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The Near Vacuum Campaign on the National Ignition Facility has sparked an interest on the nature of the gold/carbon interface at high velocity (400 km/s), high electron temperature (2 keV), low-electron density (1e21). Indeed radiation-hydrodynamic simulations using the code HYDRA have been unable to accurately reproduce the experimental shape of the hot spot resulting from implosion driven in Near Vacuum Holhraum. The experimental data are suggesting that the NIF inner beams are freely propagating to the waist of the hohlraum when the simulations predict that a density ridge at the gold/carbon interface blocks the inner beams. The discrepancy between experimental data and simulation might be explained by the fluid description of the plasma interface in a rad-hydro code which is probably not valid in when two plasma at high velocity, high temperature are meeting in a Near Vacuum Hohlraum. To test our assumption that a kinetic description is more appropriate in this regime, we went to the Omega laser facility to study gold/carbon interface in the relevant regime. We will present results comparing the plasma interface of a C/C, Al/C and Au/C under the same laser drive. Time resolved images of the self-emission of the interface as well as Thomson scattering data will be presented.

Summary form only given. Accurate phase diagrams for simple molecular fluids (H/sub 2/, H/sub 2/O, NH/sub 3/ and CH/sub 4/) and their constituent elements at temperatures of several thousand Kelvin and pressures of several Mbar are integral to planetary models of the gas giant planets ( Jupiter, Saturn, Uranus and Neptune). Experimental data at high pressure has, until recently, been limited to around I Mbar. These pressures are usually achieved dynamically with explosives and two-stage light-gas guns, or statically with diamond anvil cells. Current high intensity laser facilities can produce tens of Mbar pressures in these light fluids. This presentation will first describe recent shock compressed Hugoniot data for water at pressures up to 8 Mbar. At Hugoniot pressures near I Mbar, water becomes an electronic conductor as observed through the shock front reflectivity. Similar experimental results will be shown for carbon starting from the diamond phase. Reflectivity data reveal diamond metalizes near the Hugoniot pressure of 11 Mbar and is perhaps coincident with the melt transition. To obtain high pressure data very close to planetary isentropes, techniques are being developed to generate off Hugoniot data (lower temperature and higher density than standard Hugoniot track). Two techniques to achieve such high density states (double shock and precompressed samples) have been tested. These techniques and preliminary data from these experiments will be described.