高速CT阻滞产生X射线辐射的数值模拟研究

以Ar等离子体为例,应用一维辐射流体力学模型,对高速度、高密度的紧凑等离子体环(CT)撞击静态靶减速产生软X射线辐射的物理过程进行了数值模拟研究。利用分裂格式方法计算得到了描述碰撞物理过程的各力学量随时间的演化关系,以及固定CT动能时使停滞CT成为最有效辐射源的初始速度和质量的最优搭配。对计算过程中相关物理量的跟踪分析表明,在1%的误差范围内计算格式满足能量守恒方程。     

Pt等离子体不透明度的理论计算

利用考虑l能级分裂的屏蔽氢离子模型SHML,计算了重核等离子体Pt在密度温度分别为时束缚—束缚、束缚—自由、自由—自由的吸收系数,并由此计算了Pt等离子体随光子能量变化的辐射不透明度.SHML模型计算的辐射不透明度好于SHM模型的计算结果这是肯定无疑的.     

等离子体中电子弹性散射截面及电导率计算

本文研究了近理想等离子体中的电子弹性散射过程.利用Debye-Hückel模型考虑等离子体环境对电子与离子间相互作用的屏蔽效应.结合分波法计算了不同Debye长度情况下,电子与不同核电荷数离子散射的分波相移和微分散射截面.研究了散射波函数、分波相移和微分截面随等离子体屏蔽参数的变化规律.最后,基于Spitzer公式, 初步讨论了分波法计算的等离子体的电导率与卢瑟福公式计算的电导率之间的区别.     

离子推力器束流引出状态对栅极刻蚀的影响

为了研究30 cm离子推力器束流引出状态对栅极刻蚀的影响,建立了束流引出模型,并采用PIC-MCC方法对CEX离子造成的栅极腐蚀速率进行了计算,最后将计算结果与1500 h寿命试验结果进行比对分析。结果显示:束流正常聚焦时,在3 kW和5 kW两种工作模式下,加速栅和减速栅的质量刻蚀速率分别为(1.11～1.72)×10?15 kg/s及(1.22～1.26)×10?17 kg/s。在5 kW工况下,当屏栅上游等离子体密度达到4.03×1017 m?3时,束流出现欠聚焦现象,此时加速栅和减速栅的最大离子刻蚀速率分别为4.33×10?15 kg/s和4.02×10?15 kg/s;在3 kW工况下,当屏栅上游等离子体密度达到0.22×1017 m?3时,束流出现过聚焦现象,此时加速栅和减速栅的最大离子刻蚀速率分别为3.24×10?15 kg/s和5.01×10?15 kg/s。寿命试验结果表明,加速栅孔质量刻蚀速率的计算值与试验值比对误差较小,而由于束流离子对减速栅孔的直接轰击,导致减速栅孔刻蚀速率的计算值和试验值差异极大。经研究认为,对屏栅小孔采用变孔径设计,是降低当束流处于欠聚焦或过聚焦状态下,CEX离子造成加速栅孔和减速栅孔刻蚀速率,并提升推力器工作寿命的有效措施。     

夸克-胶子等离子体在相对论性核-核碰撞中形成的一种信号

从热力学关系,计算来自相对论性核-核碰撞的富重子夸克-胶子等离子体的初值.接着基于(3+1)维相对论性流体力学模型研究了系统的双轻子产生.发现随着碰撞核入射能量的增加,一个标志夸克-胶子等离子体形成的特征平台出现在双轻子的总产额中.这样的特征可在CERN和Brookhaven未来的实验中得到检验. 关键词：     

等离子体中重离子碰撞过程的理论研究

本文使用经典轨道蒙卡方法研究了弱耦合等离子体环境中的裸核离子与基态氢原子碰撞的电荷转移和电离过程,碰撞能量在10-900 kev/amu范围.粒子间的相互作用使用了含与入射速度相关的动力学效应的Debye-Hückel模型.确定了等离子体屏蔽效应所造成的初态电子坐标与动量的微正则分布.研究了电荷转移和电离过程的总截面与等离子体参数、入射离子电荷、速度的关系.计算结果表明:等离子体环境效应对重离子碰撞过程的影响显著,特别是在低速碰撞时.同时给出了在不同Debye长度(1-50a0)和不同入射离子核电荷数(1～14)条件下的计算结果.     

