Towards diffusivity measurements in laser shocked material with X-Ray Photon Correlation Spectroscopy*

The understanding of transport properties in shocked materials is paramount in explaining the dynamic behaviour of materials at high pressure. Transport in high pressure materials influences a plethora of phenomena ranging from the growth rate of hydrodynamic instabilities in inertial fusion experiments to melting and rotational dynamics in planetary cores. However, there is a simultaneous lack of experimental quantification of such properties and disagreement between theoretical treatments. Experimental quantification of transport coefficients at high pressures is therefore required to provide validation or contradiction to differing theoretical models.

X-ray photon correlation spectroscopy utilises coherent X-ray sources to measure time correlations of density fluctuations, thus providing measurements of length and time scale dependent transport properties. While over the previous decade, its use in material science has been established, X-ray photon correlation spectroscopy has not yet been applied to plasma physics experiments. We present the development of an X-ray free electron laser-based platform to conduct X-ray photon correlation spectroscopy in laser shock compression experiments to measure diffusivity in a plasma on nanosecond timescales. We will report on analysis of a recent experiment at the MEC end station at LCLS in which PET foams are shocked to 30GPa and probed using X-ray Diffraction, X-ray Thomson Scattering, VISAR and X-ray Photon Correlation Spectroscopy.