Effect of electron-neutral collisions on the satellites of the Thomson scattering spectrum in arc plasmas

The effect of electron-neutral collisions on the high frequency spectrum of laser radiation scattered by the free electrons of a plasma is investigated for a partially ionized H₂ are plasma at atmospheric pressure. The calculations are carried out along Gorog's theory solving the linearized Boltzmann equation for electrons with a collision term. The collision integral is approximated by a Krook relaxation model with the collision frequency determined from experimental electron-atom scattering data. The collisions influence size, half width, and position of the high frequency satellites. In a H₂ arc plasma, the change of the satellites' position is negligible as well as the change in half width within experimentally attainable error limits. The change of size is of minor importance, since the general evaluation procedure uses only normalized scattering intensities. Thus, for laser scattering experiments in are plasmas the collision-free theory can be applied.     

Two-Dimensional MHD Simulations of Magnetic Field Penetration in the Plasma Opening Switch

Three mechanisms for anomalous magnetic field penetration have been investigated in computer simulations of Sandia's plasma opening switch (POS). The POS simulations have been performed using the two-dimensional (2-D) two-temperature single-fluid magnetohydrodynamic (MHD) code HAM [1], [2]. The three penetration mechanisms considered are 1) the Chodura model based on the ion-acoustic instability where the saturated value of the anomalous collision frequency is approximated by the ion plasma frequency; 2) a model based on the lower hybrid instability in which the anomalous collision frequency is proportional to both the ion plasma frequency and the electron drift velocity; and 3) a model that limits the ion drift velocity to the plasma influx velocity. Two-dimensional MHD calculations of the POS will be presented which show these models to be qualitatively similar for densities above a few 1013 cm-3, though at lower densities they can be quite different. The calculations are compared to experiments, and some agreement is seen with the lower hybrid model. The other models compare only marginally to experimental results.     

多成分电负性碰撞等离子体的鞘层玻姆判据

采用双流体模型研究了多成分的电负性碰撞等离子体鞘层的玻姆判据,讨论了一维稳态情形下不同的带电粒子对鞘层玻姆判据的影响。采用拟牛顿法,得到了数值解。结果表明：玻姆判据存在上限和下限。二次电子发射系数越大,离子的马赫数越大;负离子的含量越多,离子的马赫数越小。鞘层中离子的温度、离子与中性粒子的碰撞以及离子的带电量对玻姆判据的上下限的取值都有一定的影响。     

等离子体天线色散关系和辐射场数值计算

研究了电磁波沿轴向对称柱形等离子体天线传播的特性、色散关系及辐射方向图、增益等天线参数.通过对腔体材料介电系数、内外半径、等离子体密度、碰撞频率等参数的分析，结果表明要减小波沿等离子体天线传播的衰减，应当增加等离子体密度，减小碰撞频率，增加等离子体半径，减小腔体厚度，采用介电系数较小的材料.计算了在不同参数条件下，等离子体天线的辐射方向图、增益的变化，这些结果对于等离子体天线的设计很有参考价值. 关键词： 等离子体天线 色散关系 增益 辐射方向图     

Dynamics of heating of weakly ionized plasma in a self-consistent electric field

The dynamics of heating of a weakly ionized plasma in a pulsed discharge with allowance for the back reaction of the currents excited in the plasma on the field is analyzed on the basis of a kinetic equation with the Bhatnagar-Gross-Krook (BGK) model elastic collision integral. It is shown that the nature of the heating depends essentially on the ratio of the frequency of elastic collisions of an electron with neutrals and the plasma frequency. Analytic expressions for the dynamic electron distribution function and its moments are obtained. The limits of applicability of the approximation used are determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 12–16, June, 1986.     

The stationary confinement of plasma by a magnetic field at anisotropic pressure

The method of moments of the Boltzmann-Vlasov equation is used to derive relations between the macroscopic quantities of high-temperature plasma (i.e. the density of particles, the mass velocity and the generally anisotropic tensor of the kinetic pressure of particles) and the static electromagnetic field by which the plasma is stationarily confined. The well-known relation between the isotropic pressure of particles and the pressure of the magnetic field is then obtained from this as a special case. Plane geometric configuration of the plasma boundary and negligible collision interaction of the particles are assumed. The results are verified on a simple kinetic model of plasma with known trajectories of the particles.     

Isotropic matrix elements of the collision integral for the Boltzmann equation

We have proposed an algorithm for constructing matrix elements of the collision integral for the nonlinear Boltzmann equation isotropic in velocities. These matrix elements have been used to start the recurrent procedure for calculating matrix elements of the velocity-nonisotropic collision integral described in our previous publication. In addition, isotropic matrix elements are of independent interest for calculating isotropic relaxation in a number of physical kinetics problems. It has been shown that the coefficients of expansion of isotropic matrix elements in Ω integrals are connected by the recurrent relations that make it possible to construct the procedure of their sequential determination.     

