Thermonuclear performance variability near ignition at the National Ignition Facility
L. Divol, A. Pak, B. Bachmann, K. L. Baker, Salmaan H. Baxamusa, Juergen Biener, R. M. Bionta, T. Braun, D. T. Casey, C. Choate, D. S. Clark, E. L. Dewald, T. Döppner, D. N. Fittinghoff, Kelly Hahn, T. J. Hilsabeck, M. Hohenberger, J. P. Holder, O. A. Hurricane, N. Izumi, S. Kerr, S. F. Khan, B. Kozioziemski, A. L. Kritcher, B. J. MacGowan, A. G. MacPhee, M. M. Marinak, E. V. Marley, A. S. Moore, A. Nikroo, R. Nora, J. E. Ralph, M. S. Rubery, N. W. Ruof, D. J. Schlossberg, Chris Schroeder, S. M. Sepke, S. J. Shin, P. T. Springer, Stanislav Stoupin, R. Tommasini, C. Trosseille, P. L. Volegov, C. R. Weber, C. V. Young, A. J. Mackinnon, J. D. Moody, V. A. Smalyuk, O. L. Landen, Michael Stadermann, R. P. J. Town, L. Aghaian, N. Alfonso, A. Allen, K. Clark, J. W. Crippen, M. Havre, H. Huang, J. F. Hund, C. Kong, Pavel N. Lapa, M. Mauldin, S. Pajoom, M. Ratledge, K. Sequoia, W. Vakki, T. Fehrenbach, C. Wild, A. B. Zylstra, N. Birge, M. S. Freeman, V. Geppert-Kleinrath, Hermann Geppert-Kleinrath, Y. Kim, Kevin Matthew Lamb, K. D. Meaney, C. H. Wilde
Abstract
We describe our current understanding of the variability and degradation mechanisms observed through a series of five indirectly driven inertial fusion implosions fielded at the National Ignition Facility in the fall of 2021, four of which attempted to reproduce the first experiment to achieve Lawson's criterion for ignition with a thermonuclear yield of 1.35 MJ on August 8, 2021. A large number of absolutely calibrated (imaging, time-resolved, and spectrally resolved) x-ray and neutron diagnostics are fielded on the NIF along multiple lines of sight for each experiment. This allows for a reconstruction of the DT fuel and ablator mix injected into the hotspot around peak burn. We show that nuclear yield variations are well reproduced by numerical modeling when the measured low mode asymmetries and mix mass are included. Furthermore, these observed perturbations during burn are linked to small variations in laser delivery and capsule defects. Stringent specifications are then set to achieve robust ignition with the implosion design studied in this paper.