Gas Discharge Theory Research Articles

Mechanism of runaway electron generation in nanosecond pulsed plate-plate discharge at atmospheric-pressure air

Classical discharge theory (Townsend theory and streamer theory) has limitations in explaining nanosecond pulsed gas discharge. In recent years, the research on nanosecond pulsed gas discharge theory based on the high-energy runaway electrons has attracted extensive attention. But so far, there have been few studies of the generation mechanism of runaway electrons in atmospheric-pressure-air nanosecond pulsed plate-to-plate discharge, which seriously hinders the application and development of nanosecond pulse discharge plasma. In this paper, a one-dimensional implicit particle-in-cell/Monte Carlo collision (PIC/MCC) model is developed to investigate the mechanism of runaway electron generation and breakdown in a 1 mm-long atmospheric-pressure-air gap between the plate electrode and plate electrode driven by a negative nanosecond pulse voltage with an amplitude of 20 kV. The results show that under the influence of space charge dynamic behavior, the electric field enhancement region appears between the plate electrode and plate electrode, so that electrons can satisfy the electron runaway criteria and behaves in the runaway mode. In addition, it is also observed that the pre-ionization effect of the runaway electrons in front of the discharge channel can cause the secondary electron avalanches. As the secondary electrons avalanche and the discharge channel continues to converge, the discharge is guided and accelerated, eventually leading to the breakdown of the air gap. This study further reveals the mechanism of nanosecond pulsed plate-plate discharge, expands the basic theory of nanosecond pulsed gas discharge, and opens up new opportunities for the application and development of nanosecond pulsed discharge plasma.

Effect of Environmental Parameters on Streamer Discharge in Short Air Gap between Rod and Plate

Environmental meteorological parameters (temperature, humidity, air pressure, etc.) have an important impact on short gap streamer discharge. Based on the streamer theory and particle continuity equation of gas discharge, a short gap streamer discharge simulation model is established, and the influence of environmental parameters on the dynamic development process of streamer discharge is simulated and analyzed. The short gap air gap discharge characteristics were tested in a self-made gas discharge chamber. The results show that at low humidity (relative humidity <80%), with the increase of humidity, the electron density of the streamer channel increases, the field strength of the streamer head increases, the streamer development speed speeds up, and the gap breakdown voltage decrease; At higher humidity (relative humidity >80%), with the increase of humidity, the electron density of the streamer channel decreases, the field strength of the streamer head decreases, the development speed of the streamer slows down, and the gap breakdown voltage increase. With a decrease of gas pressure, the electron density of the streamer channel decreases, the field strength of the streamer head decreases, the development speed of the streamer increases, and the gap breakdown voltage decreases; The temperature change has little effect on the streamer development process.

Research on Improved Arc Model of Isolating Switch and VFTO Characteristics

The simulation of very Fast Transient overvoltage (VFTO) requires an accurate isolating switch arc model. Based on gas discharge theory, the trend of electron number in the gap is analyzed by particle continuity equation simulation. Based on this, the traditional time-domain arc resistance model is improved, and combined with the characteristics of time-domain arc resistance model, dynamic arc model and normal distribution, the improved arc model is established, which conforms to the physical law of arc discharge process of isolating switch. The simulation model of simulation experiment platform was established, and the simulation waveform obtained by the improved arc model, exponential resistance arc model and other arc models was compared with the experimental waveform to prove the accuracy of improved arc model.

Kinetic theory of high-voltage low-pressure gas discharge with electron initiation on a cathode in a planar gap

We report one-dimensional kinetic simulation of electron and ion transport and multiplication (based on the Boltzmann kinetic equations) in a self-consistent electric field after electron injection from the cathode. The 1D1V Boltzmann equations take into account the electron impact ionization, elastic electron scattering, and resonant ion recharging. The spatio-temporal evolution of the gas breakdown in a planar diode with a gap of 5 mm filled with nitrogen at pressure of 1 Pa, with applied voltage of 2.5 kV, was demonstrated in detail. In the vicinity of these parameters, an intermediate gap breakdown mode is realized when the discharge exists in the form of relaxation current oscillations. The simulation showed that, during plasma generation, the electric potential acquires non-monotonic spatial distribution in the gap. Under the non-monotonic potential distribution, anode-directed ion flow is formed inside the gap. An extended hump of potential may appear, forming ion fluxes with kinetic energy nominally exceeding the voltage drop (in the calculated spectrum the mean ion energy was at the level of 6–7 keV at an applied voltage of 2.5 kV).

