Ultrafast time-resolved imaging of void collapse in ICF ablator materials *

Decades of research have been devoted to the realization of inertial confinement fusion (ICF) [1]. However, hydrodynamic instabilities seeded by mesoscale imperfections, such as micro-voids, remain a persistent problem for achieving the conditions required for fusion ignition  [2]. It is thus crucial to understand the process by which voids seed instabilities in ICF ablator materials under extreme conditions, and to visualize the evolution of these hydrodynamic instabilities. Here, we demonstrate a novel experimental platform for ultra-fast imaging of materials under dynamic compression developed at the Matter in Extreme Conditions (MEC) instrument at the LCLS x-ray free electron laser (XFEL).

The unique spatial coherence and ultra-fast timescale of the XFEL probe at LCLS enables x-ray phase-contrast imaging (XPCI) with high spatial (~100 nm) and temporal (~fs) resolution. For the first time, we have used the LCLS four-pulse train and an ultra-fast multi-frame detector (the Icarus V2 [3]) to collect time-resolved images of samples embedding 40µm voids during laser-driven shock compression. Furthermore, we performed single-shot Talbot XPCI with sub-micron resolution. This work demonstrates a novel ultra-fast x-ray imaging technique, with the spatial and temporal resolution needed to resolve in situ the motion of a shock wave during a single shot and from a single sample.

[1] J. H. Nuckolls LLNL, Early Steps toward Inertial Fusion Energy (IFE) (1952 to 1962) (1998).

[2] V. A. Smalyuk et al., High Energ Dens Phys 36, 100820 (2020).

[3] P. A. Hart et al., 11038, 110380Q (2019).