Application and Analysis of the Isoelectronic Line Ratio Temperature Diagnostic in a Planar Ablating-Plasma Experiment at the National Ignition Facility

The Mn/Co isoelectronic emission-line ratio from a microdot source in planar CH foil targets was measured to infer the electron temperature ($T_{\mathrm{e}})$ in the ablating plasma during two-plasmon--decay experiments at the National Ignition Facility (NIF). We examine the systematic uncertainty in the $T_{\mathrm{e}}$ estimate based on the temperature and density sensitivities of the line ratio in conjunction with plausible density constraints, and its contribution to the total $T_{\mathrm{e}}$ estimate uncertainty. The potential advantages of alternative microdot elements (e.g., Ti/Cr and Sc/V) are considered. The microdot mass was selected to provide ample line strength while minimizing the effect of self-absorption on the line emission, which is of particular concern, given the narrow linewidths of mid-$Z$ emitters at subcritical electron densities. Atomic line-formation theory and detailed atomic-radiative simulations show that the straight forward interpretation of the isoelectronic ratio solely in terms of its temperature independence remains valid with lines of moderate optical thickness (up to $\sim 10$) at line center. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.