Research on fuze microswitch based on corona discharge effect

Abnormal voltages such as electrostatic, constant current, and strong electromagnetic signals can erroneously trigger operation of MEMS pyrotechnics and control systems in a fuze, which may result in casualties. This study designs a solid-state micro-scale switch by combining the corona gas discharge theory of asymmetric electric fields and Peek’s Law. The MEMS switch can be transferred from “off” to “on” through the gas breakdown between the corona electrodes. In the model, one of the two electrodes is spherical and the other flat, so a non-uniform electric field is formed around the electrodes. The theoretical work is as follows. First, the relation among the radius of curvature of the spherical electrode, the discharge gap, and the air breakdown voltage is obtained; to meet the low voltage (30–60 V) required to drive the MEMS switch, the radius of curvature of the spherical electrode needs to be 10–50 μm and the discharge gap between the two electrodes needs to be 9–11 μm. Second, the optimal ratio ε is introduced to parameterize the model. Finally, the corona discharge structural parameters are determined by comparing the theoretical and electric field simulation results. The switch is then fabricated via MEMS processing. A hardware test platform is built and the performing chip tested. It is found that when the electrode gap is 9 μm, the electrostatic voltage is at least 37.3 V, with an error of 2.6% between the actual and theoretical air breakdown voltages. When the electrode gap is 11 μm, the electrostatic voltage is at least 42.3 V, with an error of 10.5% between the actual and theoretical air breakdown voltages. Both cases meet the design requirements.

Modeling the dielectric strength variation of supercritical fluids driven by cluster formation near critical point

Density fluctuation driven by cluster formation causes drastic changes in the dielectric breakdown characteristics of supercritical fluids that cannot be described solely based on the conventional Townsend’s gas discharge theory and Paschen’s law. In this study, we model the dielectric breakdown characteristics of supercritical CO2 as a function of pressure based on the electron scattering cross section data of CO2 clusters that vary in size as a function of temperature and pressure around the critical point. The electron scattering cross section data of CO2 clusters are derived from those of gaseous CO2. We solve the Boltzmann equation based on the electron scattering cross section data to obtain critical electrical fields of various cluster sizes as a function of pressure. To validate our model, we compare the modeled breakdown voltage with the experimental breakdown measurements of supercritical CO2, which show close agreement.

Breakdown characteristics of carbon dioxide–ethane azeotropic mixtures near the critical point

The properties of traditional dielectric media have been a major limiting factor impacting the design and operation of many applications spanning from particle accelerators over x-ray radiography and radiotherapy to electrical power systems. Supercritical fluids (SCFs) combine the properties of high dielectric strength, low viscosity, and excellent heat transfer capability. Here, we show, for the first time, the anomalous breakdown strength characteristics of SCF mixtures, such as carbon dioxide (CO2) and ethane (C2H6) mixtures and their azeotropic mixture under supercritical conditions. Our experiments suggest that the dielectric behavior deviates significantly from the established theory of gas discharge known by the work of Townsend and Paschen. Our results reveal that not only pure substances such as CO2 exhibit a discontinuity of the dielectric strength near the critical point, but the supercritical mixture also manifests a discontinuity. The effect of random particle clustering in the pure substance and the mixture is observed, which impacts the mean free path of electrons. We present the measured breakdown voltage in a 0.1 mm gap with a uniform electric field over a wide range of mixture ratios and fluid densities and use a mathematical model by Stanley to show the density fluctuations that peak at around the critical point. By adjusting the mixing ratio, we prove that the mixture forms a useful combination of dielectric strengths and critical points and broadens the applicability of SC mixtures for a variety of purposes.

