Experimental tests are in progress to evaluate the accuracy of the modeled iron opacity at solar interior conditions , in particular to better constrain the solar abundance problem [ S. Basu and H.M. Antia , Physics Reports 457 , 217 ( 2008 ) ] .
Here we describe measurements addressing three of the key requirements for reliable opacity experiments : control of sample conditions , independent sample condition diagnostics , and verification of sample condition uniformity .
The opacity samples consist of iron/magnesium layers tamped by plastic .
By changing the plastic thicknesses , we have controlled the iron plasma conditions to reach i ) T _ { e } =167 \pm 3 eV and n _ { e } = \mathrm { \left ( 7.1 \pm 1.5 \right ) \times 10 ^ { 21 } cm ^ { -3 } } , ii ) T _ { e } =170 \pm 2 eV and n _ { e } = \mathrm { \left ( 2.0 \pm 0.2 \right ) \times 10 ^ { 22 } cm ^ { -3 } } , and iii ) T _ { e } =196 \pm 6 eV and n _ { e } = \mathrm { \left ( 3.8 \pm 0.8 \right ) \times 10 ^ { 22 } cm ^ { -3 } } , which were measured by magnesium tracer K-shell spectroscopy .
The opacity sample non-uniformity was directly measured by a separate experiment where Al is mixed into the side of the sample facing the radiation source and Mg into the other side .
The iron condition was confirmed to be uniform within their measurement uncertainties by Al and Mg K-shell spectroscopy .
The conditions are suitable for testing opacity calculations needed for modeling the solar interior , other stars , and high energy density plasmas .