Light element opacities from ATOMIC

We present new calculations of local-thermodynamic-equilibrium (LTE) light element opacities from the Los Alamos ATOMIC code. ATOMIC is a multi-purpose code that can generate LTE or non-LTE quantities of interest at various levels of approximation. A program of work is currently underway to compute new LTE opacity data for all elements H through Zn. New opacity tables for H through Ne are complete, and a new Fe opacity table will be available soon. Our calculations, which include fine-structure detail, represent a systematic improvement over previous Los Alamos opacity calculations using the LEDCOP legacy code. Our opacity calculations incorporate atomic structure data computed from the CATS code, which is based on Cowan's atomic structure codes, and photoionization cross section data computed from the Los Alamos ionization code GIPPER. We make use of a new equation-of-state (EOS) model based on the chemical picture. ATOMIC incorporates some physics packages from LEDCOP and also includes additional physical processes, such as improved free–free cross sections and additional scattering mechanisms. In this report, we briefly discuss the physics improvements included in our new opacity calculations and present comparisons of our new opacities with other work for C, O, and Fe at selected conditions.     

The reduced detailed configuration accounting (RDCA) model for NLTE plasma spectral calculations

The purpose of this work is to continue development of a model to provide a fast and accurate in-line NLTE capability for calculating plasma spectral properties in large-scale radiation-transport hydrodynamic simulations. A method has recently been developed to transform the large detailed atomic models into very small models that can be used for fast in-line calculations. The reduced model is more accurate than the average-atom models conventionally used in such simulations. In the present work, spectra calculated with the reduced model are compared to the original detailed model and the average-atom model. The spectra of iron and gold plasmas under various plasma conditions are compared.     

Versatile code DLAYZ for investigating population kinetics and radiative properties of plasmas in non-local thermodynamic equilibrium

A versatile code DLAYZ based on collisional-radiative model is developed for investigating the population kinetics and radiative properties of plasmas in non-local thermodynamic equilibrium. DLAYZ is implemented on the detailed level accounting (DLA) approach and can be extended to detailed configuration accounting (DCA) and hybrid DLA/DCA approaches. The code can treat both steady state and time-dependent problems. The implementation of the main modules of DLAYZ is discussed in detail including atomic data, rates, population distributions and radiative properties modules. The complete set of basic atomic data is obtained using relativistic quantum mechanics. For dense plasmas, the basic atomic data with plasma screening effects can be obtained. The populations are obtained by solving the coupled rate equations, which are used to calculate the radiative properties. A parallelized version is implemented in the code to treat the large-scale rate equations. Two illustrative examples of a steady state case for carbon plasmas and a time-dependent case for the relaxation of a K-shell excited argon are employed to show the main features of the present code.     

Advances in NLTE modeling for integrated simulations

The last few years have seen significant progress in constructing the atomic models required for non-local thermodynamic equilibrium (NLTE) simulations. Along with this has come an increased understanding of the requirements for accurately modeling the ionization balance, energy content and radiative properties of different atomic species for a wide range of densities and temperatures. Much of this progress is the result of a series of workshops dedicated to comparing the results from different codes and computational approaches applied to a series of test problems. The results of these workshops emphasized the importance of atomic model completeness, especially in doubly-excited states and autoionization transitions, to calculating ionization balance, and the importance of accurate, detailed atomic data to producing reliable spectra.We describe a simple screened-hydrogenic model that calculates NLTE ionization balance with sufficient accuracy, at a low enough computational cost for routine use in radiation-hydrodynamics codes. The model incorporates term splitting, Δn = 0 transitions, and approximate UTA widths for spectral calculations, with results comparable to those of much more detailed codes. Simulations done with this model have been increasingly successful at matching experimental data for laser-driven systems and hohlraums.Accurate and efficient atomic models are just one requirement for integrated NLTE simulations. Coupling the atomic kinetics to hydrodynamics and radiation transport constrains both discretizations and algorithms to retain energy conservation, accuracy and stability. In particular, the strong coupling between radiation and populations can require either very short time steps or significantly modified radiation transport algorithms to account for NLTE material response. Considerations such as these continue to provide challenges for NLTE simulations.     

