Laser-shock-driven laboratory measurements of the equation of state of hydrogen isotopes in the megabar regime

Abstract

A high intensity laser has been used to shock-compress liquid deuterium to pressures from 0.22 Mbar, near the upper end of gas-gun shock data, to 3.4Mbar. Using a variety of diagnostics, the density, pressure, and reflectivity of the shocked deuterium were determined, culminating in a knowledge of the behavior of hydrogen isotopes along the principal Hugoniot into the Mbar regime. It was found that hydrogen isotopes become highly compressible near 1 Mbar as a result of molecular dissociation and simultaneous ionization. Reflectivity measurements confirmed that deuterium transitions from an insulating state to a conducting phase at pressures near 0.5 Mbar on the Hugoniot and appears to do so in a continuous manner. At pressures above 0.5 Mbar, the measured reflectivity of the shocked deuterium is characteristic of a liquid metal.