Parallax diagnostics of radiation source geometric dilution for iron opacity experiments

Abstract

Experimental tests are in progress to evaluate the accuracy of the modeled iron opacity at solar interior conditions [J.E. Bailey et al., Phys. Plasmas 16, 058101 (2009)]. The iron sample is placed on top of the Sandia National Laboratories z-pinch dynamic hohlraum (ZPDH) radiation source. The samples are heated to 150 - 200 eV electron temperatures and 7e21 - 4e22 e/cc electron densities by the ZPDH radiation and backlit at its stagnation [T. Nagayama et al., Phys. Plasmas 21, 056502 (2014)]. The backlighter attenuated by the heated sample plasma is measured by four spectrometers along +/- 9 degree with respect to the z-pinch axis to infer the sample iron opacity. Here we describe measurements of the source-to-sample distance that exploit the parallax of spectrometers that view the half-moon-shaped sample from +/-9 degree. The measured sample temperature decreases with increased source-to-sample distance. This distance must be taken into account for understanding the sample heating.