Li-like Fe-L壳层等离子体辐射光谱模拟

利用碰撞辐射平衡和离化平衡下的等离子体X-射线发射谱理论,对铁元素L壳层等离子体,在中高能区电子温度范围内,以碰撞激发、离化、辐射复合和双电子复合等动力学过程为主的Fe24 、Fe23 和Fe22 三离子体系X射线谱进行了理论模拟,得到其X射线光谱图,反映出X射线谱辐射波长、辐射强度同电子温度、密度之间的关系,得到了等离子体诊断所关心的电子温度、密度参量的定性关系.     

超高速碰撞2A12铝靶过程中Al~+的光谱辐射特征

材料受到强冲击会产生闪光和等离子体效应。通过超高速碰撞实验并结合多种先进测试手段,推导出了适用于计算超高速碰撞产生等离子体电离度的沙哈(Saha)公式,为超高速碰撞过程中弹丸和靶板的物质组成分析提供了强有力的工具。基于二级轻气炮加载系统结合等离子体特征参量诊断的Triple Langmuir probe诊断系统和光谱辐射测量的ESA4000光谱仪系统,进行了3种不同碰撞速度条件下的超高速碰撞实验。实验结果表明,超高速碰撞2A12铝靶产生闪光辐射中包含Al+的光谱辐射;通过实验数据的解析进一步揭示了光谱强度与弹丸速度的关系。随着弹丸速度的增加,Al+的辐射光谱强度增大,由2A12铝激发的Al+光谱中小波长所对应谱线的辐射光谱强度比长波长所对应谱线的辐射光谱强度增加更快。关于2A12铝靶在超高速撞击载荷下产生铝离子的光谱辐射特征以及辐射温度研究在航天器防护空间碎片、导弹拦截、天体物理及深空探测领域具有重要的应用价值,此外,等离子体的特征参量测量和光谱辐射特征研究,对于在微观层面深刻揭示超高速碰撞现象具有重要的理论意义。     

束缚态特征温度方法及应用

随着高超声速飞行器速度增大,激波层空气等离子体中的原子发射谱线成为辐射加热主要来源,因此研究原子激发非常重要.考虑到处于热非平衡态的空气等离子体,平衡态统计理论不适用.精细物理模型(如碰撞辐射模型)虽然可以处理热非平衡问题且准确度高,但计算量太大,难于工程应用.本文采用束缚态特征温度法,结合FIRE II激波管实验中的非平衡空气等离子体,对原子激发进行了分析.计算得到的原子能级布居与碰撞辐射模型符合,说明简化计算是合理的,计算效率提高了2000倍以上,且能够保证一定的精度.     

一种计算非平衡等离子体中粒子能级布居的简化方法

获得粒子能级布居是研究非平衡等离子体辐射性质的一个重要方面.对于复杂三维等离子体,采用细致碰撞辐射模型虽然精确,但计算耗费大.本文提出了一种束缚态特征温度法,能够快速计算得到非平衡等离子体中的粒子能级布居.对非平衡氖等离子体算例的研究表明,本文方法是有效的,在等离子体非平衡程度不太高时与碰撞辐射模型符合较好.在计算效率上,本文方法比碰撞辐射模型至少提高了3000倍,可极大节约计算资源和成本,在工程计算中有重要实际意义.     

实验室光致电离等离子体中激发过程的研究

光致电离等离子体在宇宙中广泛存在于强辐射场附近. 近年来随着高能量密度实验装置的发展, 在实验室内也能构造出光致电离等离子体. RCF是一个基于The Flexible Atomic Code 数据的针对光致电离等离子体的辐射碰撞模型, 该模型模拟了两个光致电离实验, 其 理论结果中电离态分布和光谱与测量值符合得很好. 在理论模拟中发现, 光致电离等离子体中光致激发和碰撞激发过程对离子态布居和发射光谱都有非常重要的影响. 光致激发过程可以通过将离子激发到双激发态从而间接电离离子; 碰撞激发过程会因为电子将基态离子激发到电离截面小的单激发态而抑制光子对等离子体的电离. 光致激发过程可以加强类锂离子的类氦离子的卫线, 而碰撞激发过程会影响类氦离子谱线的线强之比.     

电子与氦原子激态碰撞速率的光谱法研究

在电子密度5×10~(14)cm~(-3),电子温度1.1eV的氦等离子体中,用激光共振荧光,敏化荧光和激光“烧通”三种光谱技术,研究了电子与激态氦原子的碰撞速率.并与以文献上沿用的电子碰撞速率为基础的氦原子的多能级碰撞和辐射模型的计算进行了比较,发现该模型在很大程度上不能预言此类等离子体的特性.实验结果表明,氦原子激态间的电子碰撞转移速率的实际值远比理论值低.     

