Streamer Development Research Articles

Relationship Between Sprite Current and Morphology

AbstractOn June 2 and 3, 2019, 63 sprites were captured from Langmuir Laboratory in central New Mexico. The two storms investigated were located in northwest Texas, 400–800 km away from the observation site. Optical recordings were made with a Phantom V2010 camera operating at up to 100,000 frames per second. Electromagnetic remote sensing of lightning and sprite electric fields was performed with a sensitive slow antenna (LEFA). Data from the Earth Networks Total Lightning Network (ENTLN) were used to locate the sprite parent flashes. The combined information of these three data sets reveals that a staggering fraction of more than half of the sprites observed have a distinguishable electromagnetic signature attributed to currents flowing within the sprite body. Furthermore, these sprite current signatures were unusually large in comparison to previous reports. The sprite electric field changes have roughly half the amplitude of their parent lightning flash's, corresponding to sprite peak currents of 26–58 kA on average. The largest sprites have current moments of up to 2,700 kA km, as inferred from a computationally efficient method to solve Maxwell's equations. Detailed comparison between the sprites' electromagnetic signatures and high‐speed optical recordings show that optically large sprites containing upward streamers (carrots and jellyfish) tend to have larger electrical currents than the ones displaying only downward streamer development (column sprites). Finally, a clear increasing trend in peak current moment is evident with increasing morphological complexity, from columns to carrots to jellyfish sprites.

Nano-sized composite improving the insulating performance of insulating paper using low-temperature plasmas

Nanostructured dielectric composite has been considered as a promising manner in improving the flashover performance of oil-paper which has been widely used in power systems. In this paper, plasma-enhanced chemical vapor deposition (PECVD) is used to deposit SiO2 on the ceramic fiber-reinforced insulating paper. Scanning electron microscope images show a large number of SiO2 nanoparticles with diameters of 100 nm–250 nm uniformly attached to the fiber surface after the plasma deposition. The surface flashover voltage of the insulating paper was tested in the air and the transformer oil, respectively. Results show that the corresponding DC surface flashover voltages increased by 15.1% in the air and breakdown between liquid and solid interface increased by 24.6% after the PECVD. It is believed that nanoparticles constructed in ceramic fibers change the electron injection barrier which inhibits the injection of negative charges and hinders the accumulation of charges in the dielectric. Nanoparticles can capture electric charges formed in the transformer oil which affects the generation and development of streamers, resulting in an increased dielectric strength. This study provides a new method to comprehensively improve the surface insulating property which has the prospect of promoting other dielectric materials.

Study of streamer development in Resistive Plate Chamber

This work has been carried out to simulate a Resistive Plate Chamber and corroborate it with experimental measurements in order to develop a numerical tool for studying the performance of the device for any gas mixture. This will allow us to explore the feasibility of operating these chambers in their avalanche mode within the Iron Calorimeter setup at India-based Neutrino Observatory with any eco-friendly substitute. The simulation has considered a hydrodynamic model of charge transport to emulate the electronic and ionic growths in the device as a function of the applied voltage which determines its working mode as either of the avalanche or streamer. In order to validate, the simulation result has been compared with compatible experimental data available in the literature.

Simulation Study on Discharge Process of Negative Polarity in UHV Tower-line Air Gap

Carrying out the research on the physical simulation model of the negative polarity discharge process in UHV tower-line air gap is of great significance to the lightning protection of UHV transmission lines. Based on the physical mechanism of negative discharge in long air gap, a physical simulation model including initial corona initiation and streamer development, leader initiation, streamer-leader system development, and final jump is established. The model considers the characteristics of corona initial development, the randomness of the leader path, and the negative development of the negative leader. Finite element software was used to calculate the background potential distribution of the gap, and the experimental observations were used to verify the model established in this paper. Finally, the model was used to simulate the discharge process of the negative polarity in tower-line air gap under actual size of tower window structure. The results show that the simulation calculations agree well with the test results.

