In-flight observations of low-mode ρR asymmetries in NIF implosions
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In-flight observations.pdf
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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.
Date Issued
April 2015
Journal
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
Abstract
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.
MIT Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
Massachusetts Institute of Technology. Plasma Science and Fusion Center
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Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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DOI of Published Version
https://doi.org/10.1063/1.4918355
