Measurement of Cu temperature, density, and phase using Extended X-ray Absorption Fine Structure at the National Ignition Facility

The temperature of dynamically compressed materials is the largest uncertainty in modern equation of state modeling, and developing new tools to measure temperature is important to complement data from existing diffraction and equation-of-state platforms. In experiments performed at the National Ignition Facility (NIF), Extended X-ray Absorption Fine Structure (EXAFS) has been measured and used to constrain temperature, density, and phase near 400 GPa. These fine-structure modulations in the X-ray absorption are caused by photoelectron scattering off nearby atoms, and are sensitive to both local atomic spacing and thermal disorder. Measured EXAFS signals are consistent with face-center-cubic structure in Cu up to 5,500K near 400 GPa, and also reveal an unexpected temperature sensitivity to the material layers adjacent to the Cu sample.