Code Comparison Workshop Research Articles

Charged-particle transport in high energy density plasmas

This Special Topic Collection grew out of two gatherings of researchers active in the high energy density (HED) physics community: a mini-conference on charged-particle transport in HED plasma held during the 64th annual meeting of the American Physical Society's Division of Plasma Physics (Spokane, WA, November 2022) and a dedicated charged-particle transport coefficient code comparison workshop (Livermore, CA, July 2023). These gatherings provided opportunities for theoretical, computational, and experimental researchers to discuss the state of the field, including current capabilities and methods, needs of hydrodynamic simulations, and frontiers for future research. This special issue collects a total of 13 research and review articles on charged-particle transport in HED plasmas.

Computation of transport properties of warm dense matter using Abinit

The dynamics of an inertial confinement fusion capsule, or of a stellar or planet interior, obey a very similar set of equations: magneto-radiative-hydrodynamic equations. The solutions of these equations, however, depend entirely on the transport properties associated with the different materials at play. To properly model the dynamics of these systems, it is necessary to determine with high accuracy the transport coefficients of several materials over a large range of thermodynamic conditions. Experimental capabilities in this respect are still limited due to the nature of the microphysics at play and the extreme conditions involved. Numerical simulations are thus necessary, and in this respect, molecular dynamics simulations based on density functional theory offer exquisite possibilities to constrain the transport properties in the warm to hot dense matter regime. In this paper, we report the methodology used to extract different transport properties based on molecular dynamics performed with the software Abinit. The examples shown are based on the specific cases identified for the purpose of the second charged-particle transport code comparison workshop.

Review of the second charged-particle transport coefficient code comparison workshop

We report the results of the second charged-particle transport coefficient code comparison workshop, which was held in Livermore, California on 24–27 July 2023. This workshop gathered theoretical, computational, and experimental scientists to assess the state of computational and experimental techniques for understanding charged-particle transport coefficients relevant to high-energy-density plasma science. Data for electronic and ionic transport coefficients, namely, the direct current electrical conductivity, electron thermal conductivity, ion shear viscosity, and ion thermal conductivity were computed and compared for multiple plasma conditions. Additional comparisons were carried out for electron–ion properties such as the electron–ion equilibration time and alpha particle stopping power. Overall, 39 participants submitted calculated results from 18 independent approaches, spanning methods from parameterized semi-empirical models to time-dependent density functional theory. In the cases studied here, we find significant differences—several orders of magnitude—between approaches, particularly at lower temperatures, and smaller differences—roughly a factor of five—among first-principles models. We investigate the origins of these differences through comparisons of underlying predictions of ionic and electronic structure. The results of this workshop help to identify plasma conditions where computationally inexpensive approaches are accurate, where computationally expensive models are required, and where experimental measurements will have high impact.

Review of the 1st EUV Light Sources Code Comparison Workshop

We review the results of the 1st Extreme Ultraviolet (EUV) Light Sources Code Comparison Workshop. The goal of this workshop was to provide a platform for specialists in EUV light source plasma modeling to benchmark and validate their numerical codes using well-defined case studies. Detailed consideration of a plethora of atomic collisional and radiative processes is required for modeling EUV light source plasmas. Eight institutions spanning four countries contributed data to the workshop. Two topics were addressed, namely (i) the atomic kinetics and radiative properties of tin plasmas under EUV-generating conditions and (ii) laser absorption in a fully ionized, one-dimensional hydrogen plasma. In this paper, we summarize the key findings of the workshop and outline plans for future iterations of the code comparison activity.

Review of the first charged-particle transport coefficient comparison workshop

We present the results of the first Charged-Particle Transport Coefficient Code Comparison Workshop, which was held in Albuquerque, NM October 4–6, 2016. In this first workshop, scientists from eight institutions and four countries gathered to compare calculations of transport coefficients including thermal and electrical conduction, electron–ion coupling, inter-ion diffusion, ion viscosity, and charged particle stopping powers. Here, we give general background on Coulomb coupling and computational expense, review where some transport coefficients appear in hydrodynamic equations, and present the submitted data. Large variations are found when either the relevant Coulomb coupling parameter is large or computational expense causes difficulties. Understanding the general accuracy and uncertainty associated with such transport coefficients is important for quantifying errors in hydrodynamic simulations of inertial confinement fusion and high-energy density experiments.