Modeling of flowing gas discharge – Part I

A physical model of flowing gas discharge is presented. This model extends Townsend's discharge model for static gases to flowing gases and can be applied to a wider range of gas discharge situations and the breakdown laws of flowing gases are analytically solved. The process of modeling reveals that the discharge of flowing gases includes three basic characteristics: the deflection of the major discharge path, the blowing away of some of electrons, and a decrease in gas density. The presented model enables quantitative calculations of the ionization coefficient and breakdown voltage in flowing gases. Comparisons between the present results and the corresponding ones obtained experimentally show good consistency. These results supplement the theory of gas discharge and provide some support for insulation protection in flowing gases.

Boltzmann equation studies on electron swarm parameters in Townsend breakdown of copper vapor plasma using independently assessed electron-collision cross sections

Electron transport coefficients in copper vapor plasma are calculated both by two-term expansion of electron Boltzmann equation Bolsig+ and tracking the random motion of electrons using Monte Carlo collision code METHES based upon recently evaluated cross section sets. The copper atoms are evaporated from hot electrode during the post-arc phase of vacuum circuit breakers, in which Townsend breakdown between electrode gaps is probable. The electron energy probability function, electron mean energy, flux/transport mobility and diffusion coefficients, as well as Townsend ionization coefficients are shown in reduced fields 10∼1000 Td at a typical vapor temperature 2000 K. The validity of two-term approximation is checked by comparison to well benchmarked METHES code. If the electrode temperature varies between 1500∼2500 K, the influence of vapor temperature on ionization coefficients is about 5% at 200.4 Td, and drops to 0.5% at 493 Td according to Bolsig+ results. Similar to classic gas discharge theory, the Paschen curve is proposed for Townsend breakdown of metal vapor. Using the calculated ionization coefficient and a constant secondary electron yield, the Paschen minimum is determined to be 106∼122 V at a critical value of the product of vapor density and gap length (4.7∼5.7)×1019 m-2. A satisfactory agreement was found with the previously measured ignition voltage between vacuum interrupter contacts after the arcing.

A Simple Analytical Method of Gas Discharge Based on Logistic Model

Current research on gas discharge theory has made significant development in terms of numerical simulation, but its analytical description of streamer mechanism remains overly simplified, as it is still based on the electron avalanche model characterized with the exponential growth and infinite breakdown current. This paper presents a simple analytical method of gas discharge based on the classic logistic model and covers four aspects. First, it gives the exact definition of generation and mortality rate of electron number, establishes a logistic differential equation and a logistic iteration model for streamer mechanism, and derives deterministic analytical and iterative solution. Second, we also extend the mortality rate to include negative value, thus allowing the logistic model to describe both exponential growth and S shape growth scenarios, and provide criteria for categorizing spark breakdown, Townsend discharge, and stable discharge (glow, arc, aka saturated streamer). Third, the logistic differential model can be transformed into an iterative model. From that we derive the criteria for evaluating discharge instability. Last, although our model is 1-D, but it is still practical and easy to use given its clear analytical expression of underlying physical mechanism.

Polarity Effect of Flowing Air Discharge

Gas discharge theory as an important subject has been widely employed to solve various questions related to discharge. However, previous concerns about gas discharge were mainly related to some discharge situations in static gases, which do not consider the influence of airflow on discharge. In this paper, the influence of both the airflow direction that is parallel to the field direction and the airflow velocity on air discharge is studied. The airflow is found to induce an obvious polarity effect, which results in a substantial difference in the breakdown voltage values. Compared with the breakdown voltage in static air, the breakdown voltage in airflow decreases because of the downwind effect and increases because of the headwind effect. The relative mean free path of electrons, the diffusion radius of electrons, and the air density are the three major factors affecting the discharge process, and they change with the airflow direction and airflow velocity. The combined effects of those three factors determine the variation trends in breakdown voltage with airflow velocity. These results can provide guidance for the design and insulation coordination of high-voltage equipment in an airflow environment.

