New regimes of materials science at ultrahigh pressures and densities*

Our work in the high energy density science (HEDS) field started in the 1990s on facilities such as the Nova laser at LLNL, the Z facility at SNLA, and the Omega laser at LLE, where drive techniques, target fabrication, diagnostic techniques, and the basics of ramped compression were developed.  With NIF came good pulse shaping and more energy, opening the door to experiments that could reach solid state conditions in samples to tens of Mbar pressures. Examples from some recent highlights in HEDS include the following. (1) Knudson and Celliers et al. independently observed that high pressure and density deuterium underwent an abrupt insulator to metal transition at 2-3 Mbar pressures in experiments at Z and on NIF. (2) Marshall et al. observed the formation of diamond from doubly shocked CH polymer at Omega EP, with the carbon forming nanograins of diamond, leaving the hydrogen free to flow. (3) Knudson and Millot independently have studied water (H₂O) at 100s of GPa pressures at Z and at Omega, where the H₂O can transition to the superionic phase of matter, with the oxygen locked into a bcc or fcc lattice, and the hydrogen remaining free to flow. (4) Brygoo et al. demonstrated at high density at Omega the demixing of He from a homogeneously mixed gas sample of He-H, where the He can come out of solution (demix) as He droplets. (5) Gorman et al. have studied magnesium at terapascal pressures on NIF, where they observed the peculiar electride phase of matter. (6) Polsin et al. also observed an electride phase in high density Na at Omega EP. (7) Kraus et al carried out experiments on NIF to map out the high pressure melt curve of Fe up to peak pressures of 10 Mbar, relevant to super-Earth core conditions. (8) Coppari et al. make connections to planetary interiors by studying iron oxide (FeO) ramp compressed to 700 GPa at Omega. (9) And Krygier et al. are studying high pressure, high rate, solid state plastic flow in metals at NIF.  A selection of examples from frontier HED science will be presented.