A variational atomic model of plasma accounting for ion radial correlations and electronic structure of ions (VAMPIRES)

We propose a model of ion-electron plasma (or nucleus-electron plasma) that accounts for the electronic structure around nuclei (i.e. ion structure) as well as for ion-ion correlations. The model equations are obtained through the minimization of an approximate free-energy functional, and it is shown that the model fulfills the virial theorem. The main hypotheses of this model are 1) nuclei are treated as classical indistinguishable particles 2) electronic density is seen as a superposition of a uniform background and spherically-symmetric distributions around each nucleus (system of ions in a plasma) 3) free energy is approached using a cluster expansion (non-overlapping ions) 4) resulting ion fluid is modeled through an approximate integral equation. In the present paper, the model is described only in its average-atom version

Application of Hartree-Fock theory of fluctuations to opacity calculation

The Hartree-Fock theory of fluctuations leading to simple formulae for configuration probabilities is used in a Detailed Configuration Accounting calculation of opacity in the case of an iron plasma. A direct Detailed Term Accounting method is also applied. The correlations of subshell occupation numbers, which are accounted for in the HF theory, show small effect on the theoretical spectrum corresponding to conditions of a recent measuremen

Thermodynamic coherence of the Variational Average-Atom in Quantum Plasmas (VAAQP) approach

A new code called VAAQP (Variational Average-Atom in Quantum Plasmas) is reported. The model as well as main results of previous studies are briefly recalled. The code is based on a new fully variational model of dense plasmas at equilibrium with quantum treatment of all electrons. The code can calculate the Average Atom structure and the mean ionization from the variational equations respecting the virial theorem and without imposing the neutrality of the Wigner-Seitz sphere. The formula obtained for the electronic pressure is simple and does not require any numerical differentiation. A description of the principal features of the code is given. The thermodynamic consistency of the results obtained with VAAQP is shown by a comparison with another approach on the example of the aluminium 10 eV isotherm EOS curve. A first comparison to an INFERNO-type model is also presented

Measurement of XUV-absorption spectra of ZnS radiatively heated foils

Time-resolved absorption of zinc sulfide (ZnS) and aluminum in the XUV-range has been measured. Thin foils in conditions close to local thermodynamic equilibrium were heated by radiation from laser-irradiated gold spherical cavities. Analysis of the aluminum foil radiative hydrodynamic expansion, based on the detailed atomic calculations of its absorption spectra, showed that the cavity emitted flux that heated the absorption foils corresponds to a radiation temperature in the range 55 60 eV. Comparison of the ZnS absorption spectra with calculations based on a superconfiguration approach identified the presence of species Zn6+ - Zn8+ and S5+ - S6+. Based on the validation of the radiative source simulations, experimental spectra were then compared to calculations performed by post-processing the radiative hydrodynamic simulations of ZnS. Satisfying agreement is found when temperature gradients are accounted for

An equation of state from cool-dense fluids to hot gases for mixed elements

An equation of state for the domain extending from hot gases to cool-dense fluids is formulated for a hydrogen-helium mixture. The physical processes take account of temperature ionization and dissociation, electron degeneracy, Coulomb coupling and pressure ionization. Pressure ionization and Coulomb coupling are studied with simple and comprehensive modeling. A single and complete algorithm is achieved with explicit expressions available for the whole domain from hot gases to cool dense fluids ($T>10^2$). Pressure ionization and Coulomb coupling have been examined for their contributions to the pressure and internal energy. The result reveals that their contributions smooth the variation of the pressure and internal energy in the region of pressure ionization even at very low temperatures.Comment: 10 pages, 8 figures, ApJ, accepted, E-mail: [email protected]

Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments

Seismology of stars is strongly developing. To address this question we have formed an international collaboration OPAC to perform specific experimental measurements, compare opacity calculations and improve the opacity calculations in the stellar codes [1]. We consider the following opacity codes: SCO, CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large differences for Fe and Ni in equivalent conditions of envelopes of type II supernova precursors, temperatures between 15 and 40 eV and densities of a few mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar results and differ from OP ones for the lower temperatures and for spectral interval values [3]. In this work we discuss the role of Configuration Interaction (CI) and the influence of the number of used configurations. We present and include in the opacity code comparisons new HULLAC-v9 calculations [5, 6] that include full CI. To illustrate the importance of this effect we compare different CI approximations (modes) available in HULLAC-v9 [7]. These results are compared to previous predictions and to experimental data. Differences with OP results are discussed.Comment: 4 pages, 3 figures, conference Inertial Fusion Sciences and Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences 201

Radiative properties of stellar plasmas and open challenges

The lifetime of solar-like stars, the envelope structure of more massive stars, and stellar acoustic frequencies largely depend on the radiative properties of the stellar plasma. Up to now, these complex quantities have been estimated only theoretically. The development of the powerful tools of helio- and astero- seismology has made it possible to gain insights on the interiors of stars. Consequently, increased emphasis is now placed on knowledge of the monochromatic opacity coefficients. Here we review how these radiative properties play a role, and where they are most important. We then concentrate specifically on the envelopes of $\beta$ Cephei variable stars. We discuss the dispersion of eight different theoretical estimates of the monochromatic opacity spectrum and the challenges we need to face to check these calculations experimentally.Comment: 6 pages, 5 figures, in press (conference HEDLA 2010