Control and diagnosis of temperature, density, and uniformity in x-ray heated iron/magnesium samples for opacity measurements

TL;DR

This paper reports on experiments controlling and diagnosing the temperature, density, and uniformity of iron/magnesium samples to improve the accuracy of opacity measurements relevant to solar and stellar models.

Contribution

It introduces a method to precisely control and verify sample conditions and uniformity in opacity experiments using spectroscopic diagnostics.

Findings

Controlled plasma conditions with specified temperature and density achieved.

Sample uniformity confirmed within measurement uncertainties.

Experimental setup suitable for testing opacity models for astrophysical applications.

Abstract

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.