Radiation cooling rates of a selenium plasma

The development of a scalable hydrogenic ionization model is described. The model utilizes correct energy and level structure data for each ionization stage and can be coupled self-consistently to a radiation transport calculation of the full nonhydrogenic X-ray spectrum. Thus it can be used to calculate accurately the effects of opacity on radiation emission rates that are of relevance to plasmas designed to produce recombination pumped population inversions due to rapid plasma cooling. The model is applied to a selenium plasma. It is found that, at ion densities where X-ray lasing has been observed, line emission from Δn≠0 transitions is a more important contributor to selenium's cooling rate than line emission from the Δn=0 transitions. Plasma opacity can also play an important role     

Effect of dielectronic recombination on the charge-state distribution and soft X-ray line intensity of laser-produced carbon plasma

The effect of dielectronic recombination in determining charge-state distribution and radiative emission from a laser-produced carbon plasma has been investigated in the collisional radiative ionization equilibrium. It is observed that the relative abundances of different ions in the plasma, and soft X-ray emission intensity get significantly altered when dielectronic recombination is included. Theoretical estimates of the relative population of CVI to CV ions and ratio of line intensity emitted from them for two representative formulations of dielectronic recombination are presented.     

神光Ⅱ间接驱动内爆实验ArX射线谱线模拟研究

ICF内爆物理研究中,示踪元素X射线谱诊断方法是推测内爆压缩温度、 密度以及燃料混合状态的有效方法.针对其中的非平衡物理过程, 研制了非局域热动平衡(non-LTE)下一维谱线输运程序Alpha.程序以辐射流体计算给出的温度、 密度等量为输入条件,求解细致组态(DCA)模型下的原子动力学方程和辐射输运方程, 自洽给出谱线不透明度,和成像面上的X射线谱分布.
利用该程序,模拟了神光Ⅱ装置上的掺Ar靶丸内爆示踪元素X射线谱诊断实验, 研究结果表明,谱线的自吸收效应影响发射的X射线谱的强度和形状, 谱线的宽度对自吸收效应的强弱也有影响.因此,在对X射线谱的数值模拟中应该考虑自吸收效应. 另外,与LTE近似下的发射谱的比较表明, LTE近似下,等离子体电离度大～1, 发射谱的形状与non-LTE的结果不同,且LTE近似下,谱线的强度比non-LTE的谱线强度大5-10倍, 采用LTE近似是不合适的.     

等离子体X射线吸收谱及发射谱研究

 报道计算高温高密等离子体吸收谱和发射谱（光学薄）的理论方法；该方法基于相对论原子理论，可以计算任何单元素以及多元素等离子体的谱分辨X射线吸收谱和发射谱（光学薄）；应用了量子亏损理论，可以减少计算量。利用该方法计算金等离子体LTE吸收谱，计算结果与实验符合良好。本文还对金等离子体LTE的光学薄发射谱进行了研究, 这将有利于对实验进行进一步的诊断分析。该理论计算方法还可提供等离子体内各电离度能级布居等重要物理参数。因此经“标准实验”检验的该理论计算方法将是提供ICF“精密”物理辐射参数的重要基础。     

Systematic trends in the radiative emission rates for low- and medium-Z elements in high-temperature plasmas

The power radiated by an optically thin, low-density (N_e ≤ 10¹⁴ electrons/cm³) plasma has been calculated for the electron temperature range 1–10⁶ eV taking into account resonance line emission, direct recombination radiation, dielectronic recombination radiation, and bremsstrahlung from the ions of a given element. The ionization structure has been determined by using a corona equilibrium model in which collisional ionization and inner-shelled excitation followed by autoionization are balanced by direct radiative and dielectronic recombination. Based on the results for respresentative elements from carbon through nickel, graphs are presented of the maximum radiated power, the maximum emission temperature, and the mean charge at the maximum for each shell as functions of the atomic number Z. Assuming that the maximum emission temperature can be achieved, aluminum and iron are predicted to be the most efficient K-shell radiators for Z ≤28.     

