外加磁场、电流及弧柱半径对电弧螺旋不稳定性的影响

采用与时间有关的线性微扰理论，研究了存在气流作用下，外加磁场、弧电流以及弧柱半径对电弧螺旋不稳定性的影响，给出了稳定性条件和不稳定性增长率等定量结果. 关键词： 电弧 稳定性 轴向磁场 弧柱半径     

非均匀纵向场对等离子体平衡的影响

讨论了纵向不均匀磁场导致磁面与等离子的畸变。对于锐边界情形和具有体电流分布情形求解了平衡方程，特别是给出了磁面变形依赖于各参量变化的表达式。     

圆柱形等离子体中漂移波的稳定性

在平板模型下,所谓普适模是绝对稳定的。对于圆柱形等离子体,情形又如何呢?两者的主要差别在于:代替平板模型下的外行波边条件,在柱模型下则在r=0和r=∞处都没有波能外流。这可有效地改变模的稳定性。假设了指数型密度和电流分布,本文导出了漂移波的积分本征方程。在模径向慢变的情形下,它可变为二阶微分方程。对此方程作了数值计算,结果表明确实存在不稳定模。对两种模型(平板模型与柱模型)作了比较。 关键词：     

等离子体放电柱磁螺旋不稳定性的线性理论

在静电磁流体方程基础上,提出了柱状放电电弧等离子体磁螺旋不稳定性的一种新的线性分析方法.通过数量级分析得到的简化扰动能量方程研究了外轴向磁场中阻抗粘滞m=1慢模,解析地给出了全部解和不稳定性增长率.并讨论了外加轴向磁场、弧电流和弧柱半径与外管壁半径相对大小等对电弧不稳定性的影响 关键词：     

Ar-O_2混合气体电弧的数值模拟

混合气体电弧被广泛地应用于焊接制造领域,为了深入理解混合气体电弧的传热和传质特性,本文建立了Ar-O_2混合气体电弧的二维稳态数学模型.模型基于局域热平衡假设,混合气体电弧的热力学参数和输运系数是温度和氧浓度的函数,分别采用组合普通扩散系数和组合温度扩散系数描述氧和氩两种组分之间的扩散行为,研究了不同电流条件下的氧分布及其对电弧温度场和流场的影响.结果表明,对于Ar-5%O_2的混合气体电弧,氧在电弧中呈现极不均匀的分布,在电弧中心轴线附近和靠近两极的区域,氧浓度高于混合气体浓度,而在其他区域则明显小于混合气体浓度.在小电流时,氧集中分布于阴极和阳极附近,且在阴极附近出现峰值;而在大电流时,氧的分布明显向阳极集中,且在阳极中心附近出现峰值.两种情形下,氧在距离阳极表面0.1 mm的区域分布都不均匀.与纯Ar保护相比,混入5%的O_2使电弧出现一定程度的收缩,温度和等离子体流速升高.     

圆域隧道结中自场的影响及其解的稳定性

本文讨论自场对圆域隧道结电流密度分布的影响.在结半径比较小的情形给出电流密度分布、磁场强度分布以及临界电流值的近似解析公式.在结半径很大时,通过结的临界电流与结半径成正比.对于一般的情形给出数值计算结果.因为对于给定的偏置电流,由自场方程得到的解不是唯一的。所以本文还讨论了解的稳定性问题.     

真空电弧等离子体发射光谱诊断

真空断路器的开断容量限制其在高压大电流开断领域的应用,获取燃弧过程中的等离子体参数对于提高真空断路器的开断容量至关重要。利用发射光谱法对真空电弧内的等离子体参数进行了诊断,研究了在不同电流幅值条件下真空电弧内电子温度、电子密度、谱线强度的轴向分布规律,结合真空电弧高速图片对真空电弧内不同粒子的扩散过程与弧柱直径之间的关系进行了分析。得到的电子温度在8000～10 000 K量级,电子密度在1019～1020 m?3量级,电子温度与电子密度从阴极向阳极逐渐下降,同时铜原子谱线强度主要集中在两极而一价铜离子谱线强度由阴极向阳极逐渐升高。铜原子谱线强度的径向分布呈现类平顶波分布、一价铜离子谱线强度的径向分布呈现类高斯分布的特点,且铜原子的谱线范围略大于弧柱直径,一价铜离子的谱线范围略小于弧柱直径,两种粒子的扩散速度存在差异。     

