Filamentary Streamer Discharges Research Articles

Propagation of multi-burst streamer in the hot gas channel

We report the evolution of multi-burst filamentary streamer discharge generated by a Tesla coil power in normal air. The multi-burst discharge shows a self-similar pattern from successive branching discharge. The upstream streamer is also observed in the experiment with a floating electrode. The trajectory of the streamer produced in the second wave packet follows the pathway of the streamer produced in the first wave packet. The expanding speeds of the second burst streamers are found to be faster than the speeds of the first burst streamers. We show that the second (and the following) burst streamer propagates inside the hot gas channel generated by the first (and the previous) burst streamer. The rotational temperature of the nitrogen molecules in the hot gas channel generated by the streamer in the first wave packet was measured by the optical spectrum method. By interrupting the hot gas channel, the presence of the hot gas channel is found to be crucial for the propagation of the following burst streamer.

Evolution of N(4S) atoms produced under nitrogen streamer conditions: time-resolved TALIF study at reduced pressures

The evolution of N(4S) species produced by filamentary streamer discharge was investigated by two-photon absorption laser-induced fluorescence technique. A triggered single streamer filament was periodically produced in pure nitrogen at pressures of 20, 50, 100 and 200 Torr, and N(4S) species were monitored in the center of the discharge gap during the streamer formation, decay and afterglow. Under all of the investigated pressures, the population maxima of nitrogen atoms were observed in a microsecond timescale; i.e. well after the extinction of the streamer event. The concentration of nitrogen atoms increased with pressure. The maximum N(4S) concentration measured at 20 Torr was about 1013 cm−3, while it exceeded 1015 cm−3 at 200 Torr. After reaching maxima, atomic densities exhibit hyperbolic decay, which was followed up to the post-discharge time of 0.5 ms. Our results show that only a small part of N(4S) is produced during the streamer transit or within 200 ns after the transit (20%–25% increase with respect to the background density), while most of the nitrogen N(4S) atoms are produced during the streamer channel decay in timescales from units to several tens of microseconds.

Application of the Position-State Separation Method to Simulate Streamer Discharges in Arbitrary Geometries

In this paper, we extended the recent work of Liu and Becerra to employ the position-state separation (POSS) method to simulate filamentary streamer discharges. POSS is a semi-Lagrangian method, which solves convection-dominated continuity equations without numerical flux correction. An improved interpolation strategy for POSS is here introduced to overcome the excessive numerical diffusion of the method when very small time step is used. Several benchmark tests in the literature are used to validate the improved method. Numerical experiments show that POSS is an accurate, efficient, and robust numerical method to simulate streamer discharges in arbitrary geometries when combined with finite-element method.

Sprite streamer initiation from natural mesospheric structures.

Sprites are large, luminous electrical discharges in the upper atmosphere caused by intense cloud-to-ground lightning flashes, manifesting an impulsive coupling mechanism between lower and upper atmospheric regions. Their dynamics are governed by filamentary streamer discharges whose propagation properties have been well studied by past work. However, how they are initiated is still under active debate. It has recently been concluded that ionospheric/mesospheric inhomogeneities are required for their initiation, but it is an open question as to what the sources of those inhomogeneities are. Here we present numerical simulation results to demonstrate that naturally-existing, small-scale mesospheric structures such as those created by gravity waves via instability and breaking are viable sources. The proposed theory is supported by a recent, unique high-speed observation from aircraft flying at 14-km altitude. The theory naturally explains many aspects of observed sprite streamer initiation and has important implications for future observational work.

LIF study of N2(A3, v = 0–10) vibrational kinetics under nitrogen streamer conditions

The evolution of individual v = 0–10 vibrational levels of N2(A3) metastable species produced by filamentary streamer discharge was investigated by the laser-induced fluorescence technique. Triggered single streamer filament was periodically produced in pure nitrogen at a pressure of 200 torr and metastable species were monitored during the streamer channel decay in the centre of the discharge gap. The observed dynamics of N2(A3) vibrational levels follow two very different scenarios: while higher (v > 6) vibronic levels decay exponentially in hundreds of nanoseconds, the populations of lower levels (v ≤ 6) definitely increase, first reaching a local maximum on a microsecond timescale and then decreasing afterwards. Population maxima of N2(A3, v ≤ 6) levels occur after the streamer onset with a certain delay, which decreases with increasing vibrational number. Interpretation of experimental observation based on a 0D kinetic model of the post-discharge period takes into account the most important processes redistributing populations between the N2(A3), N2 and N2 vibronic levels. The model reproduces experimental observations fairly well, including observed maxima delays occurring due to the collisional cascade, which transfers metastable species from higher even/odd vibrational levels towards v = 0/v = 1 terminal levels through the Δv = 2 vibrational relaxation mechanism. A calibration procedure based on the rate of energy-pooling processes was used to determine absolute populations of the v = 0 and 1 levels from LIF data, and the model results were utilized to place on an absolute scale all the higher (v > 1) measured vibronic levels. Vibrational distributions obtained from calibrated LIF data at selected instants show a reasonable qualitative agreement with model predictions. Population maxima exceeding 3 × 1014 cm−3 were fixed for v = 2 and 3 vibrational levels, while the lowest v = 0 level reaches only 8–9 × 1013 cm−3. Lastly, we show that the observed rate of the v = 2 level decay is not compatible with published rate constants for the v = 2 → v = 0 vibrational relaxation.

