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Title: Instability growth seeded by oxygen in CH shells on the National Ignition Facility

Fusion targets imploded on the National Ignition Facility are subject to hydrodynamic instabilities. These have generally been assumed to be seeded primarily by surface roughness, as existing work had suggested that internal inhomogeneity was small enough not to contribute significantly. New simulations presented here examine this in more detail, and consider modulations in internal oxygen content in CH plastic ablators. The oxygen is configured in a way motivated by measurement of oxygen in the shells. We find that plausible oxygen nonuniformity, motivated by target characterization experiments, seeds instability growth that is 3–5× bigger than expected from surface roughness. Pertinent existing capsule characterization is discussed, which suggests the presence of internal modulations that could be oxygen at levels large enough to be the dominant seed for hydrodynamic instability growth. Oxygen-seeded growth is smaller for implosions driven by high-foot pulse shapes, consistent with the performance improvement seen with these pulse shapes. Growth is somewhat smaller for planned future pulse shapes that were optimized to minimize growth of surface ripples. A possible modified specification for oxygen modulations is discussed, which is about 1/5 of the current requirement.
Authors:
; ; ; ; ; ; ;  [1] ;  [2]
  1. Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States)
  2. General Atomics, P.O. Box 85608, San Diego, California 92186 (United States)
Publication Date:
OSTI Identifier:
22408220
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 3; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABLATION; CAPSULES; HYDRODYNAMICS; IMPLOSIONS; INSTABILITY; MODULATION; OXYGEN; PERFORMANCE; PLASMA SIMULATION; PLASTICS; PULSE SHAPERS; ROUGHNESS; TARGETS; US NATIONAL IGNITION FACILITY