Study of shocks and ablation front in diamond ablator during a capsule implosion experiment at the National Ignition Facility

Abstract

An X-ray phase contrast imaging platform using streaked refraction enhanced radiography (RER) was recently developed for capsule implosions at the National Ignition Facility. RER was demonstrated to image in-flight capsule density gradients such as the fuel-ablator interface that is not visible in traditional absorption only radiography. The latest experiments probing the early time evolution of the implosion allowed the precise measurement of the density gradients. An iterative analysis method has been applied to the RER radiograph to allow the reconstruction of temporal evolution of the radial density distribution from the ice-ablator interface to the ablation front. The estimated density reconstruction precision is $\pm 2.4\text{\%}$ with a density gradient sensitivity threshold of $10^{23}{\mathrm{cm}}^{-3}$ over a $2\mu m$ scale length. This enabled the study of shocks velocity and density gradients as well as ablation front scale length and shape.