First-principles thermal conductivity of warm-dense deuterium plasmas for inertial confinement fusion applications

Thermal conductivity (kappa) of both the ablator materials and deuterium-tritium (DT) fuel plays an important role in understanding and designing inertial confinement fusion (ICF) implosions. The extensively used Spitzer model for thermal conduction in ideal plasmas breaks down for high-density, low-temperature shells that are compressed by shocks and spherical convergence in imploding targets. A variety of thermal-conductivity models have been proposed for ICF hydrodynamic simulations of such coupled and degenerate plasmas. The accuracy of these kappa models for DT plasmas has recently been tested against first-principles calculations using the quantum molecular-dynamics (QMD) method; although mainly for high densities (rho > 100 g/cm(3)), large discrepancies in kappa have been identified for the peak-compression conditions in ICF. To cover the wide range of density-temperature conditions undergone by ICF imploding fuel shells, we have performed QMD calculations of. for a variety of deuterium densities of rho = 1.0 to 673.518 g/cm(3), at temperatures varying from T = 5 x 10(3) K to T = 8 x 10(6) K. The resulting kappa(QMD) of deuterium is fitted with a polynomial function of the coupling and degeneracy parameters Gamma and theta, which can then be used in hydrodynamic simulation codes. Compared with the hybrid Spitzer-Lee-More model currently adopted in our hydrocode LILAC, the hydrosimulations using the fitted kappa(QMD) have shown up to similar to 20% variations in predicting target performance for different ICF implosions on OMEGA and direct-drive-ignition designs for the National Ignition Facility (NIF). The lower the adiabat of an imploding shell, the more variations in predicting target performance using kappa(QMD). Moreover, the use of kappa(QMD) also modifies the shock conditions and the density-temperature profiles of the imploding shell at early implosion stage, which predominantly affects the final target performance. This is in contrast to the previous speculation that kappa(QMD) changes mainly the inside ablation process during the hot-spot formation of an ICF implosion.