Fluid simulation model and analysis of partial discharge characteristics of tip defects

The tip discharge is modeled and the micro discharge characteristics are studied. The hydrodynamic model of tip discharge in transformer oil is established. The development process of streamer discharge under pulse voltage is analyzed. The distribution of space charge density and space electric field under different pulse voltage amplitude and rising edge is obtained. The numerical results show that: with the increase of applied voltage amplitude, the average velocity of streamer development changes more significantly with the same discharge spacing; the steeper the rising edge pulse is, the faster the average discharge development speed is and the larger the discharge radius is. At the same time, according to the change law of streamer morphology development under AC voltage, the discharge frequency is less, the amplitude is higher, and the phase distribution is narrow when the applied voltage is positive half cycle. When the applied voltage is negative half cycle, the discharge times are more and the phase distribution is wide, and the tip discharge has obvious polarity effect.

Study of the microwave streamer evolution using a new semi-analytical model

A microwave (MW) plasma channel (filament, plasmoid, and plasma dipole) shows promise for its applications for off-body non-electrode modification of a gas flow (plasma aerodynamics) and in the plasma assisted combustion process. A full-scale study of the plasma channel evolution requires a self-consistent solution of Maxwell's equations, plasma chemical kinetics equations, and gasdynamics equations. An attempt is made to develop a simple electrodynamic (based on the solution of Maxwell's equations) “fast” model for studying the evolution of the plasma channel in conjunction with a fairly complete system of plasma chemical reactions. The model is based on a simplifying assumption about the shape of the channel, which converts a 3D problem into a 1D one. The results of numerical calculations in air within the pressure range P = 20–150 Torr are presented. An experimental study of plasmoid development was carried out to verify the predictions of the model. The calculated results agree well with all available experimental data within the pressure range P = 20–150 Torr. The proposed electrodynamic approach made it possible to reveal (i) the mechanism of self-organization during the development of a MW streamer and (ii) the reason for a sharp decrease in the velocity of its elongation, as well as to obtain relations connecting the main characteristics of the streamer (the amplitude of the electric field in the channel and on its heads, the velocity of ionization waves, and the characteristic scale of their fronts). The proposed model will be useful both for estimating the channel parameters and for deciphering the dynamics of radiation scattered by the plasma dipole. The development of such an approach will allow one to study the evolution of multiplasmoid structures of a high-pressure MW discharge.

The Solar Corona during the Total Eclipse on 1806 June 16: Graphical Evidence of the Coronal Structure during the Dalton Minimum

Abstract Visible coronal structure, in particular the spatial evolution of coronal streamers, provides indirect information about solar magnetic activity and the underlying solar dynamo. Their apparent absence of structure observed during the total eclipses throughout the Maunder minimum has been interpreted as evidence of a significant change in the solar magnetic field from that during modern solar cycles. Eclipse observations available from the more recent Dalton minimum may be able to provide further information, with sunspot activity being between the levels seen during recent solar cycles and in the Maunder minimum. Here, we show and examine two graphical records of the total solar eclipse on 1806 June 16, during the Dalton minimum. These records show significant rays and streamers around an inner ring. The ring is estimated to be ≈0.44 R ⊙ in width and the streamers in excess of 11.88 R ⊙ in length. In combination with records of spicules or prominences, these eclipse records visually contrast the Dalton minimum with the Maunder minimum in terms of their coronal structure and support the existing discussions based on the sunspot observations. These eclipse records are broadly consistent with the solar cycle phase in the modeled open solar flux and the reconstructed slow solar wind at most latitudes.

Numerical simulation of streamer evolution in surface dielectric barrier discharge with electrode-array

Atmospheric pressure surface dielectric barrier discharges (SDBDs) may be composed of streamers fast propagating along a dielectric surface in ambient air, producing reactive oxygen and nitrogen species, and inducing a force on the neutral gas, which can find applications, respectively, in plasma medicine and aerodynamics. In this work, a two-dimensional self-consistent fluid model was developed to study SDBDs with an electrode-array. Emphasis was placed on the interaction of counter-propagating streamers and discharge uniformity for different applied voltages and geometric configurations of the electrode-array. When two counter-propagating streamers collide, the streamers come to a stop within a certain (ultimate) distance between the streamer heads. Optimizing the applied voltages is a convenient way to improve uniformity, making the streamer heads reach a minimum distance between each other. Shortening the electrode spacing can simultaneously shorten the streamer length and the ultimate distance between streamers. Under certain discharge parameters (such as applied voltage), there exists an optimum electrode spacing maximizing uniformity.

