Numerical Simulation of Low Current Vacuum Arc Supersonic Flow

Based on a two-dimensional axisymmetric magneto-hydrodynamic （MHD） model, low current vacuum arc （LCVA） characteristics are studied. The influence of cathode process under different axial magnetic fields and different anode radii on LCVA characteristics is also simulated. The results show that the influence of both cathode process and anode radii on LCVA is significant. The sign of anode sheath potentials can change from negative to positive with the decrease of anode radii. The simulation results are in part verified by experimental results. Especially, as the effect of ion kinetic energy is considered, ion temperature is improved significantly; which is in agreement with experimental results.     

Modeling and Simulation of Deflected Anode Erosion in Vacuum Arcs

In vacuum switch devices, the connection bus bar out of the vacuum interrupter will generate a transverse magnetic field in the arc column region, and under the influence of this magnetic field, the whole arc column will deflect from the electrode center, thus leading to deflected anode erosion. In this paper, a two-dimensional deflected anode erosion model is established, anode erosions under different deflection distance are simulated and analyzed, and results of anode surface temperature, anode melting and surface evaporation flux are obtained. The simulation results show that the deflected heat flux density will lead to deflected distribution of anode temperature, saturated vapor pressure and vapor flux correspondingly, and the morphology of the anode melting pool has also the same deflection. Moreover, the anode center temperature and its gradient along the y direction decrease with the increase of deflection distance. On the contrary, the temperature of the anode side surface, toward which the heat flux density deflects, increases with increasing deflection distance. Related experiments also verify the correctness of the model and simulation results.     

Simulation of Vacuum Arc Characteristics at Different Moments Under Power-Frequency Current

In this paper,based on the quasi-stationary magneto-hydrodynamic(MHD) model,vacuum arc characteristics are simulated and analyzed at different moments under power-frequency current.For a vacuum arc with sinusoidal current under a uniform axial magnetic field(AMF),simulation results show that at the moment of peak value current,maximal values appear in the ion number density,axial current density,heat flux density,electron temperature,plasma pressure and azimuthal magnetic field.At the same time,the distributions of these parameters along the radial position are mostly nonuniform as compared with those at other moments.In the first 1/4 cycle,the ion number density,axial current density and plasma pressure increase with time,but the growth rate decreases with time.Simulation results are partially compared with experimental results published in other papers.Simulations and experimental results both show that the arc light intensity near the cathode side is stronger than that near the anode side for diffusing vacuum arcs.     

Simulation of Vacuum Arc Characteristics Under Four Kinds of Axial Magnetic Fields and Comparison with Experimental Results

Based on a two-dimensional axisymmetric magnetohydrodynamic （MHD） model, the vacuum arc characteristics under four kinds of axial magnetic fields （AMFs） are ana...     

汽膜对熔滴水力学碎化影响的数值模拟

在熔融物与冷却剂相互作用(FCI)过程中,熔滴的水力学碎化对于后续是否产生蒸汽爆炸以及爆炸的强弱程度有着重要影响。传统的熔滴水力学碎化数值研究通常只考虑液液直接接触的两相系统;而堆芯熔化后,熔融物温度在2 500K以上,熔融物周围会迅速产生汽膜,导致熔滴和冷却剂之间的传热和阻力特性发生改变。本文基于PLIC-VOF(piecewise linear interface construction-volume of fluid)界面跟踪方法对有汽膜存在的三相系统中的熔滴水力学碎化过程进行了数值研究,通过分析熔滴在有无汽膜和不同边界速度触发情况下碎化过程中的界面特性,发现熔滴碎化程度随Weber数的增加而加剧,汽膜对熔滴的水力学碎化存在一定的抑制作用。     

真空石墨加热器温度场数值模拟与分析

石墨加热器是测量球床堆芯等效导热系数实验的关键部件,加热器温度场对系统安全及数据准确性有重要影响。本文基于Fluent计算平台,分别采用DTRM模型、P1模型、ROSSELAND模型、DO模型对真空保护环境下的石墨加热器温度场进行数值模拟,确定适合真空保护石墨加热器温度场的计算方法并讨论石墨导热系数、表面发射率对温度场分布的影响。比较分析表明：DO模型计算得到的温度分布较为接近真实情况,导热系数小于35W/(m•K)时,最高温度对其敏感;导热系数大于35W/(m•K)时,其对加热体最高温度影响较小,最高温度较为稳定。     

Simulation Research of Magnetic Constriction Effect and Controlling by Axial Magnetic Field of Vacuum Arc

Based on magnetohydrodynamic (MHD) model of vacuum arc, the computer simulation of vacuum arc was carried out in this paper. In the MHD model, mass conservation equation, momentum conservation equations, energy conservation equations, generalized ohm‘s law and Maxwell equation were considered. MHD equations were calculated by numerical method, and the distribution of vacuum arc plasma parameters and current density were obtained. Simulation results showed that the magnetic constriction effect of vacuum arc is primarily caused by the Hall effect. In addition, the inhibition of axial magnetic field (AMF) on constriction of vacuum arc was calculated and analyzed.     

