Refraction index of shock compressed water at megabar pressure (Vol. 47 No. 1)

Phase plane of water showing the experimental results for normal samples and for samples precompressed at 10 kbar.

Compressing water at megabar pressure through laser-driven shocks induces phase changes and may finally produce a metallic fluid. Such phase is particularly relevant for planetology since water is one of the main constituents of the mantles of giant planets like Uranus and Neptune, and its metallization has been recognized as a possible source of the magnetic field of such planets. In this work we study the transition of water by looking at its optical properties. Increasing pressure water changes from transparent to opaque (absorbing) and finally reflecting. We provide the first quantitative measurement of water refractive index in the megabar range, a measurement, which can give information on how the material is approaching gap closure (metallization). We also performed measurements on water precompressed at 10 kbar, allowing getting off-Hugoniot states at high pressure but low temperature. Refraction index for transparent and opaque water was measured using a VISAR system. At high compression a sharp increase of the real and imaginary part of the refraction index was observed. Experiments were performed at the LULI and RAL laboratories.

D. Batani, K. Jakubowska, A. Benuzzi-Mounaix, C. Cavazzoni, C. Danson, T. Hall, M. Kimpel, D. Neely, J. Pasley, M. Rabec Le Gloahec and B.Telaro, Refraction index of shock compressed water in the megabar pressure range, EPL 112, 36001 (2015)