Effects of background pressure on the arc characteristics of gas spark gap

Gas spark gap is widely used in any pulsed power system as the key element which directly determines its repetitive performance and output characteristics. Among many factors of threeelectrode gas spark gap, background pressure is of much importance in determining the gap performance parameters such as the delay and jitter, and relevant studies have been rarely performed. A magneto-hydrodynamic model of the arc in gas spark gap is built and the effects of background pressure on the arc characteristics are discussed in this paper. It is demonstrated that a higher background pressure may result in radial compression of the arc column, a higher arc voltage, and a lower declination rate of arc resistance in the first quarter cycle. Relevant simulation data would be helpful for the optimization of the design of gas spark gap.     

Recovery of deuterium from the separation of H-D gas mixture in concentric-tube thermal diffusion columns with transverse sampling streams

The separation equations for predicting the recovery of deuterium from H-D gas mixture in a concentric-tube thermal diffusion column with transverse sampling streams, have been derived. The effects of column length, volume flow rate and operating pressure on the performance have been discussed. The degrees of separation, as well as separation factors, for deuterium recovery in the cryogenic-wall thermal diffusion columns were estimated, with the use of the transport coefficients correlated in the previous work from the experimental data obtained by Arita et al. The separation efficiencies obtained in feeding by transverse sampling streams are rather lower than those achieved by middle feeding.     

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.     

铀矿堆浸分形动力学模型

本文采用堆浸铀矿石粒径分布分维数代替其平均粒径,对Mellado等提出的矿石堆浸动力学模型进行了改进。同时采用铀矿柱浸试验确定了铀矿堆浸分形动力学模型参数与堆浸铀矿石粒径分布分维数的关系,建立了铀矿堆浸分形动力学模型,并进一步采用柱浸试验对模型进行了验证。结果表明,所建立的铀矿堆浸分形动力学模型能很好地反映铀矿堆浸铀金属浸出的规律。     

Two-dimensional self-consistent numerical simulation of the whole discharge region in an atmospheric argon arc

A 2D self-consistent numerical model of the whole argon-arc discharge region that includes electrodes is developed in this work to facilitate analysis of the physical processes occurring in atmospheric arc plasma. The 2D arc column model contains the ionization and thermal non-equilibrium, which is coupled with a 1D electrode sheath model. The influence of plasma-species diffusion near the electrode region is investigated based on Maxwell–Stefan equations and the generalized Ohm's law. The numerical results of argon free-burning arcs at atmospheric pressure are then investigated. The simulation shows that the plasma is obviously in the state of thermal and ionization equilibrium in the arc core region, while it deviates from thermal and ionization equilibrium in the arc fringe region. The actual electron density decreases rapidly in the near-anode and near-cathode regions due to non-equilibrium ionization, resulting in a large electron number gradient in these regions. The results indicate that electron diffusion has an important role in the near-cathode and near-anode regions. When the anode arc root gradually contracts, it is easy to obtain a positive voltage drop of the anode sheath (I = 50 A), while it remains difficult to acquire a positive anode sheath voltage drop (I = 150 A). The current–voltage characteristics predicted by our model are found to be identical to the experimental values.     

大气压下大功率等离子体炬的数值模拟

主要研究直流等离子体炬的数值模拟方法，通过求解等离子体弧社区域的能量守恒，动量守恒，质量守恒及电流连续性方程，得到不同边界条件下温度，速度，电流密度分布，计算了大气压下２００Ａ自由氩弧的温度分布，电势和电流分布，并与实验数据及现有的理论计算进行了比较，得到了较好的结果，在此基础上结合本实验室５０００Ａ大功率等离子体炬，讨论了有阴极喷口存在下的弧柱部分的数值计算，以及能量守恒方程中辐射项，焦耳热项的     

Numerical Analysis of the Arc Plasma in a Simplified Low-voltage Circuit Breaker Chamber with Ferromagnetic Materials

This paper is devoted to the simulation of the arc plasma in a simplified low-voltage circuit breaker chamber. Based on a group of coupled governing equations, a three-dimensional （3-D） arc plasma model is built and solved by a modified commercial code. Firstly, this paper presents a solution of the stationary state of the arc plasma and discusses the distribution of some parameters throughout the chamber. Secondly, with the ferromagnetic materials included, the balance of the stationary state is broken and a transient course is calculated. In light of the simulation results, the temperature distribution sequence, the arc motion and the plasma jet are then described and analyzed in detail.     

“Delta-Wrinkly Zone” Observed Near Crack of Ductile Zircaloy-2 Cladding during Impact Loading Test

An equivalent linearization method has been introduced for density-wave oscillation analysis. Unlike the frequency domain approach with linearized equations assuming an infinitely small amplitude, the present method can deal with large amplitude oscillations with the nonlinearity effect on limit cycle amplitudes taken into account in the frequency domain.

