Streamer Propagation Research Articles

Streamer propagation and pressure waves produced by a nanosecond pulsed surface sliding discharge: effect of the high-voltage electrode shape

This paper aims at better understanding nanosecond sliding discharges based on a three-electrode geometry and at studying the effect of the shape of the pulsed high-voltage electrode on their electrical, optical and mechanical properties. Three different electrode shapes are considered: a typical planar electrode with a straight edge, a planar electrode with a sawtooth edge, and a wire electrode. First, we verified that the sliding discharge starts to appear when the potential difference between both air-exposed electrodes exceeds about 25 kV, corresponding to a mean electric strength (potential difference divided by the gap) a little bit higher than 6 kV cm−1, but this value differs slightly depending on the shape of the electrode. Secondly, we highlighted that the current with the wire-based discharge is slightly higher compared to the two others because the streamers are more numerous and they are more uniformly distributed along the wire. Moreover, whatever the electrode shape, intensified charge-coupled device visualizations showed that many streamers initiate from the pulsed high-voltage electrode edge and propagate on the dielectric surface toward the DC voltage electrode at a mean velocity of about 1 mm ns−1. However, the streamer trajectory depends strongly on the electrode shape. Visualizations of the pressure waves induced by the different plasma actuators have been realized with a shadowgraph system. In the presence of a sliding discharge, every streamer is at the origin of three different pressure waves. The first hemispherical pressure wave results from streamer ignition at the edge of the pulsed high-voltage electrode, the head of the streamer acting as a point heat source. The second hemispherical pressure wave is due to the corona-type discharge that ignites from the negative DC high-voltage electrode when the streamer head gets closer. Finally, the third wave is a semi-cylindrical wave as each streamer acts as a line source of heat. To conclude, pressure measurements highlighted that the peak value of the pressure is nearly constant along the spanwise direction of the wire electrode as it presents high fluctuations with the sawtooth electrode, the maximum pressure being measured above the tips, where streamers are localized.

Electric field distributions along helium plasma jets

Results of simulations of streamers propagating along the atmospheric-pressure helium plasma jets ejected from a thin tube into ambient air are presented. The computational model includes the equations governing the helium–air mixture composition along and across the jet, as well as the equations, describing streamer propagation in the mixture, for the electric field and the charged species densities. Streamer velocity and spatial–temporal profiles of plasma parameters are obtained for various values of the helium flow rate. It is shown, in agreement with available experimental data, that the electric field values in the heads of streamers increase nearly linearly with the distance from the tube exit and that the slope of this dependence decreases with the growth of the helium flow rate.

Simulation of positive streamers in CO2 and in air: the role of photoionization or other electron sources

Positive streamer discharges have been studied and modelled extensively in air. Here we study positive streamers in CO2 with and without oxygen admixtures; they are relevant for current high voltage technology as well as for discharges in the atmosphere of Venus. We discuss that no efficient photoionization mechanism is known for gases with a large CO2 fraction, as photons in the relevant energy range are rapidly absorbed. Hence positive streamers can propagate only due to some other source of free electrons ahead of the ionization front. Therefore we study positive streamer propagation in CO2 with different levels of background ionization to provide these free electrons. The effect of replacing photoionization by background ionization is studied with simulations in air. Simulating streamers in background fields of 16 to 20 kV cm−1 at standard temperature and pressure within a gap of 6.4 cm, we find that streamer propagation is rather insensitive to the level of photoionization or background ionization. We also discuss that the results depend not only on the value of breakdown field and applied electric field, and on preionization or photoionization, but also on the electron mobility μ(E) and the effective ionization coefficient α eff(E), that are gas-dependent functions of the electron energy or the electric field.

Self-organization of touching-target current with ac voltage in atmospheric pressure plasma jet for medical application parameters

In experiments with the cold atmospheric pressure plasma jet, the frequency of the current measured near the treated target shows a mismatch with the voltage frequency. The system including the plasma device and target organizes the plasma delivery differently with changing voltage frequency and amplitude. All electromagnetic and chemical processes near the target depend on the frequency of the plasma-target contacts. In experiments and in 2D fluid model simulations, the self-organization of touching-target current is studied for voltage frequencies of 10–50 kHz and amplitudes of 2.5–6 kV. The streamer propagation through the volumetric plasma cloud outside of discharge device and the mechanism responsible for variation of touching-target current frequency are discussed.

