Streamer Characteristics Research Articles

Streamer formation and branching from model hydrometeors in subbreakdown conditions inside thunderclouds

AbstractElectric field values measured inside thunderclouds have consistently been reported to be up to an order of magnitude lower than the value required for the conventional electrical breakdown of air. This result has made it difficult to explain how lightning frequently occurs in thunderclouds. A few different theories have been offered to explain the lightning initiation process, one of them being the theory of lightning initiation from hydrometeors. According to this theory, lightning can be initiated from electrical discharges originating around thundercloud water or ice particles in the measured thundercloud electric field. These particles, called hydrometeors, are believed to cause significant enhancement of the thundercloud electric field in their vicinity and then initiate streamers that are the precursor discharges for the hot lightning leader channel. Previously, Liu et al. (2012a) reported streamer formation from a model hydrometeor in an electric field value of half of the conventional breakdown threshold (Ek) for air. In this paper, we present modeling results for streamer formation in electric fields as low as one third of the breakdown threshold. According to our results, initiation of stable streamers from thundercloud hydrometeors in a 0.3Ek electric field is possible, only if enhanced ambient ionization levels (e.g., the ionization created by corona discharges around the same or other nearby hydrometeors) are present ahead of the streamer. The magnitude and distribution of this ambient density may be a determining factor on whether the streamer branches, recovers after the prebranching stage, or continues propagating stably. We investigate the streamer branching behavior and characteristics and test a theory that has recently been proposed to explain this phenomenon. We find that the geometry of the streamer head plays an important role in the streamer branching phenomena. The fast radial movement of the maximum streamer head curvature, combined with the slow reduction of the maximum curvature value, eventually leads the streamer head to branching. Finally, we compare our modeling results with laboratory experiments and realistic thundercloud conditions and discuss the implications of this study to lightning initiation and other lightning‐related phenomena.

Numerical simulation for the production of chemically active species in primary and secondary streamers in atmospheric-pressure dry air

Production of chemically active species in primary and secondary streamers is investigated using a two-dimensional axisymmetric numerical simulation model. The production processes of N2(v = 1), O(3P) and N(4S), which each have different threshold energies, are simulated using experimentally obtained pulsed voltages with peak values, Vpeak, of 18, 24 and 30 kV in dry air at atmospheric pressure. As Vpeak increases, the simulated length of the secondary streamer increases, although there is little change in the primary streamer characteristics. This means that the ratio of the secondary streamer phase to the primary streamer phase increases for increasing Vpeak. The simulated results show that as Vpeak increases, the energy efficiency of O(3P) production increases and that of N2(v = 1) production decreases. On the other hand, the energy efficiency of N(4S) production has reduced dependence on Vpeak. These characteristics can be explained by the spatiotemporal variations of the reduced electric field in the primary and secondary streamer.

Continuum emission-based electron diagnostics for atmospheric pressure plasmas and characteristics of nanosecond-pulsed argon plasma jets

Electron diagnostics based on electron–neutral atom (e–a) bremsstrahlung in the UV and visible range emitted from atmospheric pressure plasmas is presented. Since the spectral emissivity of the e–a bremsstrahlung is determined by electron density (ne) and mean electron temperature (Te) representing the Maxwellian electron energy distribution, their diagnostics is possible. As an example, emission spectra measured from capacitive discharges are presented, which show good agreement with the theoretically calculated emissivity of the e–a bremsstrahlung. For a single pin electrode nanosecond-pulsed plasma jet (n-PPJ) in argon, we investigate the electron properties and the temporal behavior of the positive streamers. Streamers with many branches are clearly observed inside the dielectric tube, while a few main streamers propagate outside the tube along the jet axis. A two-dimensional (2D) measurement of the time-averaged Te distribution was developed using a commercial digital camera and optical band pass filters based on the emissivity ratio of two wavelengths of the e–a bremsstrahlung. The viable measurement range of Te is 0.5–7 eV for the choice of two wavelengths of 300s and 900s nm and 0.5–4 eV for two wavelengths of 400s and 900s nm, which are uncontaminated by the atomic and/or molecular spectra. The 2D Te distribution obtained using 514.5 and 632.8 nm emissions helps to reveal the role of electrons in streamer characteristics in the argon n-PPJ. Time-averaged Te of 2.0 eV and 1.0 eV inside and outside the tube, respectively, were measured. The streamer dynamics of the n-PPJ is shown to be dependent on Te.