Equivalent linear equations have been derived based on a one-dimensional separated flow model. A profile fit model was adopted for subcooled boiling. The characteristics of the equivalent linear equations and factors to limit the amplitudes were phenomenologically examined.

Analyses of the experimental data by Saha et al. using the present method revealed that, given an appropriate set of two-phase flow correlations, the equivalent linearization method can predict limit cycle amplitudes after instability initiation as well as the stability boundary.     

轴向磁场中电弧螺旋不稳定性的简化数值分析

在静电近似下，通过数量级的分析，简化了能量方程。用数值方法研究了外加轴向磁场，电流分布、弧电流等对电弧曙旋不稳定性的影响。数值结果表明，在具有外加磁场情况下，当弧柱内均匀电流分布时，正向磁场能够使短波长的扰动稳定，反向磁场能够使长波长的扰动稳定。当弧柱内电流为抛物线形分布时，外加正向磁场对于短波情况下的稳定性影响很小，但对于长波情况，稳定性增强，外加反向磁场，同样能稳定中等和长波情况下的电弧。     

等离子体切割的弧特性研究

基于弧柱双区域近似的简单理论,研究了空气等离了体切割产生的等离子体弧特性,给出了不同工作条件（空气流速及喷嘴直径）下,弧的半径、电压及喷嘴出口处压强随弧电流变化的计算结果。研究结果表明,计算与实验结果符合得好。同时讨论了空气流速及喷嘴直径对等离子体功率及作用力的影响。     

Numerical simulation of constricted and diffusive arc–anode attachments in wall-stabilized transferred argon arcs

A numerical simulation is conducted to investigate arc–anode attachment behavior, especially the formation mechanism of the constricted arc attachment mode for the water-cooled anode of wall-stabilized transferred argon arcs. Argon molecular ions and the corresponding kinetic processes are included to the finite-rate chemistry model in order to capture the chemical nonequilibrium characteristics of the arc near the anode region. Modeling results show that constricted and diffusive arc–anode attachments can be self-consistently obtained at different arc currents while keeping other parameters unchanged. The dominant kinetic processes contributing to ionization and recombination in the arc center and fringes are presented. The results show that in arc fringes and the arc attachment region, molecular ion recombination plays an important role which leads to the rapid loss of electrons. The radial evolution of the production, loss and transport processes of electrons is further analyzed. It is found that for the constricted arc attachment mode, both the recombination and convection transport caused by the anode jet result in the loss of electrons at the arc fringes, which leads to the shrinkage of the arc column at the anode. The formation of the anode jet is due to the combined action of radial and axial Lorentz forces in the anode region.     

Simulation and Experimental Analysis of Arc Motion Characteristics in Air Circuit Breaker

In this paper, to simulate the arc motion in an air circuit breaker (ACB), a three-dimensional magneto-hydrodynamic (MHD) model is developed, considering the influence of thermal radiation, the change of physical parameters of arc plasma and the nonlinear characteristic of ferromagnetic material. The distributions of pressure, temperature, gas flow and current density of arc plasma in the arc region are calculated. The simulation results show some phenomena which discourage arc interruption, such as back commutation and arc burning at the back of the splitter plate. To verify the simulation model, the arc motion is studied experimentally. The influences of the material and position of the innermost barrier plate are analyzed mainly. It proved that the model developed in this paper can efficiently simulate the arc motion. The results indicate that the insulation barrier plate close to the top of the splitter plate is conducive to the arc splitting, which leads to the signi?cant increase of the arc voltage, so it is better for arc interruption. The research can provide methods and references to the optimization of ACB design.     

Numerical Simulation of Fluid Flow and Heat Transfer in a DC Non-Transferred Arc Plasma Torch Operating Under Laminar and Turbulent Conditions

In this work, a magnetic fluid dynamics (MHD) model is used to simulate the electromagnetic field, heat transfer and fluid flow in a DC non-transferred arc plasma torch under laminar and turbulent conditions. The electric current density, temperature and velocity distributions in the torch are obtained through the coupled iterative calculation about the electromagnetic equations described in a magnetic vector potential format and the modified fluid dynamics equations. The fluid-solid coupled calculation method is applied to guarantee the continuity of the electric current and heat transfer at the interface between the electrodes and fluid. The predicted location of the anodic arc root attachment and the arc voltage of the torch are consistent with corresponding experimental results. Through a specific analysis of the influence of mass flow rates and electric current on the torch outlet parameters, the total thermal efficiency, thermal loss of each part, and the laws of the variation of outlet parameters with the variation of mass flow rates and electric current was obtained. It is found that operation under a laminar condition with a limited area of the anode could increase the total thermal efficiency of the torch.     

