The atomic data and database activities are carried out at the Russian Federal Nuclear Center – All-Russian Institute of Technical Physics (RFNC-VNIITF) in collaboration with researchers from the Joint Institute for High Temperatures of the Russian Academy of Sciences and the P.N. Lebedev Institute of the Russian Academy of Sciences.
At VNIITF there is particular interest in equation-of-state (EOS) calculations and emissions and opacities of hot dense plasma utilizing superconfiguration and also detailed kinetic descriptions of the ionization balance and of the bound-bound and bound-free spectral distributions. This work relies on atomic data calculations for multielectron ions, and the group develops and maintains databases of atomic and opacity data. The models and data are applied to laboratory plasma diagnostics, to modeling of laser-plasma x-ray sources, and to other purposes.
The plasma is treated as a thermodynamic equilibrium mixture of ions with internal degrees of freedom (excited states) and free electrons. The fundamental thermodynamic quantity is the Helmholtz free energy in which there are contributions from an ionic ideal gas, from each charge state of ions with bound electrons, from a partially degenerate free-electron ideal gas, and from the interparticle interactions.
Opacities may be calculated by the code Spectr-STA, which relies on a superconfiguration model (STA, Super Transition Arrays) in which transitions between superconfigurations are modelled by effective spectral distributions corresponding to single electron transitions. The ion populations are obtained from modified Saha equations. The Gaussian or Voigt effective line shapes for the transition arrays include statistical energy dispersion and Doppler broadening or radiative plus collisional broadening. Single and two-electron atomic data and configuration properties are calculated by using the RCN36 program from the Cowan suite of codes; this is to be replaced by the FAC-code data in a new version of Spectr-STA. Opacities may also be calculated by the code Spectr-DTA, which relies on a detailed description of bound-bound and bound-free transitions (DTA, Detailed Transition Accounting). Using Spectr-DTA ionization balance and ion state populations may be obtained from superconfiguration ionization balance models and then assuming Boltzmann LTE distribution over detailed terms, or from calculations based on other NLTE collisional radiative models.
The calculation of opacities involves finally a density-matrix based approach called LineDM. This model includes the most important line-broadening mechanisms and enables to describe the effect of the plasma microfield and radiation field on the population kinetics of ionic states. The key atomic radiative transition data that are input to these Spectr-DTA calculations are obtained from the GRASP2 Multi-Configuration Dirac-Fock package and from the Flexible Atomic Code (FAC). Autoionization widths and photoionization cross-sections may be calculated using the distorted wave approach with FAC. A pilot version of the relevant database is being developed and is being filled now with consistent spectroscopic data for multielectron ions.
These calculated data together with assembled experimental and compiled data enter into the Spectr-W3 database, http://spectr-w3.snz.ru/. Spectr-W3 contains at this time about 450,000 records of ionization potentials, energy levels, wavelengths, transition probabilities, oscillator strengths, statistical weights, and line shape parameters. The database also offers fitting formulae and fitted parameters for analytical approximations of collision cross-sections and electron transition rates in atoms and ions. The data are linked to bibliographical information and other metadata. The data sources include papers published in leading physical journals, datasets submitted by the authors, and high-resolution experimental and reliable theoretical data obtained by the project participants. The Spectr-W3 project is supported by the International Science and Technology Centre (ISTC). Under the current ISTC project the Spectr-W3 database will be enhanced in content and interface; of special note for XSAMS is the intent to provide utilities to export the data in XML format, as well as plain text format and (already in place) HTML format.