Semiclassical Dynamics and Time Correlations in Two-Component Plasmas

The semiclassical dynamics of a charged particle moving in a two-component plasma is considered using a corrected Kelbg pseudopotential. We employ the classical Nevanlinna-type theory of frequency moments to determine the velocity and force autocorrelation functions. The constructed expressions preserve the exact short and long-time behavior of the autocor-relators. The short-time behavior is characterized by two parameters which are expressable through the plasma static correlation functions. The long-time behavior is determined by the self-diffusion coefficient. The theoretical predictions are compared with the results of semiclassical molecular dynamics simulation.     

On the Conductance Theory of Plasmas

In the framework of the linear response theory a quantumstatistical expression for the conductivity of nonideal plasmas is derived. In a simple approximation the influence of electron-ion scattering and that of masses of equal magnitude on the conductivity is discussed; the latter is expressed in terms of transport collision frequencies.     

On the Thermodynamics of Dense Plasmas

Thermodynamic functions of dense plasmas are determined in terms of the single particle self energy. The latter is expressed in terms of T-matrices of the scattering theory. Explicit evaluations are carried out for the highly degenerate two component plasma.     

On the Relaxation of Energetic Electrons in Plasmas

The impact of individual collision processes on the relaxation of the velocity distribution function of a group of electrons, initially localized in a narrow region at relatively high energies, has been studied. By having recourse to solutions of the non-stationary Boltzmann equation and to corresponding Monte-Carlo simulations, the temporal behaviour of electrons in CO₂ plasmas, both in the absence and the presence of an external dc field, has been investigated. A microphysical interpretation of observed relaxation phenomena, based on the data relevant to the individual collision processes, is also given.     

MHD Flow Layer Formation in Vicinities of Rational Flux Surfaces of Tokamak Plasmas

Advanced operation modes with external and internal transport barriers （ETBs and ITBs） are desirable for magnetic fusion ignition in toroidal devices. Therefore, ITB formation mechanism is an important topic of magnetic fusion plasma physics and has attracted much attention in recent years. The ITBs are often found to form in vicinities of low safety factor q rational flux surfaces and to coincide with MHD activities in experimentsI1＇2]. On the other hand, the crucial role of sheared flows in formation of ETBs and ITBs has been demonstrated in recent decades.     

On the Relevance of Plasma Parameters in Nonideal Plasmas

The use of different plasma models for composition calculations of nonideal plasmas can result in very different electron concentrations for the same experimental situation characterized e.g. by the measured temperature and pressure. This gives rise to misunderstandings at comparison of theoretical and experimental results. For extreme conditions i.e. in the region of the supposed plasma phase transition results of solid state physics give us the possibility to rule out some plasma models.     

Probe Measurements in Electronegative Plasmas: Modeling the Perturbative Effects of the Probe‐Holder

A basic property of an electronegative plasma is its separation into two distinct regions: an ion‐ion region far from boundaries, where the densities of positive and negative ions are higher then electron density, and a near‐boundary electron‐ion region, where negative ions have practically negligible density. This is due to the influence of the ambipolar electric field, which depends on electron (not negative ion) plasma parameters. This electric field “holds off” negative ions from the boundary, as the ions have lower mobility and temperature compared to the electrons. Therefore, negative ions will be repelled by any object inserted into the plasma. This can lead to errors in measurements of negative ion and electron parameters by any invasive method. Numerical modeling of electric probes in an argon‐oxygen plasma clearly demonstrates possible errors of direct measurements of negative ion probe current. This can also affect results from the photo‐detachment method and direct measurements of negative ion energy distribution (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of Plasma Resistance and Fluctuation on Probe Characteristics in Detached Recombining Plasmas

In order to find the causes of the strong anomaly of current‐voltage characteristics of Langmuir probe observed in detached recombining plasmas in a linear divertor plasma simulator, NAGDIS‐II, we have investigated plasma resistance along a magnetic field and potential fluctuations in the detached recombining plasmas. Simple calculation on the ratio between the plasma length, at which plasma resistance and resistance of ion sheath formed around a probe tip become equal, and an electron collection length indicates that the evaluation of electron temperature T_e becomes inaccurate at T_e of less than 0.6 eV when plasma density and neutral pressure are 1.0 × 10¹⁸ m^—3 and 10 mtorr, respectively. The potential fluctuation in detached recombining plasmas was found to be so large compared to T_e/e, which can also modify the probe characteristics.     

On the Instabilities of the Collisionless and Non-Magnetized Active Plasmas

Spontaneously excited instabilities in a uniform, collisionless and non-magnetized active plasma are studied, under the assumption that the polarisability of its active constituent is due to transitions of only one optical electron between two inversely populated energy levels. The attention is focused on non-resonant situations in which the modal frequencies of the excited waves differ significantly from the frequency of coherent electromagnetic radiation arising due to the presence of the active constituent. The longitudinal (‘acoustic’) waves in both low and high phase velocity domains, as well as the transverse (‘optical’) waves, are investigated. It is shown that the instabilities excited are most frequently aperiodical, and appear within, a comparatively large wavelength range. Their amplitude increments are evaluated. Under certain particular conditions, specified in the paper, the instabilities turn out to be periodical and to appear in very narrow wavelength bands only. Their modal frequencies and amplitude increments are also evaluated.     

