The Efect of the Earthed Electrode Size on the Ignition Voltage of Low-Pressure RF Capacitive Discharge in Argon

The efect of the grounded electrode diameter on the ignition voltage using 13.56 MHz in argon gas is studied experimentally.The results indicate a systematic decrease of the breakdown voltage with increasing electrode area for the same pd value.No multi-valued breakdown voltages are observed.The Paschen minimum is not afected by the electrode diameter as long as the parallel plane approximation is valid.A modified Paschen equation which takes into account indirect discharge via the chamber walls at high pd values gives reasonable fits to the experimental data.     

Effect of the Mesh Transparency on the Electrical Characteristics of DC Pseudo Discharge

A DC pseudo discharge for air has been studied.Air pressure is used in the range between 0.7 Torr and 12 Torr.The breakdown occurs between a plane cathode and a mesh anode at transparencies of 19%,46%,and 65%.The current-voltage characteristic curves of the discharge,which are measured at different pressures,distances,and mesh transparences,take effect in the region of abnormal glow.The discharge voltage decreases as the air pressure increases,while more voltage is needed to maintain the discharge when either the mesh transparency or the interelectrode distance is increased.An increment of mesh transparency causes high negative potential behind the mesh due to the high concentration of electrons,which accumulate and collide with neutral atoms.Paschen curves deviate from the expected regular one.The left side of Paschen curves appears at inter-electrode distance of 1 mm,whereas the right side appears at inter-electrode distance of 5 mm.The intermediate region is observed only at 3 mm distance between the two electrodes.For the transparency range used in this work,it is found that the decrement of the breakdown voltage,on the right side,depends on the mesh transparency.For different electrode separations,the measured Paschen curves are coincident and deviate from the standard ones of Paschen's law.     

Discharge characteristics of a needle-toplate electrode at a micro-scale gap

To understand the discharge characteristics under a gap of micrometers,the breakdown voltage and current–voltage curve are measured experimentally in a needle-to-plate electrode at a microscale gap of 3–50 μm in air.The effect of the needle radius and the gas pressure on the discharge characteristics are tested.The results show that when the gap is larger than 10 μm,the relation between the breakdown voltage and the gap looks like the Paschen curve;while below 10 μm,the breakdown voltage is nearly constant in the range of the tested gap.However,at the same gap distance,the breakdown voltage is still affected by the pressure and shows a trend similar to Paschen's law.The current–voltage characteristic in all the gaps is similar and follows the trend of a typical Townsend-to-glow discharge.A simple model is used to explain the non-normality of breakdown in the micro-gaps.The Townsend mechanism is suggested to control the breakdown process in this configuration before the gap reduces much smaller in air.     

Paschen testing of ITER prototype cryogenic axial breaks

Axial insulation breaks are needed in forced cooled cryogenic high voltage devices for the separation of the high voltage area from the grounded pipe system. The ITER cryogenic axial breaks will be surrounded by good vacuum in case of normal operation but also under vacuum breakdown conditions sufficient dielectric strength is required for a reliable fast discharge of the coil system. A Paschen tight design of the ITER prototype breaks enables high voltage operation independent on the outer vacuum or gas conditions. Consecutively two pretested ITER prototype breaks were integrated in the insulation system of a Paschen test unit and high voltage tested. Two different ways to perform the Paschen testing were used for both breaks. The preparation of the breaks and the test setup are described and the test results are given.     

Breakdown Voltage Research of Penning Gas Mixture in Plasma Display Panel

Paschen law and equations, which ignore the influence of the Penning ionization on the electron ionization coefficient （α）, are always used as the approximation of the breakdown voltage criterion of the Penning gas mixture in current researches of discharge characteristics of the plasma display panel （PDP）. It is doubtful that whether their results match the facts. Based on the Townsend gas self-sustaining discharge condition and the chemical kinetics analysis of the Penning gas mixture discharging in PDP, the empirical equation to describe the breakdown of the Penning gas mixture is given. It is used to calculate the breakdown voltage curves of Ne-Xe/MgO and Ne-Ar/MgO in a testing macroscopic discharge cell of AC-PDP. The effective secondary electron emission coefficients （γeff） of the MgO protective layers are derived by comparing the breakdown voltage curves obtained from the empirical equation with the experimental data of breakdown voltages. In comparison with the results calculated by the Paschen law and the equation which ignore the influence of the Penning ionization on α , the results calculated by the empirical equation have better conformity with experimental data. The empirical equation characterizes the breakdown of the Penning gas mixture in PDP effectively, and gives a convenient way to study its breakdown characteristics and the secondary electron emission behaviors.     