A numerical study of steady state non-linear heat flow in a Lorentz plasma

Steady state heat flow in a Lorentz plasma is investigated using a discrete ordinate method. The model problem which is studied is the calculation of the heat flow between two boundaries at which the inward flowing part of the distribution function is half maxwellian and between which there is a constant ion density and zero current. Results agree with the appropriate collisionless and collision dominated limits.     

Local commutativity for nonlocalisable fields

A definition of local commutativity for nonlocalisable field theory is given by means of a limiting procedure for the Wightman functions of the theory; it includes, as a special case, rational functions of the free field. Fields for which this limiting procedure is defined are shown to satisfy many of the desirable features of localisable fields, including the existence of a TCP operator,the clustet property, the existence of asymptotic limits, and the LSZ reduction formulas. A strengthening of the procedure allows forward scattering dispersion relations to be obtained; the effects of nonlocalisibility on rigorous high energy bounds is also considered.     

The impact of the Ramsauer effect on the frequency of elastic collisions in inductive RF discharges in inert gases

This paper presents the results of investigating the power absorption mechanism of an inductive RF discharge plasma. Dependences of the frequency of elastic electron collisions with inert gas atoms (helium, neon, argon, and krypton) on the pressure are given. In the frequency range of 3 × 10⁶–3 × 10⁷ s^?1, an equivalent plasma resistance and the power input into the plasma are determined by the values of collision frequency and electron density within a skin layer and do not depend on the type of gas within the limits of experimental error. Upon reaching the electron temperature of ～1 eV, the energy of the main part of electrons lies in the range of Ramsauer’s minimum for elastic cross section. This leads to a decreasing elastic-collision frequency in heavy inert gases as compared to helium.     

等离子体覆盖立方散射体目标雷达散射截面的时域有限差分法分析

采用分段线性电流密度递归卷积时域有限差分（PLJERC-FDTD）算法计算了均匀非磁化等离子体覆盖三维立方体目标的散射特性.分析了等离子体厚度、密度和碰撞频率对雷达散射截面（RCS）的影响.计算结果表明：等离子体包层能有效地减小雷达目标的RCS，当等离子体频率比入射电磁波频率小得多时，主要靠增大等离子体的厚度使立方散射体目标的RCS值减小，增大等离子体碰撞频率对立方散射体目标的RCS值影响不大；当等离子体频率约为入射电磁波频率的一半时，增大等离子体厚度和碰撞频率都对立方散射体目标的RCS值减小有影响；当等 关键词： FDTD算法 电磁波 等离子体隐身 雷达散射截面     

Kinetic Description of Elastic Processes in Hydrogen-Helium Plasmas

Recent experiments with high density divertor plasma operation in tokamaks and future tokamak design projects have revived interest in the much earlier work on elastic collision processes between neutral and charged components in hot plasmas. In revisiting these papers, we employ classical methods to calculate deflection functions, cross sections and collision rates for the most important of such elastic collision processes. A phyiscally motivated cut-off procedure for the model interaction potential function is introduced. An algorithm for implementation of such processes into kinetic Monte Carlo neutral gas transport models is described, which accurately accounts also for possible singularities in the deflection function. Data fits for the relevant quantities are provided for hydrogenic and helium species. The relevance of elastic neutral-ion collisions is illustrated by a numerical simulation of an ITER relevant divertor model.     

Ion-acoustic shock waves and their head-on collision in a dense electron-positron-ion quantum plasma

Ion-acoustic shock waves and their head-on collision in a dense quantum plasma comprised of electrons, positrons, and ions are studied. The extended Poincaré-Lighthill-Kuo perturbation method is used to derive the Korteweg-de Vries-Burgers equations for shock waves in this plasma. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. The effects of the ratio of positrons to ions unperturbation number density μ, the normalized kinematic viscosity ηi0, and the quantum Bohm potential H on the interaction and structure of the shock waves are investigated. It is found that there are integrally vertical downward movements for both the colliding shocks after their head-on collision, but there are no shifts of the postcollision trajectories (phase shifts). It is also found that these plasma parameters can significantly influence the collision and properties of the colliding shocks. The results may have relevance in dense astrophysical plasmas (such as neutron stars or white dwarfs) as well as in intense laser-solid density plasma experiments.     

