Sandia National Laboratories
Thursday, April 28, 2016
Abstract: How does energy propagate from the core to the surface of the Sun, where it emerges to warm the Earth? Nearly a century ago Eddington  recognized that the attenuation of radiation by stellar matter controls the internal structure of stars like the sun. Opacities for high energy density (HED) matter are challenging to calculate because accurate and complete descriptions of the energy levels, populations, and plasma effects such as continuum lowering and line broadening are needed for partially ionized atoms. This requires approximations, in part because billions of bound-bound and bound-free electronic transitions can contribute to the opacity. Opacity calculations, however, have never been benchmarked against laboratory measurements at stellar interior conditions. Laboratory opacity measurements were limited in the past by the challenges of creating and diagnosing sufficiently large and uniform samples at the extreme conditions found inside stars. In research conducted over more than 10 years, we developed an experimental platform on the Z facility and measured  wavelength-resolved iron opacity at electron temperatures Te = 156-195 eV and densities ne = 0.7 – 4.0 x 1022 cm-3 - conditions very similar to the radiation/convection boundary zone within the Sun. The wavelength-dependent opacity in the 975 – 1775 eV photon energy range is 30-400% higher than models predict. This raises questions about how well we understand the behavior of atoms in HED plasma. These measurements may also help resolve decade-old discrepancies between solar model predictions and helioseismic observations. This talk will provide an overview of the measurements, investigations of possible errors, and ongoing experiments aimed at testing hypotheses to resolve the model-data discrepancy.
++Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
A.S. Eddington, The Internal Constitution of the Stars (Cambridge Univ. Press, Cambridge, 1926).
2 J.E. Bailey et al., Nature 517, 56 (2015).
Bio: Dr. James Bailey received his PhD in Physics from the University of California at Irvine in 1984. He was a Post Doctoral scientist in the Lawrence Livermore National Laboratory Physics Department until September 1985, when he joined the Pulsed Power Sciences Directorate at Sandia National Laboratories. He is currently a Distinguished Member of the Technical Staff at Sandia. Dr. Bailey’s primary research interests are Laboratory Astrophysics, High Energy Density Physics, and fusion, with a significant emphasis on spectroscopic measurements that advance fundamental understanding. This approach has produced many firsts: z-pinch radiation-hydrodynamics measurements, x-ray microscopy of human blood cells, neon-like spectral line emission diagnostics, ion beam matter interaction experiments, the highest electric field ever measured with the Stark effect, and the first hot dense capsule implosions driven by z-pinch x-rays. His current research investigating laboratory astrophysics emphasizes laboratory measurements of astrophysical plasma properties. Dr. Bailey is an author of more than 140 scientific articles, was elected a Fellow of the American Physical Society in 2004 and is a two-time recipient of the Lockheed Martin NOVA award. He serves on the international advisory committee for the Radiative Properties of Hot Dense Matter conference and on the editorial board for the journal High Energy Density Physics.