Numerical Simulation of the Eddy Current Effects on the Arc Splitting Process

This paper focuses on a numerical simulation of the arc plasma behavior in the arc splitting process,considering the eddy currents in the electrodes and the splitter plate.Based on three-dimensional(3D) magneto-hydrodynamic(MHD) theory,a thin layer of nonlinear electrical resistance elements is used in the model to represent the voltage drop of plasma sheath and the formation of new arc root in order to include the arc splitting process in the simulation.In the arcing process,eddy currents in metal parts are generated by a time-varying magnetic field.The arc model is calculated with the time-varying magnetic field term,so that the eddy current effects can be considered.The effect of nonlinear permeability of a ferromagnetic material is also involved in the calculation.Using the simulation results for the temperature,velocity and current density distribution,the arc splitting process is analyzed in detail.The calculated results are compared with the simulation neglecting eddy currents.     

Arc Behaviours in Vacuum Interrupters with Axial Magnetic Field Electrodes

To improve the limiting current interruption capability and minimizing vacuum interrupter with axial magnetic field （AMF） electrodes, it is significant to investigate the vacuum arc behaviours between the contacts. AMF distributions of the slot type electrodes were studied by both numerical analysis and experiments. Furthermore, the behaviours of vacuum arcs for different parameters of the slot type AMF electrodes were investigated by using high-speed CCD camera. The influences of gap distance, contact diameter and phase shift time between AMF and arc current on the vacuum arc were investigated. The results provide a reference for research and development of vacuum interrupters with slot type or other types of AMF electrode.     

Simulation of the Effect of a Metal Vapor Arc on Electrode Erosion in Liquid Metal Current Limiting Device

The effect of arc plasma on electrode erosion in a liquid metal current limiter(LMCL)is studied.Based on a simplified two-dimensional magnetohydrodynamic model,the elongated GaInSn metal vapor arc and its contraction process in a liquid metal current limiter are simulated.The distributions of temperature,pressure and velocity of the arc plasma are calculated.The simulation results indicate that the electrode erosion is mainly caused by two high temperature gas jet flows arising from the pressure gradient,which is a result of the non-uniform arc temperature distribution.The gas flows,which act as jets onto the electrode surface,lead to the evaporation of the electrode material form the surface.A redesign structure of the electrode is proposed and implemented according to the analysis,which greatly increased the service life of the electrode.     

Numerical Simulation Approaches to Evaluating the Electromagnetic Loads on the EAST Vacuum Vessel

Numerical simulation approaches are developed to compute the electromagnetic forces on the EAST vacuum vessel during major disruptions and vertical displacement events, with the halo current also considered. The finite element model built with ANSYS includes the vacuum vessel, the plasma facing components and their support structure, and the toroidal and poloidal field coils. The numerical methods are explained to convince of its validity. The eddy current induced by the magnetic flux variation and the conducting current caused by the halo current are also presented for discussion. The electromagnetic forces resulting from the numerical simulation are proven to be useful for structure design optimization. Similar methods can be applied in the upgrades of the EAST device.     

Deposition of Ti-AI-N Films by Using a Cathodic Vacuum Arc with Pulsed Bias

Ti-Al-N hard films have been prepared by cathodic arc deposition by using an unipolar pulsed bias.In the present study,Ti-Al-N films were deposited on stainless steel and silicon wafers.The deposition rate,micrograph,preferred orientation and composition were systematically investigated by usingx-ray diffraction(XRD),energy dispersive X-ray spectroscopy(EDX), and a scanning electron microscope(SEM).It is shown that substate bias duty cycle and frequency have a great effect on film structure.A simple explanation for the results is also presented.     

