Temperature measurements of Magnesium Oxide shock-compressed to 1.1 TPa and 33000 K*

Equations of state of rock-forming minerals are fundamental for modeling planetary interiors and mantle convection, whereas measurements are very limited in the warm dense matter regime. In this work, we shock compressed MgO to extreme pressures and temperatures found in exoplanets' interiors. We report the first measurements of pressure, temperature, and crystal structure of MgO in the warm dense matter regime. Crystal orientation-dependent formation was investigated with in-situ x-ray diffraction by shock compressing single-crystal MgO along different orientations.

Decaying shock experiments and PXRDIP experiments were conducted at the Omega-EP at Laboratory for Laser Energetics, University of Rochester. Lasers drive up to 2 KJ over several nanoseconds were used to shock-compress MgO. Velocimetry (VISAR) and Pyrometry (SOP) were employed to monitor velocity history and thermal emissions, respectively. In previous studies, optical depth was assumed to be skin depth, in which case the emission behavior could be described as blackbody emission. Here we present the first direct measurements of optical depth in shock-compressed MgO, showing that MgO is optically semi-transparent below 500 GPa (~12µm at 400 GPa), affecting temperature measurements in decaying shock experiments. Our data suggest that optical properties can potentially be crystal orientation-dependent. Details will be discussed in the presentation.