Secondary Streamer Research Articles

Optical diagnosis of high pressure non-thermal plasma

Optical diagnosis of high pressure plasma is one of the most powerful tools for investigating chemical reaction mechanisms in the high pressure plasma region. The authors developed various optical measurement systems by using tunable lasers, such as (two-photon-)laser-induced-fluorescence, coherent-anti-Stokes Raman scattering, time evolution of optical emission imaging and others for detecting O3, O, OH, N, NO* and other radicals in atmospheric pressure plasma. Outline of basic measuring techniques developed by the authors for high pressure plasma diagnosis are explained and real examples of plasma diagnosis are demonstrated in this paper. For example, density distributions of single nitrogen (N) and excited nitrogen molecule (N2(A)) below the discharge needle generated by the pulse plasma suggest that single N might be generated in the secondary streamer, while N2(A) might be generated in the primary streamer, and single N decomposes NO more than N2(A).

Spatiotemporal analysis of propagation mechanism of positive primary streamer in water

Currently, further clarification of pre-breakdown phenomena in water such as propagation mechanisms of primary and secondary streamers are needed because applications of aqueous plasma to environmental and medical treatments are increasing. In this study, a series of primary streamer propagations in ultrapure water was visualized at 100-Mega frames per second (100 Mfps) in the range of 400 μm square using an ultra high-speed camera with a microscope lens when a single-shot pulsed positive voltage was applied to a needle electrode placed in a quartz cell. Every observation was synchronized with the waveforms of the applied voltage and the discharge current. The primary streamer, having many filamentary channels, started to propagate semi-spherically with a velocity of about 2 km/s when the pulsed currents occurred. Although most filamentary channels disappeared 400 ns after the beginning of the primary streamer, a few of them continued propagating with almost the same velocity (about 2 km/s) as long as the repetitive pulsed currents flowed. Shock waves were iteratively generated and streamer channels were formed while the repetitive pulsed currents were flowing. Thus, we concluded that the positive primary streamer in water propagates progressively with each repetitive pulsed current.

Pulsed corona discharge driven by Marx generator: Diagnostics and optimization for NOx treatment

A compact, repetitive Marx generator with an external trigger is constructed and coupled with a wire-to-plate corona reactor for a positive pulsed corona discharge studies. The reactor resistance and capacitance behavior during the pulse was observed. It was found that the reactor's capacitance increases three times during the pulse due to the streamer propagation from anode to grounded electrode. Using the time development of the capacitance and resistance during the pulse and the reactor inter-electrode distance, the streamer velocity has been calculated to be 1 × 106 m/s, for system arrangement presented in this work. As an indicator of chemical activity of pulsed corona, ozone production was measured. Emission spectroscopy measurements in the UV region were performed to detect species that appear in the discharge and to determine vibrational and rotational temperatures, which are found to be 3200 K and 340 K respectively. As a measure of pollution control potential of the constructed pulsed corona system, NO oxidation efficiency was investigated and compared with results presented in literature. It was shown that pulsed corona systems with significantly longer pulse durations are competitive with several times shorter pulse duration systems, which implies that chemical efficiency of secondary streamers is comparable with efficiency of primary streamers.

Numerical Analysis of the Heating Effects of an Atmospheric Air-Dielectric Barrier Discharge

