Some effects of radiative and collisional broadening on line emission in a spherical,laser-heated plasma

We have generalized our treatment of resonance-line radiation from a spherical, laser-heated plasma by including the effects of radiative and collisional line broadening in representing the line-emission and absorption profiles by a Voigt function. We find that the emitted profiles are broadened by factors of five or more, depending on the magnitude of the damping constant. It is also shown that the Al(XIII) to Al(XII) line ratios are seriously affected by the different escape probabilities associated with Doppler and Voigt profiles. We also find that plasma cooling via resonance-line radiation is accelerated relative to that calculated with a pure Doppler profile, and that use of the Voigt profile decreases the density of excited states relative to the Doppler values. These phenomena are analyzed in terms of the differing profile shapes and widths.     

用于研究铝等离子体软X射线光谱的碰撞-辐射模型

我们建立了一个以AlXI和AlXII离子为主的碰撞一辐射模型,模型中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.本文还分析了该模型的计算结果,包括离子丰度分布,辐射损失,及诊断的特性.     

Density dependence of solar emission lines of Si(X) and S(XII)

We have used the statistical equilibrium equation for the optically thin medium, under steadystate condition, to calculate the relative populations of 15 levels of Si(X) and S(XII) as functions of electron density at the temperature of maximum ion-abundances. The processes taken into account are collisional electron impact and radiative transitions. Proton excitation and deexcitation between the two levels of the ground state have also been accounted for. These populations are used to calculate the emissivities and intensity ratios.     

X-ray spectra of high temperature tungsten plasma calculated with collisional radiative model

Tungsten is regarded as an important candidate of plasma facing material in international thermonuclear experimental reactor （ITER）, so the determination and modeling of spectra of tungsten plasma, especially the spectra at high temperature were intensely focused on recently. In this work, using the atomic structure code of Cowan, a collisional radiative model （CRM） based on the spin-orbit-split-arrays is developed. Based on this model, the charge state distribution of tungsten ions is determined and the soft X-ray spectra from high charged ions of tungsten at different temperatures are calculated. The results show that both the average ionization charge and line positions are well agreed with others calculations and measurements with discrepancies of less than 0.63% and 1.26%, respectively. The spectra at higher temperatures are also reported and the relationship between ion abundance and temperature is predicted in this work.     

Radiative characteristics of pulsed power driven Z-pinch aluminumplasmas

In this paper, we study the dynamics of a massive aluminum Z-pinch plasma load and evaluate its performance as a soft X-ray radiator. A radiation hydrodynamic model self-consistently driven by a circuit describes the dynamics. Comparisons are made for the K- and L-shell soft X-ray emission as a function of the ionization dynamic model. The ionization dynamic models are represented by: 1) a time-dependent nonequilibrium (NEQ) model, 2) a collisional radiative equilibrium (CRE) model, and 3) a local thermodynamic equilibrium (LTE) model. For all three scenarios the radiation is treated 1) in the free streaming optically thin approximation where the plasma is treated as a volume emitter and 2) in the optically thick regime where the opacity for the lines and continuum is self-consistently calculated online and the radiation is transported through the plasma. Each simulation is carried out independently to determine the sensitivity of the implosion dynamics to the ionization and radiation model, i.e., how the ionization dynamic model affects the radiative yield and emission spectra. Results are presented for the L- and K-shell radiation yields and emission spectra as a function of photon energy from 10 eV to 10 keV. Also, departure coefficients from LTE are presented for selected levels and ionization stages     

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。     

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.     

低He气压下Rb(5P3/2)激发态有效辐射率的计算与测量

计算和测量了Rb-He混合蒸气中Rb(5P3/2)共振能级的有效辐射率,使用单模半导体激光器(泵浦激光)将Rb原子激发至5P3/2态,另一调谐到5P3/2→7S1/2的单模激光束(检测激光)与泵浦束反平行通过样品池,并在池的直径方向平行移动,通过对检测激光束的吸收测定了激发态原子密度及其空间分布.由于辐射陷获存在,有效辐射率是自然辐射率与透射因子(发射的光子在探测区域内没有被吸收的平均概率,它与吸收截面及激发态原子密度和空间分布有关)的乘积.5P3/2原子密度及其空间分布结合5P3/2←5S1/2跃迁线的碰撞增宽计算了透射因子,从而得到了不同He气压下,Rb D2线的有效辐射率.从5P3/2→5S1/2跃迁线强度I780的测量,得到的不同He气压下有效辐射率的比值与理论计算得到的比值相符.     

钠分子B^1∏u与2^1∑g^＋间的碰撞激发转移

The B 1pi(u) electronic state of Na2 was excited by the 441.6 nm He-Cd laser line. The Na atomic transitions and the A 1sigma(u)+ --> X 1sigma(g)+ band of Na2 were recorded. From the intensities and spectra of the Na and Na2 fluorescence several collisional processes in the excited sodium atom-dimer system were identified. The Na atomic lines are the result of collisional energy transfer from Na2 (B 1pi(u)) to Na(3P). Predissociation process may also contribute to atomic fluorescence. The A 1sigma(u)+ --> X 1sigma(g)+ band is interpreted through a populating mechanism involving collisional transfer from B 1pi(u) to 2 1sigma(g)+ followed by a radiative transfer to the A 1sigma(u)+ state. From the decay constants and fluorescence intensities, the rate coefficient at 360 degrees C for collisional energy transfer from Na2 (B 1pi(u)) to Na2 (2 1sigma(g)+) was found to be 5.7 x 10(-10) cm3 x s(-1). The predissociation rate of the B 1pi(u) is 2.7 x 10(6) s(-1).     

