X-Ray Phase-Contrast Imaging Sequence of Void Collapse Driven by Laser Shock Compression

The National Ignition Facility (NIF) has repeatedly exceeded scientific breakeven, most recently delivering an 8.6 MJ output from 2.08 MJ input, demonstrating the potential of inertial confinement fusion (ICF) as a clean, abundant energy source. Maximizing energy yield, however, depends critically on achieving uniform shock propagation and compression symmetry within the fuel capsule's ablator. Defects such as voids within ablator materials disrupt shock uniformity, driving complex nonlinear interactions and hydrodynamic instabilities that degrade performance and consequently lowers energy yield. To characterize these dynamics, we used an x-ray free-electron laser (XFEL) at the Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS) to capture high-resolution, single-shot 2D x-ray phase-contrast (XPC) images of ICF-relevant ablator materials with embedded 1-um thick, 40 um diameter hollow voids. The materials were shocked by a long-pulse laser, and images were acquired at multiple x-ray delays to observe successive stages of void collapse. We applied phase-retrieval algorithms to extract quantitative areal density maps from the dynamic, flat-field-corrected XPC images and compared them to xRAGE simulations. These comparisons reveal potential discrepancies between simulated and observed void-collapse dynamics, providing insights to improve compression strategies and can contribute to refining simulation parameters of void collapse.