激光诱导Al等离子体电子温度的时间空间演化特性研究

实验测定了激光烧蚀Al等离子体中Al原子在380-500nm 波长范围内的时间和空间分辨发射光谱。由Al原子390.068nm、394.4nm、396.152nm、466.3056nm、451.25nm、352 .95nm发射光谱线的强度计算了等离子体电子温度,并由实验结果讨论了激光等离子体中电子温度的时间和空间演化特性。实验结果表明,当延时在100-1500ns范围内变化时,相应的电子温度Te范围为6200K -32700K;当距离靶表面0-1.8mm范围内变化时,相应的电子温度Te范围为9800K- 32700K, 电子温度在沿激光束方向上的分布具有很好的对称性。     

A Time Domain Algorithm on the Reconstruction of Rough Surfaces

We consider the inverse scattering problem of a perfectly conducting one-dimensional rough surface in the case that the incident field is unnecessary to be time harmonic. Based on our previous investigation of the frequency domain algorithm, a new time domain algorithm is proposed, in which we approximate the incident pulse by a finite sum of time harmonic fields and then apply the frequency domain algorithm for time harmonic waves. Numerical experiments indicate that the time domain algorithm shows great accuracy of reconstruction of the surface profile and yields significant improvement than the frequency domain algorithm.     

EAST边界和芯部杂质谱线的时间延迟研究

边界杂质注入是未来聚变装置ITER用于增强边界辐射,减少第一壁热负荷的一种重要方法。但部分注入的杂质会被输运到芯部,造成主等离子体辐射损失以及约束下降。光谱观测可以获取杂质种类、含量和分布等信息,在理解等离子体中杂质输运方面起着重要作用。在EAST(experimental advanced superconducting tokamak)偏滤器氩气(Ar)注入实验中,利用偏滤器可见光谱和芯部极紫外光谱监测边界的Ar¹⁺离子谱线ArⅡ(401.36 nm)和芯部的Ar¹⁵⁺离子谱线ArⅩⅥ(35.39 nm),并获得两者强度随时间的变化。其中,ArⅡ和ArⅩⅥ的电离能分别为27和918 eV,因此,ArⅡ和ArⅩⅥ分别对应分布于等离子体边界和芯部Ar离子。为了分析二者谱线强度随时间变化的特征,发展了一种基于正则Pearson积矩相关系数的相关分析方法,计算得到两者谱线强度变化的相对延迟时间,以此表征杂质从边界向芯部输运的时间。结果显示,偏滤器注入Ar杂质后,芯部ArⅩⅥ辐射增长滞后于边界ArⅡ辐射的增长,并且在具有较高的低杂波加热功率的放电中...     

On the D.C.-Limit of the Electric Conductivity of Plasmas

A continued fraction of type 2^N is used to solve the d.c.-problem for the electrical conductivity of plasmas. The coupling parameter dependence of the expansion coefficients is determined. It is shown that this technique allows to derive different order collision times for dilute systems.     

On Self Energy and Vertex Corrections to the Electrical Conductivity of Plasmas

In the framework of linear response theory the density correction O(n^1/2 ln n) to the electrical conductivity of a nondegenerate Coulomb plasma due to equilibrium correlations is calculated.     

On the Quantum Probability Flux Through Surfaces

We remark that the often ignored quantum probability current is fundamental for a genuine understanding of scattering phenomena and, in particular, for the statistics of the time and position of the first exit of a quantum particle from a given region, which may be simply expressed in terms of the current. This simple formula for these statistics does not appear as such in the literature. It is proposed that the formula, which is very different from the usual quantum mechanical measurement formulas, be verified experimentally. A full understanding of the quantum current and the associated formula is provided by Bohmian mechanics.     

On the Direct Generation of Electricity from Heat in Plasmas via a Self-Organization Process

By combining the Nernst effect with the law of Ampere, it is shown that if a temperature gradient is present in a plasma, an electric current can be self-sustained due to the transformation of thermal into electromagnetic field energy. We call the configuration in which the above phenomenon occurs the “thermomagnetic battery” and study its steady state operation for an infinite slab geometry assuming that the plasma is fully ionized and the magnetic field is weak (ω_eτ_e ? 1) so that the heat flow is mainly transferred by electrons.     

激光诱导等离子体中Al原子发射光谱的时间、空间演化特性实验研究

实验测定了激光诱导Al等离子体中390.068,394.4,396.152,466.3056 nm等谱线的时间、空间分辨特性,由发射光谱线的强度和Stark展宽计算了 Al等离子体中的电子密度,并由实验结果讨论了电子密度的时间空间演化特性.实验结果表明,当延时在100～1500 ns变化时,等离子体巾的电子密度变化范围为0.02×1017～1.4×1017cm-3,在沿激光束方向上,当距离靶表面0～1.8 mm范围内变化时,相应的电子密度范围为0.28x1017～0.95×1017cm-3,等离子体电子密度在沿激光束方向上具有很好的对称性.     

On Light-Like Extremal Surfaces in Curved Spacetimes

In this paper, we find that under a diffeomorphic of nonlinear geodesic equations are concerned with light-like extremal surfaces in curved spaeetimes. It is interesting to transformation of variables, the light-like extremal surfaces can be described by a system Particularly, we investigate the light-like extremal surfaces in Schwarzschild spacetime in detail and some new special solutions are derived systematically with aim to compare with the known results and to illustrate the method.