Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session H5: Equation of State VI: Ramp Compression |
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Chair: William Anderson, Los Alamos National Laboratory, Jim Hawreliak, Washington State University Room: Grand I/J |
Tuesday, June 16, 2015 9:15AM - 9:30AM |
H5.00001: Results from New Multi-Megabar Shockless Compression Experiments at the Z Machine Jean-Paul Davis, Justin Brown, Marcus Knudson Quasi-isentropic, shockless ramp-wave experiments promise accurate equation-of-state (EOS) data in the solid phase at relatively low temperatures and multi-megabar pressures. In this range of pressure, isothermal diamond-anvil techniques have limited pressure accuracy due to reliance on theoretical EOS of calibration standards, thus accurate quasi-isentropic compression data would help immensely in constraining EOS models. Multi-megabar shockless compression experiments using the Z Machine at Sandia as a magnetic drive with stripline targets have recently been improved. New developments will be presented in the design and analysis of these experiments, including topics such as 2-D and magneto-hydrodynamic (MHD) effects and the use of LiF windows. Results will be presented for selected metals, with comparisons to independently developed EOS. *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, June 16, 2015 9:30AM - 9:45AM |
H5.00002: Multi-Mbar Ramp Compression of Copper Rick Kraus, Jean-Paul Davis, Christopher Seagle, Dayne Fratanduono, Damian Swift, Jon Eggert, Gilbert Collins The cold curve is a critical component of equation of state models. Diamond anvil cell measurements can be used to determine isotherms, but these have generally been limited to pressures below 1 Mbar. The cold curve can also be extracted from Hugoniot data, but only with assumptions about the thermal pressure. As the National Ignition Facility will be using copper as an ablator material at pressures in excess of 10 Mbar, we need a better understanding of the high-density equation of state. Here we present ramp-wave compression experiments at the Sandia Z-Machine that we have used to constrain the isentrope of copper to a stress state of nearly 5 Mbar. We use the iterative Lagrangian analysis technique, developed by Rothman and Maw, to determine the stress-strain path. We also present a new iterative forward analysis (IFA) technique coupled to the ARES hydrocode that performs a non-linear optimization over the pressure drive and equation of state in order to match the free surface velocities. The IFA technique is an advantage over iterative Lagrangian analysis for experiments with growing shocks or systems with time dependent strength, which violate the assumptions of iterative Lagrangian analysis. [Preview Abstract] |
Tuesday, June 16, 2015 9:45AM - 10:00AM |
H5.00003: Non-iterative determination of the stress-density relation from ramp wave data Damian Swift, Dayne Fratanduono, Richard Kraus In the canonical ramp compression experiment, a smoothly-increasing load is applied the surface of the sample, and the particle velocity history is measured at interfaces two or more different distances into the sample. The velocity histories are used to deduce a stress-density relation, usually via the iterative Lagrangian analysis technique of Rothman and Maw. In this technique, a stress-density relation is assumed, and is adjusted until characteristics propagated back from the step interfaces give a self-consistent load within the sample. This process is subject to the usual difficulties of nonlinear optimization, such as the existence of local minima (sensitivity to the initial guess), possible failure to converge, and relatively large computational effort. We show that, by considering the interaction of successive characteristics reaching the interfaces, the stress-density relation can be deduced directly by recursion rather than iteration. This calculation is orders of magnitude faster than iterative analysis, and does not require the solution to be guessed. Direct recursion may be less suitable for very noisy data, but it was robust when applied to trial data. The stress-density relation deduced was identical to the result from iterative Lagrangian analysis. [Preview Abstract] |
Tuesday, June 16, 2015 10:00AM - 10:15AM |
H5.00004: Determining the phase diagram of lithium via ab initio calculation and ramp compression Luke Shulenburger, Chris Seagle, Thomas Haill, Eric Harding Diamond anvil cell experiments have shown elemental lithium to have an extraordinarily complex phase diagram under pressure exhibiting numerous solid phases at pressures below 1 Mbar, as well as a complicated melting behavior. We explore this phase diagram utilizing a combination of quantum mechanical calculations and ramp compression experiments performed on Sandia National Laboratories' Z-machine. We aim to extend our knowledge of the high pressure behavior to moderate temperatures at pressures above 50 GPa with a specific focus on the melt line above 70 GPa. [Preview Abstract] |
Tuesday, June 16, 2015 10:15AM - 10:30AM |
H5.00005: Structure of Molybdenum Under Dynamic Compression to 1 TPa Thomas Duffy, Jue Wang, Federica Coppari, Raymond Smith, Jon Eggert, Amy Lazicki, Dayne Fratanduono, Ryan Rygg, Thomas Boehly, Gilbert Collins Molybdenum (Mo) is a refractory 4d transition metal that is widely used as a standard in static and dynamic high-pressure experiments. However, there are significant unanswered questions and unresolved discrepancies about the melting curve and high-pressure phase stability of this fundamental material. Similar questions surround the melting curve and phase stabilities of other transition metals including Ta and Fe, and so a better understanding of Mo has broad implications for high-pressure science and geophysics.~Here we use x-ray diffraction to determine the crystal structure of molybdenum under both shock and ramp compression to pressures as high as 1 TPa. Under shock loading, we find that Mo remains in body centered cubic (BCC) structure until melting begins at near 390 GPa. Our results are in good agreement with recent theoretical calculations and recent re-measurement of sound speeds along the Hugoniot. We also carried out x-ray diffraction measurements of ramp-loaded molybdenum up to 1050 GPa. Our x-ray diffraction patterns are consistent with the persistence of the BCC phase up to the highest pressure achieved. The measured densities under ramp loading are intermediate between those achieved under shock compression and those expected from extrapolation of room-temperature data. We do not observe evidence for the theoretically predicted transition to face centered cubic or double hexagonal close packed phases above 600 GPa. [Preview Abstract] |
Tuesday, June 16, 2015 10:30AM - 10:45AM |
H5.00006: In-Situ Diffraction on the National Ignition Facility (NIF) Jon Eggert, Dave Braun, Ryan Rygg, Amy Lazicki, Dayne Fratanduono, Ray Smith, Federica Coppari, Rick Kraus, Damian Swift, Jim McNaney, Yuan Ping, Kerri Blobaum, Mike Wilson, Marium Ahmed, Gilbert Collins, Tom Arsenlis Ramp compression experiments have opened a path toward the measurement of extreme states of compression for solid-state materials on lasers, pulsed power, and gas guns. While most experiments have measured wave profiles as an integrated probe of the material state, there is a trend toward making direct measurements of the material state in situ using diffraction, phase-contrast imaging, EXAFS, and XANES. This past year we succeeded in obtaining high-quality diffraction on the NIF using the TARget Diffraction In Situ (TARDIS) diagnostic. I will present some of our NIF results on lead and tantalum, including the prospects for determining not only structure, density, and stress, but also temperature and grain size in these experiments. I will close with future plans for further improving TARDIS. [Preview Abstract] |
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