Spectrum Simulation of Li-Like Aluminium Plasma

X-ray emission spectra for L-shell of Li-like aluminium ions are simulated by using the flexible atomic code based on the collisional radiative model. Atomic processes including radiative recombination, dielectronic recombination, collisional ionization and resonance excitation from the neighbouring ion （Al^9＋ and Al^11＋ ） charge states of the target ion （Al^10＋） are considered in the model. In addition, the contributions of different atomic processes to the x-ray spectrum are analysed. The results show that dielectronic recombination, radiative recombination, collisional ionization and resonance excitation, other than direct collisional excitation, are very important processes.     

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.     

Recombination lasing in heliumlike silicon: a possible path to thewater window

A major goal of current X-ray laser research is the achievement of gain in the 23.3-43.7 Å wavelength region, known as the `water window'. Silicon is the lowest atomic number element for which all the heliumlike 3-2 transitions lie in this region. The authors examine the fundamental kinetics of recombination lasing in this species, and conclude that the Si XIII 1s3d¹D ₂-1s2p¹P₁ line at 39.1 Å is an attractive candidate for recombination-pumped lasing. Attainment of gain in this line is somewhat more energetically favorable than for the hydrogenic Al XIII 3-2 transitions, but radiative trapping may be somewhat more troublesome than for H-like Al     

Dirac R-matrix calculations of photoionization cross sections of Ni XII and atomic structure data of Ni XIII

We performed R-matrix calculations for photoionization cross sections of the two ground state configuration 3s²3p⁵ (²P^o_3/2,1/2) levels and 12 excited states of Ni XII using relativistic Dirac Atomic R-matrix Codes (DARC) across the photon energy range between the ionizations thresholds of the corresponding states and well above the thresholds of the last level of the Ni XIII target ion. Generally, a good agreement is obtained between our results and the earlier theoretical photoionization cross sections. Moreover, we have used two independent fully relativistic GRASP and FAC codes to calculate fine-structure energy levels, wavelengths, oscillator strengths, transitions rates among the lowest 48 levels belonging to the configuration (3s²3p⁴, 3s3p⁵, 3p⁶, 3s²3p³3d) in Ni XIII. Additionally, radiative lifetimes of all the excited states of Ni XIII are presented. Our results of the atomic structure of Ni XIII show good agreement with other theoretical and experimental results available in the literature. A good agreement is found between our calculated lifetimes and the experimental ones. Our present results are useful for plasma diagnostic of fusion and astrophysical plasmas.     

Radiative energy losses from low and moderate Z elements

Radiative energy losses from twelve low and moderate Z elements are calculated for temperatures ranging from 2 eV to 20 keV. Each element is assumed to be in coronal equilibrium, so that the ionization structure is determined by balancing collisional ionization and autoionization against radiative and dielectronic recombination. The radiative losses are calculated by adding the emission due to bremsstrahlung, radiative and dielectronic recombination, 2-photon processes, and line radiation. Polynomial fits to the loss rates, suitable for use in computer programs, are given for each element.     

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.     

Influence of electron-atom cross section uncertainties on shock wave structure

The exact value of the electron-atom collisional ionization cross section for argon is not accurately known. The purpose of the present research is to determine numerically the effect of varying the magnitude of the electron-atom cross section on nonequilibrium shock-wave structure. Mach 18 shock waves propagating into an argon-like gas at 1 cm-Hg and 300°K have been analyzed. Thermal, ionizational, and excitational non-equilibrium are considered in the relaxation region behind the shock wave. Electrons in the relaxation region are formed by a two-step collisional process, wherein the atom is first excited and then it is ionized. The precursor is formed by ground and excited state continuum radiation and line radiation which is emitted, but not reabsorbed, in the region behind the shock wave. When the electron-atom ionization cross section is varied from 1·86 × 10^?4to 1·86 × 10^?2cm²/erg, the results show that (1) it influences the coupling between the precursor and relaxation region through the radiative source functions, (2) it does not influence the distance necessary to attain equilibrium behind the shock wave, (3) it inversely influences the magnitude of the precursor ionization, and excitation, and (4) it inversely influences both the free electron and excited state population in the relaxation layer.     

用Monte Carlo模拟方法研究ICP－AES中的电离和激发过程──Ⅱ．有关电离激发机理的讨论

本文应用ＭｏｎｔｅＣａｒｌｏ模拟所得到的结果，定量地评价ＩＣＰ中各种可能发生的反应过程对电离激发的贡献，详细讨论了不同条件下ＩＣＰ中分析元素电离激发机理。结果表明ＩＣＰ中存在的电离激发机理很大程度上取决于电子密度，温度以及氢等粒子的密度。     

Study of recombination — Processes in a late stage of a spark discharge

In this work the recombination processes in the stage of a decay of a spark discharge,burning in air under atmospheric pressure. have been examined. The time variation of density of ionized particles was described by the model of radiative — collisional plasma decay. Effective recombination coefficient was gained from the measured time dependence of the electron density, determined from the Stark spectral line widths.     

Radiative and collisional effects in a cylindrically confined plasma—I. Optically thin considerations

A rigorous model has been formulated to determine the effect of collisional and radiative processes on electronic state populations in a cylindrically confined plasma. The model has been solved for an atmospheric argon arc plasma assuming optically thin conditions for all but the resonance line radiation, which is allowed to be optically thick. From parametric calculations and comparisons with experiment, the relative effects of the various processes on excitation conditions have been delineated and the nature and degree of excitation non-equilibrium have been determined.     

“Bottleneck” calculation of ion-electron recombination coefficients for lithium-like ions

Collisional-radiative recombination coefficients, including pure radiative and three-body recombination contributions, are computed for C(IV), O(VI), Ne(VIII), Si(XII), and Ar(XVI) by the “bottleneck” method of Byron et al. A convenient expression is developed for electron collisional excitation of ions and is used in the calculation.