In-flight observations of low-mode ρR asymmetries in NIF implosions
Author(s)
Rygg, J. R.; Kritcher, A.; Hicks, D. G.; Friedrich, S.; Bionta, R.; Meezan, N. B.; Olson, R.; Atherton, J.; Barrios, M.; Bell, P.; Benedetti, R.; Berzak Hopkins, L.; Betti, R.; Bradley, D.; Callahan, D.; Casey, D.; Collins, G.; Dewald, E. L.; Dixit, S.; Döppner, T.; Edwards, M. J.; Glenn, S.; Grim, G.; Hatchett, S.; Jones, O.; Khan, S.; Kilkenny, J.; Kline, J.; Knauer, J.; Kyrala, G.; Landen, O.; LePape, S.; Lindl, J.; Ma, T.; Mackinnon, A.; Meyerhofer, D.; Moses, E.; Nagel, S. R.; Nikroo, A.; Parham, T.; Pak, A.; Prasad, R.; Ralph, J.; Robey, H. F.; Ross, J. S.; Sangster, T. C.; Sepke, S.; Spears, B.; Tommasini, R.; Town, R.; Weber, S.; Wilson, D.; Yeamans, C.; Zacharias, R.; Zylstra, Alex Bennett; Frenje, Johan A; Seguin, Fredrick Hampton; Rosenberg, Michael Jonathan; Rinderknecht, Hans George; Gatu Johnson, Maria; Li, C. K.; Manuel, Mario J.-E; Petrasso, Richard D; Sinenian, Nareg; Sio, Hong Weng; ... Show more Show less
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Charged-particle spectroscopy is used to assess implosion symmetry in ignition-scale indirect-drive implosions for the first time. Surrogate D³He gas-filled implosions at the National Ignition Facility produce energetic protons via D+³He fusion that are used to measure the implosion areal density (ρR) at the shock-bang time. By using protons produced several hundred ps before the main compression bang, the implosion is diagnosed in-flight at a convergence ratio of 3–5 just prior to peak velocity. This isolates acceleration-phase asymmetry growth. For many surrogate implosions, proton spectrometers placed at the north pole and equator reveal significant asymmetries with amplitudes routinely ≳10%, which are interpreted as ℓ=2 Legendre modes. With significant expected growth by stagnation, it is likely that these asymmetries would degrade the final implosion performance. X-ray self-emission images at stagnation show asymmetries that are positively correlated with the observed in-flight asymmetries and comparable in magnitude, contradicting growth models; this suggests that the hot-spot shape does not reflect the stagnated shell shape or that significant residual kinetic energy exists at stagnation. More prolate implosions are observed when the laser drive is sustained (“no-coast”), implying a significant time-dependent asymmetry in peak drive.
Date issued
2015-04Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering; Massachusetts Institute of Technology. Plasma Science and Fusion CenterJournal
Physics of Plasmas
Publisher
American Institute of Physics (AIP)
Citation
Zylstra, A. B. et al. “In-Flight Observations of Low-Mode ρR Asymmetries in NIF Implosions.” Physics of Plasmas 22, 5 (May 2015): 056301 © 2015 AIP Publishing
Version: Author's final manuscript
ISSN
1070-664X
1089-7674