Effects of spectral variability on material response in x-ray-generated impulse experiments at the National Ignition Facility*

Thermomechanical shock experiments aim to study the response of materials in extreme conditions. We use the National Ignition Facility (NIF) to generate high fluence x-ray atomic line emission sources, which irradiate material samples of interest. Under sufficiently high energy deposition, thermomechanical shocks are generated in the materials. While it is known that the characteristics of x-ray generated impulses vary as a function of incident x-ray spectra, unknown is how possible shot-to-shot spectral variations and uncertainties in NIF spectral reconstructions affect our understanding of the material response to impulsive loading. In this presentation, we show results of 1D radiation hydrodynamics simulations of x-ray induced thermomechanical shocks to investigate the effects of spectral variability in NIF line-emission sources on aluminum and titanium alloy samples. We compare the experimental results from NIF experiments to the simulated material response for several different cases of spectral reconstruction. We find that the material response is highly sensitive to assumptions made about the spectral contents and that knowledge of spectral uncertainties bounds our understanding of the resulting material response. The results of this effort help to extend our ability to extract quantitative material properties from x-ray experiments on NIF, which study material properties at the extremes of current laboratory capabilities.