Nuclear Instruments and Methods in Physics Research A

In this paper experimental measures of the reflectivity change in carbon compressed to megabar pressures are presented. The experiments were performed at ILE, Osaka University. The GEKKO-XII laser facility was used to produce shock waves into ‘‘two-layer–two-materials’’ targets made of porous carbon deposited on a transparent substrate. Target design allowed the exploration of the phase diagram by means of samples with different carbon initial density and exploiting the reflection of the shock wave at the interface between carbon and the denser substrate to increase pressure. At the same time, carbon reflectivity could be probed with a secondary laser pulse through the transparent substrate. Also, shock dynamics has been studied thoroughly with numerical simulations performed with the hydrodynamical-radiative code M ULTI. An increase in carbon reflectivity was evidenced at 2.5 Mbar and 14,000 K.