Experimental results of radiation-driven, layered deuterium-tritium implosions with adiabat-shaped drives at the National Ignition Facility
Authors: Smalyuk V. A. , Robey H. F. , Döppner T. , Casey D. T. , Clark D. S. , Jones O. S. , Milovich J. L. , Peterson J. L. , Bachmann B. , Baker K. L. , Benedetti L. R. , Berzak Hopkins L. F. , Bionta R. , Bond E. , Bradley D. K. , Callahan D. A. , Celliers P. M. , Cerjan C. , Chen K.-C. , Goyon C. , Grim G. , Dixit S. N. , Eckart M. J. , Edwards M. J. , Farrell M. , Fittinghoff D. N. , Frenje J. A. , Gatu-Johnson M. , Gharibyan N. , Haan S. W. , Hamza A. V. , Hartouni E. , Hatarik R. , Havre M. , Hohenberger M. , Hoover D. , Hurricane O. A. , Izumi N. , Jancaitis K. S. , Khan S. F. , Knauer J. P. , Kroll J. J. , Kyrala G. , Lafortune K. N. , Landen O. L. , Ma T. , MacGowan B. J. , MacPhee A. G. , Mauldin M. , Merrill F. E. , Moore A. S. , Nagel S. , Nikroo A. , Pak A. , Patel P. K. , Ralph J. E. , Sayre D. B. , Shaughnessy D. , Spears B. K. , Tommasini R. , Turnbull D. P. , Velikovich A. L. , Volegov P. L. , Weber C. R. , Widmayer C. C. , Yeamans C. 
Published: October 2016

Radiation-driven, layered deuterium-tritium (DT) implosions were carried out using 3-shock and 4-shock “adiabat-shaped” drives and plastic ablators on the National Ignition Facility (NIF) [E. M. Campbell et al., AIP Conf. Proc. 429, 3 (1998)]. The purpose of these shots was to gain further understanding on the relative performance of the low-foot implosions of the National Ignition Campaign [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] versus the subsequent high-foot implosions [T. Döppner et al., Phys. Rev. Lett. 115, 055001 (2015)]. The neutron yield performance in the experiment with the 4-shock adiabat-shaped drive was improved by factors ∼3 to ∼10, compared to five companion low-foot shots despite large low-mode asymmetries of DT fuel, while measured compression was similar to its low-foot companions. This indicated that the dominant degradation source for low-foot implosions was ablation-front instability growth, since adiabat shaping significantly stabilized this growth. For the experiment with the low-power 3-shock adiabat-shaped drive, the DT fuel compression was significantly increased, by ∼25% to ∼36%, compared to its companion high-foot implosions. The neutron yield increased by ∼20%, lower than the increase of ∼50% estimated from one-dimensional scaling, suggesting the importance of residual instabilities and asymmetries. For the experiment with the high-power, 3-shock adiabat-shaped drive, the DT fuel compression was slightly increased by ∼14% compared to its companion high-foot experiments. However, the compression was reduced compared to the lower-power 3-shock adiabat-shaped drive, correlated with the increase of hot electrons that hypothetically can be responsible for reduced compression in high-power adiabat-shaped experiments as well as in high-foot experiments. The total neutron yield in the high-power 3-shock adiabat-shaped shot N150416 was 8.5 × 1015 ± 0.2 × 1015, with the fuel areal density of 0.90 ± 0.07 g/cm2, corresponding to the ignition threshold factor parameter IFTX (calculated without alpha heating) of 0.34 ± 0.03 and the yield amplification due to the alpha heating of 2.4 ± 0.2. The performance parameters were among the highest of all shots on NIF and the closest to ignition at this time, based on the IFTX metric. The follow-up experiments were proposed to continue testing physics hypotheses, to measure implosion reproducibility, and to improve quantitative understanding on present implosion results.