Theoretical investigation of streamer characteristics in Ne–Xe–HCl pulsed high-pressure discharges

The aim of this work is to highlight some quantities characterizing the anode-directed streamer generated in the Ne/Xe/HCl gas mixture plasma at high pressure and under non-uniform preionization conditions. This mixture is used as excitation medium for XeCl excimer lasers. A comprehensive model of discharge is presented. This model gives the space-time evolution of electron density and electric field, streamer appearance time, streamer expansion distance and velocity. The effect of HCl concentration in the gas mixture, as well as gas pressure and gap distance on streamer characteristics, have been investigated and discussed. Calculations suggest that the streamer velocity is patently affected by the gap distance with a significant dependence on the HCl concentration in the gas mixture.

Comparison of interplanetary signatures of streamers and pseudostreamers

AbstractIf the source of the slow solar wind is a web comprising pseudostreamer belts connected to the streamer belt, then one expects the properties of interplanetary pseudostreamer flows to be similar to those of streamer flows. That expectation is tested with data from the slow wind preceding stream interfaces in stream interaction regions at 1 AU, where the interfaces separate what was originally slow and fast wind. Pseudostreamer cases were separated from streamer cases with the aid of the streamer identification tool developed by Owens et al. (), and superposed epoch analysis was performed to compare the patterns of a number of plasma and composition parameters. The results reveal that pseudostreamer flows have all of the slow‐wind characteristics of streamer flows except that they are slightly less pronounced than streamer characteristics when compared to fast wind. The results are consistent with the concept that the solar wind displays a continuum of dynamic states rather than only slow and fast states.

Luminosity and propagation characteristics of sprite streamers initiated from small ionospheric disturbances at subbreakdown conditions

This paper reports a modeling study on sprite streamer formation at subbreakdown conditions, i.e., the initiation of sprite streamers in a lightning field below the breakdown threshold field Ek. Successful formation of streamers is observed for a variety of electric fields with the lowest field of 0.3Ekwhen an appropriate ionization column is introduced. The simulation results also indicate that the initial ionization patch from which a streamer is initiated may become very bright following the streamer formation, and its brightness persists as the streamer continues its propagation. The overall luminous structure of the streamer and the ionization patch is very similar to the appearance of initiation of a single sprite streamer on high‐speed images. The brightness of the patch depends on its initial density, and the patch with smaller density is brighter than the denser one. An analytical formula describing the temporal and spatial variation of the electric field in the streamer channel is derived to explain the brightening of the ionization column as well as the luminous streamer trail. Finally, comparisons between the streamers from the ionization patch and those forming in the vicinity of a conducting sphere in an electric field belowEk show that the exponential growth rates associated with streamer characteristics are similar.

Evaluation of the Effectiveness of Light Streamer Tori-Lines and Characteristics of Bait Attacks by Seabirds in the Western North Pacific

To improve the effectiveness of tori-lines it is necessary to evaluate the ability of tori-lines to mitigate seabird bycatch and determine what kind of seabird species gather during line settings, attack the bait and are incidentally caught. We conducted two experiments in the western North Pacific and examined the effectiveness for seabird mitigation of light streamer tori-lines which have no long streamers but many light (short) streamers and are mainly used in the North Pacific area. Firstly, the effectiveness of two different types of tori-line (light streamer (1 m) and long streamer (up to 7 m) tori-line) and of two different colors (yellow and red) of light streamers for seabird bycatch avoidance was evaluated using 567 sets based on data from 20 offshore surface commercial longliners. No significant difference in the bycatch number between the different tori-line types and streamer colors was found. Secondly, we investigated the characteristics of the seabird bycatch in the North Pacific and the effectiveness of three different types of streamers (light, hybrid and modified light types) by detailed observations of seabird attacks using a chartered longline vessel. Although the appearance rate of albatrosses and shearwaters were 40.9% and 27.7%, Laysan albatross was the main seabird species that followed the vessel but shearwaters seldom followed the vessel and did not aggregate during line setting. In all attacks on bait observed during line settings, 81% and 7% were by albatrosses and shearwaters, respectively. In the number of primary attacks by Laysan albatrosses which attacked most aggressively of all seabirds, there were no significant differences among the tori-line types. No individuals of shearwater were caught. The results of both experiments indicated that light streamer tori-lines were as effective as tori-lines with long streamers for mitigating seabird bycatch in the North Pacific.

