Equation of state measurements in the Gbar regime

We are developing laser-driven loading platforms that allow the equation of state (EOS) of matter to be measured at pressures of up to several tens of terapascals (hundreds of megabars). For low-Z samples, measurements can be made using radiography of a spherically-converging shock, which allows a range of pressures to be probed in each experiment and yields absolute states on and near the shock Hugoniot. For higher-Z samples, a conically-converging shock produces a Mach wave which can be used for shock measurements relative to a standard material by impedance-matching. Pressures achievable at the OMEGA laser facility and National Ignition Facility are high enough to explore the effects of ionizing successive electron shells. Results so far suggest that the Thomas-Fermi model is not adequate and shell effects appear to be significant, though the measurements do not appear entirely consistent with average-atom treatments of high temperature EOS.