Constraining Hypotheses for Apparently High X-Ray Opacities on the National Ignition Facility*

There is little spectrally resolved experimental opacity data of plasma at temperatures and densities relevant to the physics of the sun, other stars, and laboratory high-energy-density experiments. Prior and ongoing opacity experiments on the Sandia National Laboratories Z machine have shown up to factor-of-2 discrepancies with theory - a challenging puzzle.  Since 2015, and additional set of experiments on the NIF have begun measuring opacities of iron and oxygen at temperatures ~150 eV, and since 2021 those measurements have been extended to densities above 10²² electrons/cm3. The higher-density NIF data show typically higher opacities than expected theoretically. This talk summarizes the current NIF experiments and efforts to constrain various hypotheses for potential systematic errors. This data may have implications for modeling the structure of the sun and for determining the age of white dwarf stars.