AlMg transmission measurements on the National Ignition Facility with novel uncertainty quantification method for point-projection geometry

The opacity platform on the National Ignition Facility (NIF) was developed to study the opacities of important elements in the solar mixture such as Fe and O as well as mid- to high-Z elements. The platform is intended to help address the discrepancy between measured vs calculated opacities first demonstrated in experiments at the Sandia National Laboratories Z-machine. This discrepancy lies at the heart of the solar problem: the fact that helioseismic measurements disagree with stellar structure models, which depend sensitively on calculated opacities. If correct, the opacity measured on Z would substantially reduce the disagreement. An independent platform has been developed at the National Ignition Facility to verify this result and extend opacity measurements to other elements and plasma conditions. The NIF platform employs different methods from Z. Point-projection absorption spectroscopy provides information about the unattenuated, attenuated, and self-emission signals needed to infer transmission, but the measurement is complicated by non-ideal effects. The work described here is based on the Monte Carlo-based uncertainty analysis pioneered by the Z experimental team. Here, we provide similar methods that introduce the capability of accounting for these effects in point-projection geometry for the first time in a statistically rigorous way. The uncertainty analysis method presented here requires dedicated calibration datasets. Enough dedicated calibration datasets have been obtained to enable development of the framework. Additional data will need to be obtained to refine the uncertainty analysis. We apply the method to transmission spectra from Al:Mg plasmas in the ∼1100–1800 eV photon energy range collected using an elliptical crystal spectrometer in a spatially resolving, point-projection geometry.