Abnormal polarity effect in nanosecond-pulse breakdown of SF6 and nitrogen

The breakdown of gas gaps in an inhomogeneous electric field at subnanosecond and nanosecond voltage pulse rise times are studied, and the famous polarity effect in point-to-plane gaps is investigated. It is shown that at a voltage pulse rise time of ∼0.5 ns, the inversion of polarity effect takes place not only in electronegative gases such as SF₆, but also occurs in electropositive nitrogen. The inversion of polarity effect is related to a delay of electron emission from the plane cathode on arrival of the ionization wave front anode to the cathode. It is found that with a voltage pulse rise time of ∼0.5 ns, the inversion of polarity effect occurs at SF₆ and SF₆–N₂ pressures of 0.25 MPa and lower, and with a voltage pulse rise time of 15 ns, at a SF₆ pressure lower than 0.12 MPa.     

Local charge formation in LiNbO3 using a mobile needle-shaped electrode

It is shown that local formation of electric charge in a region near the surface of lithium niobate crystals can take place both by local polarization switching of the sample and by local injection of electric charge from a needle-shaped electrode. A local change, due to the electrooptic effect, in the birefringence of the sample near the charged region is used to investigate the nature and the formation mechanism of the charge relief. Fiz. Tverd. Tela (St. Petersburg) 41, 510–512 (March 1999)     

电极结构对触发管型开关击穿特性的影响

基于600 kV触发管型SF6气体开关,设计了三种具有典型电场分布的电极结构,计算分析了各个场分布特点,在-600 kV/400 ns脉冲电压下对不同电极结构进行了击穿特性实验,分析了场分布对开关击穿特性的影响。实验结果表明:三种结构中平头形电极触发击穿模式与其欠压比相关,触发抖动较小;球头形电极自击穿电压抖动最小,能够稳定工作于长时间触发击穿模式;锥头形电极击穿模式较不稳定,可能与其两个间隙击穿特性较相近有关。     

电极结构对触发管型开关击穿特性的影响

基于600kV触发管型SF6气体开关,设计了三种具有典型电场分布的电极结构,计算分析了各个场分布特点,在-600kV/400ns脉冲电压下对不同电极结构进行了击穿特性实验,分析了场分布对开关击穿特性的影响。实验结果表明:三种结构中平头形电极触发击穿模式与其欠压比相关,触发抖动较小;球头形电极自击穿电压抖动最小,能够稳定工作于长时间触发击穿模式;锥头形电极击穿模式较不稳定,可能与其两个间隙击穿特性较相近有关。     

EHD atomization characteristics of a point-plate system with a porous point electrode

An electrohydrodynamic (EHD) atomization from a point-to-plate system, with a wet porous point as a corona electrode, has been studied. And the atomized water droplets from the wet porous point, as well as the water droplet traces, the water droplet charge-to-mass ratios, and the water droplet number concentrations, were investigated. It was observed that the wet porous point can atomize abundant amounts of water droplet, 2.8, 2.6 and 2.2 mg/min for negative, AC and positive corona, respectively. The migrated water droplet traces were observed. The positive wet porous point atomized very fine water droplets than those obtained with the negative wet porous point. Moreover, the water droplets atomized from the AC corona showed granular-like larger traces. A weak corona discharge can atomize water droplets very effectively. On the other hand, an intensive corona discharge can eject more water droplets. As a result with the wet porous point, the maximum corona-current-based and corona-power-based water droplet atomization yields of Y_C = 3.34, 3.32 and 3.25 μg/μAs and Y_P = 0.35, 0.40 and 0.27 mg/Ws have been obtained for the negative, AC and positive corona discharges.     

空气和SF6气体击穿对微波传输的影响

通过喇叭有效口径渐变法进行了L波段、脉宽30 ns的高功率微波空气以及SF6气体击穿实验,给出了实验中得到的典型波形,分析了空气以及SF6气体击穿对微波传输的影响。实验表明:空气击穿产生等离子体对微波传输的影响主要表现为对微波功率的反射,使微波脉宽变窄,而SF6击穿则主要体现为对微波功率的吸收,使峰值功率降低。关键词: Abstract:Key words:     