氢化钛镍合金阴极真空弧放电离子特性研究

本文将氢化钛镍合金材料应用于强流长脉冲（200 A/270 μs）真空弧放电实验中,该材料能在强流长脉冲真空弧放电产生的高温条件下保持较好的稳定性。使用飞行时间谱仪获得了氢化钛镍合金阴极真空弧放电产生的离子电荷态分布和离子成分。结果表明：Tiⁿ⁺和Niⁿ⁺电荷态为1+、2+和3+,在放电过程的早期（0~30 μs）,H⁺成分随时间逐渐增加,在30 μs时达到最大比例57%,而Tiⁿ⁺和Niⁿ⁺（n=1,2,3）离子成分随时间逐渐减少,在30 μs时达到最小比例43%;在放电过程的后期（30~270 μs）,H⁺成分迅速下降且在75 μs后保持在总离子流的12%左右直至放电结束,Tiⁿ⁺和Niⁿ⁺（n=1,2,3）含量随时间逐步增加,且在75 μs后保持在总离子流的88%左右直至放电结束。     

Influence of Gap Distance on Vacuum Arc Characteristics of Cup Type AMF Electrode in Vacuum Interrupters

The greenhouse effect of SFe is a great concern today. The development of high voltage vacuum circuit breakers becomes more important. The vacuum circuit breaker has minimum pollution to the environment. The vacuum interrupter is the key part of a vacuum circuit breaker. The interrupting characteristics in vacuum and arc-controlling techniue are the main problems to be solved for a longer gap distance in developing high voltage vacuum interrupters. To understand the vacuum arc characteristics and provide effective technique to control vacuum arc in a long gap distance, the arc mode transition of a cup-type axial magnetic field electrode is observed by a high-speed charge coupled device （CGD） video camera under different gap distances while the arc voltage and arc current are recorded. The controlling ability of the axial magnetic field on vacuum arc obviously decreases when the gap distance is longer than 40 ram. The noise components and mean value of the arc voltage significantly increase. The effective method for controlling the vacuum arc characteristics is provided by long gap distances based on the test results. The test results can be used as a reference to develop high voltage and large capacity vacuum interrupters.     

Simulation of Magnetically Dispersed Arc Plasma

Magnetically dispersed arc plasma [1] exhibits typically dispersed uniform arc column as well as diffusive cathode root [1,2] and diffusive anode root.In this paper magnetically dispersed arc plasma coupled with solid cathode is numerically simulated by the simplified cathode sheath model of LOWKE [3].The numerical simulation results in argon show that the maximum value of arc root current density on the cathode surface is 3.5×10 7 A/m 2,and the maximum value of energy flux on the cathode surface is 3×10 7 J/m 2,both values are less than the average values of a contracted arc,respectively.     

Study of Distortion of a Vacuum Arc at a Long-Gap Distance

Experimental study of the long-gap distance vacuum arc distortion for three types of axial magnetic field (AMF) contacts, by using high-speed charge coupled device (CCD), is presented. The arc current was of a half-cycle sine wave with a frequency of 50Hz, produced by an L-C discharging circuit. The time of appearance and duration of vacuum arc distortion under three conditions were studied. It was found that the gap distance, current and diameter of the electrode affected the characteristics of vacuum distortion at a long-gap distance. Some characteristics of the vacuum arc at a long-gap distance was revealed and the experience and data for further investigation were provided.     

真空弧氘离子源中杂质氕对束流品质的影响

分析了真空弧氘离子源中杂质的主要构成,并着重分析了杂质氕的成因及其对氘离子源性能的影响.对单次脉冲和低重复频率脉冲工作状态下的真空弧氘离子源进行了光谱诊断实验和核反应分析实验,结果表明,氘离子源等离子体中的确含有较多的杂质氕,可对氘离子源的引出束流品质产生较大的危害.并对如何减小杂质氕的影响提出了建议.     

真空弧离子源引出束流在加速空间的分布

采用数码相机直接照相的方法来确定真空弧离子源引出束流在加速空间的分布。实验在动态真空实验系统中进行,系统真空度优于2×10-3 Pa。在离子源脉冲工作的条件下,采用数码相机拍摄到离子源引出束流在加速空间的积分图像,得到引出束流的幅亮度在拍摄平面上的相对分布,然后再通过Abel转换得到引出束流在加速空间的径向分布。实验结果表明:真空弧离子源引出束流近似高斯分布,离子源出口处的束流比靶入口处的束流强40%。     

Numerical Modeling of the High-Intensity Transferred Arc with a Water-Cooled Constrictor Tube

Fig.1 Schematic diagram of the high-intensity transferredarc with a water-cooled constrictor tubeFig.2 Computational domain employed in this studyplasma axial-velocities at the upstream boundary (H-Pin Fig. 2) of computational domain.In a recent experimental study of the high-intensitytransferred arc reported by Hartmann and Heberlein[8],a new experimental arrangement has been adopted, i.e.,each water-cooled segment of the constrictor tube isseparated by co-axial boron nitride spacer discs s…