Session 12HE: Laboratory Studies of Dense Matter I

X-ray diffraction from shocked materials: investigating solid-solid phase transitions

X-ray diffraction on nanosecond and sub-nanosecond time-scales has proven to be a useful tool in investigating the transient response of shocked crystals. Perhaps the most notable success in this area has been the direct observation of the $\alpha - \epsilon$ transition in laser-shocked single crystals of [001] iron. [1,2] The information extracted from the diffraction patterns has been shown to be in remarkable agreement with multi-million atom molecular dynamics calculations. [3] Having successfully observed the transition in single crystals shocked along the principal axis, several further challenges remain. Amongst these are the exploration of the response of single crystals to shocks propagating along other crystallographic directions (where significantly different response is predicted [4]) the role of pre-existing defects in the time-scale of the elastic/plastic response of the material, and any differences that may occur in polycrystalline compared with single crystal samples.[5] A further challenge will be the development of rapid compression techniques that take samples to off-Hugoniot states (for example so-called quasi-isentropic compression). If such states can be produced in a controlled way, much could potentially be learnt about the state of certain planetary cores, including our own. [1] D.H. Kalantar, J.F. Belak, G.W. Collins, J.D. Colvin, H.M. Davies, J.H. Eggert, T.C. Germann, J. Hawreliak, B.L. Holian, K. Kadau, P.S. Lomdahl, H.E. Lorenzana, M.A. Meyers, K. Rosolankova, M.S. Schneider, J. Sheppard, J.S. Stolken and J.S. Wark, Phys. Rev. Lett., {\bf 95} 075502, 2005 [2] J. Hawreliak, J.D. Colvin, J.H.Eggert, D. Kalantar, H.E. Lorenzana, J.S. St\"olken, H.M. Davies, T.C. Germann, B.L. Holian, K. Kadau, P.S. Lomdahl, A. Higginbotham, K. Rosolankova, J. Sheppard, and J.S. Wark, Phys. Rev. B, {\bf 74}, 184107, 2006 [3] K. Kadau, Timothy C. Germann, Peter S. Lomdahl, and Brad Lee Holian, Science, {\bf {296}}, 1681, 2002 [4] Kai Kadau, Timothy C. Germann, Peter S. Lomdahl, and Brad Lee Holian, Phys. Rev. B, {\bf {72}}, 064120, 2005 [5] K. Kadau, T.C. Germann, P.S. Lomdahl, R.C. Albers, R.C. J.S. Wark, A. Higginbotham, and B.L. Holian, Phys. Rev. Lett. Phys. Rev. Lett. {\bf{98}}, 135701 (2007)   

Creating and probing matter compressed and heated by shock waves on OMEGA

A physical understanding of the energy transport from the laser-deposition region to the target is required for many laser-driven, high-energy-density experiments and to achieve energy gain with inertial confinement fusion. Direct-drive target-physics experiments are initiated by the ablation of material from the outside surface of the target with intense laser beams. The ablated shell mass forms a coronal plasma that can accelerate the target via the rocket effect. Laser absorption occurs in the underdense corona via inverse bremsstrahlung and the energy is transported by electrons to the ablation surface. The ablation process launches shock waves into the target that set the target on the desired isentrope. Using a planar target geometry, time-resolved Al 1$s$--2$p$ absorption spectroscopy is used to probe shock-heated and compressed matter on OMEGA. The measured Al absorption spectra were modeled with the atomic physics code \textit{PrismSPECT} [Prism Computational Sciences, Inc., Madison, WI 53711] to infer the $T_{e}$ and $n_{e }$of the nearly Fermi-degenerate matter ($T_{e} \quad \sim $ 10 to 30 eV, $n_{e} \quad \sim $ 1 to 6 $\times $ 10$^{23}$~cm$^{-3})$. Detection of low charge states (i.e., F, O, N, C) indicates the 10- to 50-Mbar shock wave has transited an Al layer buried in a CH target, while evidence of even higher charge states indicates the arrival of the heat front. Simulations of the shock heating and heat-front penetration, performed with the 1-D hydrodynamics code \textit{LILAC} [J. Delettrez \textit{et al.}, Phys. Rev. A \textbf{36}, 3926 (1987)] using a nonlocal transport model, are close to the measured results. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. *In collaboration with H. Sawada, D. D. Meyerhofer, P. B. Radha, J. A. Delettrez, R.~Epstein, V. N. Goncharov, D. Li, V. A. Smalyuk, T. C. Sangster, and B. Yaakobi, \textit{UR/LLE}; R. C. Mancini, \textit{UNR}