Hydrogen Line Shapes in Plasmas with Large Magnetic Fields

We report on hydrogen line shape calculations in the presence of an external magnetic field, at conditions such that the quadratic Zeeman effect is important. The latter is described through a term proportional to B2 in the Hamiltonian, accounting for atomic diamagnetism. It provides a shift and an asymmetry on Lorentz triplets, and it leads to the occurrence of forbidden components. Motivated by investigations performed at the fifth edition of the Spectral Line Shape in Plasmas (SLSP5) code comparison workshop, we perform new calculations of hydrogen Lyman line profiles. Field values representative of magnetized white dwarf atmosphere conditions are taken. The calculations are done using a computer simulation technique, designed for Stark broadening modeling. A discussion of the results is done in the framework of plasma diagnostics.

On certain aspects of the THERMOS toolkit for modeling experiments

The THERMOS toolkit has been developed to calculate radiative properties of plasmas. This article contains a brief survey of some of its key features used by calculation of opacities and emissivities and by analysis of specific experiments. The code has recently been upgraded to account for the effect of ionization potential lowering in dense plasmas. The functionality of the code is illustrated for several cases from the 10th NLTE Code Comparison Workshop [1], in particular, for the experimental spectra of chlorine [2] and for the measured transmission of a silicon plasma [3].

Review of the 10th Non-LTE code comparison workshop

We report on the results of the 10th Non-LTE code comparison workshop, which was held at the University of San Diego campus November 28 through December 1, 2017. Non-equilibrium collisional-radiative models predict the electronic state populations and attendant emission and absorption characteristics of hot, dense matter and are used to help design and diagnose high-energy-density experiments. At this workshop, fifteen codes from eleven institutions contributed results for steady-state and time-dependent neon, aluminum, silicon, and chlorine cases relevant to a variety of high-density experimental and radiation-driven astrophysical systems. This report focuses on differences in the predictions from codes with different internal structure, completeness, density effects, and rate fidelity and the impact of those differences on hot, dense plasma diagnostics.

Plasmas Computed with ATMED CR of the 3rd Non-LTE Code Comparison Workshop Database

In this paper, there are presented some results calculated with ATMED CR of the 3rd Non-LTE Code Comparison Workshop held in December 2003, when this software didn’t exist, having been released in 2017. NLTE population kinetics codes were tested of steady-state cases for C, Al, Ar, Ge, Xe and Au plasmas selected for detailed comparisons. The scope of the meeting consisted of analyzing steady-state dense plasma cases of carbon, low temperature plasmas of aluminium and argon, X-ray laser experiments of germanium also with imposing a Planckian radiation field, medium- and high-Z multicharged ions of hot “experiment-related” plasmas of xenon, using real electron temperature and density parameters inferred from electronic and ionic Thomson scattering spectra and finally plasmas of gold. Being motivated by germanium X-ray laser experiments, the time history of electronic temperature Te and density Ne for a temporal dependent case is provided in Workshop NLTE-3. The calculation with ATMED CR has been carried out to t = 1.975 ns considering the non-uniform time grid along with the corresponding values of Te and Ne presented, being the initial condition LTE at low temperature. 
 The results for plasma properties can be considered as relatively precise and optimal, being checked fundamentally the high sensitivity of calculations to changes in regime, local thermodynamic equilibrium (LTE) or non-LTE (NLTE), electronic and radiation temperatures, electronic density and the percentage of hot electrons. Frequency resolved and mean opacities are also displayed computed with ATMED CR using UTA (Unresolved Transition Array) or Mixed UTA formalisms.

Spectral Line Shapes in Plasmas II

The Spectral Line Shapes in Plasmas (SLSP) code comparison workshop series [...]

Plasmas Computed with ATMED CR of the 4th Non Local Thermodynamic Equilibrium Code Comparison Workshop Database

Plasmas Computed with ATMED CR of the 4th Non Local Thermodynamic Equilibrium Code Comparison Workshop Database

The Third and Fourth Workshops on Spectral Line Shapes in Plasma Code Comparison: Isolated Lines

The purpose of the Spectral Line Shapes in Plasmas (SLSP) code comparison workshop is to compare different computational and analytical methods, in order to pinpoint sources of disagreements, infer limits of applicability, and assess accuracy. The present paper reviews a part of the results of the third (2015) and fourth (2017) workshops related to isolated lines.

Report on the third SLSP code comparison workshop

A summary of results obtained at the third Spectral Line Shape in Plasmas code comparison workshop (SLSP3) is given. As in the SLSP1 and SLSP2, a standardized set of case problems was decided on in advance and then investigated at the workshop. A presentation of these cases, together with a discussion of selected results, is provided here.

