Mitigating Laser Imprint with Hybrid Shock Drive in Polar Illumination on OMEGA*

Laser imprint is a major degradation mechanism for direct-drive inertial confinement fusion (ICF) affecting low adiabat designs that would otherwise reach high performance and possibly high gain in megajoule drivers. This is despite established beam smoothing techniques (such as SSD) currently used in direct-drive experiments on OMEGA. The beam-quality issue is solved in indirect-drive ICF by using a hohlraum to convert the laser energy into x-ray radiation, which has excellent high-mode smoothness at the cost of energy efficiency. To help mitigate laser imprint while maintaining the efficiency of direct-drive, a novel scheme called "hybrid-shock-drive" (HSD) was first suggested by L. Ceurvorst et al., Phys. Rev. E 101, 063207 (2020). Here, we discuss a polar HSD design for OMEGA, in which two gold-coated CH domes surround a spherical implosion target. The laser, initially incident on the domes, drives a high-mode, smooth x-ray shock into the target and establishes a coronal atmosphere. The subsequent laser drive is directly absorbed in this atmosphere, and thermal conduction smoothing leads to imprint mitigation. We show results from 1D and 2D simulations, which achieve low adiabats and high neutron yields, and corresponding cone-in-shell experiments on OMEGA that intend to demonstrate the efficacy of this design. Such designs are adapted to polar illumination for experiments on both OMEGA and NIF.