Beam-Plasma Heating Model

A one-dimensional ionization and heating model is applied to results of several electron-beam-plasma interaction experiments. Beam energy is deposited resistively in the plasma at a rate ?j2, where j is the return current density and ? the plasma resistivity both classical and anomalous due to ion acoustic or e-e-mode turbulence. Principal energy losses include ionization, line radiation, inelastic electron impact excitation, bremsstrahlung and radiative recombination. The level of ionization and plasma heating are computed as a function of neutral gas pressure, beam rise time, pulsewidth and current density, and resistivity model. Plasma dynamics and kinetic effects such as expansion and end loss are not explicitly included in the model.     

Al等离子体辐射损失的数值研究

建立了一个用于研究Al等离子体中的离子丰度和辐射损失的碰撞辐射模型,模型考虑了碰撞电离和复合,碰撞激发和退激发,辐射复合和自发辐射跃迁等原子过程,在恒离子密度和光性薄近似下,讨论了该模型给出的离子丰度和辐射损失的动态结果。 关键词：     

Time-dependent behavior of a pulsed high power xenon flashlamp. Application to the Mega-Joule laser pumping

A numerical model has been developed for studying the time-dependent behavior of cylindrical high power xenon flashlamp. The equations of local energy conservation and mass conservation are solved using the finite volume method to give plasma parameters such as radial temperature profiles, instantaneous emission spectra, pressure, velocity, arc conductance, etc. In a first approximation the plasma is described under local thermodynamic equilibrium, LTE. The results are given as a function of time over the pulse and for several nodes in the cross section. Then the detailed spectral and temporal calculations of the output radiation from xenon flashlamp and radiation efficiencies are provided.     

类Li氧等离子体光谱模拟

 在FAC程序包中碰撞辐射模型的基础上,模拟出了L壳层的类Li氧等离子体的X射线辐射光谱,其中包括了单、双和三离子模型。经过分析得出,除了碰撞激发以外,级联效应和其它的动力学过程(如：碰撞电离、双电子复合、辐射复合以及共振激发等)对光谱的贡献都是不能被忽略的。并分析了类Li氧等离子体各动力学过程与温度和光谱相对强度之间的关系,分析结果表明X射线光谱的强度能及时响应等离子体温度的变化。     

Determination and Analysis of the Thermodynamic Regimes of Xenon Plasmas

Xenon is a common element employed, for example, as impurity in magnetically confined plasmas or the medium in which radiative shocks propagate in laboratory astrophysics. In both situations, it is required the knowledge of plasma parameters such as the average ionization, the charge state distribution, the atomic level populations and the radiative properties. In most cases, the plasmas are under non‐local thermodynamic equilibrium (NLTE) conditions and these quantities should be determined by means of the so‐called collisionalradiative models. For a high Z element like xenon this is a complex task and entails a high computational cost since it is necessary to solve a very large set of rate equations. In this work are characterized the thermodynamic regimes of xenon plasmas as a function of the matter density and temperature. This fact will allow us to establish in which regions of density and temperature the assumption of local thermodynamic equilibrium (LTE) is accurate and also in which regions it can be retained to estimate some plasma parameters but not others. Moreover, it is also provided information about the average ionization in a wide range of plasma conditions which covers both LTE and NLTE regimes which is valuable information in order to optimize subsequent calculations. Finally, it is also performed an analysis of the differences of NLTE and LTE simulations on several relevant plasma parameters. With this purpose, a comparison is made between the results of the calculation using detailed NLTE modeling with simulations that use the same energy level structure, but atomic populations that are forced into LTE (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bank of optical and physical characteristics for solving problems of radiative plasma dynamics

A bank of data on the thermophysical and optical properties of the plasma of a number of elements and their mixtures is presented, which is the basis for simulating the problems of radiative plasma dynamics. For a substance in the state of thermodynamic equilibrium, this bank contains information on the equations of state, thermodynamic functions, shock adiabatics, and also spectral, group, and mean absorption coefficients. In the state of shock-radiative equilibrium, using a radiational-collisional model, the steady states of an optically transparent plasma and its spectral and integral radiative losses are determined, and evaluations of the role of self-radiation reabsorption are given. The rates of the processes of ionization and recombination in an unsteady plasma are discussed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 238–243, March–April, 2000. The work was carried out with financial support of the International Scientific-Technical Center (project ISTC V23-96) and of the Republican Fundamental Research Foundation (project T96-132).     