等离子体中电子弹性散射截面及电导率计算

本文研究了近理想等离子体中的电子弹性散射过程．利用Debye-Htickel模型考虑等离子体环境对电子与离子间相互作用的屏蔽效应．结合分波法计算了不同Debye长度情况下，电子与不同核电荷数离子散射的分波相移和微分散射截面．研究了散射波函数、分波相移和微分截面随等离子体屏蔽参数的变化规律．最后，基于Spitzer公式，初步讨论了分波法计算的等离子体的电导率与卢瑟福公式计算的电导率之间的区别．     

等离子体中重离子碰撞过程的理论研究

本文使用经典轨道蒙卡方法研究了弱耦合等离子体环境中的裸核离子与基态氢原子碰撞的电荷转移和电离过程，碰撞能量在10—900kev／amu范围．粒子问的相互作用使用了含与入射速度相关的动力学效应的Debye-Htickd模型．确定了等离子体屏蔽效应所造成的初态电子坐标与动量的微正则分布．研究了电荷转移和电离过程的总截面与等离子体参数、入射离子电荷、速度的关系．计算结果表明：等离子体环境效应对重离子碰撞过程的影响显著，特别是在低速碰撞时．同时给出了在不同Debye长度（1—50a0）和不同入射离子核电荷数（1～14）条件下的计算结果．     

高能离子在稠密等离子体中的传输和能量沉积

用相对论福克-普朗克方程对高能离子在稠密氘氚等离子体中的碰撞动力学进行了研究，用球谐函数来展开方程的解：格林函数，然后简明地求出了不同能量质子和α粒子在等离子体中的停止时间、减速距离、纵向弥散距离和横向偏转距离.与以前研究离子在等离子体中运动的方法相比，没有假设高能离子在等离子体中损失能量远远小于入射离子能量，求解了纵向弥散距离；并且可以求解横向偏转距离.这些计算对实验上用高能离子加热冷的稠密等离子体，然后进行科学研究具有指导作用，并且可以用来研究快点火的可能性. 关键词： 高能离子 福克-普朗克方程     

激光尾波场中光子加速研究

在SILEX-Ⅰ激光装置上,测量了超短超强激光脉冲与稀薄等离子体相互作用之后的透射谱. 实验中发现,激光尾波场产生的密度扰动导致等离子体折射率随时间空间不断变化,导致光子的加速/减速. 透射谱上主要表现为激光频率谱峰的劈裂和随密度变化的展宽,没有发现与前向受激拉曼散射或自调制不稳定性相联系的边频波. 同时,利用LPIC++无碰撞粒子模拟程序模拟了超短超强激光与稀薄等离子体相互作用后的透射谱,模拟结果也发现了明显的光子加速过程. 关键词： 超短超强激光脉冲 透射谱 光子加速/减速     

Electronic fluctuation,the nature of interactions and the structure of liquid metals

Summary Interactions controlling ionic motion and structure in liquid metals can be systematically developed beginning with the ultimate view of such systems as neutral assemblies of nuclei and electrons, and proceeding to standard reduced Hamiltonians reflecting assemblies ofions and electrons. The assumption of electronically rigid ion leads via response methods and pseudopotentials to statically screened ion-ion potentials and beyond. Fluctuations are introduced into this otherwise common viewpoint by relaxing the assumption of electronically rigid ion cores and also by treating electronic response beyond linear order. It is argued that both effects can lead to more attractive pair interactions and possibly to effects much larger than, for example, Friedel oscillations. These contributions are state (i.e. density) dependent and their presence might be expected on the basis of clustering behavior seen for some systems in theirvapour phases. This leads to two limiting viewpoints on the liquid-state structure of such systems, the first as an entirely monoatomic phase but with a pair interaction that is unusual, the second as a system supporting transient clusters whose presence reflects the complexities argued on the basis of a more extended treatment of the electron problem. Paper presented at the workshop ?Highlights on Simple Liquids?, held in Turin at ISI on 1– May, 1989.     

