Advances toward hydro-equivalent ignition in OMEGA direct-drive implosions*

Recent progress in direct-drive inertial confinement fusion has considerably improved the prospects for achieving thermonuclear ignition with megajoule-class lasers. recent OMEGA implosions are expected to produce about 600 kJ of fusion yield and 75% of the Lawson triple product required for ignition at 1.9MJ of symmetric illumination when hydrodynamically scaled to laser energies typical of the National Ignition Facility (NIF). Those implosions have benefited from a significant increase in implosion velocity obtained through larger-diameter targets. A new statistical approach [Gopalaswamy et al, Nature 565 (2019) 581–586.] used in designing OMEGA targets has demonstrated a considerable predictive capability, thereby enabling the design of targets with improved performance, leading to quadrupling the fusion yield and increasing the areal density by over 60%. Recent record yield of 1.75e14 was achieved with 1.02 mm size capsules. Systematic experiments such as scans of SSD (smoothing by spectral dispersion) bandwidth, age of the DT fill and beam over target size are used to identify mechanisms of performance degradation and implosion optimization. Ongoing experiments test improved coupling by zooming of the laser beams after the initial picket and the picket-only laser smoothing using the multi-driver configuration (MPD) where SSD is turned off after the picket and the laser beam diameter is reduced from 831 to 751 mm. New Si-doped CH ablators are used to suppress the two plasmon decay (TPD) instability, reduce hot electrons and improve the areal densities. All these improvements are expected to further augment implosion performance toward the goal of demonstrating implosion core conditions that scale to ignition at NIF energies. Based on these recent results, a path to demonstrating hydro-equivalent ignition on OMEGA is presented.