Zinc Oxide Surface Flashover Triggering of Pseudospark Switch

Accurate and reliable triggering is one of the most important issues with high power pseudospark switch,because it not only has an impact on the design of discharge chamber of switch,but also has an influence on the dynamic range of operation voltage,repetition frequencies and lifetime of switch.The unique feature of pseudospark switch is its hollow cathode geometry.The hollow cathode effect produced by the hollow cathode provides the protection of the swithch for the triggering unit from erosion by high discharge plasma.In this paper,a zinc oxide(ZnO) surface flashover triggering is presented.This trigger unit possesses an excellent time delay(80ns-360ns) and jitter (20ns-50ns)at the switch voltage of 30kV-2kV.The emitted plasma electron density is high enough to trigger switch reliably down to switch voltage of 440V.     

Development of a 4 MV Laser-Triggered Multi-Stage Switch

A 22-stage 4 MV laser-triggered multistage multi-channel switch （LTS） was designed according to the hypothesis that the well-proportioned electrical field distribution is helpful in reducing the jitter of delay. Field distribution in the switch section is regulated by a metal field regulation ring and several gradient rings. In order to reduce the jitter further, a SFB/N2 mixture is chosen as the switching medium. The generalized standard deviation of the self-breakdown voltage and the deviation of the average value from the prediction is less than 4.4% and 13% respectively. Linearity of the self-breakdown voltage is better than 0.95. Triggered by a laser pulse of 35 mJ/3 ns, the delay is about 26 ns at a working voltage of 85±3% USB （Self-breakdown Voltage）. Maximum deviation of delay is less than =t=2.5 ns. Jitter is less than 1.5 ns. The delay and jitter decrease with the increase in the working ratio （the ratio of working voltage to USB）, pressure or voltage.     

基于微机电系统技术的薄膜离子源制备与实验研究

基于微机电系统技术的薄膜离子源是芯片型中子发生器的关键部件。本文通过在陶瓷基底上制备图形化钛膜并利用3层陶瓷重叠的方法获得了薄膜离子源样品,采用平板探针法和激光共聚焦显微镜得到了薄膜离子源的离子电流及其电极烧蚀特性,并进一步利用高速相机和光谱仪得到了薄膜离子源的放电发光演化图像和等离子体组分信息,最后基于实验结果分析揭示了薄膜离子源放电的工作机制。     

Influence of Surface Carburization of Machinable Ceramics on Its Pulsed Flashover Characteristics in Vacuum

For pulsed power devices, surface flashover phenomena across solid insulators greatly restrict their overall performance. In recent decades, much attention has ...     

Experimental Investigations on Trigger Characteristics of Pseudospark Switch Based on Surface Flashover Technology

A trigger device and a triggered pseudospark switch （TPSS） were designed based on surface flashover technology, in order to meet the requirements from present pulse power technology and pulse current test technology such as a long lifetime, reliability in a wide voltage range, a short delay time, as well as small delay jitters. The trigger devices were made from different dielectric materials, with their permittivities from tens to thousands. The trigger characteristics of TPSS were investigated. The results indicate that the high-dielectric trigger device shows better performance and higher emitted charge of the electron emission within all adjusted parameters including the gas pressure and applied voltage. For the dielectric material with relative permittivity εr of 3460, when the gas pressure is 7 Pa, the hold-off voltage of TPSS is 28 kV, the minimum trigger switch voltage drops to 128 V, the minimum discharging delay time and delay jitter are less than 35ns and 6ns, respectively, and the reliable operation can be reached within a very large range of charging voltage, between 0.46% and 99% of its self-breakdown voltage.     

气体开关串级环形间隙放电相互影响机制研究

针对中空和非中空触发电极结构的两间隙开关,进行了触发击穿特性实验,对比两个间隙的击穿抖动和通道数,分析了串级两间隙的相互影响机制。实验结果表明：两只开关触发间隙击穿抖动和通道数变化规律基本一致;非中空开关自击穿间隙击穿抖动随工作系数的增大而减小,最小约3 ns,中空开关自击穿间隙击穿抖动始终约1 ns;非中空开关自击穿间隙难形成多通道放电,中空开关自击穿间隙通道数明显多于其他间隙。触发间隙首先放电产生紫外光,通过触发电极中空通孔预先照射自击穿间隙产生初始电子,是自击穿间隙击穿抖动减小、通道数增加的主要作用机制。     

Surface charge accumulation behavior and its influence on surface flashover performance of Al2O3-filled epoxy resin insulators under DC voltages

Surface charge accumulation on insulator surface can have great influence on surface flashover performance. An experimental system is established to investigate surface charge accumulation and decay characteristics ofAl₂O₃-filled epoxy resin insulators in 0.1 MPa SF₆ under DC voltages. Surface potential is recorded by a Kelvin vibrating probe connected to an electrostatic voltmeter. By pre-depositing charges on insulator surface, the influence of surface charges on surface flashover performance is studied. The results reveal that surface charge distribution appearance is the combined effect of electrode injection, back discharge and gas ionization. Surface charge distribution has obvious polarity effect. It is concentrated near the HV electrode under positive voltages and dispersed under negative voltages. The difference in positive and negative surface flashover voltage is attributed to the difference in surface charge distribution under DC voltages of different polarities. Surface charge decay contains two stages, which satisfies the law of double exponential function. At first stage, surface charge decays fast, which corresponds to charges escaping from shallower traps. While it decays slowly at the second stage, which corresponds to charge escaping from deeper traps. Surface charge decay process is dominated by surface conductivity mechanism. The pre-deposited charges on insulation surface have great influence on surface flashover performance. The deposited positive charges can increase positive flashover voltage but decrease negative flashover voltage.     