Spatiotemporal analysis of streamer discharge in a wire-to-wire reactor with positive nanosecond pulse supply

The spatial and temporal distribution of the discharge streamers in positive pulsed wire-to-wire electrode configuration in atmospheric air is investigated by an electrical-optical diagnostic system. Time-resolved ICCD images show that the discharge streamers in wire-to-wire electrode develop in three phases: the primary streamer, the secondary positive streamer, and the secondary negative streamer. It is observed that the evolution of discharge streamers is strongly influenced by the amplitude of the applied voltage. The optical emission spectroscopy measurement of hydroxyl radical OH indicates that the OH is mainly generated in the secondary positive streamer near the anode region. But in the region near the cathode the emission of OH radicals can also be detected due to the secondary negative streamer. The influences of rise time, fall time and pulse duration on streamer dynamics and the subsequent radical production are observed. It is shown that the average propagation velocity of the primary streamer decreases with the increase of the rise time, while the variation of pulse width and pulse duration parameters have little effect on that of the primary streamer. The response surface methodology based on Box–Behnken design model is implemented to evaluate the contribution of the three critical pulse parameters on ozone production. The results of the response surface quadratic model show that the pulse rise time plays the most prominent role in the generation of ozone among the three pulse parameters of rise time, fall time and pulse duration.

Ion Cluster Formation by Nonthermal Plasma Induced by Pulse Corona Discharge Toward Indoor Air Cleaning

During pulsed corona discharges, both negative and positive ions react with moisture to generate ion clusters. These ion clusters are useful for cleaning environmentally hazardous materials such as hazardous chemicals, pollutants, and allergens. In this study, numerical simulations are carried out on the ion cluster formation of such ion-generation devices. The behavior of streamer evolution and cluster formations is simulated, and we show that the clustering progresses toward H3O+(H2O)4 and O2−(H2O)4 when the chemical species of H3O+(H2O) n and O2−(H2O) n ( n = 0−5) are considered. Ion number densities measured in the study are smaller than those calculated because of known differences between the numerical model and the experimental apparatus (in particular, the difference due to the loss of ions in the path of the chamber). The evaluation of the lifetime and diffusion coefficients of the ion clusters could be important.

Numerical simulation of streamer discharge development processes with multi-component SF6 mixed gas

In recent years, more stringent environmental protection requirements have led to increasingly higher voltage power equipment that adopt SF6 mixed gas as an insulation medium. In this paper, the streamer development in SF6 mixed gas and the distribution of each gas component were studied over time. Thus, a discharge model of the needle plate electrode with SF6 mixed gas was established. The hydrodynamic model for SF6 mixed gas discharge in uneven electric fields was created by coupling the Boltzmann drift-diffusion equation and Poisson's equation. The influence of different factors, such as the applied voltage, gas mixture ratio, and electrode spacing, on the streamer discharge of SF6/N2 mixed gas, and the influence of the type of mixed gas (air and CO2) combined with SF6 on the streamer development process were studied. The simulation results showed that the higher SF6 content in the mixed gas made breakdown more difficult, and a higher pressure led to a more concentrated streamer. Comparing and analyzing the discharge processes under different SF6 mixed gases (SF6/CO2, SF6/air, and SF6/N2) showed that the streamer for the SF6/CO2 mixture took longer to develop toward the plate electrode with a more difficult breakdown. The presented simulation results provide a microscopic interpretation for the needle-plate discharge defects that appear in power equipment that utilize SF6 mixed gas.

Effects of TiO2 nanoparticles and electrodes surface-modified by low-temperature plasma on impulse breakdown voltage of propylene carbonate

Insulating and energy-storage materials, such as propylene carbonate, require high dielectric strength. To improve insulation performance of propylene carbonate, we surface treated a copper electrode with a low-temperature plasma based on liquid nanometer modification technology. Thus, a TiO 2 nano-modified liquid was prepared and the surface of the copper electrode was modified by sputtering a TiO 2 film. The surface morphologies of the electrode surface before and after modification and the impulse breakdown voltages and space charge distributions of pure and nano-modified propylene carbonate were studied. These results indicate that the TiO 2 film deposition on the surface of the copper electrode markedly reduced the surface roughness. Furthermore, after the surface modification, the breakdown voltage of pure propylene carbonate and nano-modified propylene carbonate increased by 9.4 and 14.3%, respectively. We analyzed the effects of the electrode surface modification and nanoparticles on the breakdown voltage of propylene carbonate from the perspective of space charge. The nanoparticles introduced shallow traps, which increased the rate of charge dissipation. Furthermore, surface modification of the electrodes inhibited charge injection into the liquid, which affected the generation and development of streamers in the liquid, thereby further improving the breakdown performance of the propylene carbonate.