Gas breakdown in radio-frequency field within MHz range: a review of the state of the art

Low-temperature plasmas (LTPs) driven by 1–100 MHz radio-frequency (MRF) are essential for many industrial applications, and their breakdown characteristics are different to that of direct current (DC) breakdown. This review seeks to understand the state of the art of electric breakdown in the MRF field and provide references for related basic and applied research. We have given a brief history of research into MRF-driven breakdown, including Paschen curves, the corresponding discharge modes and parameter spaces, and the evolution of the parameters during the breakdown process. It is shown that the focus has been transferred from the breakdown voltage and V-I characteristics to the evolution of plasma parameters during the breakdown, both in experiments and simulations. It is shown that many fundamental and applied problems still need to be investigated, especially with the new global model and the incorporation of the external circuit model.     

高温气冷堆氦气环境中电气设备绝缘设计研究

应用巴申定律研究了氦气的电气击穿特性,并与空气的绝缘特性进行比较。以高温气冷堆氦气透平发电系统电机腔室的设计参数为例,结合氦气的巴申曲线,对氦气条件下气体压力和极间距离的关系进行深入探讨,并提出氦气环境中电气设备绝缘设计需关注的问题。研究结果表明,氦气最小击穿电压为150~200V,绝缘特性较差,电气设备绝缘结构设计应考虑氦气环境压力的影响,现有针对压水堆电站电气设备绝缘结构的验收准则和试验方法并不完全适用于氦气环境。     

Attainment of Gigavolt Potentials by Fluid Dynamic Suppression of the Stepped Leader—Its Significance for Thermonuclear Ignition

It is proposed to levitate a conducting sphere in a high pressure Taylor flow and to charge it up to gigavolt potentials, either mechanically as in a Van de Graaff electrostatic generator, or inductively by a rising magnetic field. If the Taylor flow is sufficiently fast, it should overcome the electric pressure and breakdown by stepped leader formation, leading to the maximum attainable voltage by the Paschen law. Discharging the electro-statically stored energy can be done by controlled breakdown. With gigajoule energies stored and released in about 10⁻⁸ s, this implies and electric pulse power of the order 10¹⁷ W, opening the prospect of large driver energies for thermonuclear ignition.     

Study on the plasma generation characteristics of an induction-triggered coaxial pulsed plasma thruster

At present,spark plugs are used to trigger discharge in pulsed plasma thrusters (PPT),which are known to be life-limiting components due to plasma corrosion and carbon deposition.A strong electric field could be formed in a cathode triple junction (CTJ) to achieve a trigger function under vacuum conditions.We propose an induction-triggered electrode structure on the basis of the CTJ trigger principle.The induction-triggered electrode structure could increase the electric field strength of the CTJ without changing the voltage between electrodes,contributing to a reduction in the electrode breakdown voltage.Additionally,it can maintain the plasma generation effect when the breakdown voltage is reduced in the discharge experiments.The induction-triggered electrode structure could ensure an effective trigger when the ablation distance of Teflon increases,and the magnetic field produced by the discharge current could further improve the plasma density and propagation velocity.The induction-triggered coaxial PPT we propose has a simplified trigger structure,and it is an effective attempt to optimize the micro-satellite thruster.     

Investigation on the electrode surface roughness effects on a repetitive self-breakdown gas switch

In this work, the influence of the electrode surface roughness on the self-breakdown gas switch is investigated by physical analysis, computer simulation and experiment. Cu-W electrodes of different surface roughness were tested under the conditions of a pulse repetitive frequency of 50 Hz, self-breakdown voltage of ∼30 kV, and peak current of ∼2 kA for ∼93000 shots (the total charge transferred was ∼15 C). The coefficients of variation of the self-breakdown voltage of Cu-W 0.8, Cu-W 3.2 and Cu-W 12.5 electrodes were ∼2.95%, ∼1.62% and ∼1.16%, respectively. With the increase of electrode roughness, the erosion area decreased continuously, indicating that the breakdown positions were more stable and the coefficient of variation of breakdown voltage decreased. The method showed that decreasing the coefficient of variation of the self-breakdown voltage by increasing the surface roughness of electrode greatly improves the stability of the self-breakdown switch, which is significant for their application in compact high-power pulse power devices over a long time with stable operation.     

