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

Time-resolved spectroscopy using a novel Ultra-fast X-ray Imager (UXI) is transforming stellar interior opacity measurements at the Sandia Z facility. Models for the Sun and stars are uncertain because opacity models are unable to reproduce previous iron opacity measurements at stellar conditions [1,2]. The unprecedented new data help resolve this dilemma in three important ways. First, prior opacity data recorded on x-ray film had duration given by the 3-ns backlighter. One hypothesis for the opacity model-data discrepancy is that the temporal integration influenced the results. Time-resolved data directly test this hypothesis. Second, Sandia’s UXI technology [3,4] enables measurements of iron opacities at multiple conditions from a single experiment. This increases the learning rate since fewer experiments are needed to test the model predictions for trends in opacity changes with plasma conditions. Third, measurements of the iron sample temperature and density evolution refine the experimental understanding. Better understanding enables improved experimental design. For example, both the measured temperature and the density of the iron opacity sample increase with time. This contradicts expectations based on simulations and provides insight into how to reach more extreme experimental conditions. We will discuss the first results from experiments designed to take advantage of newly acquired time-resolved knowledge to tailor the opacity experimental conditions. Obtaining the first time-resolved absolute opacity data on Z is in progress. The strategy and prospects for obtaining multiple opacity measurements from a single Z experiment will be discussed.