PNNL

Abstract

Supercritical fluids (SCFs) can be found in a variety of environmental and industrial processes. They exhibit anomalous thermodynamic behavior, which originate from their fluctuating heterogeneous microscopic structure. Characterizing the dynamics of these high pressure high temperature fluids at nanometer length scales and picosecond time scales has been very challenging. The advent of hard X-ray free electron lasers has enabled the development of novel multi-beam ultrafast X-ray scattering techniques, such as X-ray photon correlation spectroscopy (XPCS) and X-ray pump X-ray probe. These techniques offer new means of resolving the ultrafast microscopic behavior in SCFs at the unprecedented spatio-temporal resolution necessary to resolve the dynamics of their microscopic structure. However, harnessing these capabilities requires a bespoke high pressure high temperature sample system optimized to maximize signal intensity and address instrumentspecific challenges such as X-ray and optics drift and multi-X-ray-beam overlap. We present a pressure-cell compatible with a wide range of SCFs with built-in optical access for XPCS and X-ray pump X-ray probe, and discuss critical aspects of the pressure-cell design, with a particular focus on design optimization for XPCS.