  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) Te=167+/-3 eV and ne=(7.1+/-1.5)e21 e/cc, ii) Te=170+/-2 eV and
ne=(2.0+/-0.2)e22 e/cc, and iii) Te=196+/-6 eV and ne=(3.8+/-0.8)e22 e/cc,
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.