直流电弧炉偏弧和控弧的计算机仿真

根据电弧弧柱在微元电流相互作用下的受力以及空间载流导线在电弧区所造成电磁力动态平衡的原理，建立了研究直流电弧电磁偏弧，多底电极分电流控弧和顶电极倾动控弧的数学模型，并通过计算机仿真实验，对载流导线的电磁影响和一些纠正和控制偏弧的方法进行了考察和研究。     

考虑金属蒸汽的钨极惰性气体保护焊电弧与熔池交互作用三维数值分析

基于局域热平衡状态假设并考虑金属蒸汽的作用, 建立了钨极惰性气体保护焊电弧与熔池交互作用的三维数学模型. 电弧等离子体的热力学参数和输运系数由温度和金属蒸汽浓度共同决定, 并使用第二黏度近似简化处理金属蒸汽在氩等离子中的输运过程. 在考虑熔池流动时, 主要考虑了浮力、电磁力、表面张力和等离子流拉力的作用. 通过对麦克斯韦方程组、连续性方程、动量守恒方程、能量守恒方程和组分输运方程的耦合求解, 得到了金属蒸汽在电弧中的空间分布、电弧和熔池的温度场、速度场和电流密度分布等重要结果. 通过与未考虑金属蒸汽的结果对比, 研究了熔池上表面产生的金属蒸汽对电弧等离子体行为的影响, 以及电弧等离子对熔池行为的影响. 结果表明, 金属蒸汽主要富集在熔池上表面附近; 金属蒸汽对电弧等离子体有明显的收缩作用, 而对等离子速度和电势影响较小; 金属蒸汽的出现对熔池上表面速度分布和剪切力分布以及熔池形貌并无明显影响. 求解结果与已有的实验结果和计算结果符合良好.     

微束等离子体弧焊电弧物理特性多场耦合分析

根据磁流体动力学方程组,建立了微束等离子电弧模型,使用有限元分析软件COMSOL进行模拟计算。结果表明,电弧中心温度分布从钨针至焊件整体呈"毛笔"状,其中,喷嘴下方电弧形态呈"钟罩"形,在焊件上温度分布符合高斯分布特征;电弧等离子体在喷嘴内部速度较大,离开喷嘴后,其方向由喷嘴内的竖直向下逐渐变为到达工件时的向四周扩散;电流由焊件表面流出,经过弧柱区域流入钨针下端面,在钨针下端面附近取得最大值;电弧磁通密度分布呈"肺叶"状。最后进行了相应的熔焊试验,试验过程中拍摄的电弧轮廓与仿真电弧形态基本一致。     

轴向磁场中辐射对电弧的螺旋不稳定性的影响

采用抛物型电导率、抛物型透明辐射和与时间有关的线性微扰理论，给出了中、小电流弧的热势分布（温度分布）、稳定性条件以及不稳定性增长率等定量结果．得出辐射对中、小电流弧的螺旋不稳定性的影响是降低稳定性 关键词：     

轴向磁场中线性热势模型电弧的螺旋不稳定性

采用线性热势电导率模型和与时间有关的线性微扰理论,给出了氢弧和其它气体中低电流弧的热势分布(温度分布)、稳定性条件以及不稳定性增长率等定量结果.与均匀电流分布比较,稳定性区域变大. 关键词：     

宏观速度对电弧螺旋不稳定性影响的数值分析

采用抛物型电导率和与时间有关的线性微扰理论,给出了有宏观速度存在的热势分布(温度分布)、稳定性条件以及不稳定性增长率等定量结果。     

Low frequency ion acoustic instability in the positive column of A D.C. discharge

The one-dimensional dispersion equation of the electroacoustic instability of the low pressure column is analyzed numerically. The column steady state parameters were obtained from the plasma balance equations based on a Maxwell distribution. The computed curves are compared with the experimental dispersions measured for spontaneously existing anode directed wave observed at the cathode end of the column. Although the agreement between the observed and computed dispersion curves is fairly good the current driven electroacoustic instability does not provide a universal explanation for all of these waves.     

