热动平衡态下热等离子体内的离子丰度研究

用相对论哈特里-福克-斯莱特自洽场方法计算热等离子体内的原子结构和平均离化度，应用玻耳兹曼关系和熵涨落理论，对一定温度、物质密度下的热等离子体内的离子丰度作了细致的研究，给出了一种快速求解离子丰度的物理方法，研究了离子离化度、丰度的变化规律. 关键词：     

无碰撞等离子体中电子束流不稳定性的时空演化

强激光在冕区等离子体中传播到临界面附近生成相对论电子和相对论电子束流在随后较长一段稠密等离子体区的能量传输是快点火中的关键问题。对快点火条件下的激光等离子体参数，临界面附近产生的前向快电子电流往往超过阿尔芬极限电流，必须在稠密等离子体中产生中和回流，快电子流才能在稠密等离子体中向前输运。横向电磁不稳定性（类Weibel不稳定性，WI）和纵向静电双流不稳定性（TSI）很容易在这种电子双流体系中激发，前向电子束会被调制或成丝状结构，同时激发电磁场，粒子部分动能会转化为电磁场能量。不稳定性在非线性饱和后，发生电流丝的合并、磁场重联等过程，部分电磁场能量会再转化为粒子能量，表现为对离子体的横向加热。Weibel不稳定性的作用可能形成围绕传播电子束的磁通道，对快电子的定向和准直传播是重要的。TSI激发的纵向静电场对磁场通道会有明显的调制甚至破坏作用，直接影响高能电子流从激光吸收区到燃料压缩区的准直传播。     

高能质子束探测稠密不均匀氘氚等离子体密度的SIRT算法

应用同时迭代重建算法(SIRT)重建不均匀稠密氘氚等离子体的密度分布.在二维等离子体密度重建的数值模拟中,探测稠密等离子体的高能质子束可以由强激光和等离子体相互作用产生,且质子束经过稠密等离子体后的能量损失是比较重要的.如果已知入射质子束和出射质子束的能量分布,可以在出射质子束能量测量的误差水平未知的情况下用SIRT算法重建等离子体的密度分布.结果显示,SIRT算法的精确度高于以L-曲线为准则的Tikhonov正则化方法,并可以在数据量不完全时重建密度分布.     

等离子体二维密度重建的影响因素

利用超强超短激光脉冲产生的高能质子束的库仑能量损失可以重建稠密等离子体的二维密度分布，使用同时迭代重建算法（SIRT算法）研究等离子体二维密度重建的影响因素.研究等离子体密度梯度、密度量级和质子束入射能量对重建误差的影响，分析质子束成像探测等离子体密度之前获得等离子体大概方位的重要性，通过数据拟合确定了能量噪声和重建误差之间的解析关系式.     

重离子碰撞与核内夸克分布

在假定核内存在多夸克态的前提下, 利用三分量福克-普朗克方程来研究重离子碰撞, 对C+C, Ne+NaF, Ar+KCI在入射能量为400, 800, 2100MeV/N时作了计算, 计算结果与实验符合得较好.     

磁镜场对射频等离子体中离子能量分布的影响

运用阻碍栅极型能量分析器,在不同磁镜场参数下测量了低温等离子体中离子的能量分布. 结果表明,在放电管中心处离子能量分布,随磁镜场强度的增加而向低能方向偏移,但离子能量分布宽度却没有明显的变化;而随着磁镜比的增加离子能量分布却向高能方向偏移,并且离子能量分布宽度也将变宽.由此可见,磁镜场参数对离子能量分布有很大影响. 关键词： 磁镜场 辉光放电 低温等离子体 离子能量分布     

高能带电粒子库仑对数量子力学效应研究

先进燃料D-3He聚变产生的高能带电粒子在本底等离子体中慢化时间的准确性直接影响到能量平衡和高能离子压强的计算结果。结果表明：高能带电粒子与本底等离子体的离子相互作用的库仑对数量子力学效应明显。应使用高能带电粒子库仑对数力学效应来研究聚变产生的高能端部粒子慢化过程;能量大于等于25Z2iZ2iAi keV的高能粒子与本底等离子体中离子的相互作用库仑对数最好也使用量子截断。     