Deviations from LTE in a stellar atmosphere

Deviations from LTE are investigated in an atmosphere of hydrogen atoms with one bound level, satisfying the equations of radiative, hydrostatic, and statistical equilibrium. The departure coefficient and the kinetic temperature as functions of the frequency dependence of the radiative cross section are studied analytically and numerically. Near the outer boundary of the atmosphere, the departure coefficient b is smaller than unity when the radiative cross section α_ν grows with frequency ν faster than ν²; b exceeds unity otherwise. Far from the boundary the departure coefficient tends to exceed unity for any frequency dependence of α_ν. Overpopulation (b > 1) always implies that the kinetic temperature in the statistical equilibrium atmosphere is higher than the temperature in the corresponding LTE atmosphere. Upper and lower bounds on the kinetic temperature are given for an atmosphere with deviations from LTE only in the optically shallow layers when the emergent intensity can be described by a radiation temperature.     

Au激光等离子体X射线发射光谱的理论研究

采用细致组态(detailed configuration accounting,DCA)方法和碰撞辐射模型(collisional radiative equilibriummodel),Cowan的相对论的原子结构理论程序,选取与初、末离子组态有关的平均组态,取Hartree-Fock-Slater自洽势,考虑了非局域热动力学平衡条件下等离子体的主要原子动力学过程,建立了描述等离子体中碰撞辐射模型的离子布居和能级布居的速率方程,得到了Au元素的离子分布和能级分布,电荷态分布和平均电离度,并模拟出Au激光等离子体的5f-3d跃迁的X射线发射光谱的谱线强度,计算得出的谱线强度与实验数据相比符合得较好.     

X-ray spectra simulation of Li-like nickel L-shell Ions

The X-ray emission spectra of nickel plasma were simulated under the collisional radiative model (CRM) by using the flexible atomic code (FAC). The dynamical processes including collisional excitation (CE), radiative recombination (RR), dielectronic recombination (DR), collisional ionization (CI) and resonance excitation were considered in the model, and the rate coefficients of DR, RR as well as CI were consistent with previous results within 15%. It was found that the contributions to spectra from cascades and indirect processes could not be ignored. The intensities of spectral lines for lithium-like nickel L-shell ions are sensitive to the electron temperature. The good agreement between present spectral peaks and earlier observed results can be taken as a measure of the accuracy of the present work.     

Radiative cooling of tokamak plasmas due to multiply-charged Fe impurity ions

Calculations are presented for the rates of radiative energy loss from tokamak plasmas arising from radiation processes involving collisions between electrons and multiply-charged Fe impurity ions. The distribution of ionization states is determined from the steady-state corona model. The inclusion of dielectronic recombination raises the temperature at which each ion has its maximum equilibrium abundance. For certain nonhydrogenic ions, the dielectronic recombination rates obtained from previous calculations are found to be overestimated due to the neglect of autoionization into an excited state of the recombining ion. Electron impact excitation of resonance line radiation in the far ultraviolet and X-ray regions is the dominant radiative cooling mechanism at temperatures where ions with bound electrons are abundant. However, the radiation emitted during dielectronic recombination can be more important than direct recombination radiation and bremsstrahlung.     