Temperature dependence of DC electrical tree initiation in silicone rubber considering defect type and polarity

In this article, the electrical tree initiation behavior in silicone rubber (SIR) under DC voltage was studied. Tests were conducted to reveal the effects of temperature (20–120 °C), defect type and voltage polarity on electrical tree initiation. In samples with an undamaged needle-tip (N samples), we find that the average tree initiation voltage (Fa«) decreases exponentially with increasing temperature by 42%. Single-branch trees and multiple-branch trees are observed. The probability of generating multiple-branch trees decreases with increasing temperature. In samples where an air gap or crack is in the needle (AN samples), Vati is 55.7% of that in N samples at 20 °C. In AN samples, Vati and tree shape do not change monotonically and Vati varies in a small range as temperature rises. Vati for N samples under negative voltage is much larger than that under positive voltage. This polarity effect is reversed in AN samples. Gas discharge theory and Frohlich's theory of dielectric breakdown explain electrical tree initiation behavior at different temperatures. Based on differential scanning calorimetry (DSC) results, we believe that partial segment relaxation of SIR at high temperature leads to Vati decreasing. Electrical trees previously generated inside the cable or an air gap created due to mechanical damage cause Vati to of a subsequently generated tree to drop to nearly half of its typical level. This information is useful for the design of HVDC cable insulation.

Pattern formation based on complex coupling mechanism in dielectric barrier discharge

The pattern formation of cinque-dice square superlattice pattern (CDSSP) is investigated based on the complex coupling mechanism in a dielectric barrier discharge (DBD) system. The spatio-temporal structure of CDSSP obtained by using an intensified-charge coupled device indicates that CDSSP is an interleaving of two kinds of subpatterns (mixture of rectangle and square, and dot-line square) which discharge twice in one half voltage, respectively. Selected by the complex coupling of two subpatterns, the CDSSP can be formed and shows good stability. This investigation based on gas discharge theory together with nonlinear theory may provide a deeper understanding for the nonlinear characteristics and even the formation mechanism of patterns in DBD.

From an electron avalanche to the lightning discharge

The goal of this work is to describe qualitatively the physics of processes which begin with an electron avalanche and finish in a lightning discharge. A streamer model is considered that is based on studies of the recently discovered processes occurring in the prestreamer region. The investigation and analysis of these processes enabled making the conclusion that they are, in essence, the attendant processes, which ensure the electron avalanche-to-streamer transition, and may be interpreted as a manifestation of properties of a double charge layer exposed to the external electric field. The pressing problems of physical processes which form a lightning discharge are considered from the standpoint of new ideas about the mechanism of the streamer formation and growth. Causes of the emergence of coherent super-high-frequency radiation of a leader and the neutron production in a lightning discharge are revealed that have not been explained so far in the theory of gas discharge. Based also on new ideas about the lightning discharge, a simple ball-lightning model, providing answers to almost allquestions formulated from numerous observations on the behavior of ball lightning, is offered, and the need of a new design of lightning protection instead of the traditional rod is discussed.

Analyzing of AC Corona Discharge Parameters of Atmospheric Air

Corona on transmission line conductors is a significant source of electromagnetic interference and corona loss. In order to analyze variable atmospheric condition on corona inception voltage gradient of bundle conductors a calculation model was established. The voltage gradient around stranded conductors for calculating corona inception voltage gradient is required. For the high voltage transmission lines, it is necessary to know the electric field in vicinity of the conductor's surface to determine the conditions for corona inception. The conditions under which corona discharge occurs for any arrangement of conductors are an important design consideration since corona can limit the performance of any given configuration of transmission line conductors. The AC corona inception voltage gradient criterion should involve the line characteristics, i.e., arrangement and size of conductors as well as atmospheric condition of the air in which the conductor is immersed. The numerical calculation method, as well as empirical equations, combined with gas discharge theory is adopted to investigate corona inception voltage gradient. The electrical field enhancement at the tip of each strand is about 14% higher than the electrical field for a cylindrical conductor of the same overall diameter. According to self-sustained corona discharge criterion in a severe non-uniform electric field, variations of pressure, temperature and humidity on corona inception voltage gradient of bundle conductors are analyzed. Increased voltages in 400kV electric power network of Bosnia and Herzegovina causes increase the value of voltage gradient and higher power losses due to AC corona. Therefore, it is important to determine the value of the voltage gradient in vicinity of conductor's surface as well as corona inception voltage gradient to accurate determined power losses due to AC corona.

