Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session C6: HED: Shock and Ramp Compression I |
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Chair: Chad McCoy, SNL Room: Broadway III/IV |
Monday, June 17, 2019 11:00AM - 11:30AM |
C6.00001: Pseudo-Atom Molecular Dynamics: A model for warm and hot dense matter Invited Speaker: Didier Saumon We have developed an efficient and versatile model to describe warm and hot dense matter that couples an average atom model with the integral fluid equations for the ion correlations. This model provides all bound and free electronic states and wave functions, the interaction potentials and all correlation functions without adjustable parameters. The electrons can be described quantum mechanically (Schr\"odinger equation) or semi-classically with the Thomas-Fermi model. The ion-ion pair potential can be used in a classical molecular dynamics simulation to yield equation of state and dynamic properties of dense plasmas, including mixtures. This "pseudo-atom molecular dynamics" model, or PAMD, is more approximate than ab initio methods such as Path Integral Monte Carlo and Density-Functional-Theory Molecular Dynamics but presents distinct computational advantages. Extensions of the model allow the calculation of diffusion coefficients, viscosity, X-ray Thomson Scattering spectra, DC conductivities and opacities. We will describe the model and present comparisons with ab initio simulations and experimental data in a wide range of applications. LA-UR-19-21380 [Preview Abstract] |
Monday, June 17, 2019 11:30AM - 11:45AM |
C6.00002: Equations of state of ablator materials Shuai Zhang, Burkhard Militzer, Heather Whitley We use path integral Monte Carlo (PIMC) and density functional theory molecular dynamics (DFT-MD) to calculate equations of state (EOS) of a series of ablator materials (CHx, B, BN, and B4C) over a wide range of temperatures (0.1—10$^4$ eV) and densities (0.01—100 g/cc). We demonstrate remarkable thermodynamic consistency between the EOSs from DFT-MD calculations using different exchange-correlation functionals and those derived from PIMC with free-particle nodes. This provides strong evidence for the applicability accuracy of PIMC and DFT-MD to predict the properties of warm dense matter. Our predictions constrain the EOS to better than 4\%, with the largest uncertainties occurring at 10$^6$ K where $K$ shell starts to ionize. We study the ionic and electronic structure over a wide range of temperature, density and composition. We find the linear mixing approximation to be valid with high accuracy. We make predictions for the effects of oxygen content and C:H ratio on shock compression. We conclude by discussing other simulation methodologies and reviewing existing Hugoniot experiments across the GPa-TPa warm dense regime. By combining experimental and theoretical EOS data we construct consistent EOS tables for inertial confinement fusion and high-energy-density simulations. [Preview Abstract] |
Monday, June 17, 2019 11:45AM - 12:00PM |
C6.00003: Investigating kinetic properties of warm dense hydrocarbons in shock release experiments. James Hawreliak, Max Karasik, Jaechul Oh, Yefim Aglitskiy Kinetic processes like diffusion, viscosity, and thermal conduction are time-dependent processes governed by particle collisions at the atomic scale. These processes are the mechanism by which systems with large gradients (both in stress and temperature) reach equilibrium. Viscosity, in particular, is important in rapidly deforming systems as it provides a resistance force which depends on the rate of deformation. In this case mechanical energy is covered into thermal energy. We used the NIKE laser at the Naval Research Laboratory to determine the release velocity of shock compressed CH using time-dependent x-ray radiography. We observed that the release was significantly slower than hydrodynamic estimates assuming an isentropic release. We investigate the kinetic process that could be responsible for the observed reduction in velocity. [Preview Abstract] |
Monday, June 17, 2019 12:00PM - 12:15PM |
C6.00004: Precision Measurements of Stopping Power in Shock-Compressed Carbon J. R. Rygg, A. B. Zylstra, P. Grabowski, M. Millot, J. A. Frenje, M. Gatu-Johnson, B. Lahmann, R. D. Petrasso, F. H. Seguin, H. Sio, Y. H. Ding, S. X. Hu The slowing of energetic charged particles in matter is a sensitive probe of coupling and degeneracy effects on the Coulomb interactions, and is intimately connected to other charged-particle--transport quantities such as thermal and electrical conductivity. We will present the results of precision measurements of the stopping power of carbon, shock-compressed to 1-TPa pressure, on an isotropic source of monoenergetic 15-MeV protons. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority. [Preview Abstract] |
Monday, June 17, 2019 12:15PM - 12:30PM |
C6.00005: Crystal Structure of Ramp-Compressed Silicon up to 550 GPa Xuchen Gong, Danae Polsin, Reetam Paul, Rahul Saha, Ryan Rygg, Gilbert Collins A double-hexagonal close-packed (dhcp) phase of silicon has been recently predicted theoretically at pressures between 40 and 80 GPa. In this work, Si was ramp compressed by the OMEGA EP laser along a quasi-isentropic thermodynamic path and studied using x-ray diffraction and velocimetry. The observed diffraction pattern matches that of the dhcp phase at the predicted pressure range. Moreover, this work also studied the crystal structure of silicon at pressures up to 550 GPa; and no new phases were observed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority. [Preview Abstract] |
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