Review of the 9th NLTE code comparison workshop

We review the 9th NLTE code comparison workshop, which was held in the Jussieu campus, Paris, from November 30th to December 4th, 2015. This time, the workshop was mainly focused on a systematic investigation of iron NLTE steady-state kinetics and emissivity, over a broad range of temperature and density. Through these comparisons, topics such as modeling of the dielectronic processes, density effects or the effect of an external radiation field were addressed. The K-shell spectroscopy of iron plasmas was also addressed, notably through the interpretation of tokamak and laser experimental spectra.

Special Issue on Spectral Line Shapes in Plasmas

Line-shape analysis is one of the most important tools for diagnostics of both laboratory and space plasmas. Its reliable implementation requires sufficiently accurate calculations, which imply the use of analytic methods and computer codes of varying complexity, and, necessarily, varying limits of applicability and accuracy. However, studies comparing different computational and analytic methods are almost non-existent. The Spectral Line Shapes in Plasma (SLSP) code comparison workshop series [1] was established to fill this gap. Numerous computational cases considered in the two workshops organized to date (in April 2012 and August 2013 in Vienna, Austria) not only serve the purpose of code comparison, but also have applications in research of magnetic fusion, astrophysical, laser-produced plasmas, and so on. Therefore, although the first workshop was briefly reviewed elsewhere [2], and will likely be followed by a review of the second one, it was unanimously decided by the participants that a volume devoted to results of the workshops was desired. It is the main purpose of this special issue.

Influence of Microfield Directionality on Line Shapes

In the framework of the Spectral Line Shapes in Plasmas Code Comparison Workshop (SLSP), large discrepancies appeared between the different approaches to account for ion motion effects in spectral line shape calculations. For a better understanding of these effects, in the second edition of the SLSP in August, 2013, two cases were dedicated to the study of the ionic field directionality on line shapes. In this paper, the effects of the direction and magnitude fluctuations are separately analyzed. The effects of two variants of electric field models, (i) a pure rotating field with constant magnitude and (ii) a time-dependent magnitude field in a given direction, together with the effects of the time-dependent ionic field on shapes of the He II Lyman-α and -β lines for different densities and temperatures, are discussed.

Comparison and analysis of collisional-radiative models at the NLTE-7 workshop

We present the main results of the 7th Non-Local Thermodynamic Equilibrium Code Comparison Workshop held in December 2011 in Vienna, Austria. More than twenty researchers from nine countries, who actively work on development of collisional-radiative codes for plasma kinetics modeling, attended the meeting and submitted their results for a number of comparison cases. The cases included free-electron-laser-inspired time-dependent relaxation of photoexcited Ne-like Ar, ionization balance and spectra for highly charged tungsten, spectroscopic diagnostics of krypton L-shell spectra, and an investigation of Ne model convergence with principal quantum number.

Review of the 1st Spectral Line Shapes in Plasmas code comparison workshop

A review is given of the first workshop dedicated to the detailed comparison of various approaches to the calculation of spectral line shapes in plasmas. A standardized set of case problems was specified in advance, together with the prescribed atomic data and assumptions to be used. In this brief review, motivations for the case problems chosen are outlined, followed by a discussion of selected results. Plans for the next workshop are discussed in the conclusion.

Modeling of Atomic Processes of Multiple Charged Ions in Plasmas and Its Application to the Study of EUV Light Sources

Atomic processes of multiple-charged ions of high-Z elements from tin to dysprosium are investigated for their application to light sources for extreme-ultra-violet (EUV) lithography. Modeling of these ions in plasmas, including tungsten, which is being considered for use as a divertor and wall material in the fusion devices, is discussed. Atomic spectra become very complex in the case of low-charged ions below Pd-like ions, which calls for a new atomic code for calculating the energy levels and rate coefficients of collisional and radiative processes. The collisional radiative model is validated through code comparison workshop activities. An alternative method for investigating the formation of the non-uniform structure of the plasmas is also presented.

Review of the 4th NLTE Code Comparison Workshop

We review the critical results of the 4th Non-LTE Code Comparison Workshop held in December 2005. To test the NLTE population kinetics codes, both steady-state and time-dependent cases for C, Ar, Fe, Sn, Xe, and Au plasmas were selected for detailed comparisons. Additional features such as the effects of non-Maxwellian free electrons, the influence of a Planckian radiation field, and the emission spectra were required in specific cases. The scope of problems was expanded from the previous workshops to include two problems outside the dense plasma physics, namely, the EUV lithography sources and the astrophysical photoionized plasmas. We briefly outline the technical organization of the workshop, present motivations for the chosen cases, and discuss some representative results.