Magneto-fibrillation augments the breakdown strength of ferrofluid dielectrics

The present article reports experimental evidence with a theoretical formalism on the enhancement of the dielectric breakdown strength of ferrofluids by inducing magneto-fibrillation with an external magnetic field. The dielectric breakdown strengths of oil based ferrofluids are determined, and it is further shown that the strength enhances due to the presence of a localized magnetic field in the streamer development zones. The improvement in breakdown strength is also supplemented by improvement in the reliability of the liquid dielectrics, which is established by a two parameter Weibull analysis. It is also noted that a horizontal magnetic field is more potent toward improved breakdown strength than an equivalent vertical field. The enhanced scavenging of electrons from the streamer development zones due to localized magnetic fibrillation by the nanoparticles is proposed as the crux mechanism. Microscopy studies are conducted to provide visual evidence of the fibrillation process in the ferrofluids due to the local magnetic field. A theoretical formalism is proposed to predict the ferrohydrodynamics of fibrillation, and this is further used to develop a model to predict the increment in breakdown strengths. The proposed model predictions are noted to agree well with the experimental observations. The study may find strong implications in design and development of high voltage liquid dielectrics with tunable electrical stress bearing caliber.

Evolution of three-electrode pulsed surface dielectric barrier discharge: primary streamer, transitional streamer and secondary reverse streamer

The streamer evolution of three-electrode pulsed surface dielectric barrier discharge (SDBD) in atmospheric air is studied with basic morphologic features, electrical characteristics and numerical simulation. Time resolved ICCD images demonstrate that besides the primary and secondary reverse streamers, a novel discharge mode-transitional streamer is also responsible for sustaining the streamer development in the three-electrode pulsed SDBD, which is different from the streamer mechanism in traditional two-electrode pulsed SDBD. Moreover, the discharge mode transition from the primary streamer to the transitional streamer is observed in a relative narrow discharge gap of 5 mm, while a relative large discharge gap of 19 mm results in a new phenomenon in which the primary streamer transits to the secondary reverse streamer without the process of transitional streamer. To determine the deposited energy of each streamer phase, an equivalent circuit model is built and it shows that the transitional streamer possesses the main energy. To make a further understanding of the formation and propagation of three streamer phases, a 2D fluid model is implemented and the streamer evolution and species distribution are analyzed. The results exhibit that the gathered positive ions in primary streamer head does not move forward when it is close to the second grounded (SG) electrode surface, because the same positive polarity of a cathode layer is formed on the SG electrode surface.

Emerging and expanding streamer head in low-pressure air

The emergence of a streamer from an ionisation wave and its expansion are ultra-fast processes shaping the very first moments of the streamer development, and are usually accessible only by complex numerical models. In this Letter, we report experimental evidence of the emergence of a streamer from an ionisation wave in 1.3 kPa air, a laboratory analogue of early-stage streamers emerging in geophysical Blue Starters and Jets. The radially and temporally resolved electric field patterns of an expanding streamer are determined by sub-nanosecond optical emission spectroscopy. As the emerged streamer expands, the electric field decreases by a factor of 1.4 in 1 ns. We quantify the radial expansion of the streamer head and its axial acceleration, reaching the velocity of 107 m s−1. In combination with electrical measurements, the transferred charge, electron density, and mean electron energy are quantified, enabling detailed insight into this ultra-fast phenomenon at its characteristic time-scale.

Blocking streamer development by plane gaseous layers of various densities

Streamer interaction with gaseous layers of various densities is numerically simulated in ambient air on the basis of a two-dimensional fluid model. It is shown that rarefied layers are greater obstacles to streamer propagation in comparison with dense layers. When intersecting a low-density layer, the streamer tends to initiate a radial ionization wave, which screens and weakens the electric field both on the axis in the layer and behind it. As a result, it is difficult to form a secondary streamer behind the low-density gas layer. A streamer interacting with a high-density layer also can initiate a radial ionization wave, which develops in undisturbed air along the outer surface of the layer. The streamer can overcome a high-density layer at not-too-high values of the layer thickness. The effects of the streamer polarity, layer thickness and density on the streamer interaction with the layer are studied. It is shown that the discharge gap with a thin low-density layer behaves like a diode in which streamer discharges of negative polarity can pass through the gap, while discharges of positive polarity are blocked.

