Improved Self‐Energy Calculations for Pressure Broadening of Spectral Lines in Dense Plasmas

Pressure broadening of Lyman‐lines of hydrogen‐like lithium (Li²⁺) has been studied using a quantum statistical approach to the line shape in dense plasmas, for details see [1]. In this communication, we concentrate on the electronic self‐energy, which is a basic input to the theory of spectral line profiles. We discuss the effect of strong, i.e. close, collisions which have been neglected so far for Li²⁺ plasmas, but play generally an important role in dense plasmas, as has been shown in [2]. We present a method to calculate an improved electronic self‐energy including strong collisions based on a two‐body T‐matrix and an effective optical potential. The method is tested for level broadening of the ground state of hydrogen (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

水窗波段附近激光等离子体X光辐射产生的途径

讨论了利用激光等离子体产生水窗波段Ｘ光辐射的可能途径。靶材，即原子序数的选取是决定产生这一波段辐射的基本因素，利用激光等离子体的平衡态和非平衡态特性都可在水窗波段产生亮度Ｘ光辐射，提出利用黑体辐射来实现水窗波段Ｘ光显微成像研究的方案。     

修正屏蔽库仑势下二维尘埃等离子体的动力学和结构特性

本文考虑等离子体密度分布变化, 得到了修正屏蔽库仑势的解析解. 数值分析以及分子动力学模拟表明, 在常见实验室参数情况下, 等离子体密度分布变化引起的屏蔽库仑势修正对二维尘埃等离 子体系统的动力学和结构特性影响很小. 在极限参数情况下, 本模型的计算结果表明二维尘埃等离子体系统的扩散能力明显降低, 并且系统组态呈圆形分布. 此外, 本文还研究了实验室常见大小磁场对二维尘埃等离子体系统的影响. 关键词： 修正屏蔽库仑势 二维尘埃等离子体 分子动力学模拟     

Recent microgravity experiments with complex direct current plasmas

Complex plasmas are low‐temperature plasmas containing micrometer‐sized particles. They are useful as models for strongly coupled many‐body systems. Since the microparticles are strongly affected by gravity, microgravity experiments with complex plasmas are conducted. Here we report on recent microgravity experiments with the experimental facility PK‐4 performed in parabolic flights. In particular, we discuss electrorheological and demixing experiments and the image analysis tools used.     

一种计算氩等离子物态方程的简单模型

将Thomas-Feimi统计模型电离势的数值结果进行函数逼近，给出一个便于近似数值求解的解析表达式和计算电离度的近似计算方法，计算了Ar元素LTE情况下的电离度和物态方程，结果与Saha模型的计算结果和实验结果符合较好.所提出的简单模型也适用于计算混合物物态方程，可以在电磁发射技术领域中的强电离等离子体中有广阔的应用前景. 关键词： 等离子体 物态方程 电离势 电离度     

Influence of vacuum space on formation of potential sheath in plasmas

Properties of potential sheaths developed in plasmas are investigated in terms of the plasma Debye length and the dimension of vacuum space. Biased plasma potential and the potential profile depend very sensitively on the geometrical configuration of plasma and vacuum space. The potential sheath is never developed near electrodes in high-density plasmas where the Debye length is much less than the dimension of the vacuum space. In this case, most of the potential drops occur in the vacuum space and almost no electric field exists inside the plasma. Parametric investigation of the potential sheath in terms of the vacuum-space and plasma dimensions is carried out.     

Electron captures by positrons from hydrogenic ions in nonideal classical plasmas

In nonideal classical plasmas, the electron captures by positrons from hydrogenic ions are investigated. An effective pseudopotential model taking into account the plasma screening effects and collective effects is applied to describe the interaction potential in nonideal plasmas. The classical Bohr-Lindhard model has been applied to obtain the electron capture radius and electron capture probability. The modified hyperbolic trajectory method is applied to the motion of the projectile positron in order to visualize the electron capture probability as a function of the impact parameter, nonideal plasma parameter, projectile velocity, and plasma parameters. The results show that the electron capture probability in nonideal plasmas is always greater than that in ideal plasmas descried by the Debye-Hückel potential, i.e., the collective effect increases the electron capture probability. It is also found that the collective effect is decreased with increasing the projectile velocity. Received 21 January 2000 and Received in final form 27 April 2000     

Non-steady interaction of plasma with aircraft in its near wake region

Non-steady interactions between plasmas and aircraft in its near wake region are investigated in detail. Under the non-static limit, a set of equations that describe these interactions are obtained. The results of the numerical simulation show that the cavitons of transverse plasmas are excited and density cavitons appear when the envelope of plasma becomes sufficiently intensive. This is very important for detecting the moving body that has a `stealth' characteristic.     