Resistance Measurements and Interpretations Relating to Flashover of Artificially Contaminated Ceramic Insulator Strings

The flashover of insulator strings occurring at normal working voltages under contaminated/polluted conditions, obviously deserves serious consideration. Though much research has been gone into pollution-induced flashover phenomena but grey areas still exist in our knowledge. In the present experimental study the breakdown (flashover) voltages across gaps on insulator top surfaces and gaps between sheds (on the underside of an insulator), also the flashover studies on a single unit and a 3-unit insulator strings were carried out. An attempt has been made to correlate the values obtained for all the cases. From the present investigation it was found that resistance measurement of individual units of a polluted 3-unit string before and after flashover indicates that strongly differing resistances could be the cause of flashover of ceramic disc insulator strings.     

Surface modification of silicone rubber by CF4 radio frequency capacitively coupled plasma for improvement of flashover

The flashover performance of insulating materials plays an important role in the development of high-voltage insulation systems. In this paper, silicone rubber(SIR) is modified by CF₄ radio frequency capacitively coupled plasma (CCP) for the improvement of surface insulation performance. The discharge mode and active particles of CCP are diagnosed by the digital single-lens reflex and the spectrometer. Scanning electron microscopy and x-ray photoelectron spectroscopy are used for the surface physicochemical properties of samples, while the surface charge dissipation, charge accumulation measurement, and flashover test are applied for the surface electrical characteristics. Experimental results show that the fluorocarbon groups can be grafted and the surface roughness increases after plasma treatment. Besides, the surface charge dissipation is decelerated and the positive charge accumulation is inhibited obviously for the treated samples. Furthermore, the surface flashover voltage can be increased by 26.67% after 10 min of treatment. It is considered that strong electron affinity of C–F and increased surface roughness can contribute to deepening surface traps, which not only inhibits the development of secondary electron emission avalanche but also alleviates the surface charge accumulation and finally improves the surface flashover voltage of SIR.     

双通道α表面污染测量仪的研制

研制了一款电脑操控的双通道宽量程α表面污染测量仪,仪器具有测量范围广、操作与分析便利、灵敏度高、可多点组网远程测量等特点,适用于包括异形物体表面的核辐射α污染监测。文章介绍了此仪器软硬件结构,并对其基本性能做了评价。     

A Thermal Fragmentation Model Induced by Surface Solidification

A fragmentation phenomenon of a melt droplet induced by surface solidification has been studied for many years, but the fragmentation rate model, based on such a thermal mechanism, is not available for numerical simulation tools. In this study, in order to develop a fragmentation rate correlation of a melt droplet, induced by surface solidification, a thermal fragmentation mechanism is proposed, based on the Taylor instability. The theoretical fragmentation model is developed and a simplified non-dimensional correlation is proposed for convenient application to simulation tools. The developed fragmentation rate correlation is verified by simulating the MIXA experiment.     

Reflooding Experiments on a Vertical Surface with Radiation-Induced Surface Activation

In this study, reflooding experiments were performed on a vertical rod surface before and after γ-ray irradiation to see the effect of Radiation-Induced Surface Activation (RISA) on the quenching speed. The test section was an annular channel with a concentric inner rod made of stainless steel SUS304 and an outer tube made of quartz glass. The inner rod was irradiated by ⁶⁰Co γ-rays with predetermined radiation intensity and period to improve the surface wettability based on the radiation-induced surface activation phenomenon. Prior to the reflooding experiments, the contact angle of a droplet on the inner rod surface was measured using a CCD camera. It was indicated that the irradiated surface wettability was clearly improved and the quenching speed was enhanced after γ-ray irradiation.     

核谱数据的一种无损压缩方法

针对核物理研究中多道谱数据的特点,提出了一种可用于无损压缩的变换关系,成功地实现了其中的一种算法,获得了０．５至０．２５的压缩比,所得数据还可方便地用哈夫曼等基于概率的压缩方法进行二次压缩。     

Flashover Characteristics along Coil Insulation under Intense Gamma-Ray Irradiation

The results of an experimental investigation of the surface flashover under an intense ⁶⁰Co γ-ray irradiation in air are reported. The AC voltage of 50 Hz was applied to model coils under an exposure rate of 1×10⁶R/h. It is found that flashover voltages (FOV) of the model coils are not affected at this exposure rate. The FOV of sphere gap and along polymeric cylindrical bar were also measured under irradiation, showing a slight decrease for the sphere gap at an exposure rate of 4×10⁵R/h.

Further, results obtained from flashover tests for DC voltage under an extremely high exposure rate of about 10¹³ R/h with pulsed X-ray beam show a significant decrease of FOV for the sphere gap and a slight decrease for the cylindrical bar. These results are closely related to whether partial discharges exist before the flashover or not.

Considerations on the effect of the intense irradiation on the flashover characteristics are presented qualitatively.     

Estimation of Surface Roughness due to Electrode Erosion in Field-Distortion Gas Switch

Field distortion gas switch is one of the crucial elements in a Marx generator, fast linear transformer driver and other pulsed power installations. The performance of the gas switch, which is dramatically affected by the surface roughness due to electrode erosion during the discharge process, directly influences the output parameters, stability and reliability of the pulsed power system. In this paper, an electrode surface roughness (ESR) calculation model has been established based on a great deal of experimental data under operating current. The discharge current waveform, the peak height of the burr, the radius and the depth of etch pits in the electrode erosion region were used to predict the ESR. Also, experimental results indicate that this calculation model can effectively estimate the ESR of the test gas switch.