NIF Result: Ignition metrics describing the NIF path from alpha heating to Gain>1, and OMEGA implosions hydro-scaled to NIF energies

Recent progress in laser inertial confinement fusion has considerably improved the prospects for achieving significant energy gains with megajoule-class lasers. On December 5^th 2022, an indirect drive implosion on the National Ignition Facility (NIF) achieved for the first time a target gain above unity with a fusion yield of 3.15MJ for a laser energy on target of 2.05 MJ (target gain of 1.5). This record performance comes a year after the previous record yield of 1.37 MJ with a target gain of 0.7 in August 2021 [1]. When comparing the fusion energy to the actual energy transferred to the fusing DT fuel, the gains are much greater exceeding ~100 indicating that thermonuclear ignition and propagating burn has taken place in these experiments. Lawson-type [2] ignition metrics are capable of describing the NIF implosion path through the alpha heating, burning plasma [3] and ignition [1] regimes. Recent direct-drive implosions [4] on OMEGA have also exhibited significant improvements in performance with neutron yields of 2.1e14 and areal densities of 0.16 g/cm.² When hydrodynamically scaled to NIF energies, those implosions reach 86% of the Lawson parameter required for ignition, and multiple options to demonstrate hydro-equivalent ignition are available to achieve that milestone in the short term. Because of the general Lawson’s formulation of the ignition criterion, a comparison can be made between the above inertial fusion results and the highest performing tokamak discharges.

[1] H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022).

[2] J. D. Lawson, Proceedings of the Physical Society. Section B 70, 6 (1957).

[3] A. B. Zylstra et al., Nature 601, 542 (2022); A. L. Kritcher et al., Nature Physics 18, 251 (2022).

[4] V. Gopalaswamy et al, submitted to Nature Physics; C.A. Williams et al, submitted to Nature Physics