Electronic stopping power for Monte Carlo simulation of ion implantation into SiC

A new electronic stopping power model for Monte Carlo simulation of ion implantation into 6H–SiC is presented. This model is based on the nonlinear density functional approach of Echenique et al. for the energy loss of slow ions moving through an electron gas and the ab initio pseudopotential calculations of Park et al. for the map of valence electrons of 6H–SiC crystal. A modified linear response theory has been used to treat the core electrons stopping. This model does not need fitting parameters and allows to fit the experimental distributions of implanted dopants in SiC both the peak region and the channeling tail of the SIMS profiles.     

Evaluation of Computational Models for Fission and Spallation Reactions Used in Accelerator Breeding and Transmutation Analysis Code

Computational models for spallation and fission reactions used in an accelerator breeding and transmutation code have been evaluated by performing calculations for thin targets of Bi, Pb, Th and U in the energy range of 50–1,000 MeV. Proton and neutron non-elastic and fission cross sections have been derived from the counts of real collisions and fission events in the targets.

Several fission models in combination with a spallation model are compared with the experimental data due to Steiner et al. and Schimmerling et al. A good agreement has been obtained for a model with the level density parameters a_n = A/10 and a_f/a_n fitted to the data due to Il'inov et al. The mass dependence of the non-elastic cross sections has been calculated also with the use of the best fit model. A good agreement with the experimental data was obtained over a wide range of nuclear masses.     

Influence of near-wall modelling on boiling flow simulation

The capability of the three-dimensional two-fluid codes to simulate the local boiling flow processes has been assessed. Boiling flow experiments of Roy et al. [Roy, R.P., Kang, S., Zarate, J.A., Laporta, A., 2002. Turbulent subcooled boiling flow—experiments and simulations, J. Heat Transfer 124, 73-93] and Lee et al. [Lee, T.H., Park, G.C., Lee, D.J., 2002. Local flow characteristics of subcooled boiling flow of water in a vertical concentric annulus. Int. J. Multiphase Flow 28, 1351-1368], both performed in annular vertical channels were used as an experimental benchmark data set. The boiling flow is strongly affected by local mechanisms in the boundary layer near the heated wall. In this paper, the influence of near-wall modelling on the distribution of flow parameters at flow boiling has been analyzed. A generic wall function model for 3D two-fluid codes, based on surface roughness analogy has been proposed instead of commonly used single-phase log-law model. The new model has been implemented in the code CFX-4.4. In general, better agreement of phase velocities with experimental data were obtained with the new model. Presented results show that the influence of nucleating bubbles on the near-wall velocity profile should be taken into account. The second goal of this paper is to compare the NEPTUNE_CFD simulations against CFX-4.4 results and experimental data.     

基于多元线性回归模型的中性束质子比分析

中性束质子比的高低对其注入等离子体后的加热效果具有重要的影响。实验中,强流离子源的灯丝电压、弧压、进气量等宏观运行参数决定了中性束质子比的大小。以东方超环中性束注入测试台束引出实验为基础,利用多元线性回归模型对引出中性束质子比进行分析,建立了影响中性束质子比的预测方程,并对该模型的正确性进行了检验。结果表明,中性束质子比可利用以灯丝电压和弧压为自变量的多元线性回归模型进行分析,灯丝电压是影响质子比的关键参数,弧压次之。     

ITER液态锂铅回路鼓泡柱中提取氚的理论

建立了1个描述ITER液态锂铅回路鼓泡提取器复杂的流体动力学的数学模型。模型中的等式无量纲,有合适的边界条件,依据正交搭配完成模拟计算。为更好地理解不同参数对鼓泡器性能的影响,引入许多假设,并将提取效率作为过程参数进行分析与计算。在此基础上提出了鼓泡柱提取系统的初步设计参数。     

Simulation,Design, Construction of Duoplasmatron and Diagnostic Neutral Beam System for Alborz Tokamak

Diagnostic Neutral Beam (DNB) has been used for measuring plasma parameters of tokamaks such as ion and electron temperature, safety factor, impurity concentration and etc. Ion source and electrical power supply specification are the main part of DNB. Arc discharge current value is affected by filament current and anode voltage. Beam current changes with arc current signal in our experiment that agree with theoretical relations. Sixty milli-ampere (60 mA) pulse beam current is because of arc current of about 40 A and extraction voltage of about 20 kV. The increase of beam current with arc current has been reported experimentally and effect of arc current on beam current has been investigated for several high extraction voltages. Optimum condition, which means having a telescopic beam (minimum divergence) for specific parameters of duoplasmatron, has been simulated and verified with experimental test. The best extraction voltage for these parameters has been found to be about 16-kV. The ratio of the perpendicular velocity to parallel velocity has been calculated to be about 0.012. It has been shown experimentally with optical emission spectroscopy that increase in arc current and magnetic current increase proton content of beam.