Numerical Analysis of the Joule Heating Effect on Plasma Heat Transfer

The application of thermal plasmas particularly in the field of plasma chemistry and plasma material processing requires a basic understanding of the heat transfer process. This paper is concerned with an analysis of the heat transfer to a positively biased body exposed to a plasma flow. Because of the induced current flow due to the biasing potential, the plasma surrounding the biased body will experience an increase in temperature caused by Joule heating. The fraction ? of the dissipated heat which is transferred to the body is calculated for an atmospheric argon plasma flow at temperatures between 104 and 2 × 104K and Reynolds numbers of 40 and zero. The results indicate that ? increases with increasing plasma temperature for Re = 40 and decreases slightly with increasing plasma temperature for Re = 0. As the Re number increases at constant plasma temperature ? decreases.     

Elementary Many‐Particle Processes in Plasma Microfields

The effect of electric and magnetic plasma microfields on elementary many‐body processes in plasmas is considered. As detected first by Inglis and Teller in 1939, the electric microfield controls several elementary processes in plasmas as transitions, line shifts and line broadening. We concentrate here on the many‐particle processes ionization, recombination, and fusion and study a wide area of plasma parameters. In the first part the state of art of investigations on microfield distributions is reviewed in brief. In the second part, various types of ionization processes are discussed with respect to the influence of electric microfields. It is demonstrated that the processes of tunnel and rescattering ionization by laser fields as well as the process of electron collisional ionization may be strongly influenced by the electric microfields in the plasma. The third part is devoted to processes of microfield action on fusion processes and the effects on three‐body recombination are investigated. It is shown that there are regions of plasma densities and temperatures, where the rate of nuclear fusion is accelerated by the electric microfields. This effect may be relevant for nuclear processes in stars. Further, fusion processes in ion clusters are studied. Finally we study in this section three‐body recombination effects and show that an electric microfield influences the three‐body electron‐ion recombination via the highly excited states. In the fourth part, the distribution of the magnetic microfield is investigated for equilibrium, nonequilibrium, and non‐uniform magnetized plasmas. We show that the field distribution in a neutral point of a non‐relativistic ideal equilibrium plasma is similar to the Holtsmark distribution for the electrical microfield. Relaxation processes in nonequilibrium plasmas may lead to additional microfields. We show that in turbulent plasmas the broadening of radiative electron transitions in atoms and ions, without change of the principle quantum number, may be due to the Zeeman effect and may exceed Doppler and Stark broadening as well. Further it is shown that for optical radiation the effect of depolarization of a linearly polarized laser beams propagating through a magnetized plasma may be rather strong. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonthermal effects on the entanglement fidelity for elastic scatterings in Lorentzian plasmas

The nonthermal effects on the entanglement fidelity for the elastic electron-ion scattering are investigated in generalized Lorentzian plasmas. The dynamically screened effective potential and partial wave analysis are employed to obtain the entanglement fidelity in Lorentzian plasmas as a function of the spectral index, collision energy, and plasma parameters. It is shown that the entanglement fidelity increases with decreasing the collision energy, especially, for small Debye radii. It is also shown that the nonthermal effect enhances the entanglement fidelity in Lorentzian plasmas. In addition, it is found that the entanglement fidelity increases with an increase of the plasma temperature.     

Electrostatic solitons in unmagnetized hot electron-positron-ion plasmas

Linear and nonlinear electrostatic waves in unmagnetized electron-positron-ion (e-p-i) plasmas are studied. The electrons and positrons are assumed to be isothermal and dynamic while ions are considered to be stationary to neutralize the plasma background only. It is found that both upper (fast) and lower (slow) Langmuir waves can propagates in such a type of pair (e-p) plasma in the presence of ions. The small amplitude electrostatic Korteweg-de Vries (KdV) solitons are also obtained using reductive perturbation method. The electrostatic potential hump structures are found to exist when the temperature of the electrons is larger than the positrons, while the electrostatic potential dips are obtained in the reverse temperature conditions for electrons and positrons in e-p-i plasmas. The numerical results are also shown for illustration. The effects of different ion concentration and temperature ratios of electrons and positrons, on the formation of nonlinear electrostatic potential structures in e-p-i plasmas are also discussed.     