H2O/N2脉冲流光放电和介质阻挡放电发射光谱比较

本文采用脉冲流光放电和介质阻挡放电两种放电形式分别获得了H2O / N2等离子体的发射光谱。 OH荧光辐射在两种放电等离子体中均出现,而Ha荧光辐射仅存在于脉冲流光放电等离子体中。实验还对脉冲流光放电条件下H、OH 荧光信号进行了时间分辨测量,结果显示Ha荧光信号滞后OH荧光信号约10 ns。根据时间分辨测量结果以及水分子离解的相关文献,实验判断等离子体内水分子离解的主要产物是基电子态的H原子和OH自由基,Ha荧光辐射源于快电子对H原子的次级碰撞激发。介质阻挡放电等离子体的放电脉冲宽度较窄,不能对基态 原子进行有效地次级碰撞激发,所以H2O / N2介质阻挡放电等离子体发射光谱中没有出现Ha荧光辐射。实验结论证实放电脉冲宽度对放电等离子体内次级碰撞激发过程有影响。     

碰撞辐射稳态等离子体电荷态分布的一种扩展模型

通过等离子体中离子激发-退激发平衡关系,构造一种离子激发组态之间满足的非Boltzmann分布,利用这个分布作为权函数对原子过程速率系数进行平均,构造出一个扩展的碰撞辐射稳态模型.利用该模型计算从低Z到高Z元素等离子体平均离子电荷随电子温度的变化.进而研究非Boltzmann分布对平均电离度和激发组态相对密度的影响.结果表明,它对相对激发组态密度的影响非常显著. 关键词： 扩展的碰撞辐射稳态 概率分布 能级动理学     

铝丝阵Z箍缩辐射产生机理初步研究

利用一维非平衡辐射磁流体力学程序研究了铝丝阵内爆过程中的能量转化规律和辐射产生机理.细致讨论了Z箍缩过程中脉冲功率驱动器电磁能馈入等离子体,等离子体动能转化为内能以及通过一系列原子过程电子内能转化为X射线辐射的能量转化机理.结合离子布居信息深入分析了Z箍缩过程中的辐射产生机理.结果表明,在内爆压缩阶段,电离和激发过程占优,线辐射占据总辐射的绝大部分.在滞止时,离子大都处于裸核离化度,连续谱辐射达到峰值.在滞止附近,线辐射出现两个峰值.在膨胀过程中,光电复合过程优于三体复合,线辐射占总辐射的份额逐渐下降.     

Li-like镁等离子体X射线光谱模拟

利用碰撞辐射平衡和离化平衡下的等离子体X射线发射谱理论,对镁元素等离子体在中低电子密度、中高电子温度范围内,以碰撞激发、共振激发、离化、辐射复合和双电子复合等动力学过程为主的Mg10 、Mg9 和Mg8 三离子体系X射线谱进行了理论模拟,得到其X射线光谱,反映出X射线辐射谱波长、强度同电子温度之间的关系,得到了等离子体诊断所关心的电子温度的定性关系.     

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     

Monte Carlo方法研究低能电子束曝光沉积能分布规律

建立一个描述低能电子在多元多层介质中散射的物理模型,运用MonteCarlo方法模拟低能电子在靶体胶衬底中的复杂散射过程,在此基础上通过大量计算研究入射束能、胶层厚度、衬底材料等不同曝光条件对抗蚀剂沉积能密度分布的影响,获得沉积能分布规律:适量的低束能、薄胶层、低原子序数衬底可以使前散射电子对胶中沉积能密度分布的贡献增大、背散射电子的贡献减小,从而提高曝光分辨率. 关键词： 电子束曝光 MonteCarlo方法 低能电子散射 能量沉积     

Influence of electron energy distribution on helium recombining plasma diagnostics using line emissions

The influence of electron energy distribution on helium recombining plasma diagnostics is investigated using a helium collisional‐radiative model. The population densities of excited helium atoms are calculated for Maxwellian and non‐Maxwellian distribution plasma cases. In the case of the Maxwellian distribution plasma, the electron temperature and electron density determined by the Boltzmann plot method agree well with the input plasma parameters. On the other hand, it is indicated that the electron temperature and electron density are significantly underestimated in the bi‐Maxwellian distribution plasma case, even though the density of the hot electron components is three orders smaller than that of the bulk electrons. This result indicates that in a non‐Maxwellian helium recombining plasma, evaluation of the particle balance based on line emissions from excited helium atoms would be difficult because the reaction rate of atomic and molecular processes is strongly dependent on the electron temperature and density.     

13.56 MHz/2 MHz柱状感性耦合等离子体参数的对比研究

通过Langmuir双探针和发射光谱诊断方法,对比研究了驱动频率为13.56 MHz和2 MHz柱状感性耦合等离子体中电子密度和电子温度的径向分布规律.结果表明:在高频和低频放电中,输入功率的增加对等离子体参数产生了不同的影响,高频放电中主要提升了电子密度,低频放电中则主要提升了电子温度.固定气压为10 Pa,分别由高频和低频驱动时,电子密度的径向分布均为"凸型".而电子温度的分布差异比较明显,高频驱动时,电子温度在腔室中心较为平坦,在边缘略有上升;低频驱动时,电子温度随径向距离的增加而逐渐下降.为了进一步分析造成这种差异的原因,在相同放电条件下采集了氩等离子体的发射光谱图,利用分支比法计算了亚稳态粒子的数密度,发现电子温度的径向分布始终与亚稳态粒子的径向分布相反.继续升高气压到100 Pa,发现不论高频还是低频放电,电子密度的径向分布均从"凸型"转变为"马鞍形",较低气压时电子密度的均匀性有了一定的提升,但低频的均匀性更好.     