High-resolution Near-infrared Polarimetry and Submillimeter Imaging of FS Tau A: Possible Streamers in Misaligned Circumbinary Disk System

Abstract We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2–1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to ∼240 au from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an local standard of rest kinematic (LSRK) velocity of 1.19–5.64 km s−1. Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17–16.43 km s−1. From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems.

A two-dimensional air streamer discharge model based on the improved Helmholtz equation at low temperature and sub-atmospheric pressure

In this paper, an efficient boundary condition is applied to solve the photoionization rate, and a two-dimensional numerical simulation is carried out for the development and propagation of an air streamer at low temperature and sub-atmospheric pressure. The results show that the new boundary condition improves the calculation accuracy, but the influence of photoionization on the streamer discharge process is not obvious. The discharge current in the development of streamer discharge is defined, and the corresponding expression of the positive and negative streamer discharge current is given. The influence of the electric field exceeding the threshold value on the discharge process is preliminarily introduced. In the process of discharge, only the propagation velocity of the streamer is obviously higher than that of normal temperature and pressure, and the trend of the other parameters is basically the same as that described in the previous paper. The above results give us a deeper understanding of the discharge characteristics under low temperature and sub-atmospheric pressure, which has certain significance for the development of aviation and high voltage engineering.

Optical and Energetic Investigation of an Advanced Corona Ignition System in a Pressure-Based Calorimeter

In recent years, radio-frequency corona igniters have been extensively studied for their capability to ensure an effective ignition also in lean or diluted mixtures. Corona ignition is volumetric, with streamers coming from a star-shaped electrode. During the discharge, many radicals and excited species, able to speed up the combustion onset, are generated. At the same time, corona igniters are able to release a considerable amount of thermal energy inside the combustion chamber. The correct determination of such energy is crucial to evaluate the effectiveness of the ignition. In this work, corona discharge is experimentally evaluated inside an optical vessel. In this apparatus, the released thermal energy is measured by means of pressure-based calorimetry, and at the same time the natural luminosity of the streamers is recorded with a high-speed camera. The goal is to find a relationship between thermal energy release and streamers luminosity. Tests are performed using nitrogen as medium, at different pressure levels inside the vessel. The peak electrode voltage is varied to characterize the igniter behaviour in different operating conditions. The results of this work can be used to quantify the corona ignition capabilities to involve a wide amount of medium while releasing a high amount of thermal energy. A repeatability evaluation of streamer evolution is investigated as well.

Near-Sun observations of an F-corona decrease and K-corona fine structure.

Remote observations of the solar photospheric light scattered by electrons (the K-corona) and dust (the F-corona or zodiacal light) have been made from the ground during eclipses1 and from space at distances as small as 0.3 astronomical units2-5 to the Sun. Previous observations6-8 of dust scattering have not confirmed the existence of the theoretically predicted dust-free zone near the Sun9-11. The transient nature of the corona has been well characterized for large events, but questions still remain (for example, about the initiation of the corona12 and the production of solar energetic particles13) and for small events even its structure is uncertain14. Here we report imaging of the solar corona15 during the first two perihelion passes (0.16-0.25 astronomical units) of the Parker Solar Probe spacecraft13, each lasting ten days. The view from these distances is qualitatively similar to the historical views from ground and space, but there are some notable differences. At short elongations, we observe a decrease in the intensity of the F-coronal intensity, which is suggestive of the long-sought dust free zone9-11. We also resolve the fine-scaleplasma structure of very small eruptions, which are frequently ejected from the Sun. These take two forms: the frequently observed magnetic flux ropes12,16 and the predicted, but not yet observed, magnetic islands17,18 arising from the tearing-mode instability in the current sheet. Our observations of the coronal streamer evolution confirm the large-scale topology of the solar corona, but also reveal that, as recently predicted19, streamers are composed of yet smaller substreamers channelling continual density fluctuations at all visible scales.