Understanding Laser-Imprint Effects on Plastic-Target Implosions on OMEGA with New Physics Models

Using the state-of-the-art physics models (nonlocal thermal transport, cross-beam energy transfer, and first-principles equation of state) recently implemented in our two-dimensional hydrocode \textit{DRACO}, we have performed a systematic study of laser-imprint effects on plastic-target implosions on OMEGA by both simulations and experiments. Through varying the laser picket intensity, the imploding shells were set at different adiabats ranging from $\alpha \mbox{\thinspace }=\mbox{\thinspace }2$ to $\alpha \mbox{\thinspace }=\mbox{\thinspace }6.$ As the shell adiabat $\alpha $ decreases, we observed: (1) the measured shell thickness at the hot spot emission becomes larger than the uniform prediction; (2) the hot-spot core emits and neutron burn starts earlier than the corresponding 1-D prediction; and (3) the measured neutron yields are significantly reduced from their 1-D designs. Most of these experimental observations are well reproduced by our \textit{DRACO} simulations with laser imprints. These studies clearly identify that laser imprint is the major cause for target performance degradation of OMEGA implosions of $\alpha \mbox{\thinspace }\le \mbox{\thinspace }3.$ Mitigating laser imprints must be an essential effort to improve low-$\alpha $ target performance in direct-drive inertial confinement fusion ignition attempts. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.