气体开关触发间隙与过压间隙击穿特性研究

为研究快脉冲直线变压器驱动源（FLTD）多间隙气体开关的触发击穿特性，针对一种环形电极两间隙等效实验开关，开展不同触发电压、工作系数和电极材料下的击穿特性实验，对比两个间隙的击穿延时和抖动，分析间隙击穿特性的主要影响因素和作用机制。实验结果表明：触发间隙击穿延时主要受触发电压影响，而工作系数是过压间隙击穿延时的主要影响因素；开关抖动主要来自于触发间隙，触发间隙抖动随触发电压的增大明显减小，过压间隙抖动基本不随触发电压和工作系数变化且维持在较低值；石墨电极开关的击穿延时和抖动明显小于不锈钢、黄铜和钨铜电极开关，具有良好的触发击穿性能。通过分析指出，是否有预电离可能是两个间隙击穿特性差异的主要原因。     

Experimental study of rotating wind turbine breakdown characteristics in large scale air gaps

When a wind turbine is struck by lightning,its blades are usually rotating.The effect of blade rotation on a turbine's ability to trigger a lightning strike is unclear.Therefore,an arching electrode was used in a wind turbine lightning discharge test to investigate the difference in lightning triggering ability when blades are rotating and stationary.A negative polarity switching waveform of 250/2500 μs was applied to the arching electrode and the up-and-down method was used to calculate the 50%discharge voltage.Lightning discharge tests of a 1:30 scale wind turbine model with 2,4,and 6 m air gaps were performed and the discharge process was observed.The experimental results demonstrated that when a 2 m air gap was used,the breakdown voltage increased as the blade speed was increased,but when the gap length was 4 m or longer,the trend was reversed and the breakdown voltage decreased.The analysis revealed that the rotation of the blades changes the charge distribution in the blade-tip region,promotes upward leader development on the blade tip,and decreases the breakdown voltage.Thus,the blade rotation of a wind turbine increases its ability to trigger lightning strikes.     

Numerical Study of Pulsed Dielectric Barrier Discharge at Atmospheric Pressure Under the Needle-Plate Electrode Configuration

In this paper,we study the characteristics of atmospheric-pressure pulsed dielectric barrier discharge (DBD) under the needle-plate electrode configuration using a one-dimensional self-consistent fluid model.The results show that,the DBDs driven by positive pulse,negative pulse and bipolar pulse possess different behaviors.Moreover,the two discharges appearing at the rising and the falling phases of per voltage pulse also have different discharge regimes.For the case of the positive pulse,the breakdown field is much lower than that of the negative pulse,and its propagation characteristic is different from the negative pulse DBD.When the DBD is driven by a bipolar pulse voltage,there exists the interaction between the positive and negative pulses,resulting in the decrease of the breakdown field of the negative pulse DBD and causing the change of the discharge behaviors.In addition,the effects of the discharge parameters on the behaviors of pulsed DBD in the needle-plate electrode configuration are also studied.     

Insulation characteristics of triple mixtures of c-C4F8/N2/CO2 under lightning impulse voltage

This paper has researched the insulation characteristics of 10%c-C₄F₈/N₂/CO₂ mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C₄F₈/N₂/CO₂ gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF₆ and the comprehensive GWP is about 5% of SF₆ , and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF₆ , 10%c-C₄F₈/N₂/CO₂ gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.     

Characteristics of Electrode-Water-Electrode Discharge and its Application to Water Treatment

Atmospheric air discharge above the surface of water is an effective method for water treatment.The leakage current and Joule heating of water are reduced by the air gap,which raises the energy efficiency of the water treatment.However,the application of this kind of discharge is limited by a pair of conflicting factors：the chemical efficiency grows as the discharge gap distance decreases,while the spark breakdown voltage decreases as the gap distance decreases.To raise the spark breakdown voltage and the chemical efficiency of atmospheric pressure water surface discharge,both the high-voltage electrode and the ground electrode are suspended above the water surface to form an electrode-water-electrode discharge system.For this system,there are two potential discharge directions：from one electrode to another directly,and from the electrodes to the water surface.The first step in utilizing the electrode-water-electrode discharge is to find out the discharge direction transition criterion.In this paper,the discharge direction transition criterions of spark discharge and streamer discharge are presented.By comparing the discharge characteristics and the chemical efficiencies,the discharge propagating from the electrodes to the water surface is proved to be more suitable for water treatment than that propagating directly between the electrodes.     