Double-gap Alfvén eigenmodes: revisiting eigenmode interaction with the alfvén continuum

A new type of global shear Alfvén eigenmode is found in tokamak plasmas where the mode localization is in the region intersecting the Alfvén continuum. The eigenmode is formed by the coupling of two solutions from two adjacent gaps (akin to potential wells) in the shear Alfvén continuum. For tokamak plasmas with reversed magnetic shear, it is shown that the toroidicity-induced solution tunnels through the continuum to match the ellipticity-induced Alfvén eigenmode so that the resulting solution is continuous at the point of resonance with the continuum. The existence of these double-gap Alfvén eigenmodes allows for potentially new ways of coupling edge fields to the plasma core in conditions where the core region is conventionally considered inaccessible. Implications include new approaches to heating and current drive in fusion plasmas as well as its possible use as a core diagnostic in burning plasmas.     

Electron-ion Coulomb Bremsstrahlung in nonideal plasmas

The classical electron-ion Coulomb Bremsstrahlung process is investigated in nonideal plasmas. An effective pseudopotential model taking into account the plasma screening and collective effects is applied to describe the electron-ion interaction potential in a classical nonideal plasma. The classical straight-line trajectory method is applied to the motion of the projectile electron in order to visualize the variation of the differential Bremsstrahlung radiation cross-section (DBRCS) as a function of the scaled impact parameter, nonideal plasma parameter, projectile energy, photon energy, and Debye length. The results show that the DBRCS in ideal plasmas described by the Debye-Hückel potential is always greater than that in nonideal plasmas, i.e., the collective effects reduce the DBRCS for both the soft and hard photon cases. For large impact parameters, the DBRCS for the soft photon case is found to be always greater than that for the hard photon case. Received 1st December 1999     

亚大气压六相交流电弧放电等离子体射流特性数值模拟

以临近空间高超声速飞行器和航天器再入大气环境飞行过程中其表面产生的高密度非平衡态等离子体为研究对象,基于本研究组所建立的多相交流电弧放电等离子体实验平台(MPX-2015),开展了非平衡态氩等离子体射流特性的二维数值模拟研究.在亚音速条件下二维、非平衡数值模拟所得到的计算结果与实验测量结果符合良好.超音速条件下的数值模拟结果表明,随着真空腔压强的降低,等离子体射流流速明显增大,覆盖钝体头部的等离子体鞘套的厚度先减小,而后又增加,鞘套的空间均匀性以及等离子体向钝体表面的总传热量均显著降低,而钝体头部的局部电子数密度则增大.数值模拟结果为在MPX-2015上开展超音速条件下的实验研究提供了理论指导.     

Asymptotic theory of boundary layers of weakly ionized thermalplasmas on emitting electrodes

The paper deals with collision-dominated boundary layers of weakly ionized thermal plasmas on emitting electrodes. The case considered is when the dominating ionization mechanism in the plasma is ionization by electron impact, and the dominating recombination mechanism is recombination with an electron as a third body. The ratio of the Debye length to the recombination length is treated as a small parameter, and the method of matched asymptotic expansions is employed. Analytical formulas have been obtained for the distributions of the number densities of ions and electrons and of the electrostatic potential in each asymptotic zone. Formulas have been obtained describing the voltage drop in the boundary layer as a function of the density of the electric current coming from the plasma to the electrode     

Influence of ion-beam plasma on ion extraction efficiency in a single-grid ion source

The influence of ion-beam plasma on ion extraction efficiency in a single-grid ICP ion source is researched. The single-grid ion source is considered as a system with two plasmas, ion-beam plasma and the source plasma, separated by an extraction grid. Results of experimental measurements of the potentials of the two plasmas and the ion beam current dependence on these potentials are presented. It is shown that the ion extraction efficiency depends equally on both the acceleration potential and on the potential of the ion-beam plasma. The obtained results demonstrate the key role of the ion-beam plasma in the ion source operation, which is important in technological applications and space thrusters.     

Dephasing time of a positron accelerated by a laser pulse

The dephasing time of a positron in the total field associated with a laser pulse in a plasma J28is studied numerically. It is shown that the dynamics of the positron is quite different from that of an electron due to the electrostatic potential in the body of the pulse. The dephasing time of the positron increases with the pulse length and decreases with the pulse intensity nonlinearly. In the long pulse case (L》λ_p) the dephasing time is proportional to the pulse length. These results provide a scientific basis for experiments to observe the positron acceleration scheme, and may be important to the physics of laser-article interactions in multi-component plasmas.     

Quantum macroscopic equations from Bohm potential and propagation of waves

Bohm’s interpretation of Quantum Mechanics leads to the derivation of a Quantum Kinetic Equation. In the present work, moments of this kinetic equation are taken, thus deriving conservation equations. These macroscopic equations are then applied to study the propagation of longitudinal density perturbations in neutral gases and plasmas, of either fermions or bosons. The dispersion relation is derived and the effect of the Bohm potential shown; the speed of propagation calculated and the difference between fermions and bosons investigated. Pseudosonic waves in quantum plasmas are obtained including the effect of the Bohm potential.