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Title: In-flight observations of low-mode ρR asymmetries in NIF implosions

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.
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  1. Massachusetts Institute of Technology, Cambridge, MA (United States). Plasma Science and Fusion Center, High Energy Density Physics Div.
  2. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts (United States)
  3. Lawrence Livermore National Laboratory, Livermore, California (United States)
  4. Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
  5. Laboratory for Laser Energetics, University of Rochester, Rochester, New York (United States)
  6. Lawrence Livermore National Laboratory,Livermore, California (United States)
  7. General Atomics, San Diego, California (United States)
Publication Date:
OSTI Identifier:
1178796
Grant/Contract Number:
NA0001857
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 22; Journal Issue: 5; Conference: Rochester, NY (United States), 22-24 Apr 2015; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Massachusetts Institute of Technology, Cambridge, MA (United States). Plasma Science and Fusion Center, High Energy Density Physics Div.
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY