Foam-Supported Hybrid Shock Drive for Low-Adiabat Direct-Drive Fusion Experiments at the Omega Laser Facility*

Improving the performance of DT-layered laser direct-drive (LDD) fusion experiments hinges upon the growth of Rayleigh–Taylor (RT) hydrodynamic instabilities, which compromise the integrity of the imploding target. An important RT seed in LDD fusion implosions is laser imprint, which imparts high-ℓ-mode perturbations on the target. These grow rapidly with convergence increasing the adiabat floor at which a target can be driven. Presently, high-performance LDD implosions suppress the growth of laser imprint by imploding high-adiabat (α > 4) targets. This, however, does not eliminate the source of the imprint, and limits the maximum realizable yield, ρR, and Lawson parameter. One proposed method to effectively mitigate imprint is the hybrid shock drive. The concept indirectly drives the target with x rays via a burn-through converter foil and then switches to a direct-illumination scheme once a plasma has been established and high-ℓ-mode perturbations from the laser have been conductively smoothed. Our design simplifies engineering challenges found in other hybrid proposals by supporting the high-Z converter foil on top of an ultralow-density foam layer instead of the typical vacuum standoff. The proposed platform offers a more compact and robust assembly comparing to alternative hybrid designs, while simplifying fabrication, enabling permeation filling, and overall providing a pathway to field low-adiabat cryogenic hybrid implosions on OMEGA. Planar experiments on OMEGA EP are planned which will quantify the efficacy of this novel design.