针板型大气压氦气冷等离子体射流的二维模拟

大气压冷等离子体射流的传播机理一直是人们研究的一个热点. 本文采用自洽的二维等离子体流体模型, 研究了大气压氦气冷等离子体射流在自身环境气体中以及在介质管中的传播问题. 得到了电子密度、电离速率、空间电场以及电子温度等参量的时空分布规律, 分析了介质管大小以及介质管介电常数对射流放电性质的影响, 得到了一种提高电子密度和射流尺寸的新方法. 关键词： 大气压冷等离子体射流 等离子体子弹 数值模拟 流体模型     

脉冲放电产生螺旋流注的等离子体特性研究

通过脉冲放电方式产生三维螺旋形的等离子体放电通道,在高速摄像机拍摄下观察到放电通道中的发光电离体以流注形式沿螺旋轨迹快速传播.建立电磁模型解释螺旋放电的形成机制,对造成对称性破缺及影响其手性性质的极向电场进行分析.研究表明,螺旋放电产生的放电通道存在两种不同的手性特征,而脉冲重复频率等放电参数及边界条件对螺旋流注的传播特性存在影响.脉冲电源驱动的电磁场在介质管内所形成的波模是极向电场形成的一个重要来源,当极向电场与轴向电场强度相近时则形成螺旋流注放电.     

Creepage discharge along the surface of solid dielectrics in water

Experimental data is given for the discharge voltage for creepage discharge in tap water as a function of the thickness, flange length, (creepage path over dielectric surface), permittivity of the solid dielectric, field configuration, polarity of the applied voltage pulse, and a number of other parameters. The experimental data discussed are the delay time with dielectric flange sparkover by creepage discharge, the average discharge propagation rate for both polarities, and the creepage discharge current and leakage resistance.     

Stochastic model for dielectric breakdown

We discuss a model for the development of discharge patterns in dielectric breakdown based on the Laplace equation associated with a probability field. The model gives rise to random fractals with well-defined Hausdorff dimensions. The relations of this model with the diffusion-limited aggregation are discussed in detail. The possibility of application to other stochastic phenomena like fracture propagation is proposed.     

Origin of surface microwave discharges

The high-pressure gas discharge initiated at the focus of pulsed powerful microwave radiation is a branched network of thin plasma channels completely filling the volume of the focal zone. A detailed experimental investigation of such discharges is carried out with a setup operating at a wavelength of 8.9 cm and at pressures ranging from 0.05 to 1.00 atm. When the initiator is placed on a dielectric plate, the discharge channels are found to propagate solely over the surface of the dielectric. It is shown that electrodynamic interaction between the gas discharge and dielectric is the main reason for the surface propagation of the discharge.     

Single-focusing regime of propagation of femtosecond light packets when self-focused in a condensed medium

Numerical simulations are used to investigate the propagation of tightly focused megawatt femtosecond light packets in a nonlinear condensed medium in the single-focusing regime. A plasma is shown to be generated in a small region whose length and diameter increase with power in the single-focusing regime of propagation of a femtosecond light packet in a transparent dielectric. The limiting electron density in the microplasma formation region is virtually independent of the laser pulse power but increases with numerical aperture of the focusing optics. At a fixed femtosecond pulse power exceeding the critical self-focusing power, the transmission of light by a dielectric layer decreases with increasing numerical aperture of the focusing optics.     

The mechanism of hot spot formation in condensed explosives

The hypothesis of an electrical mechanism of formation of detonation initiation zones (hot spots) in condensed explosives is considered. The hypothesis is based on the generation of electric fields and the appearance of shock-induced conductivity in the propagation of a shock wave (compression wave) in condensed dielectric media, including explosives. These physical phenomena can cause a local electrical breakdown, whose channel is identified with a hot spot. The available experimental data are analyzed from the point of view of the hypothesis suggested, and a procedure for verifying this hypothesis is outlined.     