Streamer propagation along a profiled dielectric surface

We investigate the propagation of positive streamers along a profiled dielectric surface in air at atmospheric pressure. Results from experiments and two-dimensional planar low-temperature plasma fluid simulations are presented and analysed. The test object consists of a disk-shaped high voltage electrode and a dielectric slab with 0.5 mm deep corrugations. The corrugated surface has a 47% larger surface area than the smooth reference surface. The experiments and simulations are performed at voltage levels that lead to either gap-bridging or arrested streamers. In both experiments and simulations, the streamers take a longer time to reach the ground electrode when propagating along the profiled surface than along the smooth reference surface. Also, arrested streamers stop closer to the high voltage electrode when a profiled surface is used. Streamers propagate closely along the surface profile in the simulations, which suggests that the observed surface profile effect is mainly a result of elongated streamer channels. Compared to the streamers propagating along the smooth surface, the elongated streamers on the profiled surface have less residual voltage at the streamer front to drive the streamer advancement.

Pressure-dependent propagation of streamers under step voltage in a long point-plane gap in transformer oil

The effect of pressure on positive and negative streamer propagation in a mineral transformer oil is studied in an 80 mm point-plane gap under step voltage. Increased pressure causes reduced stopping length for non-breakdown streamers, higher breakdown voltage, reduced background current, reduced branching in positive streamers and virtually no change in negative streamer shape. The velocities and acceleration voltages are close to being independent of pressure, indicating that the velocity controlling mechanisms take place in the liquid phase. Amplitude and frequency of small current pulses (probably small reilluminations) during negative 1st mode is reduced with increasing pressure, but the effect on reilluminations during 2nd and 3rd mode is small in both polarities.

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.

A 3D numerical study of positive streamers interacting with localized plasma regions

Residual charged particles from previous discharges or external sources can produce some localized plasma regions, so called plasma patches in a discharge gap. Such plasma patches can affect the propagation morphology of passing streamers. Here we investigate how positive streamers interact with the plasma patches using a 3D PIC/MCC model. Simulations are performed in air with two planar electrodes, considering either an electron-ion or a purely positive ion plasma patch. When a positive streamer propagates through the electron-ion plasma patch, it shows a lower field enhancement, a weaker growth of electron density and a slower propagation velocity. If the plasma density in the patch is sufficiently high, it can even stop the propagation of streamer, however, streamer can restart from the other end of the patch after a while. In addition, the electron-ion plasma patch can change streamer’s direction by electrostatic attraction or repulsion. If the plasma patch consists of purely positive ions, it can also slow down the propagation of streamer and change its direction by repulsion. In case of sufficiently high ion density, streamer’s direction and velocity are strongly disturbed, resulting in splitting around the tip of the patch, the number of splitting channels increases with background electric field.

How pulse polarity and photoionization control streamer discharge development in long air gaps

A 2D approach is used to simulate the properties of positive and negative streamers emerging from a high-voltage electrode in a long (14 cm) air gap for standard pressure and temperature. The applied voltage varies from 100 to 500 kV. To reveal the influence of photoionization, the calculations are made for various rates of seed electron generation in front of the streamer head. The difference between the properties of positive and negative streamers is associated with the different directions of the electron drift ahead of the streamer head. As a result, the peak electric field at the streamer head and the streamer velocity are higher for positive voltage polarity. The average electric field in the negative streamer channel is approximately twice that in the positive streamer channel, in agreement with available measurements in long air gaps. It is shown that photoionization in front of the streamer head is important not only for the development of strong positive discharges, but for the development of strong negative discharges as well. An increase in the photoionization rate increases the propagation velocity of the positive streamer and retards the propagation of the negative streamer.

Electrical breakdown characteristics in non-uniform electrode system with bakelite barrier under the lightning ımpulse voltage

Electrical breakdown voltage (VBD) and streamer propagation path characteristics in highly non-uniform electrode system were investigated to clarify the dielectric barrier effects. The experimental results showed that VBD is affected by both the barrier dimension and the barrier position. As the position of the dielectric barrier becomes closer to the needle electrode, the rising rate of VBD according to the barrier dimension increases. In addition, streamer propagation path could be identified into two categories, depending on the dielectric barrier position and the dimension. Finally, it is found that VBDs were determined by the electrical insulation structure, not the streamer propagation path or length.

Electromagnetic and Thermal Phenomena Modeling of Electrical Discharges in Liquids

Electrical discharges in liquids have received lots of attention with respect to their potential applications in various techniques and technical processes. Exemplary, they are useful for water treatment, chemical and thermal processes acceleration, or nanoparticles production. In this paper the special utility of discharges for cold pasteurization of fruit juices is presented. Development of devices for its implementation is a significant engineering problem and should be performed using modeling and simulation techniques to determine the real parameters of discharges. Unfortunately, there is a lack of clear and uniform description of breakdown phenomena in liquids. To overcome this limitation, new methods and algorithms for streamers propagation and breakdown phase analysis are presented in the paper. All solutions were tested in “active area” in the form of liquid material model, placed between two flat electrodes. Electromagnetic and thermal-coupled field analysis were performed to determine all the factors that affect the discharge propagation. Additionally, some circuit models were used to include the power source cooperation with discharge region. In general, presented solutions can be defined as universal and one can use them for numerical simulation of other types of discharges.

