Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session J2: CM.4 Warm Dense Matter I |
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Chair: Damian Swift, Lawrence Livermore National Laboratory Room: Grand Ballroom II |
Tuesday, July 9, 2013 11:00AM - 11:15AM |
J2.00001: Two-temperature hydrodynamics of laser-generated ultrashort shock waves in elasto-plastic solids Denis Ilnitsky, Viktor Khokhlov, Nail Inogamov, Yurii Petrov, Vasily Zhakhovsky, Kirill Migdal, Sergey Anisimov Femtosecond laser is a unique tool for generation of ultrashort shock waves producing very high deformation rates in target materials. It was recently found in experiment [1] and molecular dynamics (MD) simulation [2] that in splitting two-wave regime the elastic precursor can have longitudinal stress nearly 30 times as large as the conventional Hugoniot elastic limit. To study different regimes of shock-wave propagation including generation, interaction, and attenuation of leading super-elastic shock and following plastic wave, we developed an elasto-plastic model of solid combined with its EoS. Response of the model to ultrafast deposition of laser energy was simulated using our two-temperature hydrodynamics (2T-HD) code, which takes into account nonequilibrium of electron and ion subsystems and significant electron pressure at early stage of evolution. Results of 2T-HD simulation of plastic and super-elastic shock-wave propagation in Al and Ni at later stage are in good agreement with corresponding MD simulations. Simulation results are discussed and compared with recent experimental observations of high-speed super-elastic shock waves.\\[4pt] [1] S. I. Ashitkov, M. B. Agranat, G. I. Kanel', et al, JETP Letters, \textbf{92}, 516 (2010) \\[0pt] [2] V. V. Zhakhovskii and N. A. Inogamov, JETP Letters, \textbf{92}, 521 (2010) [Preview Abstract] |
Tuesday, July 9, 2013 11:15AM - 11:30AM |
J2.00002: Crystal-like and plasma-like properties of the two-temperature WDM Vladimir Stegailov, Genri Norman, Sergey Starikov The two-temperature warm dense matter (WDM) is produced for short times at the interaction of fs and ps laser radiation with solid surfaces, propagation of a fast ion through condensed matter and at some other advanced experiments. The theory of such transient nonequilibrium WDM states is a challenging problem since electron temperature is about several eV, but ions remain to be cold and keep original crystallographic positions for several ps. Therefore the band structure survives but electron and phonon energy dispersions are changed due to the inverse influence of the electron excitation. Ion cores survive as well but their inner shells are partially excited and their populations follow plasma behavior. So the temporary WDM states considered demonstrate both crystal and plasma features like a crystal-plasma ``centaur.'' The methods of molecular dynamics and collisional-radiative kinetics are used to investigate the plasma properties of WDM. The transient but steady (quasi-stationary for a short time) state of non-equilibrium, uniform electron plasmas can be both strongly and weakly coupled. X-ray spectral lines are emitted by ion cores embedded in electron plasma environment which influences the spectra strongly. [Preview Abstract] |
Tuesday, July 9, 2013 11:30AM - 11:45AM |
J2.00003: Equation of state measurement of shock-released carbon Katerina Falk, John F. Benage, Robert G. Watt, David S. Montgomery, James R. Williams, Derek W. Schmidt, Eliseo J. Gamboa, Paul A. Keiter, R. Paul Drake, Chad McCoy, Tom R. Boehly We present results of equation of state (EOS) measurement of carbon at a range of conditions falling into the warm dense matter (WDM) regime, solid density at temperatures $\sim 1-10$ eV. These conditions were created within diamond and graphite targets at the Omega laser facility. We employed a novel technique of laser driven shock and release, which produces different conditions from the Hugoniot states typically studied at high power laser facilities. These experiments take advantage of precise equation of state (EOS) measurements of shocked low density SiO$_2$ aerogel foam used as pressure standard, which will also be presented. A simultaneous measurements of density, temperature and ionization state within the release wave were obtained from spatially resolved x-ray Thomson scattering, while the density and temperature measurements were bracketed by independent diagnostics including velocity interferometry, optical pyrometry and radiography, providing a full EOS measurement. Results will be compared with EOS models. [Preview Abstract] |
Tuesday, July 9, 2013 11:45AM - 12:00PM |
J2.00004: Variational Perturbation Theory Path Integral Monte Carlo (VPT-PIMC): Trial Path Optimization Approach for Warm Dense Matter Jonathan Belof, Jonathan DuBois Warm dense matter (WDM), the regime of degenerate and strongly coupled Coulomb systems, is of great interest due to it's importance in understanding astrophysical processes and high energy density laboratory experiments. Path Integral Monte Carlo (PIMC) presents a particularly attractive formalism for tackling outstanding questions in WDM, in that electron correlation can be calculated exactly, with the nuclear and electronic degrees of freedom on equal footing. Here we present an efficient means of solving the Feynman path integral numerically by variational optimization of a trial density matrix, a method originally proposed for simple potentials by Feynman and Kleinert [Bachmann \emph{et al.}, \emph{Phys. Rev. A.}, 60:3429 (1999)], and we show that this formalism provides an accurate description of warm dense matter with a number of unique advantages over other PIMC approaches. An exchange interaction term is derived for the variationally optimized path, as well as a numerically efficient scheme for dealing with long-range electrostatics. Finally, we present results for the pair correlation functions and thermodynamic observables of the spin polarized electron gas, warm dense hydrogen and all-electron warm dense carbon within the presented VPT-PIMC formalism. [Preview Abstract] |
Tuesday, July 9, 2013 12:00PM - 12:30PM |
J2.00005: Theoretical Predictions of Phase Transitions at Ultra-high Pressures Invited Speaker: Brian Boates We present ab initio calculations of the high-pressure phase diagrams of important planetary materials such as CO2, MgSiO3, and MgO. For CO2, we predict a series of distinct liquid phases over a wide pressure (P) and temperature (T) range, including a first-order transition to a dense polymer liquid. We have computed finite-temperature free energies of liquid and solid CO2 phases to determine the melting curve beyond existing measurements and investigate possible phase separation transitions. The interaction of these phase boundaries with the mantle geotherm will also be discussed. Furthermore, we find evidence for a vast pressure-temperature regime where molten MgSiO3 decomposes into liquid SiO2 and solid MgO, with a volume change of approximately 1.2 percent. The demixing transition is driven by the crystallization of MgO ? the reaction only occurs below the high-pressure MgO melting curve. The predicted transition pressure at 10,000 K is in close proximity to an anomaly reported in recent laser-driven shock experiments of MgSiO3. We also present new results for the high-pressure melting curve of MgO and its B1-B2 solid phase transition, with a triple point near 364 GPa and 12,000 K. [Preview Abstract] |
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