Molecular-Dynamics Simulations and Laser-Drive Shock-Release Experiments on Polystyrene Under Inertial Confinement Fusion Conditions

We report extensive studies of polystyrene (CH) shock release by large-scale molecular dynamics and laser-drive experiments.^1,2 The simulations show species separation and H streaming ahead of C, preferentially for CH under strong shocks. Our experimental design prevents radiation preheating of the sample and employs a witness foil to investigate the release of shocked CH across a vacuum gap. We observed earlier acceleration of the foil under stronger shocks as well as reflectivity changes before the foil moved, which is consistent with the findings of our simulations that H streams ahead of C at the release front. Furthermore, our calculations show that lighter species or hydrogen isotopes can carry more mass by 1 to 2 orders of magnitude to farther distances during the release and that less than 0.1× thermal expansion (as predicted by hydrodynamics) is needed to explain the high velocities and scale lengths of low-density plasmas observed in radiation-preheated CH experiments.^3,4 These results imply general occurrences of species separation in the shock release of compounds, which shall be considered and its potential effects shall be clarified in the design, interpretation, and analysis of future high-energy-density and inertial confinement fusion experiments.