Double charge layer in high-current electron avalanche

New experimental data reported in [6] allow completed electron avalanche to be represented as a double charge layer. Based on this model, qualitative explanation is given to the issues related to formation and growth of the streamer, and the structure of the ionized channel and its stability mechanism are considered. The model defines the conditions for the growth of the channel in weak fields and explains the increase in the velocity of the streamer’s motion towards the cathode.     

On the plasma mechanism of developing the early stages of breakdown in gases

The time evolution of the initial stages of breakdown in high-pressure gases is theoretically investigated. The following three stages are considered: initial: the origination and development of an ionization avalanche, the change of this avalanche to a plasma avalanche, and the change of the plasma avalanche to a plasma streamer. The streamer ionizes the gas via its radiation, causes new avalanches propagating in an enhanced discharge field, and bridges the discharge gap. Simple formulas are derived for the times of transition between various breakdown stages and for the ionization front velocity at separate stages.     

Numerical simulation of the dynamics of current channel microstructure formation in atmospheric nanosecond discharges in a uniform electric field

The results of simulation of the current channel microstructure formation in atmospheric nano- second discharges in a uniform electric field due to the development of instability of the ionization process in the avalanche stage followed by cycling breakdowns of the avalanche are considered. It is shown that the enhancement of the electric field at the ionization front due to the intrinsic field of the avalanche leads to the contraction of the path length between consecutive avalanche breakups; after several breakups, the ionized gas passes to the plasma state. The effect of small electric field perturbations on the dynamics of microstructure formation is investigated; as a result, the possibility of “induced” avalanche breakup at the instant of action of perturbations is established.     

Specific features of electron avalanche in high gas multiplication mode

The results of studying an electron avalanche in narrow-gap wire chambers in the region of avalanche-to-streamer transition are described. The amplitude and temporal characteristics of the chambers in the high gas multiplication mode (≥10⁷) are given. Due to specific features of the electric field distribution in narrow-gap chambers and the application of a CF₄-based working gas, previously unknown processes taking place in a shower and more clearly reflecting the dynamics of avalanche development were discovered—electron velocity distribution, electrostatic oscillations of the avalanche as a whole, decrease in the anode signal duration, increase in the delay time of charge induction on the cathode by the avalanche development time, and, finally, varying shapes of the anode and cathode signal amplitude distributions. The observed processes can be explained if a completed avalanche is represented in the form of a double charged layer. The basis for such a representation is the specific features of a high-current avalanche mentioned above. The model under consideration is simple, provides answers to questions related to streamer formation and growth, and reflects the structure of an ionized channel and its stability mechanism.     

Untersuchungen über die Entwicklung des Kanaldurchschlags in Gasen

The temporal development of the current of a discharge leading to breakdown was investigated under static and homogeneous field conditions with wide band oscilloscopic techniques. The discharges were started by 10³ to 10⁵ electrons released within some 10^?9 sec along traces of single α-particles parallel to the electric field. Measurements have shown that streamer mechanism occurs in gases as CH₄ and CO₂ at static breakdown, if a sufficient density of space charge is produced by a great number of overlapping avalanches. The gas amplification of thesingle avalanche only has a value of about 10⁵. Also in O₂ and dry air at highpd-values breakdown develops with streamer mechanism. — In electronegative gases as freon 12 and O₂ a prolongation of the time necessary for streamer formation is caused by the reduction of the effective total space charge by the negative ions. The results of a detailed study of the time necessary for streamer development and the time constant of the increase of the current leading to breakdown confirm the model of streamer mechanism.     

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.     

Über die Wahrscheinlichkeit der „Kanalbildung“ aus einer großen Elektronenlawine

Investigations on avalanches of large carrier numbers (>10⁸) show the following characteristic features of the streamer mechanism, known as ?Kanal-Aufbau“.

1. 1.
   An avalanche can only start a streamer, if the carrier number of the avalanche has reached a certain critical valuen _krit. Having surpassedn _krit the probability of this streamer formation increases monotonously with growing carrier number. The applied field E₀ is kept constant.     
   
   

Role of the near-electrode regions in the formation of the volume discharge heterogeneity in nitrogen in the pin-to-plane configuration

The development of streamers and sparks in nitrogen at atmospheric pressure in the pin-to-plane electrode configuration is studied in experiments and theoretical calculations. It is demonstrated that the near-electrode regions play the decisive role in streamer initiation. At a negative pin voltage, a spark is formed in the absence of fast primary streamers. At a positive pin voltage, streamer build-up is initiated by the current spots on the anode that result from the development of the ionization instabilities in the anode region. The calculations show that the formation of the current spot on the anode leads to a redistribution of the electric field in the vicinity of the anode, so that a single avalanche is transformed into a streamer under the conditions when the known criterion for streamer breakdown (the Meek-Raether criterion) is not satisfied. Original Text ? Astro, Ltd., 2006.     

