Mitigation of cross-beam energy transfer in ignition-scale polar-direct-drive target designs for the National Ignition Facility

Abstract

Two novel target designs are presented for using direct laser ablation (direct drive) at the National Ignition Facility to assemble and ignite cryogenic fuel using the existing indirect-drive beam configuration. These are the first ignition-relevant “polar” direct-drive target designs to include the physical effects of cross-beam energy transfer (CBET) between laser beams and nonlocal electron heat transport. A wavelength-detuning strategy is used to increase absorption and reduce scattered-light losses caused by CBET, allowing for ignition-relevant implosion velocities. Two designs are described: a moderate-adiabat sub-ignition alpha-burning design with a D–T neutron fusion yield of 1.2 × 1017 and a lower-adiabat ignition design with a gain of 27. Both designs have moderate in-flight aspect ratios, indicating acceptable levels of hydrodynamic instability during the implosion.