Spatial macroscopic structure of a pulsed microsecond discharge in barrier-metal gaps with a nonuniform electric field distribution

Electric and spatial characteristics of a pulse-periodic microsecond barrier discharge are investigated in different geometries—triangular prism, plate, and corrugated electrode—that are in contact with a dielectric plate and form a dihedral angle with it. It is established that, in the space of the dihedral angle, the regions of discharge represent alternating cylindrical layers with the axes lying on the contact line. The first conducting layer is formed at some distance from the contact edge of the electrode. The number of layers and their localization are determined by the angle formed between an electrode and the dielectric plate. A physical model explaining the main features of the structure formation is proposed.     

Turbulent cooling of the gas and dielectric recovery following a spark discharge

A theoretical model is proposed for performing self-consistent calculations of the entire evolution of a spark discharge and the subsequent cooling of the postdischarge channel and dielectric recovery for a specified aperiodic discharge current pulse, taking into account the generation and dissipation of turbulent motion of the gas. The results are compared with the well-known experiments of E. P. Bel’kov, where it was discovered that the dielectric recovery rate depends on the characteristics of the discharge current pulse, which ultimately determine the intensity of the turbulent motion arising in the cooling channel. Zh. Tekh. Fiz. 68, 30–35 (February 1998)     

Characterization of the single nanosecond pulsed surface dielectric barrier plasma actuator: Geometric and electric effects

The influence of the electrode length and the voltage pulses on the discharge characteristics of the surface dielectric barrier discharge actuators were investigated numerically by using the plasma kinetic model. The governing equations including the coupled continuity plasma discharge equation, drift-diffusion equation, electron energy equation, Poisson's equation, and Navier–Stokes equation were solved in quiescent air at atmospheric pressure. The results show that the shorter pulse rising time results in higher discharge characteristics, more intense discharge, and bigger discharge region. Differently, the compared discharge characteristics for the electrodes with different lengths prove that the length of the powered and ground electrodes has little effect on the surface dielectric barrier discharge driven by nanosecond pulsed voltage.     

The influence of dielectric surface charge distribution upon thepartial discharge behavior in short air gaps

A two-dimensional breakdown model based upon the continuity equations for electrons and ions and the Poisson equation is employed to examine the influence of surface charges upon the partial discharge behavior of a short metallic-dielectric plane-parallel electrode gap of 0.05 cm in an air-like mixture at atmospheric pressure. The form of charge distribution at the dielectric electrode surface is found to significantly affect a number of important discharge parameters, such as the uniformity of the electric field, the charge density and its radial distribution within the gap, as well as the discharge propagation time     

Modeling the development of the stepped leader of a lightning discharge

A stochastic-deterministic model is presented for the propagation of a downward-moving leader. Lightning formation is described by a stochastic growth of branching discharge channels which is determined by the electrostatic field. The dynamics of the electric field and of the charge distribution over the lightning structure are calculated deterministically. The model includes the initiation of lightning, a preliminary discharge in a cloud, the propagation of a downwardmoving stepped leader toward the earth, and the initiation and upward motion of a return stroke from the earth’s surface. Numerical execution of the model yields a dynamic picture of the development of the downward-moving leader and of the intracloud discharge structure. The effect of the charge density in the cloud and the parameters of the developing channels on the spatial-temporal, current, and charge characteristics of the stepped leader’s propagation are studied. The effect of free-standing structures on the distribution of points on the earth’s surface where lightning strikes is examined. Zh. Tekh. Fiz. 69, 48–53 (April 1999)     

Modeling of discharges in spatially charged dielectrics

A stochastic-deterministic model of a discharge induced by space charge in dielectric is developed. The spatiotemporal and current characteristics of the discharge are simulated numerically. The simulation results are compared with the experimental data on discharges in polymethylmethacrylate samples charged by means of an electron beam. The interrelation among the growth of the current-carrying channels, energy transfer, and energy release during the discharge is discussed.     