电极表面特性对甘油介质击穿特性的影响

基于几种常见的电极表面处理工艺,制作了外形一致、表面不同的砂纸打磨、羊毛抛光、金属电镀和非金属电镀四种同轴电极,对比了电极在微观下的形貌特点,通过实验研究了不同电极表面特性与甘油介质耐压的关系。搭建了基于晶闸管控制的空心脉冲变压器升压实验平台,最大输出电压500 kV,上升时间26 s。实验结果表明:四种电极的微观形貌存在较大差异,并引起了甘油击穿特性的不同,在相同充电电压条件下,甘油的平均击穿场强为210~260 kV/cm;与使用常规的砂纸打磨电极相比,使用羊毛抛光、金属电镀、非金属电镀电极可分别使击穿场强提高14.51%,11.60%,19.67%,其中非金属电镀电极表面均匀程度远高于其他电极,最高击穿场强可达288 kV/cm,比对照组平均击穿场强提高33.09%。     

电极表面特性对甘油介质击穿特性的影响

基于几种常见的电极表面处理工艺,制作了外形一致、表面不同的砂纸打磨、羊毛抛光、金属电镀和非金属电镀四种同轴电极,对比了电极在微观下的形貌特点,通过实验研究了不同电极表面特性与甘油介质耐压的关系。搭建了基于晶闸管控制的空心脉冲变压器升压实验平台,最大输出电压500 kV,上升时间26 s。实验结果表明：四种电极的微观形貌存在较大差异,并引起了甘油击穿特性的不同,在相同充电电压条件下,甘油的平均击穿场强为210~260 kV/cm;与使用常规的砂纸打磨电极相比,使用羊毛抛光、金属电镀、非金属电镀电极可分别使击穿场强提高14.51%,11.60%,19.67%,其中非金属电镀电极表面均匀程度远高于其他电极,最高击穿场强可达288 kV/cm,比对照组平均击穿场强提高33.09%。     

Spectral characteristics of multiphoton IR dissociation of SF6 in a nonequilibrium pressure shock

The spectral characteristics and the selectivity of multiphoton IR dissociation of SF₆ are studied upon excitation of the molecules in a nonequilibrium pressure shock formed upon the interaction of a pulsed gas-dynamically cooled molecular flow with a solid surface, as well as in the flow incident on the surface and in an unperturbed flow. The results obtained are compared with each other and with the data available on the dissociation of SF₆ on a molecular beam. The measurements of spectral characteristics and the dissociation selectivity upon excitation of SF 6 in the pressure shock and in an unperturbed flow correlate well with each other. The influence of the rotational and vibrational temperatures of the molecules on the spectral characteristics of the dissociation yield is selectivity analyzed.     

微机电系统微尺度间隙的脉冲击穿特性

利用微机电系统(MEMS)工艺制备了5~40 m间隙的金属铝薄膜电极,测取了不同间隙下施加纳秒方波脉冲时的击穿电压,得到击穿电压和平均场强随电极间隙的变化规律,研究了脉宽、极性对击穿电压的影响,结合击穿后微电极扫描电镜观察结果讨论了其击穿机理,并与相同试样在直流下的结果进行了对比。研究表明:击穿电压随微间隙距离的增大而增大,击穿场强则随着间隙的增大迅速减小;与直流同间隙的击穿电压相比,脉冲作用下的击穿电压并不像宏观尺度下那样高出很多;试样击穿机理应为流注理论。在脉冲作用下,阳极出现了分层熔化现象,由于作用时间很短,阳极表面并未出现类似于直流击穿时留下的坑洞;阴极则出现了溅射沉积现象,只是沉积物质相对较少。     

微机电系统微尺度间隙的脉冲击穿特性

利用微机电系统(MEMS)工艺制备了5~40 m间隙的金属铝薄膜电极,测取了不同间隙下施加纳秒方波脉冲时的击穿电压,得到击穿电压和平均场强随电极间隙的变化规律,研究了脉宽、极性对击穿电压的影响,结合击穿后微电极扫描电镜观察结果讨论了其击穿机理,并与相同试样在直流下的结果进行了对比。研究表明:击穿电压随微间隙距离的增大而增大,击穿场强则随着间隙的增大迅速减小;与直流同间隙的击穿电压相比,脉冲作用下的击穿电压并不像宏观尺度下那样高出很多;试样击穿机理应为流注理论。在脉冲作用下,阳极出现了分层熔化现象,由于作用时间很短,阳极表面并未出现类似于直流击穿时留下的坑洞;阴极则出现了溅射沉积现象,只是沉积物质相对较少。     

The influence of the sand-dust environment on air-gap breakdown discharge characteristics of the plate-to-plate electrode

The experiments of plane-plane gap discharge was carried out in an environment of artificial sandstorm. By comparing and analyzing the differences in gap breakdown voltage between the sand & dust environment and clean air, some problems were investigated, such as effects of wind speed and particle concentration on the breakdown voltage, differences of gap discharge characteristics between the dust & sand medium and the clean air medium. The results showed that compared with the clean air environment, the du...     