Technique for calculating the vulnerability of explosive surface objects by lightning

A probabilistic technique for estimating the vulnerability of explosive surface objects by lightning has been proposed. It uses a combined criterion for initiation of upward streamer and leader discharges form the elements of the object and lightning diverters. This criterion takes into account the probabilistic nature of avalanche–streamer and streamer–leader transitions and also the trajectories of the lightning’s downward stepped leader and lightning current. It has been shown that, if the formation of the downward leader of incomplete streamer discharges from the elements of the object in an electric field is neglected (these discharges may set fire on explosive emissions), the probability of lightning-induced failure of the object is underestimated by several times compared with the calculated value.     

Streamer propagation mechanism on the basis of plasma oscillations

A mechanism explaining streamer propagation to the anode and to the cathode without photoionization of the gas is proposed. It is shown that the velocity of the anode streamer is determined by the electron mobility in the field of the end of the streamer. The accelerated electrons appearing at the anode end of the streamer excite longitudinal plasma oscillations in the streamer, whereupon streamer propagation to the cathode is explained. An explanation is given of the phenomenon of streamer self-propagation after the disappearance of the external field because of the stored energy of the plasma oscillations. The conditions for the transition of an avalanche into a streamer is defined as the condition for the appearance of accelerated electrons at the anode end of the avalanche.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 34–39, July, 1977.     

气体雪崩过程中光电信号的时间关联

本文报道在有限正比和SQS模式下的光信号和原初雪崩的电信号时间关联的实验结果.表明伴随有限正比雪崩过程有微弱的光发射,光脉冲的半高全宽(FWHM)为4ns;自猝灭流光光脉冲相对于原初雪崩的电信号有几ns的延迟,而且这种延迟的涨落(FWHM)也有几ns.实验还给出了它们随丝电压和猝灭气体浓度的变化情况.     

On the theory of plasma streamer development

The temporal dynamics of initial stage of breakdown development in high-pressure gases, i.e., ionization avalanche initiation and development, its transition to plasma avalanche and then to plasma streamer, is discussed. Simple formulas for times of transitions between various breakdown stages and ionization front propagation velocities at individual stages are derived.     

Mechanisms controlling the transition from glow silent discharge tostreamer discharge in nitrogen

Low-energy dielectric-barrier controlled discharges in nitrogen are studied by undertaking electrical measurements to determine mechanisms controlling the transition from glow to streamer-like discharge. The highest and the lowest values of the frequency and the amplitude of power supply voltage leading to a glow discharge have been found dependent on the gas flow and the nature of the surface in contact with the discharge. These boundary values have been related to the criteria necessary for initiating a Townsend breakdown rather than a streamer breakdown commonly observed under such conditions. This implies: (1) that the seed electron density just before the breakdown is high enough to allow the development of numerous small avalanches under a low field avoiding the formation of only one large avalanche mechanism at the origin of the streamer formation; and (2) to let the time for ions issued from the first avalanches to reach the cathode before the electrical field becomes large enough to induce the formation of large avalanches. Practically, the transition from a Townsend breakdown to a streamer breakdown is analyzed from electrical measurements data coupled to the visual aspect of the discharge. Without any gas flow, the obtaining of an atmospheric pressure glow discharge (APGD) is mainly limited by the species etched from the surface in contact with the gas. Indeed, these species can be quenchers of the nitrogen metastable molecules, which are the species at the origin of the formation of seed electrons via the Penning effect. This limitation can be overcome by the use of a laminar gas flow. However, this type of gas flow through the discharge induces a depletion of N₂ metastables and, consequently, influences the electron density at the entrance of the discharge, leading to a tendency on this part of the discharge to transit to a streamer-like one     

On peculiarities of the method for determining the probability of lightning striking terrestrial explosive objects

We have described a new probabilistic method for calculating and assessing lightning striking terrestrial explosive objects using a combined criterion for the emergence of upward streamer and leader discharges from the elements of the object being protected and lightning rods taking into account the probabilistic nature of the avalanche–streamer and streamer–leader transitions, the trajectories of a downward stepped lightning leader and lightning current. It has been shown that the disregard of possible formation of uncompleted streamer discharges from the elements of the object in the electric field of a downward lightning leader, which can ignite explosive emission, decreases the rated probability of the object being damaged by a lightning stroke by several times.     

Another Possible Interpretation of SQS Mechanism

Experiments on self quenching streamer discharge in cylindrical tube and wire chamber are performed,and an interpretation of SQS mechanism is proposed in this paper.The excited atoms or molecules created in the latent track and subsequent avalanche play an important role,they form the main photo-electron source and the interaction between them is also possibly a source of ionizing photon.A formula that describe the jump and streamer charge is deduced.The effect of electric field of the space charge is computed.The comparison between theory and experiments is made.     

