Three-Dimensional Study of Yield Degradation for Direct-Drive Inertial Confinement Fusion

The mechanism of yield degradation in the deceleration phase for direct-drive inertial confinement fusion was studied using a recently developed three-dimensional radiation--hydrodynamics code \textit{DEC3D}. Under the approximation of adiabatic hot spot, an expression that measures the degradation of neutron rate was obtained in terms of the ratio of perturbed to the clean hot-spot volume. The characteristics of perturbed hot-spot volume is identified as a key parameter to understand the departure from spherical symmetry. The role of 3-D effects on compressibility, which affects the hot-spot volume, was examined including the 3-D vorticity dynamics in the spherical converging geometry and the jet flow in P-1 perturbations. In particular, the hot spot was found to be less compressible in the nonlinear phase of the Rayleigh--Taylor instability, resulting in a poor hydrodynamic efficiency to convert the shell kinetic energy into hot-spot pressure. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE{\-}NA0001944.