In this paper, the formation of the avalanche, primary streamer, secondary streamer, neutral gas heating effects, striations, as well as the radial expansion of the discharge from the symmetry axis toward the boundaries in a constant voltage atmospheric pressure air-dielectric barrier discharge configuration are analyzed. A voltage of 11.2 kV is applied between two metallic parallel plates which are placed at a distance of 4 mm apart. Two rectangular blocks of dielectric medium of 1 mm thickness, each with a relative permittivity of 8, are attached to the cathode and anode metallic electrodes, leaving the remaining 2-mm air gap for the atmospheric air discharge to develop. A single electron is released at the cathode as an initial condition and the development of the barrier discharge with its associated heating effects is analyzed. It has been shown that the discharge exhibits phenomena of radial expansion toward the outer boundaries, forming patterns of striations/filaments along the discharge and temperature rising of ambient air to 490 °K amounting to 63% increase above the ambient temperature. A secondary streamer has been observed traveling from the anode toward the cathode, after the primary streamer hits the cathode, and the primary and secondary streamer speeds were found to exhibit similar propagation speeds within the range 0.5 × 105 - 5 × 105 ms-1. The secondary streamer was found to be associated with electron charge densities of the order of 0.5 × 1018 - 1.5 × 1018 m-3, net charge densities of 1 × 1018 m-3 and radial and axial electric fields of 0.5 × 106 Vm-1.

Effect of pulse width on the production of radicals and excited species in a pulsed positive corona discharge

The effect of pulse width on the production of various radicals and excited species (OH, O, O3, , , OH(A 2Σ), O2(v)) in a pulsed positive corona discharge is measured. The densities of these species are measured using laser-induced fluorescence, light absorption and optical emission spectroscopy. It is shown that the pulsed corona discharge can be divided into three phases related to the production of radicals and excited species: (i) primary streamer, (ii) earlier part of secondary streamer and (iii) later part of secondary streamer. It is shown that phase (iii) is inefficient for the production of most of the radicals and excited species. Therefore, a short pulse is desirable for efficient production of radicals and excited species to cut off the inefficient later part of the secondary streamer.

Various Kinds of Streamers in Atmospheric Pressure Oxygen Dielectric Barrier Discharge

An atmospheric pressure oxygen dielectric barrier discharge had been simulated using two dimensional fluid model. Three kinds of streamers had been obtained, and they are primary, small and secondary streamers. The electron density of small and secondary streamers is lower than that of primary streamers. But it was found that generation of ozone was significantly affected by these three streamers.

Streamers in Water and Along the Insulator Surface in a Wire–Cylinder Gap

Two types of streamers in water, namely, volume streamers and surface streamers, have been observed in a coaxial discharge gap where the central anode wire was surrounded by a perforated dielectric cylinder inside the discharge gap. The speed of surface streamers (~ 100 km/s), which develops along the solid-liquid interface on the outer surface of the dielectric cylinder, exceeds that of the volume streamers (~ 42 km/s) by more than a factor of two. The axial surface streamers serve as sources for numerous thin secondary radial volume streamers.

Streamer Propagation of Positive and Negative Pulsed Corona Discharges in Air

Streamer propagation of positive and negative pulsed corona discharges is observed using streak and ICCD cameras. The discharge occurs in a 13-mm point-to-plane gap in dry air. In the positive discharge, the primary streamer propagates from the point to the plane, and then, the secondary streamer develops from the point to the middle of the gap. When the voltage is high, a midgap streamer is also observed. In the negative discharge, the primary streamer develops from the point to the plane, and then, an anodic channel develops from the plane to the middle of the gap. The velocity and luminous intensity of the primary streamer in the positive discharge increase as the streamer propagates from the point to the plane, while those in the negative discharge show an opposite tendency.

Density and temperature measurement of OH radicals in atmospheric-pressure pulsed corona discharge in humid air

Plasma application for environmental improvement is desirable, and it is worthwhile to clarify the behavior of OH radicals in nonthermal plasma. Under atmospheric-pressure humid air, the time evolutions and spatial distribution of relative density and rotational temperature of OH radicals are measured in pulsed positive corona discharge using laser-induced fluorescence with a tunable optical parametric oscillator laser. The density of OH radicals generated by discharge when 28 kV is applied is estimated to be about 1×1015cm-3 at 3 μs after discharge. The OH density increases with humidity. The rotational temperature rises after discharge. The rate of temperature rise increases with humidity. This phenomenon arises from fast vibration-to-translation energy relaxation of H2O. The spatial distributions of OH rotational temperature indicate that the temperature rises in the secondary streamer channel.