Modeling of Delay Time in Planar Multi-Gap Multi-Channel Gas Switches

Planar multi-gap multi-channel gas switches working under atmospheric pressure show promise for future linear-transformer-driver (LTD). In this paper, based on the gas discharge theory, a physical model of delay time, including the switching time (statistical and formative time lags) and the commutation time (resistive phase and inductive phase), is established to understand developing process of multiple discharge channels of planar multi-gap multi-channel gas switches. After that, an experimental platform is established to study the delay time of the switch and the developing process of multiple parallel discharge channels. We outline the result of delay time test. A high speed ICCD framing camera is used to catch the images of multiple discharge channels in the breakdown process. Some useful images are obtained by the camera and help us to understand the developing process of multiple discharge channels. These work and results may give us some guidelines to design and apply a multi-gap multi-channel gas switch in the future.

Erosion Model of Trigger Electrode Based on the Theory of Microexplosion

This paper discusses the normal working mechanism of trigatron gap which leads to the erosion of trigger electrode. The theory of microexplosion is based on the gas discharge theory, explosive electron emission theory and thermodynamical theory, and the erosion model of trigger electrode can be obtained by microexplosion theory. The specific action is an important physical quantity in the theory of microexplosion, which could be determined by current density and phase-transition time. The model demonstrates that the erosion of trigger electrode is related to material parameters, discharge current waveform, and charge transfer. Due to the results of experiments, there exists no erosion under the action of trigger current, while under the action of main current, the measured erosion height is 0.51 mm after 4000 shots. Based on the theoretical analysis, it can be calculated that after 4000 shots, the erosion height is 0.54 mm. experimental and numerical results match within 5%.

Study on the Ignition Factor of Piston Kerosene Engine

After the fuel changed fromgasoline to kerosene of internal combustion engine, the engine cold startperformance is poor due to the poor spray evaporation of kerosene fuel. In thepaper, the ignition factors are to be analyzed based on the gas dischargetheory. Improving the spark plug discharge and increasing the ignition energyare used to improve the cold start performance of engine. The experimentalresults show that the method can improve the cold start performance of engine,which provides the basis for the engine burning kerosene fuel

Analysis of breakdown mechanism in trigatron switches

Analysis of breakdown mechanism in gas-insulated trigatron switches is important for the engineering design and function prediction. Based on the gas discharge theory, a physical model was proposed to estimate the breakdown time for gas-insulated trigatron switches. And the model can explain the breakdown in the trigatron switches with two modes of the breakdown mechanism, i.e., fast breakdown mode (FBM) and slow-breakdown mode (SBM). Based on Raether breakdown criterion, this paper discussed the factors affecting on the E-field enhancement. The E-field is composed of the static E-field and the dynamic E-field, which leads to transformation of breakdown mechanism. Some coefficients could be determined by experiment and simulation, which are helpful to get the quantitative solution of breakdown time.

Simulation of the Discharge Path in Discharge Process from Thundercloud to Ground

Based on fractal theory and WZ model of gas discharge, The spacial temporal behavior in discharge process from Thundercloud to Ground was simulated efficiently. Moreover, we discussed the probability index and the field intensity of the discharge path and their influence on the fractal dimension and the discharge path., and pointed out that the research should focus on the relation between the probability index and the fractal dimension.