Modeling Target Defects in Direct-Drive Inertial Confinement Fusion*

A range of evidence from both radiation-hydrodynamic simulations and experiments suggests that isolated defects on the outside of cryogenic targets are able to play a significant role in degrading direct-drive inertial confinement fusion implosion performance. The highly non-linear growth is not ablatively stabilized and can be an important degradation even for current best performing, OMEGA cryogenic implosions. A cryogenic target may have thousands of surface defects, originating from intrinsic flaws, permeation fill, radiation damage, or condensation on the target, and ranging in size from sub-micron to several microns. Previous 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 [1]. In this talk we present the results of 2-D rad-hydro simulations with DRACO of smaller (micron-scale) defects in the context of more recent cryogenic target designs, addressing the transport of ablator material into the hot spot, interaction of defects and instability growth due to laser imprint, and seeding of surface defects by interfacial defects.  [1] I. V. Igumenshchev et al., Effects of local defect growth in direct-drive cryogenic implosions on OMEGA, Phys. Plasmas 20, 082703 (2013)