Spatiotemporal control of femtosecond laser filament-triggered discharge and its application in diagnosing gas flow fields

Precise control of the discharge in space and time is of great significance for better applications of discharge plasma. Here, we used a femtosecond laser filament to trigger and guide a high-voltage DC pulse discharge to achieve spatiotemporal control of the discharge plasma. In space, the discharge plasma is distributed strictly along the channel generated by the femtosecond laser filament. The breakdown voltage threshold is reduced, and the discharge length is extended. In time, the electrical parameters such as the electrode voltage and the electrode gap affect discharge delay time and jitter. By optimizing the parameters, we can achieve sub-nanosecond jitter of the discharge. Based on the spatiotemporal control of the discharge, we applied filament-triggered discharge for one-dimensional composition measurements of the gas flow field. Besides, the technique shows great potential in studying the spatiotemporal evolution of discharge plasma.     

2×6 MV串列加速器头部附近电场设计优化

为了给2×6 MV串列加速器提供高压电极与均压环尺寸，根据设计要求及已有参数，采用电磁场仿真软件计算了串列加速器的二维电场强度分布，针对高压电极结构、均压环截面形状及环间距等因素对串列加速器电场强度分布的影响提出了优化措施。仿真结果表明：直筒结构的高压电极与均压环接壤处电场强度分布不均匀，而圆弧过渡结构的高压电极具有屏蔽作用，比直筒时电场强度分布更均匀；优化均压环截面形状与减小环间距可降低环间电场畸变，但后者对减小均压环表面的电场贡献更大。最终优化后得到高压电极与均压环的尺寸可满足新研制的串列加速器要求。     

Temporal evolution of atmospheric cascade glow discharge with pulsed discharge and radio frequency discharge

Atmospheric cascade discharges with pulsed discharge and radio frequency(RF)discharge were experimentally investigated by the temporal evolution of discharge spatial profile and intensity.The indium tin oxide(ITO)coated glass was employed as the transparent electrode to capture the discharge distribution above the electrode surface.It is demonstrated that in the pulsed discharge with dielectric barrier,the first discharge at the rising edge of pulse voltage is uniformly ignited and then forms an expanding plasma ring on the ITO electrode surface,which shrinks to the same diameter as that of bare stainless steel electrode with the generation of second discharge at the falling edge of pulse voltage.The discharge profiles along the electrode surface and discharge gap of the successive RF discharge are dependent on the intensity and spatial distribution of residual plasma species generated by the pulsed discharge,which is determined by the time interval between the pulsed discharge and RF discharge.It is demonstrated that the residual plasma species before the RF discharge ignition help to achieve the stable operation of RF discharge with elevated intensity.     

400 kV强流中子发生器的物理设计

对400 kV强流中子发生器进行了物理设计。采用Poisson/Superfish软件对中子发生器高压电极和加速管的电场分布进行了模拟,结果显示,各关键区域的空间电场最大值远低于击穿电场限值。以强流束旁轴包络方程为基本模型,发展了强流束传输系统束包络的计算机模拟程序IONB1.0,模拟了中子发生器传输系统中40 mA的D束流包络。结果显示,设计方案中所采取的两间隙高梯度加速结构有较强的聚焦性能,能有效抵消强流束空间电荷效应造成的束流发散,加速管出口处的束包络半径约3 cm,由加速管出口处的空间电荷透镜和三重四极磁透镜组成的传输系统能将束流聚焦在约140 cm处的靶上,且束斑直径小于2 cm。     

Preliminary Results of Cone Z-Pinch Device with 5 kJ

The Cone Z-Pinch Experiment with 5 kJ is designed, constructed and operated. The electric discharge takes place between an upper ring electrode and a lower pin electrode creating plasma sheath in shape of cone. The preliminary experimental results using Helium gas in discharge show that the discharge period is 35 μs, the total system inductance is 287 nH, and the total system resistance is 15 mΩ. The breakdown curve shows a minimum breakdown value at 0.2 torr pressure. The cone plasma is confined by electromagnetic force and plasma inductance has its maximum value at the pinch. The plasma current has a maximum value of 53 kA at the axis of the discharge tube. The experimental results showed that a time of 2.1 μs at least is required for the pinch to occur and that both the pinch time and the duration time decrease with increasing the charging voltage.