Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session L3: High Energy Density Physics/Warm Dense Matter I |
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Chair: Daniel Kalantar, Lawrence Livermore National Laboratory Room: Hyatt Regency Constellation D |
Tuesday, August 2, 2005 3:30PM - 3:45PM |
L3.00001: Theory and Experiment on Radiative Shocks R. Paul Drake, Amy B. Reighard The current generation of high-energy-density research facilities has enabled the beginnings of experimental studies of radiation hydrodynamic systems, common in astrophysics but difficult to produce in the laboratory. Radiative shock experiments specifically have been a topic of increasing effort in recent years. Our group and collaborators [1] have emphasized the radiographic observation of structure in radiative shocks. These shocks have been produced on the Omega laser by driving a Be piston through Xenon at velocities above 100 km/s. The talk will summarize these experiments and their results. Interpreting these and other experiments is hampered by the limited range of assumptions used in published theories, and by the limitations in readily available simulation tools. This has motivated an examination of radiative shock theory [2]. The talk will summarize the key issues and present results for specific cases. \\ $\left[ 1 \right] $ Gail Glendinning, Ted Perry, Bruce Remington, Jim Knauer, Tom Boehly, and other members of the NLUF Experimental Astrophysics Team. Publications: Reighard \textit{et al.,} \textit{Phys. Rev. Lett. } submitted; Leibrandt, \textit{et al., Ap J}., in press, Reighard \textit{et al.}, IFSA 03 Proceedings, Amer. Nucl. Soc. (2004). \\ \underline {[2] Useful discussions with Dmitri Ryutov and Serge Bouquet. } \\ Supported by the NNSA programs via DOE Grants DE-FG52-03NA00064 and DE FG53 2005 NA26014 [Preview Abstract] |
Tuesday, August 2, 2005 3:45PM - 4:00PM |
L3.00002: Observation of metallic helium: Equation of state and transport measurements under astrophysical conditions P.M. Celliers, J.H. Eggert, P.A. Loubeyre, S. Brygoo, R.S. McWilliams, D.G. Hicks, T.R. Boehly, R. Jeanloz, G.W. Collins The equation of state and opacity of warm dense helium (1 $< \rho < $ 10 g/cm$^3$, 0.5 $<$ T $<$ 5 eV) is essential for addressing a variety of astrophysical problems. High-pressure experimental data on dense helium are sparse; models used by the astrophysical community have been calibrated against a small number of gas-gun measurements much below 1 g/cm$^3$. Using coupled static- and dynamic-compression techniques it is becoming feasible to recreate the conditions of giant planetary interiors in laboratory; in recent experiments we have compressed helium to over 1.2 g/cm$^3$. We present measurements of pressure, temperature, density, and reflectivity of compressed helium using quartz as a reference material for impedance matching. Reflectivity data at these conditions show that helium is not a clear dielectric fluid but reflects like a metal. The pressure for this transition is almost independent of temperature, as would be expected for pressure-induced ionization, but it occurs at pressures 1-2 orders of magnitude lower than theoretically expected for the T = 0 K solid or fluid. [Preview Abstract] |
Tuesday, August 2, 2005 4:00PM - 4:15PM |
L3.00003: High energy density Physics on LULI2000 facility Michel Koenig, Alessandra Benuzzi-Mounaix, Alessandra Ravasio, Tommaso Vinci, Norimasa Ozaki, Sebastien Lepape, Marc Rabec, Claire Michaut, Laurent Boireau, Serge Bouquet, Stephanie Brygoo, Emeric Henry, Paul Loubeyre, David Riley, Kazuo Tanaka We present here a summary of various experiments performed on the new facility LULI 2000. High Density Energy Physics situation have been investigated: a- Study on water EOS using laser driven shock into a diamond anvil cell pre-compressed target. b- A strongly coupled and degenerated Aluminum plasma has been probed by X-ray Thomson scattering. Compton shift from electrons has been observed. c- A radiative supercritical shock has been produced into a Xe filled gas cell. We determined electron density variation, precursor and shock velocities and electron temperature. Different flyer plate targets have been tested loading shock in fused-quartz plate. [Preview Abstract] |
Tuesday, August 2, 2005 4:15PM - 4:30PM |
L3.00004: Dissociation of silica at high pressure Damien Hicks, Jon Eggert, Peter Celliers, Chuck Sorce, Gilbert Collins, Tom Boehly, Josh Miller, Elena Vianello, David Meyerhofer Measurements of the temperature and optical reflectivity of quartz and fused silica under shock loading from 100 to 1000 GPa have revealed evidence for dissociation of silica between $\sim $150 and 400 GPa. Using attenuating laser-driven shock waves a continuous record of the temperature and reflectivity dependence on pressure has been obtained in both materials allowing the specific heat capacity and electronic conductivity to be deduced. Results show that between 150 and 400 GPa the specific heat rises significantly above that expected from the Dulong-Petit law, indicating the presence of a latent energy. Coincident with this anomalous specific heat is a rapid rise in electronic conductivity. Both these observables suggest that dissociation is occurring in the dense fluid. In addition temperature measurements near 5000 K detect a discontinuity at the melt transition, as measured earlier on gas gun experiments. This work was performed under the auspices of the US DOE by LLNL under Contract No. W-7405-ENG-48 and by the University of Rochester under Cooperative Agreement No. DE-FC03-92SF19460. [Preview Abstract] |
