Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K38: Materials in Extremes: Dynamic CompressionFocus
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Sponsoring Units: DCOMP GSCCM DMP Chair: D. Swift, Lawrence Livermore National Laboratory Room: LACC 501A |
Wednesday, March 7, 2018 8:00AM - 8:12AM |
K38.00001: Ultrafast shock experiments on cryogenic liquid carbon monoxide Michael Armstrong, Joseph Zaug, Nir Goldman, Rebecca Lindsey, Sorin Bastea Shock waves propagating in organic compounds are known to induce chemical processes that lead to the formation of small, stable molecules, but for materials that have a negative oxygen balance condensed carbon is also thermodynamically favored. Indeed, self-propagating shocks (detonations) in most organic explosives produce "soot" in the form of nanocarbon polymorphs. Further, simulations are well suited to ultrafast laser-driven shock methods which can obtain hydrodynamic data over micron length- and picosecond-time scales. For ultrafast methods, sample preparation may be substantially simplified compared to large scale experiments, and ultrafast shock compression has high throughput. Here we will present results of ultrafast shock experiments in cryogenic liquid CO in a modified, commercial cryostat. These experiments allow us to obtain velocimetry data for many shots in a single cryostat load, and recovery of compression products. Our experimental results may be compared to DFT force-matched molecular mechanics simulations at substantially larger scale than conventional DFT. |
Wednesday, March 7, 2018 8:12AM - 8:24AM |
K38.00002: Early Stage Chemistry in Shock Compressed Carbon Monoxide: Development and Application of the ChIMES Model Rebecca Lindsey, Nir Goldman, Laurence Fried, Sorin Bastea The formation of carbon condensates, or “soot” resulting from strong shockwave propagation in carbon-rich energetic materials can have significant implications on performance and sensitivity of energetic materials. The nucleation mechanism and distribution of these agglomerates is largely unknown, owing partially to associated time and length scales that are outside the accessible domain of standard quantum mechanics simulations, and to the lack of appropriate parameter sets for molecular mechanics based approaches. To this effect, we have developed ChIMES, a new reactive molecular dynamics force field that has been shown capable of retaining the accuracy of Kohn-Sham density functional theory while yielding orders of magnitude increases in computational efficiency and scalability. We use our ChIMES approach to study a model system of liquid CO under shock compression conditions, where current experiments are underway to study soot formation. Our results yield the possibility of a direct one-to-one comparison to these dynamic loading experiments, which could yield mechanistic and kinetic data with quantum accuracy. |
Wednesday, March 7, 2018 8:24AM - 8:36AM |
K38.00003: High-Resolution Spatial and Temporal Probing of Dynamically-Compressed Silicon using X-Ray Diffraction and Imaging Shaughnessy Brown, Haeja Lee, Eric Galtier, Arianna Gleason, Eduardo Granados, Franz Tavella, Andreas Schropp, Frank Seiboth, Christian Schroer, Emma McBride, Andrew Higginbotham, Akel Hashim, Brice Arnold, Alan Fry, Robert Nagler We present the results of tunable x-ray temporal and spatial probing of silicon under laser-driven compression at the Matter in Extreme Conditions hutch of the Linac Coherent Light Source. Using simultaneous x-ray diffraction and x-ray contrast imaging diagnostics, we identify the influence of pressure on the multiple-shockwave sequence of compression, phase transition, and melt, and we compare our in-situ, dynamic results to previous static compression data and Hugoniot relations. We examine simulated and observed mechanisms for relieving high material strains ahead of plastic deformation and discuss the kinetics of multiple-shockwave formation and propagation. Lastly, we outline future work using the upgraded 60 J, high-power laser at the MEC hutch. |
Wednesday, March 7, 2018 8:36AM - 9:12AM |
K38.00004: Resolving nanoscale dynamics with ultrafast small-angle x-ray scattering Invited Speaker: Sheng-Nian Luo X-rays allow for probing structure of matter at multiple spatial scales, ranging from phase-contrast imaging at the μm level, to small-angle x-ray scattering (SAXS) at the nanometer scale, and to diffraction at the lattice level, in such dynamic processes as phase transitions, spall damage and cavitation, fragmentation and two-phase mixing. Here we report direct SAXS simulations on the basis of atomic configurations and kinematic theory. A GPU-accelerated, massively parallel, diffraction/scattering code is developed, which can simulate systems of 1010 atoms and scattering of polychromatic x-rays. As an application case, we characterize dynamic cavitation and fragmentation of liquid jets with SAXS, considering realistic pulsed x-ray sources including synchrotron radiation and x-ray free-electron lasers. The simulations supply a useful guide for measurement and interpretation of SAXS experiments with advanced light sources, including non-ideal scenarios of anisotropy, dispersity, superlattice, and complex x-ray spectrum. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K38.00005: Off-Hugoniot mechanical response of metal standards at the Z machine Jean-Paul Davis, Justin Brown, Christopher Seagle Static and dynamic compression experiments have historically used simple metals as standards; examples include Au and Pt in diamond-anvil cell work, Al and Cu electrodes in magnetically-driven experiments, and, more recently, Pt and Ir pushers in shock-ramp experiments at Sandia’s Z machine. These materials’ mechanical equations of state at low temperature have traditionally been deduced from shock Hugoniot measurements, a procedure that has limited accuracy at pressures > 100 GPa due to shock melting. To validate existing models, and stimulate the creation of new models, we have begun a systematic study at the Z machine of metal standards under far off-Hugoniot dynamic compression loading using shockless and shock-ramp techniques to peak stresses > 300 GPa, including measurements of strength under release from shocklessly-compressed states. After a brief introduction to the experimental approach, results and comparison to models will be presented for two or more metals. |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K38.00006: Time-dependence for the Compression of Heterogeneous Mixtures Far From Equilibrium Jonathan Belof, Philip Myint, Lorin Benedict The dynamic material properties of real materials depend crucially upon the thermodynamics of the composite system. For systems of heterogeneous composition, or those far from a state of equilibrium, the characteristic feature is the presence of interfaces. Material interfaces present new challenges to the theory and simulation of dynamic materials processes, given the need to go beyond the assumption of pressure and temperature equilibrium typically employed for the description of bulk material mixtures. We present here a new approach to the hydrodynamic simulation of a composite system out-of-equilibrium, containing pressure and temperature gradients due to an interface. