Spectroscopic measurements of Rosseland mean opacity

Abstract The first quantitative measurement of photoabsorption in the region determining Rosseland and Planck mean opacity, is obtained for an x-ray heated iron plasma, using novel techniques and instrumentation. The plasma density of 0.0113 ± 0.0013 g/cm 3 and temperature of 59 ± 3 eV are accurately constrained experimentally by imaging plasma expansion and observing and modeling absorption in sodium dopant ions. The measured iron absorption spectrum is compared with several newly developed opacity models. The data constrains Rosseland and Planck group means with of order 15% precision. This is the first quantitative experimental certification of opacity models germane to radiative transfer in LTE plasmas.