Bad Foils in Simulated Opacity Experiments

Discrepancies in Solar interior models have ignited ongoing efforts to directly measure opacities of metals in Solar interior conditions recreated in high energy density facilities. Occasionally, alloy foils made for these experiments arrive defective with cracks. However, whether these cracks can actually bias the results of experiments is unquantified. To close this gap, Cassio simulations are used to predict the dynamics of defective foils in numerical experiments on a representative iron-magnesium alloy. We find that, across a range of preheat and radiation source models, the cracks self-heal. However, for foils with visible cracks wider than 10 μm, the healing is too slow to seal the cracks by the time of the opacity measurement. Consequently, a significant amount of unattenuated backlight radiation can still reach through the cracks to the spectrograph, leading to underestimating the attenuation of the transmitted light. This bias is unrecoverable. If the foils’ density away from cracks and the nominal opacity were known a priori, the area covered by cracks at measurement time can still be estimated using partial covering models.