Fast imaging of intermittent electrospraying of water with positive corona discharge

The effect of the electrospraying of water in combination with a positive direct current (dc) streamer corona discharge generated in air was investigated in this paper. We employed high-speed camera visualizations and oscilloscopic discharge current measurements in combination with an intensified charge-coupled device camera for fast time-resolved imaging. The repetitive process of Taylor cone formation and droplet formation from the mass fragments of water during the electrospray was visualized. Depending on the applied voltage, the following intermittent modes of electrospraying typical for water were observed: dripping mode, spindle mode, and oscillating-spindle mode. The observed electrospraying modes were repetitive with a frequency of a few hundreds of Hz, as measured from the fast image sequences. This frequency agreed well with the frequency of the measured streamer current pulses. The presence of filamentary streamer discharges at relatively low voltages probably prevented the establishment of a continuous electrospray in the cone–jet mode. After each streamer, a positive glow corona discharge was established on the water filament tip, and it propagated from the stressed electrode along with the water filament elongation. The results show a reciprocal character of intermittent electrospraying of water, and the presence of corona discharge, where both the electrospray and the discharge affect each other. The generation of a corona discharge from the water cone depended on the repetitive process of the cone formation. Also, the propagation and curvature of the water filament were influenced by the discharge and its resultant space charge. Furthermore, these phenomena were partially influenced by the water conductivity.

Formation of , v = 0–3) metastable species in decaying nitrogen streamer

Evolution of , v = 0−3) metastable species produced by triggered single filamentary streamer discharge was investigated utilizing emission spectrometry and laser-induced fluorescence techniques. Triggered streamers were produced repeatedly in point-to-plane DBD electrode geometry in pure nitrogen at 200 Torr and metastable species were monitored in the centre of the discharge gap. Populations of all four monitored vibronic levels increase during streamer channel decay phase, reaching local maximum in a microsecond timescale and decreasing afterwards. Maximum population of an individual , v) vibronic level occurs with a certain delay after streamer onset τd(v), which decreases with increasing vibrational number. The longest delay τd = 5 ± 0.5 µs was fixed for the lowest metastable level v = 0, whereas τd values of 4.4 ± 0.5, 1.75 ± 0.25 and 0.85 ± 0.25 µs were fixed for v = 1, 2 and 3, respectively. Coupled evolution of the two lowest , v = 0, 1) levels was monitored independently by applying an indirect method based on emission intensity of the N2 Herman infrared system. Very good agreement between emission and fluorescence based diagnostics was achieved for later post-discharge times t > τd. A simple 0-D model of , v) post-discharge kinetics based on vibrational relaxation and electronic quenching of individual vibronic levels reproduces experimental observations fairly well. According to the model, observed maxima likely occur due to the collisional cascade that transfers metastable species from higher even/odd vibrational levels towards v = 0/v = 1 terminal levels through the Δv = 2 vibrational relaxation mechanism.

PIC/MCC Simulation of the Ionization Process for Filamentary Streamer Plasma Jet at Atmosphere Pressure in Argon

Recently, we have reported a microwave plasma jet at atmosphere in argon, capable of generating filamentary streamer discharges within the entire quartz tube, while several bifurcations yield at the end of the copper wire immediately in the quartz tube when incident power reaches 20 W. However, the ionization process for the discharges is still not very well clarified. This paper shows a numerical study of the proposed plasma jet by means of the 2D3V particle in cell with Monte Carlo collision method. The detailed information about the distributions of plasmas and electromagnetic fields is obtained by sampling the simulated results at different time steps. The simulation results suggest that the production of the proposed plasma jet is attributed to the seed plasmas triggered by the enhanced electric field of surface plasmon polaritons and its interaction with plasmas.

