First-principles investigations on ionization and thermal conductivity of polystyrene for inertial confinement fusion applications

Using quantum molecular-dynamics (QMD) methods based on the density functional theory, we have performed first-principles investigations of the ionization and thermal conductivity of polystyrene (CH) over a wide range of plasma conditions (rho = 0.5 to 100 g/cm(3) and T = 15 625 to 500 000 K). The ionization data from orbital-free molecular-dynamics calculations have been fitted with a Saha-type model as a function of the CH plasma density and temperature, which gives an increasing ionization as the CH density increases even at low temperatures (T < 50 eV). The orbital-free molecular dynamics method is only used to gauge the average ionization behavior of CH under the average-atom model in conjunction with the pressure-matching mixing rule. The thermal conductivities (kappa(QMD)) of CH, derived directly from the Kohn-Sham molecular-dynamics calculations, are then analytically fitted with a generalized Coulomb logarithm [(ln Lambda)(QMD)] over a wide range of plasma conditions. When compared with the traditional ionization and thermal conductivity models used in radiation-hydrodynamics codes for inertial confinement fusion simulations, the QMD results show a large difference in the low-temperature regime in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Hydrodynamic simulations of cryogenic deuterium-tritium targets with CH ablators on OMEGA and the National Ignition Facility using the QMD-derived ionization and thermal conductivity of CH have predicted similar to 20% variation in target performance in terms of hot-spot pressure and neutron yield (gain) with respect to traditional model simulations. (C) 2016 AIP Publishing LLC.