X-ray line emissions from tamped thin aluminum targets driven by subpicosecond-duration laser pulses

We report on atomic kinetics and X-ray line spectra modeling work of plasmas generated by high-intensity, ultrashort-duration pulsed lasers. Our work is motivated by the need to analyze and interpret experiments with laser-irradiated layered targets performed at the Max-Planck-Institut für Quantenoptik. The focus of this Paper is on the theoretical characterization of the properties of X-ray line emissions as signatures of plasma conditions. Our model considers several spectral features with detailed attention paid to atomic kinetics, intrinsic spectral lineshapes in a high-density plasma environment (in particular Stark broadening and line shift effects), and spectroscopic-quality radiation transport (opacity effects). We apply our model to the analysis of time-integrated K-shell aluminum X-ray line spectra and time-resolved total line intensities obtained from the layered targets. Modeling calculations indicate that red line shifts observed in these experiments cannot be explained by shifts in the centers of gravity of composite spectral features due to blending with enhanced satellite contributions, but are consistent with intrinsic line shift effects in both resonance and satellite lines. We also investigate the sensitivity of our results to the selection of one of three adopted models for laser-energy deposition and transport within the target.     

Review of the NLTE-5 kinetics workshop

We review the 5th non-LTE kinetics code comparison workshop, held in November 2007. Both steady-state and time-dependent cases for elements ranging from carbon to gold were examined in detail. Calculations of radiative power losses and specific spectra were requested in addition to typical plasma quantities such as the ionization balance. Non-Maxwellian electrons, external Planckian radiation and opacity effects in spectra were also included in the comparisons. We discuss the organization of the workshop and present a set of representative results. The particular case of a tungsten plasma at tokamak operating densities was considered for the first time. Due to its importance to the ITER project, more detailed results of these comparisons will be published elsewhere.     

Nonlinear fluctuations in a plasma with Coulomb interaction

The theory of thermodynamic plasma fluctuations is now fairly well developed [1–31]. However, in practice, one often comes across plasma states which are very far from being in equilibrium. Flucuations in such nonequilibrium states have been investigated by a series of authors [4–9] in terms of a linear approximation.It must, however, be noted that, under specific conditions, neglect of nonlinear effects may turn out to be unjustified. This relates particularly to plasma states which are close to being unstable. In this region the fluctuations of various physical quantities are very large. A similar situation occurs, for example, in the experimentally observed critical opalescence in plasma, i.e., the anomalously strong scattering of electromagnetic waves by an unstable plasma [10]. The dependence of the transport coefficient on ion-sound oscillations at a fairly large ratio of electron and ion temperatures [11] is another example illustrating the insufficiency of the linear approximation. Finally, nonlinear effects may be significant in a plasma with highly developed turbulence.All this points to the necessity of expressing the various correlation functions characteristic of fluctuation processes in terms of higher correlation functions. In doing so, it is natural to confine oneself, for a start, to the first approximation in order of nonlinearity.The present paper solves this problem for plasma with Coulomb interaction.     

The reduced detailed configuration accounting (RDCA) model for NLTE plasma calculations

The motivation for this work is to provide a more accurate and cost effective in-line NLTE capability for calculating plasma properties in large scale radiation-transport hydrodynamic simulations. A method is developed to transform the large detailed atomic models to very small models that can be used for fast in-line calculations. An averaging technique is used to reduce detailed models involving tens of thousands of states into just a few, 10–40 states, per ionization state. The reduced model is more accurate than the average atom models conventionally used in such simulations. In the present work, the averaging scheme is presented and results of the reduced model are compared to the original detailed model and the average atom model. The average ionization state of iron and uranium plasmas under various conditions of material temperature, atom number density, and radiation temperature are compared.     

Spectroscopic analysis of Cu wire array implosions on the refurbished Z generator

Experimental investigations of pinches on the refurbished Z (ZR) generator using Cu arrays have been initiated and more are planned for the near future. Significant X-ray emissions in the K-shell from moderately high atomic number plasmas such as Cu generate extreme interest. However, the production of these hard photons from high Z materials comes with a price. There is substantial loss of radiative yield due to stripping through many electrons present in high Z materials to reach to the H- or He-like ionization stages. Production of hard X-rays for materials with atomic number higher than Cu such as Kr is very difficult and theoretical predictions are even more uncertain. Previous experimental efforts using Cu as a plasma pinch load are encouraging and promote further investigations of this element on the refurbished Z machine for achieving photon energies higher than 5 keV and obtaining sufficient radiative yield. We will analyze the ionization dynamics and generate Cu spectrum using the temperature and density conditions obtained from 1-D non-LTE radiation hydrodynamics simulations of Cu wire array implosions on ZR. These results will be compared with K- and L-shell experimental spectrum of shot Z 1975. Theoretical K- and L-shell spectroscopy provides validation of atomic and plasma modeling when compared to available experimental data and also provides useful diagnostics for the plasma parameters. Our self-consistently generated non-LTE collisional-radiative model employs an extensive atomic level structure and data for all dominant atomic processes that are necessary to model accurately the pinch dynamics and the spectroscopic details of the emitted radiation.     