Effect of the magnetization parameter on electron acceleration during relativistic magnetic reconnection in ultra-intense laser-produced plasma

Relativistic magnetic reconnection (MR) driven by two ultra-intense lasers with different spot separation distances is simulated by a three-dimensional (3D) kinetic relativistic particle-in-cell (PIC) code. We find that changing the separation distance between two laser spots can lead to different magnetization parameters of the laser plasma environment. As the separation distance becomes larger, the magnetization parameter σ becomes smaller. The electrons are accelerated in these MR processes and their energy spectra can be fitted with double power-law spectra whose index will increase with increasing separation distance. Moreover, the collisionless shocks' contribution to energetic electrons is close to the magnetic reconnection contribution with σ decreasing, which results in a steeper electron energy spectrum. Basing on the 3D outflow momentum configuration, the energetic electron spectra are recounted and their spectrum index is close to 1 in these three cases because the magnetization parameter σ is very high in the 3D outflow area.     

Phase transition in metallic plasmas

An estimate is made for the energy of a virtual atomic structure on the metallic side of the metal-nonmetal transition in a dense plasma. On the assumption of a nearly uniform valence electron density, the interatomic interaction is treated as a Madelung energy, which is found to be approximately one-third of that for the one-component plasma model. Our estimate is verified by solving numerically the pseudowave equation for the valence electrons in ellipsoidal atomic cells which are compatible with the percolation structure of overlapping classically accessible spheres. The critical value of the Coulomb coupling parameter has been shown to agree with experiment at the liquid-gas critical points of cesium and rubidium, which can be identified with the plasma-phase-transition critical points. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 11, 849–854 (10 June 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

基于Thomas-Fermi-Kirzhnits模型的物态方程研究

本文针对丝阵Z箍缩等高能量密度物理实验的数值模拟研究, 建立了一种适用温度、密度范围宽的三项式半经验物态方程. 三项式半经验物态方程包括零温自由能项, 电子热贡献项和离子热贡献项. 零温自由能项采用多项式拟合的方法确定. 多项式系数通过多项式计算的结果与高压缩比区域和压缩比为1时零温Thomas-Fermi-Kirzhnits模型计算的结果对应相等得到. 离子对物态方程的热贡献采用一种准谐振模型, 此谐振模型可以描述离子在固态相中的行为, 并且在高温度、低密度区域趋近于理想气体物态方程. 电子对物态方程的热贡献采用含温Thomas-Fermi-Kirzhnits模型计算. 利用所建立的三项式半经验物态方程计算了铝的等温压缩曲线, 并与实验数据做了对比. 给出了很宽温度、密度范围内铝的压强, 其数据与相应的SESAME数据库数据做了对比.     

Comparison research on the laser plasma spectra with and without obvious self-absorption

Characteristics of laser produced Pb plasma were investigated using the spectrograph and the fast photography by an intensified charge coupled device (ICCD) camera. The optical emission spectra and images of the plasma were recorded and analyzed. The clear self-reversed structure can be revealed in the emission spectra of the lead plasma when the target is at 6 mm before the focus of lens. However, the self- absorption can not be observed in the spectra if the target is located at the focus. The electron temperature, the electron number density and the lower level atomic number density were obtained by fitting the experimental spectra at different delay times under the two circumstances. The electron number density and the lower level atomic number density are higher, as the target is at 6 mm before the focus of lens, however the electron temperature is lower as the target is located at the focus, under the same laser energy.     

紫外激光烧蚀Cu产生等离子体辐射特性

通过时间分辨的光谱测量技术,测定了308 nm XeCl紫外激光烧蚀金属Cu在氮气环境中诱导产生等离子体的发射光谱及其强度随时间分布,实验结果表明等离子体辐射光谱线主要由原子光谱线、一价离子光谱线及连续辐射背景光组成,各种光谱线的数目、辐射强度、持续时间不同。结合实验结果对等离子辐射机理进行了探讨,认为电子通过逆韧致辐射获得较高的能量,连续辐射主要来自高能电子的韧致辐射,原子和一价离子的激发主要是通过电子与原子、离子的碰撞传能以及电子与离子的复合产生,并用其定性地解释了所观察的实验现象。     

Expansion of an Ion Sheath into a Collision-Dominated Plasma

If a large negative voltage is applied to an insulated disc inserted in a collision-dominated plasma, the electrons are expelled from the region near the disc leaving a bare cloud of ions. This "transient sheath" is well documented in ion acoustic wave experiments. This paper examines the evolution of the ions in this sheath into a collision-dominated plasma. A new sheath whose dimension is of the order of twice the transient sheath dimension if found.