Professor Justin Wark: Publications

Simulating picosecond x-ray diffraction from shocked crystals using post-processing molecular dynamics calculations

J Phys Condens Matter 20:50 (2008)

Authors:

G Kimminau, B Nagler, A Higginbotham, WJ Murphy, N Park, J Hawreliak, K Kadau, TC Germann, EM Bringa, DH Kalantar, HE Lorenzana, BA Remington, JS Wark

Abstract:

Calculations of the patterns of x-ray diffraction from shocked crystals derived from the results of non-equilibrium molecular dynamics (NEMD) simulations are presented. The atomic coordinates predicted from the NEMD simulations combined with atomic form factors are used to generate a discrete distribution of electron density. A fast Fourier transform (FFT) of this distribution provides an image of the crystal in reciprocal space, which can be further processed to produce quantitative simulated data for direct comparison with experiments that employ picosecond x-ray diffraction from laser-irradiated crystalline targets. ? 2008 IOP Publishing Ltd.

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(2007) 227

Authors:

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Modeling Planetary Interiors in Laser Based Experiments Using Shockless Compression

Astrophysics and Space Science Springer Nature 307:1-3 (2007) 285-289

Authors:

J Hawreliak, J Colvin, J Eggert, DH Kalantar, HE Lorenzana, S Pollaine, K Rosolankova, BA Remington, J St?lken, JS Wark

A geometry for sub-nanosecond X-ray diffraction from laser-shocked polycrystalline foils

AIP Conf. Proc. 955 (2007) 1345-1348

Authors:

J Wark, A Higginbotham, G Kimminau, W Murphy, B Nagler, T Whitcher, J Hawreliak, D Kalantar, M Butterfield, B El-Dasher, J McNaney, D Milathianaki, H Lorenzana, B Remington, H Davies, L Thornton, N Park, S Lukezic

Abstract:

In situ picosecond X-ray diffraction has proved to be a useful tool in furthering our understanding of the response of shocked crystals at the lattice level. To date the vast majority of this work has used single crystals as the shocked samples, owing to their diffraction efficiency, although the study of the response of polycrystalline samples is clearly of interest for many applications. We present here the results of experiments to develop sub-nanosecond powder/polycrystalline diffraction using a cylindrical pinhole camera. By allowing the incident X-ray beam to impinge on the sample at non-normal angles, the response of grains making a variety of angles to the shock propagation direction can potentially be interrogated. ? 2007 American Institute of Physics.

Atomistic simulations of shock-induced phase transformations in polycrystalline iron

AIP Conf. Proc. 955 (2007) 313-316

Authors:

K Kadau, TC Germann, PS Lomdahl, RC Albers, JS Wark, A Higginbotham, BL Holian

Abstract:

We report on large-scale non-equilibrium atomistic simulations of shock-induced transformations in poly crystalline iron samples. These simulations show that, depending on the crystallographic orientation of the body-centered-cubic (bcc) parent phase grains with respect to the shock direction, a significant fraction of the product phase can be face-centered-cubic (fcc) instead of the expected hexagonal-close-packed (hcp) structure. This observation is explained by the existence of different transformation mechanisms for shocks along different crystallographic directions. We conclude that the observation of different product phases can be explained by simple geometric considerations of the involved transformation mechanisms between the parent bcc structure and the product hcp and fcc structures. Ultrafast high-energy laser-based experiments are underway to further investigate this subject. ? 2007 American Institute of Physics.

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