Material Equation of State by Coupling Static and Dynamic Loading

Materials can be experimentally characterized up to terapascal pressures by sending a laser-induced shock wave through a sample that is pre-compressed inside a diamond-anvil cell. Pre-compression expands the ability to control the initial condition, allowing access to thermodynamic states from the principal Hugoniot and enter into the 10 TPa to 100 TPa (0.1-1 Gbar) pressure range that is relevant to planetary science. We demonstrate here a laser-driven shock wave in a water sample that is pre-compressed in a diamond anvil cell. The compression factors of the dynamic and static techniques are multiplied. This approach allows access to a family of Hugoniot curves which span the P-T phase diagram of fluid water to high density. According to the loading characteristics of the SG-Ⅱ high-power laser, the traditional diamond anvil cell is improved and optimized, and a new diamond anvil cell target adapting to high power laser loading is developed. In order to adapt to laser shock, the diamond window should be thin (100 μm) enough so that the shock can propagate to the sample before the side rarefaction erodes too much the shock planarity. With a thickness of 100 mm over an aperture of 600 μm diameter, a pre-compressed water sample at 0.5 GPa can be obtained. The water is pre-compressed to 0.5 GPa by using the diamond anvil cell. Hugoniot curve is partially followed starting from pre-compression at a pressure of 0.5 GPa. Pressure, density, and temperature data for pre-compressed water are obtained in a pressure range from 150 GPa to 350 GPa by using the laser-driven shock compression technique. Our P-ρ-T data totally agree with the results from the model based on quantum molecular dynamics calculations. These facts indicate that this water model can be used as the standard for modeling interior structures of Neptune, Uranus, and exoplanets in the liquid phase in the multi-Mbar range and should improve our understanding of these types of planets.