Numerical simulation of the positive streamer propagation and chemical reactions in SF6/N2 mixtures under non-uniform field

SF 6 /N 2 mixtures is considered as a practical alternative proposal of SF 6 in GIS and GIL. Simulating particle transportations and chemical reactions during the positive streamer propagation in SF 6 /N 2 mixtures assists in the insulation performance optimization of SF 6 /N 2 mixtures. This paper presents a fluid dynamic model coupled with the chemical reaction system for the positive streamer propagation in SF 6 /N 2 mixtures. The Townsend coefficients of the 20%SF 6 /80%N 2 mixture derived from the proposed chemical reaction system are in accordance with the measurement results. Based on this model, the propagation of the positive streamer in a 1 mm needle-plate gap in the 20%SF 6 /80%N 2 mixture is simulated. Simulated results indicate that there exists a negative space charge region in the streamer channel. It can be attributed to the increasing attachment rates of SF 6 yielding SF 5 − and SF 6 −, and the reduction of the ionization rates of N 2 and SF 6 in the streamer channel. Besides, it is noted that the ionization activities of N 2 and SF 6 at the streamer head are equally important to support the continuous propagation of the positive streamer. The ionization of N 2 in the streamer channel serves as an important factor to supply electrons and avoid the accumulation of the negative space charge.

Discharge propagation on a dielectric surface in a single-filament arrangement

Discharge development and streamer propagation on a dielectric surface were investigated in nitrogen-oxygen gas mixtures at atmospheric pressure. A coaxial pin-to-pin arrangement was used to generate single surface discharges driven by positive unipolar square wave high voltages of between 7 and 9 kV at 4.3 kHz. The development of surface discharges was recorded by ICCD and streak cameras. The discharges developed on the surface using pin electrodes attached directly to the dielectric plate. The accumulation over several discharge events showed a propagation front evolving from the electrode tip, while images of single discharges showed a non-uniform and branched structure of discharge channels. The electrode polarity influenced the discharge expansion and propagation velocity. Positive polarity of the metallic electrode (rising slope of HV pulses) led to a cathode-directed streamer with higher propagation velocities (5 × 105 m/s) than for negative polarity (relative to surface charges; falling slope). The increase in the O2 content in N2 from 0.1 to 20 vol% resulted in a decrease in discharge duration and an increase in streamer velocities.

Effect of chemical reactions on electrohydrodynamic force generation process in dielectric barrier discharge

A discharge plasma simulation based on a three-fluid model is generally utilized to understand the physical mechanism in a dielectric barrier discharge (DBD) plasma actuator. In this study, the influence of chemical reactions considered in a numerical model on the simulation results is investigated from the viewpoint of electrohydrodynamic (EHD) force generation in the DBD plasma actuator. Positive and negative streamers are simulated utilizing three types of models considering different reactions and species, and the investigation is conducted in two steps. In the first step, where the influence of the neutralization process is investigated, the electron recombination with a cluster ion (O4+) plays an important role; it contributes to the decrease in seed electron production and effective coefficient of ionization for the positive streamer, and the decrease in negative ion production for the negative streamer; as a result, the propagation length and EHD force generation decrease. In the second step, where the influence of the production process is investigated, the stepwise ionization from metastable states has little influence owing to quite low production rates. Therefore, the simulation results indicate that the numerical model needs to consider the electron recombination with O4+ to accurately predict the streamer propagation and EHD force generation, while it is unnecessary to take into account the metastable molecules.

Influence of conductivities on electrical breakdown of water under microsecond pulsed voltage

A study of the electrical breakdown of water under microsecond pulsed voltages has been performed. The influence of conductivities (350–1550 μS/cm) has been reported in the needle-plate configuration. Both positive and negative applied voltages (10–30 kV) have been adopted to study the streamer propagation and breakdown phenomena. Three streamer modes are observed in our experiment, and the morphologies of streamers at different conductivities are compared. Increasing the conductivity leads to a thinner gaseous layer and stronger luminance for all streamers. However, the polarity effect of the applied voltages causes differences in the mobility of charges in water and results in different propagation velocities. The minimum breakdown voltage at different polarities exhibits different trends for positive subsonic streamers and negative subsonic streamers. This paper has evaluated the shock wave intensity and bubble dynamics after the breakdown of the water gap. The results show that the relationship of the peak pressure (Pm) and the residual energy of the capacitor at the breakdown time (Wb) is consistent and stable. The bubble dynamics and shock wave propagation are less affected by the water conductivity.