Secondary reverse streamer observed in an ester insulating liquid under negative impulse voltage

The so-called ‘secondary reverse streamer (SRS)’ in this study depicts a newly observed streamer-in-liquid phenomenon which subsequently occurs well after the extinction of the primary streamer (PS) propagation within a single shot of negative impulse voltage and has reverse polarity to the PS. Tests were carried out in a synthetic ester liquid at a 50 mm needle–plane gap under negative impulse voltages up to 140 kV. Based on the current and light waveforms as well as the photographic images, two types of SRS were found: one has a bright trunk with a high velocity of 9.79 km s−1 belonging to the 3rd mode streamer; and the other has a weak tree-like channel with a low velocity of 1.28 km s−1 resembling the 2nd mode streamer. It should be emphasized that SRS under negative impulse voltages has positive polarity being opposite to the negative PS, which is believed to be due to the reverse electric field induced by the residual space charges left by the PS. This has been confirmed by further verification tests under tail-chopped impulse voltages, for SRSs are significantly enhanced in both axial and lateral directions after the early removal of the external applied field.

Dependence of Ozone Generation on Gas Temperature Distribution in AC Atmospheric Pressure Dielectric Barrier Discharge in Oxygen

AC atmospheric pressure multi-filament dielectric barrier discharge in oxygen has been simulated using two dimensional fluid model. In the discharge, three kinds of streamers have been obtained. They are primary streamers, small scale streamers and secondary streamers. The primary streamers are main streamers in the discharge and the small scale streamers are formed after the ceasing of the primary streamers. And the secondary streamers are formed on the trace of the primary streamers. In these streamers, the primary and the small scale streamers are very effective to generate O(3P) oxygen atoms which are precursor of ozone. And the ozone is generated mainly in the vicinity of the dielectrics. In high gas temperature region, ozone generation decreases in general. However, increase of the O(3P) oxygen atom density in high gas temperature region compensates decrease of ozone generation rate coefficient. As a result, amount of ozone generation has not changed. But if the effect of gas temperature was neglected, amount of ozone generation increases 10%.

Gas density in a pulsed positive streamer measured using laser shadowgraph

Gas density in a pulsed positive streamer is quantitatively measured using a laser shadowgraph. The discharge occurs in a point–plane gap of 13 mm in humid air. After the onset of the streamer, the gas density decreases in two steps. The first step is a rapid decrease in gas density, which is caused by gas heating owing to electron impact onto molecules. This step is significant within 1 mm from the anode, although it occurs throughout the gap. The second step is a gradual decrease in gas density after the streamer pulse, which is caused by gas heating due to vibration-to-translation energy transfer. This step takes place mainly in the secondary streamer channel, not in the primary streamer channel. When the discharge voltage is 32 kV, the decrease in gas density reaches 30% of the ambient density. This large decrease in gas density affects the rate of various chemical reactions in the postdischarge period.

레이져 유기형광법을 이용한 펄스 배리어 방전 공간에서의 NO분자에 대한 시·공간적 밀도변화 측정

This paper tried to find out NO generation and removal mechanisms in the space of the atmospheric pulsed barrier discharge using laser induced fluorescence method, which is a very effective approach to the measurement of spatio-temporal density of specific molecules. The propagation velocity of the primary streamer reaches about [m/s] and the secondary streamer is produced in the vicinity of positive electrode after the primary streamer finished. In this work, pulse Nd:Yag and Dye lasers are used for generating the specific wavelength of 226[nm], which is possible to excite NO molecules into (0,0) and fluorescence signals as the transition of (0,2) is measured. For the effective removal of NO molecules in the plasma discharge process, the lower oxygen contents are needed and the influence of secondary streamer for the reduction mechanism of NO molecules is important