雷云电场作用下长地线表面正极性辉光电晕放电的仿真研究

在雷云电场的缓慢作用下, 一种无流注的正极性辉光电晕在接地物体表面起始, 向周围空间注入大量正极性空间电荷, 从而改变雷电先导对雷击目的物的选择. 本文对雷云电场作用下起始于长地线表面的正极性辉光电晕放电进行了仿真研究; 考虑了正极性离子与其他离子的附着与碰撞作用, 建立了一种精确的二维正极性辉光电晕模型; 并通过在实验室内开展高压电晕放电试验, 测量了不同背景电场下的电晕电流; 与本文所建模型的仿真结果进行对比, 对模型的正确性进行了验证. 基于上述模型, 对正极性辉光电晕在雷云感应作用下的起始发展过程与电晕特性进行了仿真模拟, 得到了该电晕的电晕电流、正离子密度分布规律以及正离子迁移规律. 发现在雷云电场作用下, 电晕放电产生的正离子在迁移初期于垂直于地线的平面内基本呈圆对称状均匀分布, 但随着离子逐渐远离地线其分布不再均匀, 呈拉长的椭圆形分布, 多数离子最终分布于地线上方区域并逐渐向雷云方向迁移; 由于正离子在地线上方迁移区聚集形成的正空间电荷背景对行进电子束具有衰减和消耗作用, 抑制了电子崩的形成, 并降低了电子崩转化为流注的概率, 阻止了新的电子崩对流注的不断注入, 同时正空间电荷背景使气体的碰撞面增大, 增加了与电子的复合概率, 引起大量电子的消耗, 最终抑制了电子崩的形成与流注的发展, 地线表面的上行先导得到抑制.     

Features of electrical discharges in air triggered by laser

A numerical study of laser-triggered discharges in air at atmospheric pressure is presented for an ultraviolet laser in small gaps. Two models, one for the ionization of the air by the laser pulse and the second for the streamer evolution have been computed. From results of numerical simulations the influence of the laser parameters such as energy, pulse duration and beam radius is analyzed and electron distributions are obtained for different small gaps. Electric field, streamer velocity and evolution of the ionized volume are calculated by means of streamer simulations. This paper shows the main features of the laser-triggered discharges and also the importance of using numerical simulations in a laser-triggered experiment.     

Formation of ball streamers at a subnanosecond breakdown of gases at a high pressure in a nonuniform electric field

The formation of a diffuse discharge plasma at a subnanosecond breakdown of a “cone–plane” gap filled with air, nitrogen, methane, hydrogen, argon, neon, and helium at various pressures has been studied. Nanosecond negative and positive voltage pulses have been applied to the conical electrode. The experimental data on the dynamics of plasma glow at the stage of formation and propagation of a streamer have been obtained with intensified charge-coupled device and streak cameras. It has been found that the formation of ball streamers is observed in all gases and at both polarities. A supershort avalanche electron beam has been detected behind the flat foil electrode in a wide range of pressures in the case of a negatively charged conical electrode. A mechanism of the formation of streamers at breakdown of various gases at high overvoltages has been discussed.     

Test of BESⅢ RPC in the avalanche mode

The installation of the BESⅢ RPC system has been completed.Cosmic ray test results show that they perform very well in streamer mode and meet the BESⅢ requirements.We have tested several RPCs in the avalanche mode with the addition of extra SF6 in the gas mixture.We find an efficiency plateau that reaches～95%.and a time resolution of 1.8 ns.This demonstrates that the BESⅢ-type RPC can work in the avalanche mode as well.     

Incipient electric field determination for bush and streamer stage in dielectric liquid under energy balance condition

This paper introduces a new approach for streamer advance mechanism in dielectric liquid. The existing of bush-like streamer shape early and then a tree structure shape after that has been given an over view and definition by devising a breakdown index for dielectric liquid which reach a value of 25. The deviation of streamer velocity from low values of tens of meter per second, until several kilometer per second from bush-like shape, until complete breakdown has been discussed too. These different stages have been studied on an energy balance concepts. In this paper using energy balance analysis, different critical applied fields have been obtained. These values reach 2.18 MV/cm for one branch channel in bush-like streamer shape and 21.5 MV/cm, for tree streamer. After that, the initial streamer velocities concerning these stages have been introduced. From these analysis the dissociation of dielectric liquids starts when the streamer velocity reach the sound speed in air, 331 m/s. In addition, the dissociation field depends mainly on the physical values of the dielectric medium, such as density, and permittivity have been introduced. In this paper the dissociation starts at an electric field value of 21.5 MV/cm for nearly all dielectric liquids, This result is equal to tree streamer inception value, which can be considered as a new introduced finding. A new energy equation relating injected energy electric field, velocity and new deduced breakdown index in dielectric liquid has been devised. The streamer may stop or continue its advance until complete breakdown. According to many published data for streamer, there is no clear explanation for streamer stopping and continuing it advance. In this paper, the streamer must advance ahead of the bush zone in the gap toward the opposite electrode when the prospective electric field at 66% of the gap achieves a breakdown index of 25. This result can be considered as a new criterion for streamer growth until crossing the gap. These new equations and findings have been applied to several experimental works and achieve good results.