с помощью холодной плазмы диффузного наносекундного разряда в воздухе при атмосферном давлении

Очистка воды с помощью холодной плазмы диффузного наносекундного разряда в воздухе при атмосферном давлении

Spatial evolution of the plasma kernel produced by nanosecond discharges in air

This work presents an experimental investigation of the hydrodynamic effects induced by nanosecond and conventional spark discharges. The energy deposited in sparks in the short breakdown time (~1 mJ mm−1) induces hydrodynamic effects that redistribute the energy over a large volume (~1 cm3) surrounding the initial plasma channel. This process influences the subsequent formation of the ignition kernel and the initiation of combustion. The experimental results presented in this paper were obtained with a set of synchronized diagnostics including schlieren, OH planar laser induced fluorescence and electrical measurements of the energy deposited in the plasma. It is shown that the motion of the gas excited after the discharge breakdown depends not only on the total deposited energy but also on the dynamics of the energy input in the plasma. Finally, the effects of nanosecond sparks are compared with those of conventional sparks used for internal combustion engines. We show that, with 20 times less energy, the nanosecond spark produces a twice bigger excited gas volume than the conventional spark. This is because the energy deposited by the nanosecond spark during the breakdown stage is three times higher than for the conventional spark.

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.

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.

Parameters of plasma of high-current nanosecond discharge in air with small admixtures of copper vapor

Introduction . The use of a discharge in air of atmospheric pressure opens the possibility of developing windowless UV lamps that are promising for applications with significant mechanical overloads under various extreme conditions, since they do not contain any quartz elements (windows or bulbs). The output characteristics of such point lamps strongly depend on the plasma parameters of the nanosecond discharge with small admixtures of the vapor metal from which the electrodes are made. At present, there are no data on the parameters of air plasma with small admixtures of copper vapor under the operating conditions of a point lamp, which inhibits the establishment of mechanisms for populating the excited levels of atoms and copper ions in such a plasma. This in turn inhibits the long-range optimization of the output characteristics of such point sources of UV radiation. Purpose . The purpose of the study was to determine the emission characteristics in the spectral range of 200-250 nm of the plasma of high-current nanosecond discharge, between copper electrodes in air at atmospheric pressure under conditions of strong overstress of the discharge gap and to carry out a numerical simulation of the parameters of the plasma of air with small copper impurities under conditions close to those realized in the experiment. Methods . The nanosecond discharge in air of atmospheric pressure between copper electrodes was ignited. The distance between the copper electrodes was 1 mm, which led to the ignition at atmospheric pressure air of a point diffuse discharge of a spherical shape with a diameter of 1 mm. The standard program was used to solve the Boltzmann kinetic equation for the electron energy distribution function (EEDF) for modeling air plasma atmospheric pressure parameters with small copper vapor admixtures, since under the experimental conditions the maximum value of the E/P parameter reached about 530 V cm -1 torr -1 , which is less than the critical value of E/P for nitrogen according to the local electron runaway criterion – 590 V cm -1 torr -1 . Results . Numerical simulation of the plasma parameters established that for the range of reduced electric field strength 610 Td-810 Td, at which experimental studies of the characteristics of a point nanosecond discharge were carried out, mean electron energies varied within the range of 12.2 -15.6 eV; the value of the electron concentration was 10.7·10 21 m -3 – 8.7 ·10 21 m -3 at a current density of 765 · 10 6 A / m 2 on the surface of the copper electrode. The excitation constants of the 2 P 3/2, 1/2 , 2 D 3/2 , 2 D 5/2 , 4 F 7/2 , - states of the copper atom and its ionization were in the range (7.3 – 8.5) 10 -13 m 3 /c, ( 0.29 - 0.28) 10 -13 m 3 /c, ( 0.22 - 0.22) 10 -13 m 3 /c, (0.19 – 0.22) 10 -15 m 3 /c and (0.33 -0.45) 10 -13 m 3 /c,, respectively. The maximum excitation rate constant for nitrogen molecules was for the sum of the singlet states: they were (1.4 10 -14 ) m 3 / s for an electric field strength of 810 Td. The specific losses of the discharge power in the plasma on inelastic collisions of electrons with the components of the gas mixture were maximal for nitrogen molecules and reached 32% for excitation of the sum of singlet nitrogen states. Conclusion . Radiation of the plasma is concentrated in a narrow spectral interval of 200-250 nm, is promising for use as a point UV lamp; the spectral lines 248.9 and 254.4 nm Cu II are promising for estimating the electron temperature in a plasma. Mean electron energy, electron mobility, specific electric power losses and the rate constants of elastic and inelastic scattering of electrons by copper, argon and carbon dioxide, oxygen and nitrogen molecules, the ratio of which was 3: 7.098: 0.266: 159.157: 593.438, depending on the magnitude of the reduced electric field (ratio of the electric field strength (E) to the total concentration of atoms and gas molecules (N)). The range of changes in the parameter E / N = 1-1300 Td (1 ∙10 -17 - 1 ∙ 10 -15 V ∙ cm 2 ) and included the values of the parameter E / N, which were realized in the experiment (610-810) Td.

Generation of Diffuse Jets and Runaway Electron Beams in Air, SF6, and Helium at Low Pressures

Nanosecond discharges in air, SF6, and helium at pressures of units–tens of Torr are studied. Spatial inhomogeneities of diffuse jets and autographs of runaway electron (RAE) beams are recorded in all three gases during a discharge in a nonuniform electric field. It is shown that diffuse jets change their shape and their lengths increase and change from pulse to pulse in the discharge gap as the pressure decreases; further, it is confirmed that the RAE beam amplitude increases as the gas pressure decreases. It is assumed that inhomogeneities observed in the diffuse jets and RAE beams can be associated with transient luminous events in the Earth’s atmosphere that have sizes of tens of kilometers and occur at high altitudes at low pressures under high thunderstorm activity.

Numerical modeling of repetitive nanosecond discharge in air

A repetitively pulsed nanosecond glow discharge in a flow of atmospheric pressure air at 2000 K is numerically modelled in the framework of plasma assisted combustion. The plasma is modelled in quasi-neutral approximation with fluid transport and diffusion. In our simulations, 16 species and 115 reactions are considered to model the discharge and the post discharge in air flow, and each phase operates at different time scales. The steady-state regime is reached over 200 cycles from the initial composition at thermodynamic equilibrium. The shape and the electron density of the simulated discharge compare well with experimental measurements.