Drift and reactions of positive tetratomic ions in dry, atmospheric air: Their effects on the dynamics of primary and secondary streamers

The ion swarm data, namely, the reduced mobility, diffusion, and reaction rates of the positive tetratomic ions O4+ and N2O2+ in N2 and O2 have been determined from a Monte Carlo simulation using calculated and fitted elastic and inelastic cross sections. The elastic momentum transfer cross sections have been determined from a semiclassical Jeffreys-Wentzell-Kramers-Brilouin (JWKB) approximation based on a rigid core potential model well adapted for polyatomic ions. The inelastic cross sections have been approximated from considerations based on the N4+/O2 and N4+/N2 systems. The validated cross section sets in pure N2 and O2 have been used to determine the O4+ and N2O2+ swarm data in dry air over a large E/N range up to 1000 Td. However, due to the lack of experimental ion transport coefficients necessary for a more rigorous cross section validation, the present data, validated only at low E/N, should be regarded as a first approximation, susceptible to improvements as soon as measurements of ion transport coefficients become available in the literature. Then, the present data are used in a two-dimensional discharge dynamics fluid model for the simulation of the primary and secondary streamers for the case of a positive point-to-plane corona discharge in dry air. Relevant characteristics such as discharge current, charged particle densities, space charge electric field and the variation in active species like N and O radicals (very useful in many nonthermal plasma applications) are analyzed and discussed with and without the consideration of three positive tetratomic ions (N4+, O4+, and N2O2+). More particularly, the non-negligible effect of O4+, in the dynamics of the primary and secondary streamers during the discharge propagation and relaxation stages is highlighted with an emphasis on the role of the related kinetic reactions occurring between the different charged particles.

Gas Temperature of Steady Glow and Streamer Discharges in Atmospheric Air Gap

In order to analyze independently the various discharges of a point-to-plane air gap (steady glow, primary streamer, and secondary streamer discharges), the gas temperature in each of discharge region should be determined accurately by using the spectrum emitted from the second positive system bands of N2. In this experiment, we investigate the laser triggered streamer discharge with a repetition frequency of 10 Hz from the dc positive glow corona. The results show that the temperatures of the glow, primary streamer and secondary streamer are in the range of 316∼356K, 335∼350K and 370∼390K, respectively, and are considerably lower than the value of the high-stable dc positive repetitive streamer corona published in the previous references.

X-ray emission in streamer-corona plasma

X-ray emission has been detected occasionally during the streamer-corona propagation in a wire-plate corona reactor open to ambient air. A 65 kV pulse with 15 ns rise time is applied to the wire anode superimposed on a 20 kV dc bias. The duration of the driving voltage pulse (110 ns) is less than 2.5 times the primary streamer transit time. Under this condition no arc discharge occurs between the wire and the cathode plates separated by 6 cm air. The onset of x-ray emission coincides with the initiation of the primary streamers near the wire anode. No x-rays were detected later, during or after the primary or secondary streamer development. X-ray energies ranged between 10 and 42 keV, as detected by a LaBr3 (Ce) scintillator–photomultiplier combination. Time resolved imaging of the streamer propagation highlights the different stages in the streamer discharge process. The energetic electrons originate near the anode, at the moment of streamer initialization.

Two-photon absorption laser-induced fluorescence of atomic oxygen in the afterglow of pulsed positive corona discharge

Atomic oxygen is measured in the afterglow of pulsed positive corona discharge using time-resolved two-photon absorption laser-induced fluorescence. The discharge occurs in a 14 mm point-to-plane gap in dry air. After the discharge pulse, the atomic oxygen density decreases at a rate of 5×104 s−1. Simultaneously, ozone density increases at almost the same rate, where the ozone density is measured using laser absorption method. This agreement between the increasing rate of atomic oxygen and decreasing rate of ozone proves that ozone is mainly produced by the well-known three-body reaction, O+O2+M→O3+M. No other process for ozone production such as O2(v)+O2→O3+O is observed. The spatial distribution of atomic oxygen density is in agreement with that of the secondary streamer luminous intensity. This agreement indicates that atomic oxygen is mainly produced in the secondary streamer channels, not in the primary streamer channels.

