A simulation-based and analytic analysis of the off-Hugoniot response of alternative inertial confinement fusion ablator materials

The attainment of self-propagating fusion burn in an inertial confinement target at the National Ignition Facility will require the use of an ablator with high rocket-efficiency and ablation pressure. The ablation material used during the National Ignition Campaign (Lindl et al. 2014) [1], a glow-discharge polymer (GDP), does not couple as efficiently as simulations indicated to the multiple-shock inducing radiation drive environment created by laser power profile (Robey et al., 2012). We investigate the performance of two other ablators, boron carbide (B4C) and high-density carbon (HDC) compared to the performance of GDP under the same hohlraum conditions. Ablation performance is determined through measurement of the shock speed produced in planar samples of the ablator material subjected to the identical multiple-shock inducing radiation drive environments that are similar to a generic three-shock ignition drive. Simulations are in better agreement with the off-Hugoniot performance of B4C than either HDC or GDP, and analytic estimations of the ablation pressure indicate that while the pressure produced by B4C and GDP is similar when the ablator is allowed to release, the pressure reached by B4C seems to exceed that of HDC when backed by a Au/quartz layer. (C) 2016 Published by Elsevier B.V.