[en] Hydrogen at high pressures and temperatures is challenging scientifically and has many real and potential applications. Minimum metallic conductivity of fluid hydrogen is observed at 140 GPa and 2600 K, based on electrical conductivity measurements to 180 GPa (1.8 Mbar), tenfold compression, and 3000 K obtained dynamically with a two-stage light-gas gun. Conditions up to 300 GPa, sixfold compression, and 30,000 K have been achieved in laser-driven Hugoniot experiments. Implications of these results for the interior of Jupiter, inertial confinement fusion, and possible uses of metastable solid hydrogen, if the metallic fluid could be quenched from high pressure, are discussed

[en] Single-shock (Hugoniot) equation-of-state data of shock-compressed C (graphite) are reported at pressures of 480 and 760 GPa (7.6 Mbar). Graphite is shock-compressed completely into a diamond-like phase at pressures below 80 GPa. At pressures of 80--800 GPa comparison of an ensemble of experimental Hugoniot data for shock-compressed graphite and diamond, and theoretical calculations of the Hugoniots of graphite and diamond, and the 0 K isotherm of diamond suggest diamond melts at ∼300 GPa on the Hugoniot of graphite and that the diamond phase is the ground-state structure of C up to at least 600 GPa

[en] Electrical conductivities of fluid oxygen were measured between 30 and 80 GPa at a few 1000 K. These conditions were achieved with a reverberating shock wave technique. The measured conductivities were several orders of magnitude lower than measured previously on the single shock Hugoniot because of lower temperatures achieved under shock reverberation. Extrapolation of these data suggests that the minimum metallic conductivity of a metal will be reached near 100 GPa

[en] Electrical conductivities of fluid oxygen were measured between 30 and 80 GPa at a few 1000 K. These conditions were achieved with a reverberating shock wave technique. The measured conductivities were several orders of magnitude lower than measured previously on the single shock Hugoniot because of lower temperatures achieved under shock reverberation. Extrapolation of these data suggests that the minimum metallic conductivity of a metal will be reached near 100 GPa

[en] Shock-compression experiments on liquids using a two-stage gun are described. Results for H₂, He, H₂O, N₂, CO₂, and a mixture of H₂O, NH₃, and C₃H₈O (synthetic Uranus) are discussed and related to explosive reaction products, giant planets, laser-driven fusion, and metallic hydrogen

[en] Dynamic high pressure is 1 GPa (10 kbar) or greater with a rise time and a duration ranging from 1 ps (10^-12 s) to 1 μs (10^-6 s). Today it is possible in a laboratory to achieve pressures dynamically up to ∼500 GPa (5 Mbar) and greater, compressions as much as ∼15-fold greater than initial density in the case of hydrogen and temperatures from ∼0.1 up to several electronvolts (11 600 K). At these conditions materials are extremely condensed semiconductors or degenerate metals. Temperature can be tuned independently of pressure by a combination of shock and isentropic compression. As a result, new opportunities are now available in condensed matter physics at extreme conditions. The basic physics of the dynamic process, experimental methods of generating and diagnosing matter at these extreme conditions and a technique to recover metastable materials intact from ∼100 GPa shock pressures are discussed. Results include (i) generation of pressure standards at static pressures up to ∼200 GPa (2 Mbar) at 300 K, (ii) single-shock compression of small-molecular fluids, including resolution of the recent controversy over the correct shock-compression curve of liquid D₂ at 100 GPa pressures, (iii) the first observations of metallization of fluid hydrogen, nitrogen and oxygen compressed quasi-isentropically at 100 GPa pressures, (iv) implications for the interiors of giant planets within our solar system, extrasolar giant planets and brown dwarfs discovered recently and the equation of state of deuterium-tritium in inertial confinement fusion (ICF) and (v) prospects of recovering novel materials from extreme conditions, such as metastable solid metallic hydrogen. Future research is suggested

