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 Y3: High Energy Density Physics/Warm Dense Matter II |
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Chair: Peter Celliers, Lawrence Livermore National Laboratory Room: Hyatt Regency Constellation D |
Friday, August 5, 2005 8:00AM - 8:15AM |
Y3.00001: Insulator-conductor transitions at multi-Mbar pressures G.W. Collins, P. Loubeyre, S. Brygoo, R.S. McWilliams, P.M. Celliers, D.G. Hicks, T.R. Boehly, D.K. Bradley, R. Jeanloz, J. Eggert At high enough shock pressures all materials become conductors. How do wide band gap insulators transition from insulator to conductor (IC) at very high shock pressures? Is there a metal-insulator transition, a plasma-phase transition, or just a continuous thermal ionization? We have measured the optical reflectance of C, H2O, SiO2, N2, D2, H2, LiF, Al2O3, and He at shock pressures up to 30 Mbar. We determine the change in electrical conductivity through the change in optical reflectance of the shock front. For highly compressible materials we can separate the density and temperature dependence for the onset of electrical conduction by varying the initial density before shock compression. The IC transition is sometimes coincident with a change in chemistry or the melt transition, but in general provides rich insight into the material's high pressure behavior. [Preview Abstract] |
Friday, August 5, 2005 8:15AM - 8:30AM |
Y3.00002: {\sl ab-initio} simulations of the time-resolved optical properties of warm dense gold. S. Mazevet, J. Clerouin, V. Recoules, P.M. Anglade, G. Zerah Recent experiments on gold suggest that the electrical and optical properties of metals in the warm dense matter regime can be accessed by performing time-resolved measurements after the illumination of a metallic thin film by a short-pulse laser[1]. The non-equilibrium situation created in this experimental setup poses new challenges to simulation methods as the time evolution of the atomic structure needs to be followed. We used a combination of classical and {\sl ab-initio} molecular dynamics simulations, to calculate the evolution of the atomic structure and the electrical conductivity of warm dense gold during the first pico-seconds after a short-pulse laser illumination. The time-resolved electrical conductivities calculated under these non-equilibrium conditions are compared with recent measurements. [1] K. Widmann, T. Ao, M.E. Foord, D.F. Price, A.D. Ellis, P.T. Springer,and A. Ng, Phys. Rev. Lett. {\bf 92}, 125002 (2004). [Preview Abstract] |
Friday, August 5, 2005 8:30AM - 8:45AM |
Y3.00003: The Color of High Energy Density Gold Y. Ping, T. Ao, H. Tam, K. Widmann, D. Price, A. Ng The study of non-equilibrium phase transitions is a rapidly developing field. Non-thermal melting has been observed in femtosecond laser heated semiconductors such as silicon. This is thought to result from the excitation of valence electrons to the conduction band, giving rise to anti-bonding states. In metals, the process of melting under ultrafast laser excitation is not clearly understood. In our experiment, we measure the broadband (400-800nm) optical reflectivity and transmissivity of freestanding, 30nm-thick gold foils heated with 150fs, 400nm laser light. Prior to laser excitation the sample shows strong reflectivity for wavelengths above 500nm. This is due to interband (d to s/p) transitions, thus giving gold its characteristic color. The reflectivity and transmissivity spectra of the heated sample (hence the color of gold) change substantially with laser excitation energy densities. Such spectral signatures offer a new means of probing electronic and structure behaviors associated with non-equilibrium phase transitions. *Work performed under the auspices of the U.S. Department of Energy by the University of California LLNL under contract \#W- 7405-ENG-48. This research was also supported by NSERC, Canada. [Preview Abstract] |
Friday, August 5, 2005 8:45AM - 9:00AM |
Y3.00004: Ionization balance measurements in low-Z materials by x-ray scattering Gianluca Gregori, S.H. Glenzer, E. Dewald, D. Hicks, O.L. Landen, T.M. Borders, H. Sawada, S.P. Regan We have measured the ionization balance of carbon/beryllium plasmas by covering both the weakly ionized and the nearly fully ionized regimes. The plasma was created by either irradiation with x-rays or direct heating with laser beams at the Omega laser facility. Using as a probe the 4.75 keV (9.0 keV) He-$\alpha $ line radiation produced by simultaneously irradiating a Ti (Zn) foil, we have recorded time-resolved spectrally dispersed scattered spectra with a high efficiency graphite Bragg crystal coupled to a framing camera. Measured values for the plasma temperature and ionization state were obtained by fitting Doppler-broadened and Compton red-shifted scattered spectra at various times after the end of the laser heating. The underlying correlations induced by a solid-state lattice at low temperature are also included in the analysis by comparison with experimental scattering spectra obtained at the Advanced Light Source on cold samples. Comparisons with radiation-hydrodynamics codes are presented. [Preview Abstract] |
Friday, August 5, 2005 9:00AM - 9:15AM |