Filamentary streamer discharges in argon at atmospheric pressure excited by surface plasmon polaritons

This paper describes a microwave plasma jet in an argon atmosphere capable of generating filamentary streamer discharges within the entire quartz tube excited by surface waves of surface plasmon polaritons (SPPs) located in the tube. Several discharge streamers are immediately produced at the end of the copper wire when incident power reaches 20 W. From simulations, the wavelength of the surface wave was found to be approximately 5.7 cm. Although the developing streamers induce E-field enhancements favoring discharging, more streamer bifurcations requiring additional energy to maintain discharging diminish the resonant enhanced E-field. The underlying mechanism of the proposed plasma jet is resonant excitation of SPPs and its interaction with plasmas.

Plasma Catalytic Synthesis of Silver Nanoparticles

We present the experimental results of plasma catalytic synthesis of colloidal silver nanoparticles, using AgNO3 as the precursor, ethanol as the solvent and reducing agent, and poly vinyl pyrrolidone (PVP) as the macromolecular surfactant. The plasma is generated by an atmospheric argon dielectric barrier discharge jet. Silver nanoparticles are produced instantly once the plasma is ignited. The system is not heated so it is necessary to use traditional chemical methods. The samples are characterized by UV-visible absorbance and transmission electron microscopy. For glow discharge mode no obvious silver nanoparticles are observed. For low voltage filamentary streamer discharge mode a lot of silver nanoparticles with the mean diameter of ∼3.5 nm are generated and a further increase of the voltage causes the occurrence of agglomeration.

Effects of ion–neutral chemical reactions on dynamics of lightning-induced electric field

Secondary lightning phenomena in the upper atmosphere called sprites attract interest from the viewpoint of atomic–molecular and plasma physics. Lightning-induced electric field accelerates the ionospheric electrons up to tens of electron-volts, inducing electrical breakdown as well as strong optical emissions, through electron impact ionization of molecules. A large-scale structure of sprites is constructed by collective dynamics of filamentary streamer discharges in a rarified gas, which in turn is controlled by the distribution of the background electric field. In this paper, we firstly reanalyze the relationship between quasi-static field formation and local ion chemistry with first-order perturbation techniques. Secondly, we investigate with a full ion chemical model the effects of electron attachment to oxygen molecules on its density in moderate cases of undervoltage lightning electric fields rather than the cases of intense ionization in streamers. We estimate the minimum values that are provided by the chemical balance with electron detachment from negative ions. We also investigate the recovery timescale of the electron density and find that the scale (⩾1 s) is occasionally much larger than the interval of each lightning stroke (≈10 ms). We suggest that the subsequent sprite event as well as the field formation could be well affected by the ghost of the primary event. We discuss further the negative ion chemistry triggered by electron attachment in the nighttime mesosphere.

Experimental study on the transition of the discharge modes in air dielectric barrier discharge

Dielectric barrier discharge (DBD) usually manifests as a filamentary streamer discharge in atmospheric air, which limits its industrial application prospect, and the homogeneous DBD with homogeneity and stability has a wider application prospect in the field of material surface treatment, thin film deposition and plasma sterilization than the filamentary one. In order to study the generation condition for the homogeneous DBD in atmospheric air, the characteristics of DBD in the pressure range from 10 Pa to atmospheric pressure are experimentally studied by measuring their electrical discharge parameters and observing their light emission phenomena. The transition of the discharge mode with a change in pressure is observed, and a critical pressure value for generating the homogeneous DBD is obtained, with the influence of barrier materials, their thickness and surface roughness and the air gap distance on the critical pressure values being investigated experimentally. The experimental results show that three characteristic types of discharge modes, including the homogeneous mode, the mixed mode and the filamentary mode, are observed with an increase in pressure. The dielectric barrier plays an important role in the generation of the homogeneous DBD, and the critical pressure values will be larger if the barrier thickness is smaller and the air gap distance is smaller. The critical pd values (the product of gas pressure p and gas gap width d) are almost constant with the change in the air gap distance, which can be improved by reducing the thickness of the dielectric barrier and by selecting appropriate barrier materials, as is validated by the experimental results.

Streamer-induced emission and spectrometric determination of basic plasma parameters

Basic collisional and radiative processes occurring in filamentary streamer discharges driven in N2−O2 mixtures at atmospheric pressure are reviewed. Characteristic spectrometric fingerprints that allow distinguishing emissions induced by electrons from those emissions driven by molecular metastables and by atomic species are outlined. Finally, we briefly summarize emission-based diagnostics procedures capable of determining important streamer parameters.