Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session JI3: Fundamental HED ScienceInvited
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Chair: Robert Cauble, Lawrence Livermore National Laboratory Room: Oglethorpe Auditorium |
Tuesday, November 17, 2015 2:00PM - 2:30PM |
JI3.00001: High-Energy Density science with an ultra-bright x-ray laser Invited Speaker: Siegfried Glenzer This talk will review recent progress in high-energy density physics using the world's brightest x-ray source, the Linac Coherent Light Source, SLAC's free electron x-ray laser. These experiments investigate laser-driven matter in extreme conditions where powerful x-ray scattering and imaging techniques have been applied to resolve ionic interactions at atomic ({\AA}ngstrom) scale lengths and to visualize the formation of dense plasma states. Major research areas include dynamic compression experiments of solid targets to determine structural properties and to discover and characterize phase transitions at mega-bar pressures. A second area studies extreme fields produced by high-intensity radiation where fundamental questions of laboratory plasmas can be related to cosmological phenomena. Each of these areas takes advantage of the unique properties of the LCLS x-ray beam. They include small foci for achieving high intensity or high spatial resolution, high photon flux for dynamic structure factor measurements in single shots, and high spectral bandwidth to resolve plasmon (Langmuir) waves or ion acoustic waves in dense plasmas. We will further describe new developments of ultrafast pump-probe technique at high repetition rates. These include studies on dense cryogenic hydrogen that have begun providing fundamental insights into the physical properties of matter in extreme conditions that are important for astrophysics, fusion experiments and generation of radiation sources. [Preview Abstract] |
Tuesday, November 17, 2015 2:30PM - 3:00PM |
JI3.00002: Thermal transport measurements in high-energy-density matter Invited Speaker: Yuan Ping Thermal conductivity is one of the most fundamental physical properties of matter. It determines the heat transport rate and has an enormous impact on a variety of mechanical, electrical, chemical, and nuclear systems. Thermal conduction is important in high energy density (HED) matter such as laboratory fusion plasmas, planetary cores, compact stars, and other celestial objects. Examples are in the ablation and instability growth in inertial confinement fusion (ICF) capsules, in energy loss from ICF hot spot, and in the evolution of Earth's core-mantle boundary. Despite the importance of thermal conductivity in HED systems, experimental measurements under relevant conditions are scarce and challenging. We have developed a method of differential heating for thermal conductivity measurements. In this talk, experimental designs will be described for four different platforms: optical laser heating, proton heating, laser-generated x-ray heating and XFEL heating. Data from various facilities will be presented and comparison with models will be discussed. [Preview Abstract] |
Tuesday, November 17, 2015 3:00PM - 3:30PM |
JI3.00003: Non-equilibrium Warm Dense Gold: Experiments and Simulations Invited Speaker: Andrew Ng This talk is an overview of a series of studies of non-equilibrium Warm Dense Matter using a broad range of measured properties of a single material, namely Au, as comprehensive benchmarks for theory. The measurements are made in fs-laser pump-probe experiments. For understanding lattice stability, our investigation reveals a solid phase at high energy density. This leads to the calculation of lattice dynamics using MD simulations and phonon hardening in DFT-MD simulations. For understanding electron transport in two-temperature states, AC conductivity is used to evaluate DFT-MD and Kubo-Greenwood calculations while DC conductivity is used to test Ziman calculations in a DFT average atom model. The electron density is also used to assess electronic structure calculations in DFT simulations. In our latest study of electron kinetics in states with a non-Fermi-Dirac distribution, three-body recombination is found to have a significant effect on electron thermalizaiton time. This is driving an effort to develop electron kinetics simulations using the Boltzmann equation method. [Preview Abstract] |
Tuesday, November 17, 2015 3:30PM - 4:00PM |
JI3.00004: Measurements of Ion Stopping around the Bragg Peak in High-Energy-Density Plasmas Invited Speaker: Johan Frenje Over the last few decades, ion stopping in weakly- to strongly-coupled High-Energy-Density (HED) plasmas has been subject to extensive analytical and numerical studies, but only a limited set of experimental data exists to check the validity of these theories. Most of these experiments also did not probe the detailed characteristics of the Bragg peak (peak ion stopping) where the ion velocity is similar to the average thermal electron velocity. To the best of our knowledge, only one exploratory attempt to do this was conducted by Hicks et al.,\footnote{D. G. Hicks et al., Phys. Plasmas 7, 5106 (2000).} who were able to describe qualitatively the behavior of the Bragg peak for one plasma condition. The work described in this presentation makes significant advances over previous experimental efforts by quantitatively assessing the characteristics of the ion stopping, ranging from low-velocity stopping, through the Bragg peak, to high-velocity stopping for different HED plasma conditions. This was achieved by measuring the energy loss of DD-tritons, D$^{\mathrm{3}}$He-alphas, DD-protons and D$^{\mathrm{3}}$He-protons, with distinctly different velocities, and the results indicate that the stopping power varies strongly with T$_{\mathrm{e}}$ and n$_{\mathrm{e}}$. This effort represents the first experimental test of state-of-art plasma-stopping-power theories around the Bragg peak, which is an important first step in our efforts of getting a fundamental understanding of DT-alpha stopping in HED plasmas, a prerequisite for understanding ignition margins in various implosion designs with varying hot spot areal density at the National Ignition Facility. [Preview Abstract] |
Tuesday, November 17, 2015 4:00PM - 4:30PM |
JI3.00005: Properties of MgO to 1.2 TPa from high-precision experiments on Sandia's Z machine and first-principles simulations using QMC and DFT Invited Speaker: Luke Shulenburger MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine the phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility a low entropy solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. The calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties requires particular care because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. Finally, understanding the behavior of MgO as the pressure releases from the Hugoniot state is a key ingredient to modeling giant impact events. We explore this regime both through additional DFT calculations and by observing the release state of the MgO into lower impedance materials. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, November 17, 2015 4:30PM - 5:00PM |
JI3.00006: Rankine-Hugoniot experiments with unsteady waves: A new technique to measure the material sound speed and Gruneisen parameter Invited Speaker: Dayne Fratanduono Recent development of transparent shock wave standard materials, such as quartz, enables continuous tracking of shock waves using optical velocimetry, providing information on shock wave steadiness and pressure perturbations in the target. From a first order perturbation analysis, we develop a set of analytical formulas that connect the pressure perturbations at the drive surface to the shock velocity perturbations observed in measurements. With targets that incorporate a calibrated transparent witness material, such as quartz, and with the analytical formulas describing the perturbation response, it is possible to determine the sound speed and Gruneisen coefficient of an unknown sample by using evolution of the non-steady perturbations as a probe. These formulas are used to improve the accuracy of traditional shock wave impedance match Hugoniot experiments of opaque samples driven with non-steady waves. The method is well suited for use in laser-based Hugoniot experiments where the shock waves can be unsteady, with fluctuations and/or accelerating or decelerating trends. We apply this technique to recent laser-based Hugoniot measurements and the results are presented. The sound speed of deuterium and ICF ablators has been measured using this technique and are presented [Preview Abstract] |
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