Helioseismology has opened a two-way street, making the Sun's interior a laboratory to study temperature and pressure relationships of a hot dense gases under conditions that cannot be achieved on Earth. With the wealth of data from the Global Oscillation Network Group (GONG) and the spacecraft SOHO, now is a perfect opportunity for applying the extensive datasets from these solar oscillation frequency experiments to the study of the 'equation of state' describing the solar interior. Although the non-ideal effects are relatively small corrections (typically 1-10% of the pressure), the extraordinary observational accuracy makes the helioseismic data sensitive to them, imposing stringent constraints on their theoretical computation to the required level. Among the physical effects to be examined are the mechanism of pressure ionization, the influence and disappearance of bound states in denser plasmas, and the influence of the excited states in bound systems in the plasma (atoms, ions, molecules). Indirectly the solar experiment also addresses a wider range of plasmas, with applications to lower-mass stars, brown dwarfs, or laser shock experiments. Solar physics will also benefit and improved solar models will result. They will serve as the tools to tackle the future challenges of solar physics, such as the seat of the solar cycle, solar variability of all kinds, as well as other key issues in the Sun-Earth connection. A major thrust of the analysis is the application of analytic tools, geared to equation-of-state diagnostics, developed with the support of the preceding NSF award.
The broader impact of this research is given by (i) the benefit of the research activity for the P.I.'s teaching, at all levels, including General Education, (ii) the training of the P.I.'s current and future graduate students, (iii) the free dissemination of equation-of-state and opacity tables that the P.I. and Co-P.I. will continue, (iv) a potential societal benefit, because of the link of the proposed work to fundamental fusion research, and last, but not least, (v) it happens that the P.I.'s three current and one prospective graduate students are all women, which helps to broaden the participation of women in science.