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The fluid dynamics model was used to study the influence of the existence of the collisions on the dust particles in a dusty plasma sheath. The main collisions in this study consist of the ionization collision, the collision between electron and neutral particle, the collision between ion and neutral particle, the collision between electron and dust particle, the collision between ion and dust particle. Numerical calculation results are obtained by the fourth-order-Rung-Kutta method. It is shown that both the dust particles’ density and corresponding electricity quantity increase as the following collisions’ frequency enhances, such as ionization collision, the collision between electron and neutral particle, the collision between ion and neutral particle. The charge reduces due to the collisions concluding electron-dust particle and ion-dust particle. In addition, the effect produced by ions’ collision is much more obviously compared with electrons’ collision.     

碰撞对尘埃等离子体鞘层中尘埃颗粒影响

在一维平板鞘层中应用流体模型研究了尘埃等离子体鞘层中碰撞对尘埃颗粒密度和带电量的影响。 研究所涉及的碰撞主要有电离碰撞,电子、离子分别与中性粒子的碰撞,以及电子、离子分别与尘埃颗粒的碰撞。通过采用四阶龙格库塔法,得到了数值解。结果表明,随着电离碰撞或者电子、离子分别与中性粒子碰撞的频率 增加,都将导致鞘层中尘埃颗粒的数密度增大,数密度的极值位置向鞘边位置靠近,尘埃颗粒带电量增多。电子、离子与尘埃颗粒的碰撞,使得尘埃带电量减小。此外,从研究的结果来看,由离子产生的碰撞要比电子产生的碰 撞对尘埃颗粒的影响明显得多。     

非磁化等离子体中的电子碰撞频率

电子碰撞频率是非磁化等离子体的一个重要参数,它对等离子体与电磁波相互作用的性质具有较大影响。基于产生等离子体的气压条件不同,其电子碰撞频率具有较大变化范围。研究了它对非磁化等离子体吸波能力的影响,得出了当电子碰撞频率与等离子体频率和入射波频率相当时,等离子体对电磁波具有较大吸收的结论,给出了对应于最大吸收的最佳碰撞频率值。分析了通过选择放电气体来调整等离子体的电子碰撞频率。     

To the theory of the generalized collision integral. II

The method of nonstationary diagram summation, previously developed [1], is applied to constructing the collision integral for a classical plasma, in which ring diagrams with prior ladder renormalization are included, which is equivalent to including screening of a long-range potential and finite momentum transfer in binary collisions. For a spatially homogeneous plasma it is shown that in the collision integral obtained the collision cross section does not contain the characteristic Coulomb divergences.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 9, pp. 119–122, September, 1973.     

松香中杂质元素的质谱分析

建立测定松香中16个杂质元素含量的分析方法。松香经乙醇溶解稀释后直接采用电感耦合等离子体质谱(ICP-MS)法测定。高浓度乙醇对等离子体所产生的负载以及有机碳不完全燃烧可能会在采样锥和截取锥孔沉积导致信号逐渐降低,通过优化等离子体的射频功率、载气流量以及样品提升量等仪器的操作条件,增加了等离子体中心通道的温度,提高等离子体的电离效率。采用在等离子体中加入低浓度氧气使有机碳充分燃烧,消除了积碳现象,维持了质谱分析信号的稳定。通过仪器调谐和同位素的选择有效地降低了氧化物和双电荷质谱干扰,避开了大量同量异位素干扰以及多原子离子干扰,利用碰撞/反应池(CRC)技术,分别选用氦碰撞模式和氢反应模式,消除了其余质谱干扰,选择内标元素补偿了样品与标准之间的粘度差异来匹配不同基体。结果表明,该方法的检出限在0.002～0.035 μg·g-1之间,实际样品的加标回收率为94.00%～106.00%,相对标准偏差(RSD)≤3.34%。方法采用乙醇溶解松香后直接测定,无需专用的样品前处理设备,具有操作简单、分析速度快、灵敏准确等优点,为松香中杂质元素的质量评价提供了一种新的分析方法。     

Numerical simulation of the fundamental mode of a magnetoplasma rodsurrounded by a lossless dielectric layer

The propagation characteristics of magnetoplasma waveguide coated with a finite thickness of dielectric material are presented. Because the boundary conditions at all interfaces can be represented by the matrix equations, the characteristic equation can be obtained by successively using the matrix manipulations. The dependence relations of attenuation and dispersion of the fundamental mode with plasma frequency, collision frequency, and electron cyclotron frequency are shown     

A Monte-Carlo method for coulomb collisions in hybrid plasma models

A procedure for implementing Coulomb collisions into hybrid (particle-fluid) plasma models is outlined which is rapid in execution due to the use of approximate expressions for the collision integrals and conserves energy and momentum exactly. Particles undergo dynamic friction and diffusion in velocity-space at rates consistent with the velocity-dependent Fokker–Planck diffusion coefficients and there are no assumptions made about the shape or size of the particle distribution function. The method is tested against the analytical theory of test particle slowing in a background plasma and the thermal equilibration of a Maxwellian distribution.