Multidimensional Modeling of the Hybrid Shock Drive for Low-Adiabat Direct-Drive Fusion Experiments at the Omega Laser Facility*

Recent advances in multidimensional modeling of the hybrid shock drive (HSD) platform for low-adiabat spherical implosions at the 60-beam Omega Laser Facility indicate that HSD is capable of mitigating laser imprint. During the early stages of the implosion of directly driven (LDD) cryogenic targets, the laser beams impart high ℓ-mode perturbations which are not effectively smoothed by the relatively small conduction zone. These Rayleigh–Taylor-unstable modes grow rapidly with convergence, limiting current target designs on OMEGA at high adiabats (α > 4). The mechanism that allows the HSD to suppress early imprint involves the conversion of the laser picket into x rays by means of a high-Z converter foil, which fully envelops the cryogenic target and is offset by a foam cushion. The x-ray burst drives a smooth initial shock into the target, which allows enough time for the conduction zone to expand before the target is directly illuminated by the laser, thereby also mitigating imprint at later times. Multidimensional simulations show that the imploding shell of a high-performance HSD target at a low adiabat (α ≃ 2) is free from high ℓ-mode perturbations coming from the laser system, while its LDD counterpart does not survive the high ℓ-mode feedthrough. From these results, HSD appears to be a promising platform for high yield and ρR at low adiabats. Analysis of recent experiments on OMEGA EP and on the OMEGA-60, currently underway, will inform the next steps in modeling and in further optimization of the HSD platform.