Tuesday, August 2, 2005 4:30PM - 4:45PM |
L3.00005: Warm dense hydrogen in the chemical picture Ronald Redmer, Hauke Juranek, Nadine Nettelmann, Volker Schwarz The properties of hydrogen as the simplest and most abundant element in the universe are of great interest for astrophysical studies and inertial confinement fusion experiments. Thus, a precise knowlegde of the equation of state (EOS) and of the transport properties is needed for a large domain of densities and temperatures, especially for the region of warm dense matter where correlations are very important. We present theoretical results for the EOS and the transport properties of hydrogen, especially for the high pressure domain. Based on the chemical picture, the EOS of hydrogen is determined within fluid variational theory considering dissociation and ionization processes. We compare our new results with available experimental data and other theoretical predictions for the Hugoniot curve and the sound velocity. The EOS data is also used to model interiors of giant planets such as Jupiter. The composition of hydrogen as function of temperature and pressure is derived from the EOS and serves as input in calculations of transport properties such as the electrical conductivity. Using linear response theory, the various scattering mechanisms of free and bound electrons are treated, and the nonmetal-to-metal transition in hydrogen as well as in noble gases can be explained by pressure ionization. Comparison with respective experimental data for the electrical conductivity and the reflectivity shows good overall agreement. [Preview Abstract] |
Tuesday, August 2, 2005 4:45PM - 5:00PM |
L3.00006: The Free-free Opacity of Warm, Dense and Weakly Ionized Helium Piotr Kowalski, Didier Saumon, Stephane Mazevet We investigate the ionization and the opacity of warm, fluid helium under conditions found in the atmospheres of cool white dwarf stars. Our particular interest is in densities up to 3\,g/cm$^3$ and temperatures from 1000\,K to 10000\,K. For these physical conditions various approaches for modeling the ionization equilibrium predict ionization fractions that differ by orders of magnitudes. Furthermore, estimates of the density at which helium pressure-ionizes varies from 1.5 to 40 g/cm$^3$. In this context, the value of the electron-atom inverse bremsstrahlung absorption is highly uncertain. We present new results obtained from a combination of MD-DFT simulations, a non-ideal chemical model for the ionization equilibrium, and the analysis of experimental data to better understand the ionization fraction in fluid helium in the weak ionization limit. [Preview Abstract] |
Tuesday, August 2, 2005 5:00PM - 5:15PM |
L3.00007: Direct density measurements of multi-Mbar shock waves for absolute equation-of-state studies T.R. Boehly, E. Vianello, J.E. Miller, D.D. Meyerhofer, D.G. Hicks, J.H. Eggert, J.F. Hansen, P.M. Celliers, G.W. Collins Many EOS studies rely on impedance matching to a known standard but at high pressures ($>$5 Mbar) uncertainties in the EOS of that standard material (such as Aluminum) ultimately limit the accuracy of such a technique. Previous efforts to perform absolute EOS measurements using time-resolved x-ray radiography were limited by the extreme precision required to measure shock and particle velocities at such high compressions. We present results from experiments on the OMEGA Laser System that employ a new technique designed to achieve direct \underline {density} measurements in a shock wave. Side-on radiography using point-projection imaging ($\sim $5-keV x rays) is used to produce a snapshot of the expanding shock wave; this 2-D image is then tomographically inverted to determine the density profile behind the shock front. By simultaneously measuring the shock velocity using VISAR, absolute equation-of-state points are determined. This technique conveniently scales to measurements on higher-$Z$ materials using harder x rays from an intense short-pulse laser. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460, the U. of Rochester, and the NYSEDA. [Preview Abstract] |
Tuesday, August 2, 2005 5:15PM - 5:30PM |
L3.00008: Experimental Measurement of Compressibility, Temperature and Light Absorption in Dense Shock-Compressed Gaseous Deuterium Mikhail Zhernokletov In this work, gaseous deuterium with a high initial density, close to the density of liquid deuterium, was chosen as the object of investigation. The use of gaseous deuterium was dictated by the possibility of obtaining its initial parameters with a high certainty, because they are fully determined by the initial gas pressure and temperature. For tests with gaseous deuterium at high initial pressure (1500-2000 atm), we developed and manufactured capsules using steel of high strength and resistance in hydrogen atmosphere. In their geometrical sizes, the capsules correspond to hemispherical generator of shock waves, which is capable to provide pressures of $\approx $ 1.3 TPa in iron. Using the hemispherical generator of shock waves in two experiments under pressures of $\approx $83 GPa and 93 GPa in shock compressed gaseous deuterium, we measured density $\rho $=0.64 g/cm$^{3}$ and 0.70 g/cm$^{3}$, temperature T=23000 K and 24100 K, and light absorption up to 70 cm$^{-1}$\underline { } [Preview Abstract] |
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