Dry-band discharges on polluted silicone rubber insulation: control and characterization

Inclined-plane tests of silicone-rubber samples prepared with textured patterns of hemispherical protuberances are described. These are compared with the results obtained for conventional non-textured plane-surface samples of the same material. A remarkable improvement is achieved by such texturing: a material which normally fails the test is enabled to satisfy the standard test criteria, and the tracking and erosion of the samples caused by the tests are significantly reduced. These texturing techniques are currently being extended to prototype composite insulators. It is shown that this improvement for textured samples is a result of the formation of a stable, controlled dry band on the polluted surface. Although discharge inception occurs across the band, these discharges result in a fall, rather than an increase, of the leakage current. The transition to a higher current arc phase is thus inhibited, compared with non-textured samples for which stable dry bands did not occur. These observations of reproducible dry band breakdown also provide an opportunity to characterize experimentally the electrical properties of these discharges. A recent proposed model represents the dry-band discharge as a streamer-spark structure, in contrast to the standard model of an arc-like interdependence of current and voltage. These two models are tested against the present new data, and the discharge is shown to have streamer characteristics.

Phenomenology of streamer propagation during pulsed dielectric surface flashover

There is a growing demand for understanding the physics of surface flashover, as it relates to the breakdown of electric fields on high power systems in the aerospace community. Specifically, the quantitative role of vacuum ultraviolet (VUV) radiation which is self-produced during the initial nanoseconds of surface flashover is virtually unknown. An experiment was constructed which allows detailed electrical and optical measurements of VUV emission during the timescales in which streamers are propagating before the transition into spark discharge. Repeated surface flashover events are generated using a solid-state high voltage pulser, with breakdown recorded in a number of gases at atmospheric pressure. Streamers are photographed using fast optical imaging with 3 ns resolution. Fast voltage and current diagnostics revealed a number of distinct stages of streamer development ranging from the onset of cathode directed streamers to the sharp current rise during final voltage collapse. The emission of VUV radiation is discussed in context to the observed streamer and electrical characteristics.

Influence of the pre-ionization background and simulation of the optical emission of a streamer discharge in preheated air at atmospheric pressure between two point electrodes

This paper presents simulations of positive and negative streamers propagating between two point electrodes in preheated air at atmospheric pressure. As many discharges have occurred before the simulated one, seed charges are taken into account in the interelectrode gap. First, for a pre-ionization background of 109 cm−3, we have studied the influence of the data set used for transport parameters and reaction rates for air on the simulation results. We have compared results obtained in 1997 using input parameters from Morrow and Lowke and from Kulikovsky. Deviations as large as 20% of streamer characteristics (i.e. electric field in the streamer head and body, streamer velocity, streamer radius, streamer electron density) have been observed for this point-to-point configuration. Second, we have studied the influence of the pulsed voltage frequency on the discharge structure. For the studied discharge regime, a change in the applied voltage frequency corresponds to a change in the pre-ionization background. In this work, we have considered a wide range of pre-ionization values from 104 and up to 109 cm−3. We have noted that the value of the pre-ionization background has a small influence on the electron density, electric field and location of the negative streamer head. Conversely, it has a significant influence on the positive streamer characteristics. Finally, we have compared instantaneous and time-averaged optical emissions of the three band systems of N2 and (1PN2, 2PN2 and ) during the discharge propagation. We have shown that the emission of the 2PN2 is the strongest of the three bands, in agreement with experimental observations. It is interesting to note that even with a short time averaging of a few nanoseconds, which corresponds to currently used instruments, the structure of the time-averaged emission of the 2PN2 is different from the instantaneous one and shows negative and positive streamers with smaller radial expansions and more diffuse streamer heads.

