Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session J6: HED/WDM II |
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Chair: Damian Swift, Lawrence Livermore National Laboratory Room: Regency Ballroom E |
Tuesday, July 11, 2017 11:15AM - 11:30AM |
J6.00001: Shock-Adiabatic to Quasi-Isentropic Compression of Warm Dense Helium Jun Zheng Thermodynamic properties from shock-adiabatic to quasi-isentropic compression have been performed in the application of multiple reverberation compression technique. By this technique, the initial dense gaseous helium was compressed to warm dense matter (WDM). The experimental equation of state of WDM helium in the pressure-density-temperature range of 1-150GPa, 0.1-1.1g/cm3, and 4600-24000K were measured with higher precision. The results indicate that the values are totally enhanced by multi-compression in comparison with single-shock and isentropic-compression. The multiple compression ratios (1-10) are greatly improved from 3.5 to 43 based on initial precompressed helium density. For the relative compression ratio , a turning point occurs at the 3rd and 4th compression states under the different loading conditions, where relative compression ratio increases with pressure in lower density regime and reversely decreases in higher density regime. This anomalous phenomenon is explained for the equilibrium effect of the particle interactions at the onset of electron excitation and ionization. It induces the appearance of plasma phase transition of helium, which is verified by the contour with the experiments and the calculations. [Preview Abstract] |
Tuesday, July 11, 2017 11:30AM - 11:45AM |
J6.00002: Insulator-metal transition in dense fluid deuterium P.M. Celliers, M.A. Millot, A.F. Goncharov, P. Loubeyre, S. Brygoo, R.S. McWilliams, J.H. Eggert, J.R. Rygg, S. Le Pape, D.E. Fratanduono, S. Hamel, J.L. Peterson, N.B. Meezan, D.G. Braun, G.W. Collins, R. Jeanloz, R.J. Hemley Recent static and dynamic compression studies provide evidence for the insulator-metal transition in fluid hydrogen and deuterium at temperature T less than 2000 K but disagree on both the nature and pressure of the transition. There are also discrepancies in theoretical calculations with transition pressures spanning 120 GPa to 400 GPa at these temperatures. We present recent experiments using a reverberation compression scheme on the National Ignition Facility to compress cryogenic deuterium up to 600 GPa while keeping the temperature much lower than using single shock compression. Our optical measurements reveal a high index of refraction along with the onset of visible absorption, both arising from band gap closure ranging from 120 to 150 GPa (depending on temperature). Metallic reflectivity appears above 1000 K and 200 GPa. The results complement recent static and dynamic compression studies. [Preview Abstract] |
Tuesday, July 11, 2017 11:45AM - 12:00PM |
J6.00003: Double shocks on precompressed deuterium near the plasma phase transition Stephanie Brygoo, Marius Millot, Paul Loubeyre, Peter Celliers, Gilbert Collins, Jon Eggert, Ryan Rygg, Damian Swift, Raymond Jeanloz Despite extensive theoretical and experimental studies in the past decades, the high pressure properties of fluid hydrogen remain not very well understood in the vicinity of the predicted Plasma Phase Transition (100 to 300 GPa, 1000 to 3000 K). In particular there is a controversy of the location of the appearance of conducting/reflecting state of hydrogen. Measurements have been based up to now on laser heated static DAC and multishocks on cryo-D2. Here we present new experimental data in this regime using a combination of static precompression of deuterium to 6-12 GPa followed by double shocks up to 100-200 GPa. Analysis of the optical properties provide access to compressed deuterium electronic properties and suggest the onset of metallic-like conductivity around 200 GPa below 2000 K, in agreement with recent measurements with reverberation compression at the National Ignition Facility$^{\mathrm{1}}$ but in contrast with experiments at the Z facility$^{\mathrm{2}}$. Part of this work was performed at LLNL under Contract DE-AC52-07NA27344. $^{\mathrm{1\thinspace }}$Celliers et al, APS-SCCM 2017 $^{\mathrm{2\thinspace }}$Knudson, M. D. \textit{et al.} \textit{Science } 348\textbf{,} 1455--1460 (2015). LLNL-ABS-725307 [Preview Abstract] |
Tuesday, July 11, 2017 12:00PM - 12:15PM |
J6.00004: Dynamic Compression Experiments on Hydrogen and Deuterium in the Warm Dense Liquid. Michael Desjarlais, Chad McCoy, Kyle Cochrane, Thomas Mattsson, Marcus Knudson, Ronald Redmer Recently a shock-ramp platform has been developed on the Z Accelerator to access off-Hugoniot states in liquids. The accelerator delivers a two-step current pulse; the first accelerates the electrode to a constant velocity, which upon impact with the sample cell creates a well-defined shock, the subsequent current rise produces ramp compression from the initially shocked state producing relatively cool (1-2 kK), high pressure (\textgreater 300 GPa), high compression (10 to 15-fold compression) states. This technique allows experimental access to the region of phase space where hydrogen is predicted to undergo a first-order phase transition from an insulating molecular-like to a conducting atomic-like liquid. Here we discuss the experimental platform, survey various theoretical predictions for the liquid-liquid, insulator-to-metal transition in hydrogen, and present results of experiments on both deuterium and hydrogen that clearly show an abrupt transition to a metallic state. We also present results from recent experiments at higher temperatures (3-4 kK) and compare the observations to both first-principles theory and previous step-wise loading experiments that exhibited a minimum metallic conductivity. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, July 11, 2017 12:15PM - 12:45PM |
J6.00005: Path Integral Monte Carlo Simulations of Warm Dense Matter Invited Speaker: Burkhard Militzer In this presentation, we will give a review of path integral Monte Carlo (PIMC) simulations of warm dense matter. First we discuss earlier work on hot, dense hydrogen and helium. Then we present equation of state results for first-row elements including carbon, CH plastic, oxygen, water, nitrogen, and neon that were derived with restricted path calculations that relied on free-particle nodes. We compute shock Hugoniot curves and compare with experimental results. We describe how bound states can be incorporated efficiently into the nodal structure ("Development of Path Integral Monte Carlo Simulations with Localized Nodal Surfaces for Second-Row Elements", 115:176403, 2015), which enabled us to extend the applicability range of PIMC computations to lower temperatures and to heavier elements including sodium and silicon. We compare our PIMC-derived equation of state and plasma structure with results from Kohn-Sham and orbital-free density functional calculations. We conclude by discussing how yet heavier elements can be studied with PIMC and how additional properties can be calculated. This work was funded by the DOE (DE-SC0010517, DE-SC0016248). [Preview Abstract] |
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