[en] A single-stage light-gas gun was used to perform shock-recovery experiments on Berea sandstone under dry, wet and hydrostatically water-pressurized conditions. The samples were impacted by flyer-plates to achieve stress levels in the range 1.3 to 9.8 GPa. The microstructure of the shocked samples was analyzed using scanning electron microscopy (SEM), laser particle analysis and X-ray computed microtomography (XCMT). The dry samples show strongly fragmented and irregularly fractured quartz grains with a considerably reduced porosity, whereas the wet and water-pressurized specimens show less grain damage and less porosity reduction. During shock compression the water in the pores distributes the stresses and therefore the contact force between the grains is reduced. The interaction between the grains during the shock process was modeled by explicitly treating the grain-pore structure using Smooth Particle Hydrodynamics (SPH) and the Discrete Element Method (DEM)

[en] Pressures up to a few 100 GPa and temperatures as high as a few 1000 K have been achieved with high dynamic pressures using a two-stage light-gas gun. Results are reviewed for molecular fluids, metallic hydrogen, solids, implications for planetary interiors, and structures and properties of materials recovered intact from high dynamic pressures

[en] The systematics of Mott transitions in low-Z and alkali fluids H, N, O, Rb, and Cs are discussed. Such transitions have only been obtained in elemental, monatomic, and disordered systems by using high pressures and temperatures. By finding elements which undergo this transition, it is possible to test Mott's ideas in systems which are relatively simple. For fluid H, N, and O, 100 GPa pressures and ∼ 2000 K temperatures are required and were achieved by dynamic shock compression. For fluid Rb and Cs, 0.01 GPa and ∼ 2000 K are required and were achieved statically by Hensel et al. Despite the fact that these two groups of elements at ambient conditions are so different chemically and that pressures required to observe this transition differ by a factor of 10⁴ for the two groups, the metallic conductivities are essentially the same for all five and the density dependences of their semiconductivities are determined systematically by the radial extents of the electronic charge-density distributions of the various atoms. The latter observation provides a physical understanding for the Herzfeld criterion of metallization. It is the tuning of both high pressure and temperature which permits these two apparently different classes of elements at ambient conditions to become quite similar in nature at extreme conditions

[en] The Voyager 2 spacecraft discovered the unusual non-dipolar and non-axisymmetric magnetic fields of the Ice Giants Uranus and Neptune (U/N) in the 1980's. Those field shapes are unique in the Solar System and their cause has been a major scientific question since their discovery. Their likely explanation lies in electrical conductivities of fluids that generate those magnetic fields. External magnetic fields of U/N are made by dynamo action of convecting, electrically conducting fluids relatively close to their surfaces at pressures (P) and temperatures (T) up to a few 100 GPa and several 1000 K, respectively. Relevant P/Ts are achieved in a laboratory by adiabatic shock compression and quasi-isentropic multiple-shock compression. Over the past ~30 years a substantial database of measured electrical conductivities of representative planetary fluids at representative planetary P/Ts has been accumulated. Although neither exact compositions nor P/Ts in U/N are known, this database, gravitational moments measured by Voyager 2, estimated chemical abundances of the Solar System and the recent discovery that rotational motion of Earth’s strong, rock mantle is strongly coupled to its fluid outer core suggest: (i) There is little nebular ''Ice'' in the Ice Giants. (ii) Magnetic fields of U/N are made by convecting metallic fluid H relatively close to the outer surfaces of U/N. (iii) Thus, it is reasonable to observe non-dipolar non-axisymmetric magnetic fields. (iv) Those field shapes are probably caused by decoupling of rotational motion of U/N from convective motions in their dynamos, unlike Earth with strong coupling between its mantle rotation and convective fluid Fe outer core and a dipolar field. Basically, the magnetic field of Earth reverses from time to time because of fluctuations in the dynamo. The strong coupling either causes the dipolar magnetic field to remain virtually parallel to the axis of rotation or, if a fluctuation is so great that the magnetic field essentially reverses, the strong coupling causes the reversing dipolar magnetic field to align virtually anti-parallel to the axis of rotation. In U/N the weak fluid H/He envelops are weakly coupled to convection in the fluid core and so the magnetic fields probably wander over the age of the Solar System with magnetic field shapes and orientations dictated by fluctuations in their convecting fluid interiors. The full paper on this work is published.