The use of the ghost fluid method for Poisson's equation to simulate streamer propagation in point-to-plane and point-to-point geometries

This paper presents the application of the ghost fluid method (GFM) to solve Poisson's equation for streamer discharge simulations between electrodes of complex geometries. This approach allows one to use a simple rectilinear grid and nevertheless take into account the influence of the exact shape of the electrode on the calculation of the potential and the electric field. First, the validity of the GFM approach concerning the computation of the electric field is demonstrated by performing direct comparisons in a point-to-plane geometry of the Laplacian potential and electric field calculated with this method and given by the analytical solution. Second, the GFM is applied to the simulation of a positive streamer propagation in a hyperboloid-to-plane configuration studied by Kulikovsky (1998 Phys. Rev. E 57 7066–74). Very good agreement is obtained with the results of Kulikovsky (1998) on all positive streamer characteristics during its propagation in the interelectrode gap. Then the GFM is applied to simulate the discharge in preheated air at atmospheric pressure in point-to-point geometry. The propagation of positive and negative streamers from both point electrodes is observed. After the interaction of both discharges, the very rapid propagation of the positive streamer towards the cathode in the volume pre-ionized by the negative streamer is presented. This structure of the discharge is in qualitative agreement with the experiment.

Streamer head structure: role of ionization and photoionization

Results from experiments and numerical modelling of streamer propagation are presented. The 2D hydrodynamic numerical description of the pulsed discharge based on the local ionization and photoionization models adequately describes the streamer shape and dynamics over a wide range of pressures and voltages. This work presents a method for imaging the instantaneous emission distribution in the streamer head. A method for restoring the electrodynamic radius of the streamer head was developed on the basis of the streamer head images that were obtained with subnanosecond exposure time. The electrodynamic radius has been determined as the distance between the maxima of the electric field at the position where the streamer head transforms into the streamer channel. The dependence of the electrodynamic radius on voltage and pressure has been determined. We show that a 2D numerical model using hydrodynamic approximation predicts the streamer characteristics with an accuracy of about 15% in the 0.5–1 atmosphere pressure range and up to 40% in the 0.2–0.3 atmosphere pressure range for a voltage of U from 20 kV up to 40 kV in the 30 and 40 mm discharge gap.

Streamer and leader discharge propagation characteristics leading to breakdown in electronegative gases

This paper describes the propagation characteristics and mechanisms of partial discharge (PD) leading to breakdown (BD) in electronegative gases such as SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 </sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixtures for AC voltage application. An established PD measuring system of highly time-resolved PD current and light intensity waveforms, streak and light emission images enabled us to discuss the physical mechanisms of PD generation and propagation in terms of space charge behavior. Experimental results revealed that the time-resolved PD generation was divided into different groups composed of the first large PD and the subsequent small PDs; the former was identified as the leader discharge, and the latter corresponded to the streamer discharges. The successive generation of the streamer and leader discharges was interpreted by the change of critical volume size. The time-resolved PD generation characteristics leading to BD were also measured and discussed. The leader discharge would be obliged to take a detour along the periphery of the positive space charge area in the vicinity of the needle electrode, and finally result in BD in electronegative gases

An adaptive grid refinement strategy for the simulation of negative streamers

The evolution of negative streamers during electric breakdown of a non-attaching gas can be described by a two-fluid model for electrons and positive ions. It consists of continuity equations for the charged particles including drift, diffusion and reaction in the local electric field, coupled to the Poisson equation for the electric potential. The model generates field enhancement and steep propagating ionization fronts at the tip of growing ionized filaments. An adaptive grid refinement method for the simulation of these structures is presented. It uses finite volume spatial discretizations and explicit time stepping, which allows the decoupling of the grids for the continuity equations from those for the Poisson equation. Standard refinement methods in which the refinement criterion is based on local error monitors fail due to the pulled character of the streamer front that propagates into a linearly unstable state. We present a refinement method which deals with all these features. Tests on one-dimensional streamer fronts as well as on three-dimensional streamers with cylindrical symmetry (hence effectively 2D for numerical purposes) are carried out successfully. Results on fine grids are presented, they show that such an adaptive grid method is needed to capture the streamer characteristics well. This refinement strategy enables us to adequately compute negative streamers in pure gases in the parameter regime where a physical instability appears: branching streamers.