Stability of a DC SF6 arc in an axially acceleratingflow

The stability of a DC arc burning in an axially accelerating flow of SF₆ is investigated. The method of normal modes is applied to the equations governing an axisymmetric, infinitesimal perturbation of a self-similar arc, and solutions are obtained numerically. Results are presented for a range of discharge conditions. The physical mechanisms causing instability are deduced from equations for the time-averaged, squared enthalpy, and velocity of a perturbation. The steep radial gradient of the density at the edge of the arc is shown to cause instability. The effect of density fluctuations in comparison with velocity fluctuations is not negligible, and the possible implication of this result for turbulent arc modeling is discussed     

Experimental and theoretical investigation of high-pressure arcs.I. The cylindrical arc column (two-dimensional modeling)

The properties of the free-burning arc column are studied for ambient pressures of 0.1 MPa (i.e., atmospheric) to 10 MPa for applications in underwater welding and cutting as well as arc discharge lamps. The influence of transverse magnetic fields is studied in Part II. A DC current of 50-100 A is applied to an argon discharge with a conical tungsten cathode and a plane water-cooled anode which are separated by several millimeters. The electrical properties are measured, and the temperature distribution is determined by spectroscopic means utilizing a two-dimensional charge-coupled device (CCD) sensor. A self-consistent numerical solution of the conservation equations yields the temperature, velocity, pressure, and current distributions. The predicted arc temperatures agree well with the measured temperature distributions. An analysis of the conservation equations shows that the arc column becomes radiation dominated with increasing pressures resulting in small temperature gradients within the column and large gradients at the boundaries. It is found that a net emission coefficient might be used to account for the radiative heat transfer in the investigated parameter range. The arc constricts due to increased convective cooling especially at the cathode, while temperatures and velocities are decreasing. The power expended in the column scales approximately with the square root of the ambient pressure in line with the radiation dominance, whereas the voltage drop across the electrode sheaths exhibits no pressure dependence for a given current     

Experimental and theoretical investigation of high-pressure arcs.II. The magnetically deflected arc (three-dimensional modeling)

While Part I deals with cylindrical arcs, Part II studies the influence of transverse magnetic fields on the arc column for ambient pressures of 0.1-5.0 MPa. If exposed to a magnetic induction of several millitesla, the column of an arc is deflected by the Lorentz forces. In this paper, heat transfer and fluid flow with coupled electromagnetic forces are modeled for the magnetically deflected arc. To verify the predictions, the three-dimensional temperature distributions of the arc column are determined by line and continuum radiation measurements using tomographic methods. These temperature maps are compared with the results of the numerical simulations. To gain insight into the physical professes of the discharge and to make the arc properties available which are not readily measured, a self-consistent numerical model of the arc column is applied to the time-dependent and three-dimensional case. The temperature, velocity, pressure, and current densities are predicted by solving the conservation equations for mass, momentum, and energy, and Ohm's and Biot-Savart's law using material functions of the plasma. A control volume approach facilitates a numerically conservative scheme for solving the coupled partial differential equations. The predictions are in fair agreement with experimental results. A time-dependent fully implicit simulation of the arc was used to investigate the arc instabilities for large magnetic inductions     

Finite conductivity and the interchange instability in railgun arcs

A first-order perturbation expansion of the MHD (magnetohydrodynamic) equation is used to describe the onset of the interchange instability due to the high accelerations in railgun plasma-arc armatures. J.D. Powell (1986) considered the problem of perturbing an initial isothermal equilibrium with appropriate distributed current and density profiles, treating the perturbation equations with infinite conductivity. Here, the authors model the arc the same way, but they include the effects of finite conductivity σ. A fourth-order mode equation is derived and solved numerically. The authors find continuous spectra of unstable modes for a nonzero plasma acceleration g, whose growth rates are mostly greater than √kg, depending on the values of k and σ. The resistivity always raises growth rates higher than Powell's especially for large k and large resistivity. The resulting growth rates in typical railgun situations are large enough to permit full development of the instability     

Effect of Hall Current on the Magnetogravitational Instability of Anisotropic Plasma with Generalized Polytrope Law

The effect of Hall current on the propagation of small perturbations through self gravitating anisotropic collisionless pressure plasma with generalized polytrope law is investigated. The poly-trope law for pressure components parallel and perpendicular to the direction of magnetic field is utilized in the analysis. The effect of Hall current and finite conductivity is introduced in the generalized Ohm's law. Using the polytrope law and Ohm's law dispersion relations are obtained from linearized perturbation equations for wave propagation along and perpendicular to the direction of magnetic field. The dispersion relations incorporating polytrope indices are able to represent the Chew, Goldberger and Low approximation with double adiabatic equation of state for the anisotropic pressure and the magnetohydrodynamic set of equations with isothermal equation of state for the isotropic pressure. The effect of Hall current, finite conductivity and polytrope indices is discussed on the well known hose and gravitational instability. It is found that Jeans' criterion depends on polytrope indices and the condition of gravitational instability is determined for different special cases of interest.