Transforming opacity science on Z using novel time-resolved spectroscopy*

Models for the Sun and stars remain uncertain today because opacity models are unable to reproduce previous iron opacity measurements at stellar interior conditions [1,2]. Time-resolved spectroscopy using a novel hCMOS Ultra-fast X-ray Imager (UXI, [3,4]) is transforming stellar interior opacity measurements at the Sandia Z facility. First, we can directly measure whether temporal gradients affected the published results. Prior data recorded on x-ray film had duration given by the 3-ns backlighter and one hypothesis for the opacity model data discrepancy is that temporal integration influenced the results. Second, this technology can eventually enable time-resolved Fe opacity measurements. This can not only provide Fe opacities at multiple conditions from a single experiment but can also test Fe-opacity models at more extreme conditions. Third, sample conditions evolution measurements have revealed Fe-opacity samples evolve differently from simulations and the refined understanding has provided insight into how to reach more extreme opacity experiment conditions. We will discuss if the model-data discrepancies are explained by the measured gradient. We will discuss the remaining challenges and our strategy to obtain the first time-resolved opacity measurements on Z.