Modeling the hot-dense plasma of the solar interior in and out of thermal equilibrium

The developments in helioseismology ensure a wealth of studies in solar physics. In particular, with the high precision of the observations of helioseismology, a high-quality solar model is mandated, since even the tiny deviations between a model and the real Sun can be detected.;One crucial ingredient of any solar model is the thermodynamics of hot-dense plasmas, in particular the equation of state. This has motivated efforts to develop sophisticated theoretical equations of state (EOS). It is important to realize that for the conditions of solar-interior plasmas, there are no terrestrial laboratory experiments; the only observational constraints come from helioseismology. Among the most successful EOS is so called OPAL EOS, which is part of the Opacity Project at Livermore. It is based on an activity expansion of the quantum plasma, and realized in the so-called "physical picture". One of its main competitor is the so called MHD EOS, which is part of the international Opacity Project (OP), a non-classified multi-country consortium. The approach of MHD is via the so-called "chemical picture". Since OPAL is the most accurate equation of state so far, there has been a call for a public-domain version of it. However, the OPAL code remains proprietary, and its "emulation" makes sense. An additional reason for such a project is that the results form OPAL can only be accessed via tables generated by the OPAL team. Their users do not have the flexibility to change the chemical composition from their end. The earlier MHD-based OPAL emulator worked well with its modifications of the MHD equation of state, which is the Planck-Larkin partition function and its corresponding scattering terms. With this modification, MHD can serve as a OPAL emulator with all the flexibility and accessibility. However, to build a really user-friendly OPAL emulator one should consider CEFF-based OPAL emulator. CEFF itself is already widely used practical EOS which can be easily implemented within any solar model code.;In the present work we have carried the technique of the MHD-based OPAL emulator to the CEFF-based OPAL emulator and successfully accomplished this goal. At the same time, we went beyond the earlier work by adding more terms. In particular, the previous MHD-based OPAL emulator was restricted to the approximation of a hydrogen plasma; our work is extended to the more realistic H-He mixture.;In a separate part of the present work, we have examined a non-equilibrium effect in the solar interior. The effect is located in the zone of the sharp transition between the differential rotation in the convection zone and the solid-sphere rotation in the radiation zone beneath it. This transition was discovered by helioseismology in the 1980s, and the transition zone is called the solar tachocline. The tachocline is subject to strong shear and in many theories of the solar dynamo it plays important role. Being inspired by the well-known Soret effect, which states the mass diffusion drive by a temperature gradient, we have examined if there could also be mass diffusion by a shear flow. If such an effect were to exist, it would have potential applications to the solar tachocline and dynamo. We have run a so-called reverse non-equilibrium molecular dynamics (RNEMD) simulation. As a test, we first confirmed the Soret effect by the simulation, then we tested for a shear- driven analogous effect. As a result, we did not see the shear-driven Soret effect in our simulation. We do observe the normal Soret effect due to the temperature gradient caused by the numerical scheme we used.