GEKKO/HIPER-driven shock waves and equation-of-state measurements at ultrahigh pressures

The GEKKO/HIPER-laser [N. Miyanaga et al., in Proceedings of the 18th International Conference on Fusion Energy (IAEA, Sorrento, Italy, 2001), IAEA-CN-77] driven shock experiments were characterized in detail for studies on equation-of-state (EOS) at ultrahigh pressures. High-quality shock waves were produced with the bundled 9 laser beams optically smoothed by spectral dispersion technique and Kinoform phase plates. The laser beams were directly focused on targets at up to an intensity of 10(14) W/cm(2) or higher with a wavelength of 351 nm and a duration of 2.5 us. Key issues on dynamic EOS research; the spatial uniformity and temporal steadiness of shock wave were estimated, and the preheating problem was also investigated by measurements of the self-emission and reflectivity from target rear surface. The experimental and analytical methods were validated by using double-step targets consisting of two Hugoniot standard metals. Extreme pressures only accessed in nuclear explosion experiments were generated with reproducibility and good accuracy using the laser direct-drive experimental system, for Al, Cu, polystyrene, and Ta. It was indicated that new and reliable EOS data at the ultrahigh pressures could be provided for materials ranging from low to high initial density by the laser direct-drive experimental technique. (C) 2004 American Institute of Physics.