New radiographic image processing tested on the simple and double-flux platform at OMEGA

Abstract

Ablation fronts and shocks are two radiative/hydrodynamic features ubiquitous in inertial confinement fusion (ICF). A specially designed shock-tube experiment was tested on the OMEGA laser facility to observe these two features evolve at once and to assess thermodynamical and radiative properties. It is a basic science experiment aimed at improving our understanding of shocked and ablated matter which is critical to ICF design. At all time, these two moving "interfaces" separate the tube into three distinct zones where matter is either ablated, shocked or unshocked. The {\it simple-flux} or {\it double-flux} experiments, respectively one or two halfraum-plus-tube, have been thought up to observe and image these zones using x-ray and visible image diagnostic. The possibility of observing all three regions at once was instrumental in our new radiographic image processing used to remove the backlighter background otherwise detrimental to quantitative measurement. By so doing, after processing the radiographic images of the 15 shots accumulated during the 2013 and 2015 campaigns, a quantitative comparison between experiments and our radiative hydrocode simulations was made possible. Several points of the principal Hugoniot of the aerogel used as a light material in the shock-tube were inferred from that comparison. Most surprisingly, rapid variations of relative-transmission in the ablated region were observed during radiographic irradiations while it remained constant in the shocked region. This effect might be attributed to the spectral distribution variability of the backlighter during the radiographic pulse. Numerically, that distribution is strongly dependent upon NLTE models and it could potentially be used as a mean to discriminate among them.