Enhanced direct-drive implosion performance on NIF with wavelength separation

Abstract

Cross-beam energy transfer (CBET) can significantly affect the energy coupling and symmetry of direct-drive implosions. We report on a series of direct-drive shots with 2.1 mm outer diameter capsules conducted on NIF for diagnostic development and calibration in which the wavelength separation ($\Delta \lambda$ ) between the inner and outer cone beams was varied. We observe a strong improvement in performance as $\Delta \lambda$ is applied, with the nuclear yield increasing by up to a factor of $4\times$ . Other data including the nuclear bang time and implosion symmetry suggest that increasing $\Delta \lambda$ suppresses CBET and improves both the energy coupling and drive symmetry. These results provide a strong and important benchmark for CBET models applicable to direct-drive ignition designs.