The characteristics of a negative corona discharge in He/Xe/SF6 mixture

The results of investigation of the electrical and optical characteristics of a negative corona discharge in the electrode system of the type needle-grid lit in a He/Xe/SF₆ mixture under the pressure of 100–300 kPa are presented in this paper. The given medium is working for a pulse-periodic excimer lamp on = 351 nm XeF(B–X). Distributed on the length of a lamp active media a bipolar corona discharge is intended for using in the electric circulation of the XeF-lamp working medium. It is shown that the given discharge is ignited steadily in the He/Xe/SF₆ mixture, containing 0, 5kPa SF₆ molecules and is characterised by a low power consumption; the current of the discharge is limited to the development of instability by increasing the voltage on the needles; in hot zones of corona discharge SF₆ molecules cause the effective population 6s of XeI state.     

Particle densities in a decaying SF6 plasma

Particle densities are determined for a decaying axially blown SF₆ are between current zero and brekdown, some 100 μs later. During the time of interest, primarily only atoms, diatomic molecules and ions can be built up by reactions. Therefore, in a first approach equilibrium densities are derived for SF₆ which has decomposed into its considemic and diatomic components. In a second approach reaction kinetics are considered. It turns out that the development of densities occurs in two steps. During the first approx. 100 μs there is a strong deviation from equilibrium. Afterwards the most abundant particles remain near their partial, diatomic equilibrium values. Near breakdown the degree of ionization is of the order of 10¹³ cm⁻³ with the most abundant ions S ₂ ⁺ and F⁻. This density is sufficient to distort the applied electric field. Future theories of breakdown in hot gases must take into account this principal difference as compared with the conditions in cold gases.     

Gas-discharge system with a zeolite electrode

A zeolite plate with push contacts is placed in a chamber filled with air at a controllable pressure, and the current-voltage characteristics of the zeolite plate are measured as a function of the air pressure in the chamber. It is found that the gas in zeolite pores ionizes and, accordingly, the number of electrons in the pores grows. It is shown that such a plate used as a cathode in a planar gas-discharge cell considerably reduces the ignition voltage of the gas discharge.     

Measurement of the nonlinear refractive index of SF6 with a hollow prism

We measure the nonlinear refractive index of SF₆ at three different CO₂ laser lines. Higher terms than the cubic nonlinearity are found and the behavior of the refractive index as a function of the laser intensity depends strongly on the frequency used, reflecting the characteristic SF₆ absorption dynamics.     

电激励脉冲HF激光SF_6/C_2H_6工作气体的放电特性

研究了电激励脉冲HF激光工作介质SF6/C2H6混合气体的放电特性。通过对放电等离子体荧光图像和放电波形的测量,分析比较了不同条件下放电稳定性、剩余电压、能量沉积效率等特性参数的变化情况。实验结果表明:混合气体的放电过程存在主放电、剩余电压维持和电弧放电3个阶段,各阶段的放电特性有所差异;提高充电电压有利于放电能量的有效沉积,也会使不稳定的电弧放电提前;增加C2H6原子分数能起到抑制电弧放电的作用;混合气体总压的增加会导致剩余电压的提高以及辉光放电的能量沉积效率的降低;最佳的能量沉积出现在电弧放电阶段与辉光放电阶段即将融合的临界状态。     

Spectral and energetic characteristics of passing vibrationally excited SF6 molecules through a cooled multichannel plate

We study the spectral and energetic characteristics of SF₆ molecules excited in a pulsed molecular beam by intense IR laser radiation into high-lying vibrational states (with the energy E _v ≥ 0.3–2.0 eV) that pass through a multichannel metal plate that is cooled to T _s ? 80–85 K and is inclined to the beam axis. From comparison of the measured characteristics with the spectral and energetic characteristics of the IR multiphoton absorption of these molecules, we find that they correlate rather well with each other. The results obtained allow us to conclude that, due to different probabilities of passing vibrationally excited and unexcited molecules through the multichannel plate, it is possible to separate molecules in the beam with respect to their isotopic (component) composition.     

Stimulated brillouin scattering in SF6 with a free-running XeCl laser as pump

A XeCl laser system without dispersive elements is used to investigate near threshold reflectivity and phase-conjugation (PC) fidelity of stimulated Brillouin scattering (SBS) mirrors with SF₆ as the active medium. Using different focal-length lenses to focus the broadband laser radiation into the Brillouin medium, it was found that at threshold the effective interaction length for SBS is equal to the confocal parameter and that the SBS gain is equal to its steady-state value for monochromatic pumping. High PC-fidelity values ranging from 0.8–1.0 were found under most of the experimental conditions investigated.