August 11-15, 2014


Absorption Measurements of Stark-broadened Hydrogen Balmer Line Shapes and Strengths at White Dwarf Photospheric Conditions

Ross E. Falcon (University of Texas at Austin)

G. A. Rochau (Sandia National Laboratories), J. E. Bailey (Sandia National Laboratories), T. A. Gomez (University of Texas at Austin), M. H. Montgomery (University of Texas at Austin), D. E. Winget (University of Texas at Austin), T. Nagayama (Sandia National Laboratories), G. Loisel (Sandia National Laboratories), A. L. Carlson (Sandia National Laboratories), D. E. Bliss (Sandia National Laboratories)

We perform experiments to measure multiple hydrogen Balmer lines in laboratory plasmas at white dwarf (WD) photospheric conditions (T_e ~ 1 eV, n_e ~ 10^17 cm^-3) to test the theoretical line profiles used in WD atmosphere models. X-rays from a z-pinch dynamic hohlraum generated at the Z Pulsed Power Facility at Sandia National Laboratories irradiate a gas cell to initiate formation of a large (120x20x10 mm) plasma. We observe our plasma in emission and in absorption simultaneously along relatively long (~120 mm) lines of sight perpendicular to the heating radiation. Using a large, radiation-driven plasma aides us to achieve homogeneity along our observed lines of sight, and with time-resolved spectroscopy we can measure lines at a range of electron densities that spans an order of magnitude. Observing our plasma in absorption not only provides the signal-to-noise to measure relative line shapes, it allows us to measure relative line strengths because the lines share the same lower level population. This can constrain the theoretical reduction factors used to describe ionization potential depression or occupation probability associated with these Balmer lines. We discuss the status of our relative line shape comparisons and the potential of testing theoretical reduction factors.

Mode of presentation: oral