Calibration-free laser-induced breakdown spectroscopy for quantitative elemental analysis of materials

The application of calibration-free laser-induced breakdown spectroscopy (CF-LIBS) for quantitative analysis of materials, illustrated by CF-LIBS applied to a brass sample of known composition, is presented in this paper. The LIBS plasma is produced by a 355?nm pulsed Nd:YAG laser with a pulse duration of 6?ns focussed onto a brass sample in air at atmospheric pressure. The time-resolved atomic and ionic emission lines of Cu and Zn from the LIBS spectra recorded by an Echelle spectrograph coupled with a gated intensified charge coupled detector are used for the plasma characterization and the quantitative analysis of the sample. The time delay where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the elemental analysis of samples from the LIBS spectra, is deduced. An algorithm relating the experimentally measured spectral intensity values with the basic physics of the plasma is developed. Using the algorithm, the Zn and Cu concentrations in the brass sample are determined. The analytical results obtained from the CF-LIBS technique agree well with the certified values of the elements in the sample, with an accuracy error <1%.     

Stationary and dispersive features in resonant inelastic soft X-ray scattering at the Ge 3p resonances

Resonant inelastic soft X-ray scattering at the 3p resonances in crystalline Ge is presented. Both stationary and dispersive features are observed in a wide energy range above as well as below the ionization limits. These observations are in agreement with theoretical predictions based on a two-step model where the initially excited electron has no influence on the emission step. Excess population of states in the conduction band is found, and discussed in terms of attosecond electron dynamics.     

Effect of radiation on compressibility of hot dense sodium and iron plasma using improved screened hydrogenic model with l splitting

High pressure investigations of matter involve the study of strong shock wave dynamics within the materials which gives rise to many thermal effects leading to dissociation of molecules, ionization of atoms, and radiation emission, etc.The response of materials experiencing a strong shock can be determined by its shock Hugoniot calculations which are frequently applied in numerical and experimental studies in inertial confinement fusion, laboratory astrophysical plasma,etc. These studies involve high energy density plasmas in which the radiation plays an important role in determining the energy deposition and maximum compressibility achieved by the shock within material. In this study, we present an investigation for the effect of radiation pressure on the maximum compressibility of the material using shock Hugoniot calculations. In shock Hugoniot calculations, an equation of state(EOS) is developed in which electronic contributions for EOS calculations are taken from an improved screened hydrogenic model with-l splitting(I-SHML) [High Energy Density Physics(2018) 26 48] under local thermodynamic equilibrium(LTE) conditions. The thermal ionic part calculations are adopted from the state of the art Cowan model while the cold ionic contributions are adopted from the scaled binding energy model. The Shock Hugoniot calculations are carried out for sodium and iron plasmas and our calculated results show excellent agreement with published results obtained by using either sophisticated self-consistent models or the first principle study.     

Controlling the spectral shape of coherent soft X-rays

We demonstrate the generation of arbitrarily shaped spectra of coherent soft X-ray radiation by adaptive control of the driving laser pulse. The selection of both narrow and wide spectral ranges as well as suppression of high-harmonic emission in a selected wavelength region is achieved. Feedback-controlled spectral engineering of coherent soft X-rays paves the way to shaping of soft X-ray pulses and coherent control of electron dynamics in the sub-femtosecond regime.     

Narrow-band model for nonequilibrium air plasma radiation

A band model is developed for the prediction of radiative transfer in air plasma applications under equilibrium and non-equilibrium conditions. For non-equilibrium applications, the medium is described by rotational–translational and vibrational temperatures but the populations of electronic states can be arbitrary. A specific formulation of the statistical narrow-band (SNB) model is developed for optically thick electronic systems of diatomic molecules when their populations are described by an electronic temperature. Model parameters, deduced from line by line calculations in the Voigt regime, are shown to be also convenient for arbitrary distribution of molecular electronic populations. This model is then complemented to include optically thin electronic systems and the continuum radiation through the simple box model, and line by line calculations for atomic lines. Several tests including equilibrium, non-equilibrium, uniform, and non-uniform conditions show the ability of this hybrid model to provide accurate and efficient solutions for radiative transfer problems in air plasmas.