Assessing prospects for megajoule-class yields on the National Ignition Facility

What implosion conditions will be required to reach megajoule-class yields on the National Ignition Facility? While experimental progress is being made toward the goal of ignition, for the moment, this question can only be answered theoretically or computationally. Drawing on the data base of NIF experiments to-date, this talk reviews the results of detailed, three-dimensional modeling of NIF cryogenic implosions and the results of extrapolating those simulations to the threshold of ignition. Two approaches are followed: direct hydrodynamic scaling of post-shot simulations of recent NIF implosions to megajoule yields, and an assessment of new, higher-compression designs aiming to lower the threshold for ignition. The first approach assumes no improvement in implosion quality but an upgrade to NIF's power and energy capabilities or an increase in hohlraum-to-capsule coupling efficiency. The second, complementary approach exploits learning from past experiments to envision higher compression but stable implosions with reduced ignition requirements. Of course, both approaches can also be pursued in combination. Based on this work, capsule absorbed energies greater than 400 kJ are required to reach ignition if there are no further improvements in implosion quality. However, designs reaching compressions ~20% higher than the current best performing experiments could significantly lower this energy requirement if they can be effectively imploded.