Y3.00005: Shockless magnetic acceleration of Al flyer plates to ultra-high velocity using multi-megabar drive pressures R.W. Lemke, M.D. Knudson, D.E. Bliss, J-P. Davis, H.C. Harjes, S.A. Slutz The intense magnetic field generated in the 20 MA Z-machine is used to accelerate metallic flyer plates to high velocity for the purpose of generating strong shocks in equation of state experiments. We present results pertaining to experiments in which a 0.085 cm thick Al flyer plate is magnetically accelerated across a vacuum gap into a quartz target. Peak magnetic drive pressures up to 4.9 Mbar were produced, which yielded a record 34 km/s flyer velocity without destroying it by shock formation or Joule heating. Two-dimensional MHD simulation was used to optimize the magnetic drive pressure on the flyer surface, shape the current pulse to accelerate the flyer without shock formation (i.e., quasi-isentropically), and predict the flyer velocity. Shock pressures up to 11.5 Mbar were produced in quartz. Accurate measurements of the shock velocity indicate that a fraction of the flyer is at solid density when it arrives at the target. Comparison of measurements and simulation results yields a consistent picture of the flyer state at impact with the quartz target. [Preview Abstract] |
Friday, August 5, 2005 9:15AM - 9:30AM |
Y3.00006: Laser-Driven Shock-Timing Experiments in Planar CH and Cryogenic Deuterium Targets E. Vianello, T.R. Boehly, J.E. Miller, R.S. Craxton, V. Goncharov, I. Igumenshev, D.D. Meyerhofer, D.G. Hicks, P.M. Celliers Direct-drive inertial-confinement-fusion target designs use multiple shocks to stabilize and condition the imploding shell. The strength and timing of these shocks are critical to optimization of target designs. We present results from experiments on planar CH and cryogenic D$_{2}$ targets that use two 100-ps pulses to produce two shocks at various conditions. The velocity profiles of these shocks (from VISAR) and self-emission are used to investigate the coupling of multiple beams to the targets and to validate the ability of hydrodynamic codes to simulate multiple, laser-driven shocks. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article. [Preview Abstract] |
Friday, August 5, 2005 9:30AM - 9:45AM |
Y3.00007: Bound nucleons have unique masses that govern elemental properties Eugene Pamfiloff It is known that measured binding energies associated with elements require equivalent energy to break the nuclear bond of a nucleus. Based upon the proposals contained in recent published works [1] [2] and with support from experimental high-energy data, it can be shown that a portion of listed binding energies are attributable to bound nucleons having a unique mass for every element. The figures show, relative to the hydrogen proton, that of the: a) 1.112 MeV binding energy per nucleon for 2H, 44{\%} or 0.486 MeV represents a change in mass ($\Delta $m) for the proton or neutron; b) of 5.629 MeV binding energy per nucleon for 7Li, 87{\%} or 4.890 MeV represents a change of mass for each nucleon; c) likewise, 56Fe has 8.811 MeV binding energy per nucleon and of this 92{\%} or 8.119 MeV represents a change in mass for each nucleon, and 232Th has 7.639 MeV binding energy per nucleon and of this, 90{\%} or 6.848 MeV represents a change in mass for each nucleon. This demonstrates that the nucleons of each element have unique masses. It has been shown that if three protons are removed from 82Pb the result is not 79Au; therefore, we conclude and predict that in addition to the Z number, elemental properties are determined by the unique proton and neutron masses for each element. \href{mailto:megforce@physast.uga.edu}{megforce@physast.uga.edu} [1] ``The Order of the Forces'', [2] ``The Geatron Nuclear Model'' [Preview Abstract] |
Friday, August 5, 2005 9:45AM - 10:00AM |
Y3.00008: Experimental investigation behavior of porous media under fast volume heating Vladimir Efremov, Anton Mescheryakov, Vladimir Fortov, Boris Demidov Exact simulation of shock wave generation in porous media under powerful volume heating requires development of models of energy transformation from deposited energy to shock wave energy. Transparent nanostructural dielectric ($SiO_2$ aerogel) with density $0.04-0.25 \: g/cm^3$ was choicen as the investigated porous medium. Solid mica ($2.7\:g/cm^3$) was used for comparison. Electron beam (current 10-20~kA, energy 300~keV, duration 100~ns) was used for heating. Both aerogel and mica samples were considerable thinner than the corresponding electron stopping depths. Thin aerogel and mica plates were placed side by side and simultaneously irradiated by electron beam perpendicular to their surface for comparison of light radiation of porous and solid media. Images were recorded by fast frame cameras. Irradiated aerogel was much brighter than mica during the heating despite the equal deposited energy. Expansion velocities of aerogel and mica were measured using streak camera. Expansion velocity of mica was higher than expansion velocity of aerogal by a factor of 3. This discrepancy can be considered as a result of pore collapse immediately during the volumetric energy deposition. As a result, velocities of expansion of both porous and solid thin targets for energy density $2-10 \: kJ/g$ were measured. These data were used to obtain numerical model. [Preview Abstract] |
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