Measurement of the sound velocity and Grüneisen parameter of polystyrene at inertial confinement fusion conditions

Abstract

The principal Hugoniot, sound velocity, and Gr\uneisen parameter of polystyrene were measured at conditions relevant to shocks in inertial confinement fusion implosions, from 100 to 1000 GPa. The sound velocity is in good agreement with quantum molecular dynamics calculations and all tabular equation of state models at pressures below 200 GPa. Above 200 GPa, the experimental results agree with two of the examined tables, but do not agree with the most recent table developed for design of inertial confinement fusion (ICF) experiments. The Gr\uneisen parameter increases with density below $\ensuremath{\sim}3.1\phantom{\rule{0.16em}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$ and approaches the asymptotic value for an ideal gas after complete dissociation. This behavior is in good agreement with quantum molecular dynamics results and previous work but is not represented by any of the tabular models. The discrepancy between tabular models and experimental measurement of the sound velocity and Gr\uneisen parameter is sufficient to impact simulations of ICF experiments.