非阿贝尔介质对外源的非线性响应方程

从动力论理论出发,使用弱湍理论方法,有效地展开了夸克–胶子等离子体的动力论方程,从而给出了夸克–胶子等离子体介质对外流的非线性非阿贝尔响应方程。     

Longitudinal viscosity of liquid alkali metals

Summary The viscosity coefficient entering sound wave attenuation is evaluated for the liquid alkali metals in an ion-electron plasma approach. It is shown that the contribution from electrical conduction, though small, is by no means negligible. The calculated longitudinal viscosity is very close to the measured shear viscosity contribution, the bulk viscosity being expected to be small in the present approach.     

动力学伊辛模型在振荡外场中的成核

研究了二维的动力学伊辛模型在一个具有偏向的振荡外场中的成核过程,主要关注成核时间与外场振荡周期ω的关系．随着ω的变化,成核时间出现最小值,最小的成核时间对应的平均临界核的大小也是最小的,这表明存在一个最佳的振荡频率,相比较于一个确定的外场,它更有利于成核．同时还研究了外场的初始相位的影响．     

Kinetic theory of time correlation functions for a dense one-component plasma in a magnetic field

The time-dependent correlations of a one-component plasma in a uniform magnetic field are studied with the help of kinetic theory. The time correlation functions of the particle density, the momentum density, and the kinetic energy density are evaluated for large time intervals. In the collision-dominated regime the results agree with those found from linearized magnetohydrodynamics.     

On the kinetic Alfvén waves in nonrelativistic spin quantum plasmas

We have studied the effect of electron spin on the kinetic Alfvén waves in the presence of uniform static magnetic field in an electron–ion plasma. We deduce that the usual kinetic Alfvén waves are modified via spin quantum effects of electrons. The dimensionless parameters that determine the relative importance of the electron spin become prominent at higher densities. It is found that the kinetic Alfvén wave frequency decreases due to the electron spin contribution in the kinetic limit while in the inertial limit they are almost unaffected in a hot magnetized plasma.     

A reliable analytical algorithm for space–time fractional cubic isothermal autocatalytic chemical system

The nucleus-acoustic shock waves (NASWs) propagating in a white dwarf plasma system, which contain non-relativistically or ultrarelativistically degenerate electrons, non-relativistically degenerate, viscous fluid of light nuclei, and immobile nuclei of heavy elements, have been theoretically investigated. We have used the reductive perturbation method, which is valid for small but finite-amplitude NASWs to derive the Burgers equation. The NASWs are, in fact, associated with the nucleus-acoustic (NA) waves in which the inertia is provided by the light nuclei, and restoring force is provided by the degenerate pressure of electrons. On the other hand, the stationary heavy nuclei participate only in maintaining the background charge neutrality condition at equilibrium. It is found that the viscous force acting in the fluid of light nuclei is a source of dissipation, and is responsible for the formation of NASWs. It is also observed that the basic features (polarity, amplitude, width, etc.) of the NASWs are significantly modified by the presence of heavy nuclei, and that NASWs are formed with either positive or negative potential depending on the values of the charge density of the heavy nuclei. The basic properties are also found to be significantly modified by the effects of ultrarelativistically degenerate electrons. The implications of our results in white dwarfs are briefly discussed.     

Kinetic properties of an acoustic-like mode in a two-ion quasi-neutral plasma

Kinetic analysis of an acoustic-like mode in a plasma with hot and cold ion components has been carried out. Under the short wevelength approximation (kλ _De≫1), electrons are assumed to form a dynamic neutralising background and their contribution to the perturbation is neglected. The significant role of the hot ions to Landau damping of the acoustic-like mode is highlighted and a novel concept of plasma experiment is suggested.     

Determination of the radiation cross sections of low-energy transitions of isomeric nuclei from observation of laser-induced γ fluorescence

Theoretical estimates are given along with the first experimental results on the observation of resonance fluorescence in nuclei of rubidium isomer under conditions of laser plasma X-ray pumping of the contiguous transition with an energy of 3.4 keV. The laser plasma is prepared by irradiating a silver target by a powerful radiation of a Nd laser with a pulse duration of 600 ps. It is demonstrated how one can use the recorded number of emitted γ quanta to determine the probability of low-energy nuclear transition excited by laser plasma X rays.