Experimental and Numerical Analysis of Streamers in Pulsed Corona and Dielectric Barrier Discharges

Streamer characteristics have been experimentally and numerically analyzed for pulsed-corona discharge (PCD) and dielectric-barrier discharge (DBD) to find out how the discharge methods determine them and how they, in turn, affect the generation of radicals in flue gases. Experiments have been performed and compared for decomposition of a nitrogen oxide (NO) using PCD and DBD, and the electric field and average electron energy in the streamer are measured in each discharge by using the line ratio of N/sub 2//sup +/ to N/sub 2//sup */. The measured results of electron energy reasonably explain in terms of G-value how the measured NO removal efficiencies have come out. The PCD having high electron energy turns out to be more efficient for generating N radicals, whereas the DBD containing relatively low electron energy is more effective for producing O radicals. Three-dimensional (3-D) and one-dimensional (1-D) numerical simulations have been carried out to understand the observed streamer dynamics in both the PCD and DBD reactors. The 3-D numerical simulation has successfully illustrated the images of streamer front propagation in a wire-cylinder PCD reactor. In the 1-D simulation for the DBD, the recurrence phenomena of streamers have numerically appeared during the rising phase of an AC voltage. Furthermore, these numerical models have properly predicted the electric fields that are comparable with the corresponding average electron energies estimated from the emission spectral measurements for the PCD and DBD.

Measurements of Electron Energy by Emission Spectroscopy in Pulsed Corona and Dielectric Barrier Discharges

AbstractElectric field distributions and average electron energies are measured by an optical emission spectroscopic method to investigate streamer characteristics in a pulsed corona discharge (PCD) and a dielectric barrier discharge (DBD) in atmospheric air. In PCD, average electron energies appear to be in the range of 10 ~ 12 eV along the streamers. Time-resolved measurements show that streamers in DBD have a relatively low value of average electron energy of 9 ~ 10 eV. Enhancement of the electron energy is observed when DBD is operated in a non-uniform geometry, such as dielectric barrier with a hole.

Experimental study of streamers in pure N2 and N2/O2 mixturesand a ≈13 cm gap

Empirical data on streamer formation and propagation innear-atmospheric pressure N2 and N2/O2mixtures are presented.Thedata were obtained primarily from high-speed, high-sensitivity shutterand streak photography of streamers produced in a≈13 cm gap.The streamer propagation velocity as a function of applied voltage,polarity, total pressure, and O2 concentration are provided.In addition, information on streamer bifurcation, and streamer shape andsize is included.The breakdown process has two phases: a fast phase featuring thepropagation of streamers, and much slower phase involving the heating ofthe gas to form the spark channel.Also we found that the addition of O2significantly alters the streamer characteristics and behaviour, indicating that photoionization processes play an important role.

Predischarge Models in Dielectric Liquids

This study presents self-consistent models of streamer growth using an equivalent electrical network, the only input data being the electrode geometry and the applied voltage waveform. The growth of filamentary and bushlike discharge structures are simulated. The initiation and the development of streamers are taken into account using field criteria. The streamer instantaneous propagation velocity is obtained using a model based on energetic considerations. In the case of filamentary streamers, each branch is assumed to be a cylindrical channel represented by an RC cell (R and C are, respectively, the resistance and the capacitance associated with each branch). The hazardous discharge propagation is also taken into account. In the case of bush-like structures, the envelope of streamers is assumed to be approximately spherical. For given experimental conditions (such as applied voltage and electrode geometry), we determine the streamer characteristics such as the shape and amplitude of the streamer current, the electrical charge, the velocity, power and energy injected in the gap. The developed models also enable the simulation of an image converter working in streak or frame mode and the streamer trajectory plotted in real time. An estimate of the pressure within bushlike streamer envelope is given. A good agreement between computed and experimental results has been obtained.