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

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) T e =167±3 eV and n e = (7.1 ± 1.5) × 10 21 cm −3 , ii) T e =170±2 eV and n e = (2.0 ± 0.2) × 10 22 cm −3 , and iii) T e =196±6 eV and n e = (3.8 ± 0.8) × 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.

Note: Optical receiver system for 152-channel magnetoencephalography

“…There is a strong correlation between the measured electron temperature, T e , and the measured source-to-sample distance, h. The blue curve is a modeled radiation brightness temperature as a function of h. Figure 5 summarizes the measured h as a function of T e inferred from Mg K-shell spectroscopy. 6 We confirm a strong anti-correlation between h and T e (Pearson correlation coefficient = −0.91).…”

“…6 There are three different CH configurations and multiple different Fe thicknesses for each configuration. There is one shot where the sample is raised by 1.5 mm from its nominal location.…”

Enigmatic photon absorption in plasmas near solar interior conditions

“…the Sandia experiments include supporting measurements to test the reliability of the data [2,3,17,18].…”

A New Generation of Los Alamos Opacity Tables

“…Our approach to photoionization uses a distorted-wave approach, which is usually thought to be of acceptable accuracy for photoionization calculations from moderately and highly charged systems. On the other hand, the measurements reported in Bailey et al (2015) have been subject to considerable scrutiny (Nagayama et al 2014) in the search for experimental issues that might affect the measured opacity. No significant systematic errors that could artificially increase the measured opacity were reported by Nagayama et al (2014).…”

“…On the other hand, the measurements reported in Bailey et al (2015) have been subject to considerable scrutiny (Nagayama et al 2014) in the search for experimental issues that might affect the measured opacity. No significant systematic errors that could artificially increase the measured opacity were reported by Nagayama et al (2014). We look forward to independent verification of these measurements and to a resolution of this discrepancy.…”