Experimental results of radiation-driven, layered deuterium-tritiumimplosions with adiabat-shaped drives at the National Ignition Facility

• Published in: Physics of plasmas 2016-10, Vol.23 (10)
• Main 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, K-C, Chen, 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
• Format: Article
• Language: English
• Subjects: Ablation; Compression tests; Deuterium; Experiments; Fuels; Heating; Hot electrons; Ignition; Implosions; Mathematical analysis; Parameters; Plasma physics; Plasmas (physics); Reproducibility; Stability; Tritium
• ISSN: 1070-664X; 1089-7674

Radiation-driven, layered deuterium-tritium (DT) implosions were carried out using3-shock and 4-shock “adiabat-shaped” drives and plastic ablators on the National IgnitionFacility (NIF) [E. M. Campbell et al., AIP Conf. Proc.429, 3 (1998)]. The purpose of these shots was to gain furtherunderstanding on the relative performance of the low-foot implosions of the NationalIgnition Campaign [M. J. Edwards et al., Phys. Plasmas20, 070501 (2013)] versus the subsequent high-foot implosions [T. Döppneret al., Phys. Rev. Lett. 115, 055001 (2015)].The neutron yieldperformance in the experiment with the 4-shock adiabat-shaped drive was improved byfactors ∼3 to ∼10, compared to five companion low-foot shots despite large low-modeasymmetries of DT fuel, while measured compression was similar to its low-foot companions.This indicated that the dominant degradation source for low-foot implosions wasablation-front instability growth, since adiabat shaping significantly stabilized thisgrowth. For the experiment with the low-power 3-shock adiabat-shaped drive, the DT fuelcompression was significantly increased, by ∼25% to ∼36%, compared to its companionhigh-foot implosions. The neutron yield increased by ∼20%, lower than the increase of ∼50%estimated from one-dimensional scaling, suggesting the importance of residualinstabilitiesand asymmetries. For the experiment with the high-power, 3-shock adiabat-shaped drive, theDT fuel compression was slightly increased by ∼14% compared to its companion high-footexperiments. However, the compression was reduced compared to the lower-power 3-shockadiabat-shaped drive, correlated with the increase of hot electrons that hypotheticallycan be responsible for reduced compression in high-power adiabat-shaped experiments aswell as in high-foot experiments. The total neutron yield in the high-power 3-shock adiabat-shaped shotN150416 was 8.5 × 1015 ± 0.2 × 1015, with the fuel areal density of0.90 ± 0.07 g/cm2, corresponding to the ignition threshold factor parameterIFTX (calculated without alpha heating) of 0.34 ± 0.03 and the yield amplification due tothe alpha heating of 2.4 ± 0.2. The performance parameters were among the highest of allshots on NIF and the closest to ignition at this time, based on the IFTX metric. Thefollow-up experiments were proposed to continue testing physics hypotheses, to measureimplosion reproducibility, and to improve quantitative understanding on present implosionresults.