Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session H6: HED/WDM I |
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Chair: Richard Kraus, Lawrence Livermore National Laboratory Room: Regency Ballroom E |
Tuesday, July 11, 2017 9:15AM - 9:30AM |
H6.00001: X-Ray Diffraction: Shocked Crystals and Bragg's Law Justin Wark With the advent of 4$^{\rm th}$ generation light sources the technique of using x-ray diffraction to interrogate shocked crystalline samples has advanced significantly. The duration of the x-rays emitted by these remarkable machines ($<$ 100 fsec) is shorter than the period of the fastest phonons in the system, and the spectral purity and narrow divergence of the emission is vastly superior to that achievable with laser-plasma x-ray sources. One particular advantage that has been exploited in several experiments at LCLS is that the above characteristics allow the probing x-rays to be focussed to small spots, and good Debye-Scherrer diffraction patterns are regularly recorded by use of x-ray spots that are just a few tens of microns in diameter [1-3]. In this paper I will revisit some of the assumptions that are often used to estimate the form and intensity of the diffraction in these circumstances, and show that recent work dictates that some of our long-held beliefs may require rethinking [4]. [1] D. Milathianaki {\it et al}, Science, {\bf 342}, 220 (2013) [2] M.G. Gorman {\it et al}, Phys. Rev. Lett., {\bf 115}, 095701 (2015) [3] R. Briggs {\it et al}, Phys. Rev. Lett., {\bf 118}, 025501 (2017) [4] P.F. Fewster, Acta Cryst. {\bf A70}, 257 (2014) [Preview Abstract] |
Tuesday, July 11, 2017 9:30AM - 9:45AM |
H6.00002: Investigation of Release in Shocked Fibre-Textured Polycrystalline Tantalum by Use of X-Ray Diffraction M. Sliwa, D. McGonegle, C. Wehrenberg, A. Jenei, H.S. Park, R.E. Rudd, L. Zepeda-Ruiz, B.A. Remington, A. Higginbotham, C. Bolme, B. Nagler, H.-J. Lee, F. Tavella, J.S. Wark While {\it in situ} diffraction has proved extremely useful in studying dynamic compression, there have been relatively few experiments investigating shocked materials on release. We extend our previous work on plasticity mechanisms in shock compressed fibre-textured tantalum to study lattice rotation on release. By exploiting the extremely bright femtosecond X-ray pulses available on the MEC beamline at LCLS, we are able to characterise release wave-profiles by use of diffraction measurements, and compare these results with molecular dynamics simulations. [Preview Abstract] |
Tuesday, July 11, 2017 9:45AM - 10:00AM |
H6.00003: Ultrafast compression of graphite observed with sub-ps time resolution diffraction on LCLS Michael Armstrong, A. Goncharov, J. Crowhurst, J. Zaug, H. Radousky, P. Grivickas, S. Bastea, N. Goldman, E. Stavrou, J. Belof, A. Gleason, H. J. Lee, R. Nagler, N. Holtgrewe, P. Walter, V. Pakaprenka, I. Nam, E. Granados, C. Presher, B. Koroglu We will present ps time resolution pulsed x-ray diffraction measurements of rapidly compressed highly oriented pyrolytic graphite along its basal plane at the Materials under Extreme Conditions (MEC) sector of the Linac Coherent Light Source (LCLS). These experiments explore the possibility of rapid (\textless 100 ps time scale) material transformations occurring under very highly anisotropic compression conditions. Under such conditions, non-equilibrium mechanisms may play a role in the transformation process. We will present experimental results and simulations which explore this possibility. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Security, LLC under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, July 11, 2017 10:00AM - 10:15AM |
H6.00004: Laser-shock compression of silicon Norimasa Ozaki, Kohei Miyanishi, Tsung-Han Yang, Ryosuke Kodama, Youichi Sakawa, Takayoshi Sano, Kazuo A. Tanaka, Makina Yabashi We performed laser-shock compression experiments on silicon. We directly observed the shock front traveling into the Si sample using a infrared velocity interferometer coupled to a visible system, and measured the Hugoniot equation-of-state up to 500 GPa. We found a significant disagreement in the Hugoniot between the present and previous data in the solid-liquid regime. We will also discuss the recent results on X-ray diffraction observation of shock-compressed Si in the solid-solid phase transformation regime. [Preview Abstract] |
Tuesday, July 11, 2017 10:15AM - 10:30AM |
H6.00005: Learning Kinetic Monte Carlo Models of Condensed Phase High Temperature Chemistry from Molecular Dynamics Qian Yang, Carlos Sing-Long, Enze Chen, Evan Reed Complex chemical processes, such as the decomposition of energetic materials and the chemistry of planetary interiors, are typically studied using large-scale molecular dynamics simulations that run for weeks on high performance parallel machines. These computations may involve thousands of atoms forming hundreds of molecular species and undergoing thousands of reactions. It is natural to wonder whether this wealth of data can be utilized to build more efficient, interpretable, and predictive models. In this talk, we will use techniques from statistical learning to develop a framework for constructing Kinetic Monte Carlo (KMC) models from molecular dynamics data. We will show that our KMC models can not only extrapolate the behavior of the chemical system by as much as an order of magnitude in time, but can also be used to study the dynamics of entirely different chemical trajectories with a high degree of fidelity. Then, we will discuss three different methods for reducing our learned KMC models, including a new and efficient data-driven algorithm using L1-regularization. We demonstrate our framework throughout on a system of high-temperature high-pressure liquid methane, thought to be a major component of gas giant planetary interiors. [Preview Abstract] |
Tuesday, July 11, 2017 10:30AM - 10:45AM |
H6.00006: Computationally efficient optimization of radiation drives George Zimmerman, Damian Swift For many applications of pulsed radiation, the temporal pulse shape is designed to induce a desired time-history of conditions. This optimization is normally performed using multi-physics simulations of the system, adjusting the shape until the desired response is induced. These simulations may be computationally intensive, and iterative forward optimization is then expensive and slow. In principle, a simulation program could be modified to adjust the radiation drive automatically until the desired instantaneous response is achieved, but this may be impracticable in a complicated multi-physics program. However, the computational time increment is typically much shorter than the time scale of changes in the desired response, so the radiation intensity can be adjusted so that the response tends toward the desired value. This relaxed in-situ optimization method can give an adequate design for a pulse shape in a single forward simulation, giving a typical gain in computational efficiency of tens to thousands. This approach was demonstrated for the design of laser pulse shapes to induce ramp loading to high pressure in target assemblies where different components had significantly different mechanical impedance, requiring careful pulse shaping. [Preview Abstract] |
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