Mitigation of Two-Plasmon Decay in Direct-Drive Implosions Using Multilayer Targets

Mitigation of cross-beam energy transfer in direct-drive implosions may increase the hot-electron preheat above acceptable levels for ignition. To study preheat mitigation concepts on OMEGA, a thin layer (0.6 $\mu $m) of Si in the target ablator is being considered to increase the electron temperature at the quarter-critical surface. A beryllium inner layer (6 $\mu $m thick) is used to increase the hydrodynamic efficiency and an outer layer of CH-doped Si (4 $\mu $m thick) reduces the laser imprint. Spatially resolved Thomson-scattering measurements show a 15{\%} increase in the electron temperature at the quarter-critical surface and the time-resolved hot electrons are reduced by a factor of 8 compared with a standard CH target. The shell trajectory in the multilayer targets is significantly faster than the CH target, resulting in a factor-of-3 increase in the neutron yield. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.