μs振荡脉冲电源激励下同轴电极介质阻挡放电特性

 采用μs振荡脉冲电源激励同轴电极结构产生空气中介质阻挡放电(DBD),通过电压-电流波形的测量及发光图像拍摄研究了放电特性,计算得到了放电功率及传输电荷量等重要放电参量,研究了电压幅值、气隙距离对放电特性及放电参量的影响,在分析放电机理的基础上对实验结果进行了解释。结果表明:μs振荡脉冲电源激励下,DBD平均放电功率可达上百W,传输电荷量可达几千nC;增大电压幅值和减小放电气隙距离能获得更剧烈的放电,平均放电功率和传输电荷量均增加。     

正极性纳秒脉冲电压下变压器油中流注放电仿真研究

建立了二维轴对称流体模型, 仿真研究了正极性纳秒脉冲电压下变压器油中针-板电极流注放电的起始与发展过程, 得到了不同的外施电压幅值、脉冲上升沿时间与电极间隙距离下油中流注放电的形貌、 电场强度与空间电荷密度分布等. 仿真结果表明: 空间电荷加强了流注头部前方电场, 使流注通道更易于向前推进, 形成"电离波"; 随着外施电压幅值升高, 流注发展的平均速度显著变大; 较陡的脉冲上升沿形成的放电半径较大, 对应的最大电场强度值变小; 随着电极间隙距离的增加, 流注发展平均速度变快. 仿真显示纳秒脉冲下放电中油温无明显升高, 表明此类放电过程没有明显的油气化现象. 我们认为, 场致电离是油中带电粒子产生的主导机制; 空间电荷效应增强流注前方电场使得电离进一步发展, 最终导致击穿. 本研究有助于加深对变压器油中放电起始、发展直至击穿过程的认识以及对液体电介质中电离机制的理解. 关键词： 变压器油 流体模型 流注放电 空间电荷效应     

On the propagation characteristics of metal clad waveguides with a quantum well

The electromagnetic modes of planar metal clad dielectric waveguides containing an n-doped quantum well (QW) are studied theoretically. Special attention is paid on the coupling between metal surface plasmons and intersubband plasmons and the manifestation of this coupling in the propagation characteristics of metal/QW/dielectric and multimode metal/QW/dielectric/metal waveguide structures. The results obtained indicate that the modification of the propagation characteristic induced by the above-mentioned coupling is substantial only in the case of metal/QW/dielectric waveguide structures.     

常压DBD二维流体模型的FCT方法数值模拟

根据常压介质阻挡放电流体模型的物理方程,采用固定网格有限差分算法,分别用四阶和六阶相位误差FCT方法模拟求解二维流体连续方程.在均匀的初始条件下研究放电雪崩过程中电子密度的时空演化,具体分析和比较两种算法的差异.FCT方法模拟求解得出的计算结果与气体放电理论吻合较好,是一种具有较好的准确性和高精度的算法.     

3D Imaging of the Single Microdischarge Development in Coplanar Barrier Discharges in Synthetic Air at Atmospheric Pressure

The evolution of the luminosity of the coplanar barrier discharge in the single‐filament mode was studied by the technique of cross‐correlation spectroscopy and intensified high‐speed CCD camera. For the first time 3D‐spatially and temporally resolved investigations of the luminosity of second positive (at 337.1 nm) and first negative (at 391.5 nm) system of molecular nitrogen in this discharge type were realized. Although the coplanar barrier discharge is sometimes referred to as a pure surface discharge, it shows clear 3D structure. From these experimental data, the propagation of the cathode‐directed ionizing wave in the space above the gap is clearly seen. Also, a second ionizing wave propagating towards anode later on has been detected, too. The diffuse spots created by impact of ionizing waves onto the dielectrics and their propagation on the dielectric surface is described. The results for the coplanar barrier discharge are compared with corresponding experimental results obtained for the volume barrier discharge and basic similarities are pointed out (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)