Increasing the Reliability of Line Profile Measurements for White Dwarf Atmospheric Models

The white dwarf photosphere experiment uses the Z machine at Sandia National Labs to recreate the plasma conditions observed in the line-forming regions of white dwarf atmospheres (1 – 2 eV and 10¹⁶ – 10¹⁸ e/cm³).  Benchmark measurements of the line profiles used in models of white dwarf spectra are critical for assessing the reliability of fundamental white dwarf parameters derived from spectroscopic fits, which are quite sensitive to the details of the line shapes.  Reliable experimental determination of line shapes requires either relatively uniform plasma along our lines of sight (~12 cm long) or an accurate characterization of any nonuniformity.  In this talk, we will describe the modifications we have made to our experimental platform to allow measurements of gradients in our plasma and present the first results of these experiments.  We also discuss further platform enhancements that we are implementing to reduce systematic uncertainties and increase the reliability of our line shape measurements.