How cellulose particles influence streamer propagation and branching in transformer oil: a 2D modelling perspective

The streamer discharges and electric breakdown in insulating liquid like transformer oil are undesirable for power equipment. However, the physical processes of streamer propagation and branching events in dense liquid dielectrics are not well understood. In this paper, we develop an improved fluid model to investigate the interactions of cellulose particles with streamer propagation and branching behaviors. We elaborately select the number of cellulose particles (single or multiple particles), their size and locations to elucidate the influencing mechanisms. The simulation results show that when the heads of streamer contact with the surface of the cellulose particle, the local electric field increases sharply, hence the rise of ionization rate and velocity. The scattering electric field lines guide the streamer head away from the surface, thereby causing branching to occur. The interactions between the two split streamers allow one head to continuously propagate, while the other dies out due to insufficient ionization rate. When the particle is too small or too far away to the streamer channel, it has no pronounced impact on the streamer propagation. While placing the particle very close to or on the route of discharge channel will cause the streamer to creep on the cellulose particle and to branch more.

New approach for assessment of positive streamer penetration of long air gaps under impulse voltages

The paper comprises a new systematic approach to determine the critical ambient field needed for positive streamer propagation in nonuniform field gaps. It is shown that such critical streamer penetration field is a function of the basic value previously established for uniform field gaps and the degree of ambient field nonuniformity. The latter quantity is defined by the ratio of the maximum to mean ambient electric fields along the streamer propagation path, which can be determined either analytically or by charge simulation. Such functional dependence of the critical streamer penetration gradient on field nonuniformity has been determined for different rod topologies of rod-plane gap as well as for single and bundle conductor plane gaps. The model is used to determine critical streamer penetration fields and streamer lengths under different impulse voltage levels for different gap configurations and for a tall ground structure exposed to ambient impulse field. The findings of this method are compared to available experimental results and the agreement is found satisfactory.

Numerical simulations of stable, high-electron-density atmospheric pressure argon plasma under pin-to-plane electrode geometry: effects of applied voltage polarity

When applying high-voltage direct current to a pin-to-plane electrode geometry with a distance of 2 mm under atmospheric pressure in argon gas, electrical breakdown forms primary then secondary streamers. The polarity of the applied voltage affects this streamer-propagating phenomenon. Properties such as propagation speed, streamer head size, and plasma generation are parameterized at nanosecond scales by computational simulations of a self-consistent, multi-species, multi-temperature plasma fluid modeling approach. For positive polarity on the pin electrode, streamer-head propagation speeds up and streamer head size increases with increasing applied voltages. However, local electron density at the head decreases. For negative polarity, corona-like discharges form around the pin electrode under low applied voltages, and diffusive steamers form under high applied voltages. Secondary streamers re-propagate from the pin after primary streamer propagation, forming a plasma with a high electron density of 1021 m−3 for the positive polarity. We show that low-voltage operations with positive polarity are useful for stable high-electron-density discharges under atmospheric pressure argon.

Variation in guided streamer propagation along a DBD plasma jet by tailoring the applied voltage waveform

Experimental data on the evolution of a helium atmospheric pressure plasma jet driven by two different voltage waveforms are presented. The characteristics of directed ionization waves (guided streamers) were compared for a sinusoidal voltage waveform with a frequency of 52 kHz and a voltage waveform that was formed via the superposition of 41.6 kHz bipolar square pulses and 300 kHz oscillations. With the sinusoidal voltage, two consecutive ionization waves were observed. With a special tailoring voltage, control of the guided streamer propagation in a stepwise mode was achieved. The observed second streamer and the second step of propagation could be regarded as a secondary ionization wave for both voltages. A change in the voltage waveform led to significant variations in the secondary ionization wave formation and streamer parameters. The voltage waveform enabled the number of ionization waves and their propagation to change, which provided the possibility of controlling the plasma parameters of the jet.

Modeling of Streamer Ignition and Propagation in the System of Two Approaching Hydrometeors

AbstractFirst‐principles plasma fluid modeling is used for investigation of electrical gas discharges ignited by a configuration of two approaching conducting hydrometeors with typical radii on the order of several millimeters under thunderstorm conditions (i.e., at an elevated location in the Earth's atmosphere corresponding to half of air density at ground level and at applied electric field approximately half of that required for avalanche multiplication of electrons in air). It is demonstrated that ultraviolet photons produced by the electrical discharges developing due to the electric field enhancement in the gap between two hydrometeors and resultant photoionization in the discharge volume lead to much less stringent conditions for conversion of these discharges to a filamentary streamer form than in the case not accounting for the effects of photoionization. It is also demonstrated that this photoionization feedback is critical for understanding and correct description of the subsequent streamer discharges developing on the outer periphery of two hydrometeors whose potential is equalized due to the electrical connection established by the initial streamer discharge between them. The initial streamer ignition between the hydrometeors can be preceded by the corona development, which can have detrimental effect on the ignition. However, it is demonstrated that for hydrometeors approaching with a speed of 10 m/s the effect of this onset corona is small.