Ti类氦Kα线在高温稠密等离子体中的漂移

采用离子球模型,通过自洽求解Dirac方程和Poisson方程,得到类氦Ti离子Kα线系的两条电偶极辐射光谱能量随不同等离子体环境的变化关系.同时分析了束缚电子交换能随等离子体环境的变化规律.结果表明：光谱能量漂移量随等离子体电子密度变化呈现出很好的线性关系.对此,拟合得到Ti类氦Kα线光谱能量漂移量随等离子体环境参数变化的公式,对探索高温高密度等离子体诊断方法具有一定意义. 关键词： 类氦离子 自洽场离子球模型 光谱漂移 等离子体诊断     

用福克-普朗克方程严格解裂变速率问题

本文应用数值方法严格求解二维福克-普朗克(Fokker-Planck)方程,研究在鞍点上的速度分布、坐标和速度的二次矩以及核裂变速率随时间的演变.在相当大的粘滞性范围内,研究核裂变速率与粘滞性的依赖关系,观察到在一定粘滞性下出现裂变速率极大值的现象.对计算的各种结果进行了解释。     

弱电离尘埃等离子体的介电张量研究

忽略磁场作用,通过求解含BGK碰撞项的Boltzmann方程和尘埃粒子充电方程导出了弱电离尘埃等离子体介电张量的表达式.证明了“冷”尘埃等离子体的纵向介电张量系数与横向介电张量系数相等.完善了弱电离尘埃等离子体电磁特性的理论模型. 关键词： 弱电离尘埃等离子体 Boltzmann方程 充电方程 介电张量     

Energy loss straggling in collisions of fast finite-size ions with atoms

The influence of ion size on straggling of energy losses by fast partially stripped ions is studied using the nonperturbative approach based on the eikonal approximation. It is shown that such a consideration of collisions of ions with complex atoms can lead to considerable corrections in calculating root-mean-square straggling of energy losses by fast ions compared to the results obtained for point ions. The root-mean-square straggling of energy losses are calculated for bromide and iodine ions in collisions with copper, silver, and aluminum atoms. It is shown that allowance for the size of the electron “coat” of an ion noticeably improves the agreement with experimental data.     

Efective Parameters on Energy Losses of Fast Electron in Fusion Mediums

The stopping and scattering of fast electrons in a dense plasma relevant to inertial confinement fusion(ICF)are investigated numerically with the latest improved cross section equations.Binary and collective efects are considered to determine beam transport parameters such as range,penetration depth,spreading processes as straggling and blooming versus electron energy and plasma parameters.Blooming and straggling efects,which act as consequences of scattering with statistical assumption in collisions,lead to a non-uniform,extended region of energy deposition.Finally the mean angle of deflections is calculated for diferent plasma energies.     

Effective Parameters on Energy Losses of Fast Electron in Fusion Mediums

The stopping and scattering of fast electrons in a dense plasma relevant to inertial confinement fusion (ICF) are investigated numerically with the latest improved cross section equations. Binary and collective effects are considered to determine beam transport parameters such as range, penetration depth, spreading processes as straggling and blooming versus electron energy and plasma parameters. Blooming and straggling effects, which act as consequences of scattering with statistical assumption in collisions, lead to a non-uniform, extended region of energy deposition. Finally the mean angle of deflections is calculated for different plasma energies.     

Phase coexistence and a critical point in ultracold neutral plasmas

We show the existence of the liquid-vapor phase coexistence and a critical point for strongly coupled ions in ultracold neutral (UCN) plasmas. Expressions for the free energy of UCN plasmas and an equation of state for the ions are obtained in the mean field approximation. A van der Waals-like isotherm shows the existence of a critical point in UCN plasmas. Depending on the ion temperature, the ions are shown to exist in a mixed vapor-liquid phase for a range of the ion Coulomb coupling parameter Γ(i) (defined by the ratio between the ion interaction and the ion kinetic energies), and in a strongly coupled liquid state for values of Γ(i) above this range. The estimates of critical constants show that it may be possible to observe these phenomena in the present day UCN plasmas.     

