Instability Growth Seeded by Target Defects in Direct-Drive Inertial Confinement Fusion

A range of evidence from both radiation-hydrodynamic (rad-hydro) simulations and experiments indicates that isolated defects on the outside of cryogenic targets may play a role in degrading laser-direct-drive (LDD) inertial confinement fusion implosion performance. An OMEGA cryogenic target may have thousands of surface defects, originating from intrinsic flaws, permeation fill, radiation damage, or condensation on the target, ranging in size from submicron to several microns. Previous LDD modeling of large defects has shown that the resulting local perturbation growth can inject ablator mass into the hot spot, contributing to radiative cooling and loss of performance.[i] In this talk, we present draco results of 2D rad-hydro simulations with few-micron-scale defects, modeling any early impact of laser speckle, which generates rapid intensity changes on the laser coherence timescale, with sizes comparable to the defects. We also explore trade-offs of mitigating defect growth by means of increased adiabat versus increased shell thickness.

[i] I. V. Igumenshchev et al., Phys. Plasmas 20, 082703 (2013).