煤油简化动力学和ISAT在超燃计算中的应用

利用基于``准稳态'方法建立的模型简化软件包SPARCK, 从建立的详细模型出发得到了一个包含22组分18步总包反应的煤油简化动力学模型. 简化模型计算得到的点火延迟时间与文献计算结果和实验结果相一致, 验证了模型的有效性. 采用简化模型和当地自适应建表(ISAT)方法, 对超燃冲压发动机进行了二维并行数值模拟, 计算得到的壁面压力分布与试验结果吻合较好, 表明简化模型能够很好地用来模拟煤油燃料超燃发动机内部的复杂燃烧过程. 在并行计算环境下, 和直接积分方法相比, 该方法将化学反应项的计算速度提高了3.73倍, 大大提高了计算效率.      

Density effects in plasmas: Detailed atomic calculations and analytical expressions

In warm dense plasmas, the free-electron and ion spatial distribution may strongly affect atomic structure. To account for such effects we have implemented a potential correction based on the uniform electron gas model in the Flexible Atomic Code (FAC). This code has been applied to obtain energies, wave-functions and radiative rates modified by the plasma environment. In hydrogen-like ions, these numerical results have been successfully compared to an analytical calculation based on first-order perturbation theory. In the case of multi-electron ions, we observe level crossings in agreement with another recent model calculation.     

A new analysis of tuned circuit levitators

Investigations of a relatively new magnetic levitation device are described. This device uses an electromagnet, which is the inductive part of a resonant circuit. If the circuit is properly tuned, static stability is attainable.In order to understand the dynamic instabilities and to enable systematic design of tuned circuit levitators. a method is needed, which permits rapid analysis. In the models investigated, the frequency of supply is much higher than that associated with the mechanical vibrations, and as a result, a direct digital simulation of the equations is inefficient. This difficulty is overcome by using an approximation of slowly varying quantities. Due to the omission of the detailed high frequency oscillation from this new representation, it has been found possible to obtain a solution of an example by using only a few steps of integration. The results agree with those observed in an experimental model. They also agree with analogue simulations.     

X-ray absorption spectroscopy for wire-array Z-pinches at the non-radiative stage

Absorption spectroscopy was applied to wire-array Z-pinches on the 1 MA pulsed-power Zebra generator at the Nevada Terawatt Facility (NTF). The 50 TW Leopard laser was coupled with the Zebra generator for X-ray backlighting of wire arrays at the ablation stage. Broadband X-ray emission from a laser-produced Sm plasma was used to backlight Al star wire arrays in the range of 7–9 Å. Two time-integrated X-ray conical spectrometers recorded reference and absorption spectra. The spectrometers were shielded from the bright Z-pinch X-ray burst by collimators. The comparison of plasma-transmitted spectra with reference spectra indicates absorption lines in the range of 8.1–8.4 Å. Analysis of Al K-shell absorption spectra with detailed atomic kinetics models shows a distribution of electron temperature in the range of 10–30 eV that was fitted with an effective two-temperature model. Temperature and density distributions in wire-array plasma were simulated with a three-dimension magneto-hydrodynamic code. Post-processing of this code’s output yields synthetic transmission spectrum which is in general agreement with the data.     

Construction of a collisional radiative model of complex multiple charged ions for mid- to high-Z elements

A method of constructing a compact and complete collisional radiative model of multiple charged ions of mid- to high-Z elements is proposed, for studying radiative properties of the plasmas. The proposed tungsten model, which is based on atomic data calculated by the HULLAC code, incorporates a computer algorithm to identify well-populated atomic states and dielectronic recombination channels that have a significant effect on the ionization balance. The model is validated by investigating the convergence of the mean charge and radiative power loss with respect to the size of the model, and by comparing results with other calculations presented at the nLTE kinetics workshop.