Nonlinear propagation of fast and slow magnetosonic waves in collisional plasmas

Low-frequency fast and slow magnetosonic waves propagating in electron ion plasmas with damping effects through ions and neutral atoms collisions are investigated. Linear wave analysis is performed to obtain dispersion relation. The reductive perturbation method is applied and it is shown that fast and slow modes of nonlinear magnetosonic wave are governed by damped Korteweg-de Vries (DKdV) equation in the presence of ion neutral collisions in plasmas. The analytical solution of DKdV soliton is presented under the assumption of weak collisional effects and numerical solutions of DKdV equation are also obtained using two-level finite difference scheme with the help of Runge–Kutta method at different plasma parameters. The damping of nonlinear fast and slow magnetosonic wave structures at different times are discussed in the context of space plasma situations where ions and neutral atoms collisions exist.     

Space distribution and energy straggling of charged particles via Fokker-Planck equation

Summary The Fokker-Planck equation describing a beam of charged particles entering a homogeneous medium is solved here for a stationary case. Interactions are taken into account through Coulomb cross-section. Starting from the charged-particle distribution as a function of velocity and penetration depth, some important kinetic quantities are calculated, like mean velocity, range and the loss of energy per unit space. In such quantities the energy straggling is taken into account. This phenomenon is not considered in the continuous slowing-down approximation that is commonly used to obtain the range and the stopping power. Finally the well-known Bohr or Bethe formula is found as a first-order approximation of the Fokker-Planck equation. The authors of this paper have agreed to not receive the proofs for correction.     

Density effects of heavy-ion stopping power in high temperature matter

Abstract

The stopping power and range for Xe ions in high temperature matter (partially ionized plasmas) have been calculated using the dielectric response function method. Calculations have been made for a target matter Al (Z = 13) over a wide range of temperatures and densities considering a finite temperature model. The stopping powers obtained have smaller values in comparison with those of a zero temperature model. The stopping power strongly depends on the density and temperature of the target material, and the projectile ion energy.     

Energy loss straggling measurements for helium ions in Mylar and polypropylene polymeric foils

In the present contribution, we report results on energy straggling of He ions penetrating Mylar and polypropylene thin polymeric foils. The measurements were performed in the 900–3000 keV incident particle energy range by using the indirect transmission technique developed previously. The experimental straggling data are corrected to consider the roughness effects due to target thickness inhomogeneity. As expected, the roughness contribution to straggling is more important for helium than for proton ions and decreases as the ion energy increases. At low velocities, (<500 keV/amu), the variation of the experimental energy straggling results differs strongly from predictions based on Bohr’s formalism, and with increasing energies, the experimental results approach gradually the Bohr values.     

Photoionization cross section of non-hydrogenic levels for weakly coupled plasmas

Photoionization process is a subject of special importance in many areas of physics. Numerical methods must be used in order to obtain photoionization cross-sections for non-hydrogenic levels. The atomic data required to calculate them is huge and self-consistent calculations increase computing time considerably, overall when we are studying plasmas where it is found million of ion levels. Analytical potentials are a useful alternative because they avoid the iterative procedures typical in self-consistent models. In this work, we present a relativistic quantum-mechanic calculation of photoionization cross-sections for non-hydrogenic ions immersed in weakly coupled plasmas. Both the energy levels and bound and free wave functions are determined by means of the Dirac equation. It is employed as effective potential an analytical one developed to model non-isolated many-electron ions making use of the Debye-Hückel approach but including the reaction of the plasma-charge density to the optical electron. The effect of the plasma screening in the photoionization cross-section and in the threshold energy is analyzed as a function of the photon energy, the Debye radius, the ionization and the mono-electronic bound level involved in the transition. Some comparisons between our results and others are also made.