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K38.00007: Equation of state measurements in the Gbar regime Damian Swift, Amy Lazicki, Natalie Kostinski, Alison Saunders, Federica Coppari, Andrea Kritcher, Tilo Doeppner, Roger Falcone, Joseph Nilsen We are developing laser-driven loading platforms that allow the equation of state (EOS) of matter to be measured at pressures of up to several tens of terapascals (hundreds of megabars). For low-Z samples, measurements can be made using radiography of a spherically-converging shock, which allows a range of pressures to be probed in each experiment and yields absolute states on and near the shock Hugoniot. For higher-Z samples, a conically-converging shock produces a Mach wave which can be used for shock measurements relative to a standard material by impedance-matching. Pressures achievable at the OMEGA laser facility and National Ignition Facility are high enough to explore the effects of ionizing successive electron shells. Results so far suggest that the Thomas-Fermi model is not adequate and shell effects appear to be significant, though the measurements do not appear entirely consistent with average-atom treatments of high temperature EOS. |
Wednesday, March 7, 2018 9:48AM - 10:24AM |
K38.00008: The Temperature of Fe at 3 Mbar Invited Speaker: Minta Akin We report on progress toward converting the measured surface temperature (T) of Fe at ~3 Mbar (near melt, on the Hugoniot) into a bulk temperature measurement as part of an effort to obtain a complete equation of state for Fe. Fe was directly coated on a LiF tamping window and shock compressed using a two-stage light gas gun. Radiance and reflectance were simultaneously measured from ~350-750 nm using four streak spectrometers. T was determined through comparison of reflected and emitted light, allowing us to calculate emissivity as a function of wavelength to correct graybody emission. We will also present results from 2D hydro simulations including heat transport, release wave propagation, and sensitivity to Fe/LiF material properties. |
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K38.00009: First-principles equations of state and shock compression predictions of carbon- and boron-materials Shuai Zhang, Burkhard Militzer, Heather Whitley Carbon- and boron-materials are important ablators in shock compression experiments for extreme physics and planetary studies. Accurate, wide-range equations of state (EOS) of these materials are crucial for interpreting the experiments and guiding the design of targets in inertial confinement fusion. In this talk, we present our latest results for a series of low-Z materials: CH, B, B4C, and BN. We obtain coherent EOS by combining path integral Monte Carlo and quantum molecular dynamics simulations. We predict shock compression profiles to be compared with ongoing laser shock experiments on both conventional and gigabar platforms at NIF and OMEGA facilities. We compare with empirical EOS models based on Thomas-Fermi and Debye-Hückel theories. We study the compression maxima in detail and provide physical explanations of their origin by investigating the thermal and pressure-driven ionization processes. We also examine the sensitivity of the fusion yield to the ablator EOS in radiation-hydrodynamic simulations. These results from our first-principles simulations may be useful to benchmark future EOS calculations and offer means to systematically improve existing EOS models. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K38.00010: Shock Compression of Strongly-Correlated Oxides: A Liquid-Regime Equation of State for Cerium(IV) Oxide Philippe Weck, Kyle Cochrane, Seth Root, J. Matthew Lane, Luke Shulenburger, John Carpenter, Thomas Mattsson, Tracy Vogler The shock Hugoniot for full-density and porous CeO2 was investigated in the liquid regime using ab initio molecular dynamics (AIMD) simulations with Erpenbeck's approach based on the Rankine-Hugoniot jump conditions. The phase space was sampled by carrying out NVT simulations for isotherms between 6,000 and 100,000 K and densities ranging from ρ = 2.5 to 20 g/cm3. The impact of on-site Coulomb interaction corrections +U on the EOS obtained from AIMD simulations was also assessed by comparison with standard DFT results. Results from dynamic compression simulations compare favorably with recent Z-machine shock data to 525 GPa and gas-gun data to 109 GPa for porous CeO2 samples. |
Wednesday, March 7, 2018 10:48AM - 11:00AM |
K38.00011: Numerical Evaluation of a Multiscale Friction Model Marvin Zocher, James Hammerberg A set of experiments designed to produce dry sliding of metal-on-metal resulting in normal pressures up to 10 GPa and sliding velocities up to 400 m/s are simulated numerically for the purpose of evaluating a multiscale friction model. These experiments involve the impact of a cylindrical copper flyer onto a composite cylindrical target composed of an aluminum inner core and a stainless steel circumferential confinement. The primary diagnostic in these experiments is a measurement of free-surface velocity. The numerical simulation is conducted using the Los Alamos continuum mechanics code FLAG. The primary metric of evaluation is a comparison of predicted free-surface velocities to those measured. The importance of accounting for friction in the simulation of these experiments is clearly demonstrated. It is shown that the FLAG implementation of the multiscale friciton model provides capabilities that are essential in the modeling of dry sliding friction. |
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