Experimental and ab initio investigations of microscopic properties of laser-shocked Ge-doped ablator.

Plastic materials (CH) doped with mid-Z elements are used as ablators in inertial confinement fusion (ICF) capsules and in their surrogates. Hugoniot equation of state (EOS) and electronic properties of CH doped with germanium (at 2.5% and 13% dopant fractions) are investigated experimentally up to 7 Mbar using velocity and reflectivity measurements of shock fronts on the GEKKO laser at Osaka University. Reflectivity and temperature measurements were updated using a quartz standard. Shocked quartz reflectivity was measured at 532 and 1064 nm. Theoretical investigation of shock pressure and reflectivity was then carried out by ab initio simulations using the quantum molecular dynamics (QMD) code abinit and compared with tabulated average atom EOS models. We find that shock states calculated by QMD are in better agreement with experimental data than EOS models because of a more accurate description of ionic structure. We finally discuss electronic properties by comparing reflectivity data to a semiconductor gap closure model and to QMD simulations.