First Measurement of Z Opacity Sample Evolution near Solar Interior Conditions Using Time-Resolved Spectroscopy

Opacity model differences with Fe opacity measurements at high temperature (T>180  eV) and high electron density (n_{e}>3×10^{22}  cm^{-3}) at nearly solar interior conditions have remained unresolved [Bailey et al., Nature 517, 56 (2015)10.1038/nature14048 and Nagayama et al., Phys. Rev. Lett. 122, 235001 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.235001]. Systematic errors from temporal gradients are one hypothesis for the discrepancy. Past data recorded on x-ray film provided spectral measurements over a time determined by the 2.8-ns backlighter duration. Here, we present the first measurements of opacity sample temporal evolution using novel hCMOS ultrafast x-ray camera technology. The measured conditions, measured backlighter time history, and modeled opacities are used to show that temporal gradients do not resolve the model-data discrepancy. The methods demonstrated provide potential advantages, including opacities at more extreme conditions, spectral line shift measurements, and improved measurements at other facilities.