Measurement of vibrationally excited O2(v = 6) in the afterglow of pulsed positive corona discharge

The density of vibrationally excited O2(v = 6) in the afterglow of a pulsed positive corona discharge is measured using time-resolved laser-induced predissociation fluorescence. Discharge occurs in a 13 mm point-to-plane gap in humid air under atmospheric pressure. When the discharge voltage is 32 kV, the O2(v = 6) density at a distance of 2.5 mm from the anode tip is 4 × 1014 cm−3 at t = 2 µs, where t is the postdischarge time, then decreases to 3 × 1013 cm−3 by t = 15 µs. The corresponding vibrational temperatures of O2, Tv, are 1400 K at t = 2 µs and 1100 K at t = 15 µs, which are calculated by assuming the vibrational equilibrium of O2. It is shown that the Tv of O2 in the secondary streamer channel is much higher than that in the primary streamer channel. Since the cross section of dissociative attachment (e + O2 → O + O−) for a low electron energy (<5 eV) increases markedly with the Tv of O2, the high Tv in the secondary streamer may lead to a marked increase in O atom production in the secondary streamer in spite of its low mean electron energy (1–2 eV).

Analysis of streamer properties in air as function of pulse and reactor parameters by ICCD photography

Streamer properties such as their velocity, diameter, intensity and density, can be obtained by analysis of temporal and spatial resolved ICCD imaging. In this paper, experimental results on streamer generation and propagation as a function of several high-voltage pulse and reactor parameters are described. Experiments were performed on a large scale wire–plate reactor in ambient air. The set-up allows for independent variation of the parameters over wide ranges. The minimum gate time of the ICCD camera is 5 ns, allowing for a high temporal resolution. The camera can be triggered with a precision of 1 ns. Both negative and positive polarity pulses are investigated. The most important conclusions are as follows. (1) The streamer velocity ((0.5–2.5) × 106 m s−1) increases if the applied electric field and/or the voltage rise rate is increased. (2) The same is true regarding the velocity ((0.2–1.2) × 105 m s−1) with which the streamer diameter (0.7–3.0 mm) increases during propagation. (3) Typical properties (velocity, diameter, etc) of negative and positive polarity streamers vary less than 25%, especially when the applied electric field is high. (4) As long as the dc bias voltage is below the dc corona onset value it does not have a separate effect on the visual streamer properties. Only the total voltage (peak voltage + dc) is of importance. (5) A simple model was used to determine the electric field in the secondary streamer channel. It was found that in the light emitting part of the secondary streamer the electric field is approximately 21.5 kV cm−1. In the remainder (dark part) of the channel the electric field is around 6.5 kV cm−1. This paper shows mainly experimental findings. Not all observed relations and phenomena could be explained. This is partly caused by the fact that current theoretical and numerical models are not yet able to describe the experimental situation as used during this study.

Experimental analysis and modelling of positive streamer in air: towards an estimation of O and N radical production

This paper is mainly devoted to the comparison between the calculation and experimental results of primary and secondary streamer development in a point-to-plane positive corona discharge in dry air at atmospheric pressure. The qualitative agreement between experimental and calculation results based on the hydrodynamics approximation shows that the O radical is mainly produced in the secondary streamer which is in good agreement with the recent literature measurements using TALIF diagnostics. However, the O radical production yield (in terms of radicals produced per energy injected) is more efficient in the primary streamer than in the secondary one. The main positive corona discharge characteristics are revisited using fast electrical and optical ICCD and streak camera measurements. The calculation shows two streamer radii of, respectively, 10 µm (associated with the radial extension of a high electron density region) and 200 µm (corresponding to the extension of the radial space charge electric field).