Title: First study of Hohlraum x-ray preheat asymmetry inside an ICF capsule

Abstract

In indirect drive inertial confinement fusion (ICF), laser induced Hohlraum preheat radiation (so-called M-band, >1.8 keV) asymmetry will lead to asymmetric ablation front and ablator–fuel interface hydrodynamic instability growth in an imploding capsule. First experiments to infer the M-band asymmetries at the capsule were performed on the National Ignition Facility for high density carbon (HDC) ICF capsules in low density fill (0.3 mg/cc ⁴He) Au Hohlraums by time resolved imaging of 2.3 keV fluorescence emission of a smaller Mo sphere placed inside the capsule. In this study, the measured Mo emission is pole hot (P₂ > 0) since M-band is generated mainly by the outer laser beams as their irradiance at the Hohlraum wall is 5× higher than for the inner beams. P₂ has a greater negative than positive swing vs time [Δ(P₂/P₀)/Δt ~ 0.2/ns], giving insight into laser heated Hohlraum dynamics. P₄ asymmetry is small at the sphere due to efficient geometric smoothing of Hohlraum asymmetries at large Hohlraum-to-capsule ratios. The M-band P₂ history is qualitatively reproduced by radiation hydrodynamic HYDRA simulations. The smaller P₂ than that calculated earlier suggests either less outer beam spot motion and/or preheat emission. At late times, the observed P₂ swing is larger andmore » P₄ is more negative than simulated, which could be due to inner beams being stopped more in the outer beams wall plasma bubble than simulated. Asymmetry at the HDC capsule inner surface (“ice–ablator interface”) is also inferred from the Mo emission asymmetry by an analytic viewfactor model, accounting for the Mo/HDC radius difference and HDC capsule opacity.« less

Authors:

Dewald, E. L.  ^[1];

• Search DOE PAGES for author "Dewald, E. L."
• Search DOE PAGES for ORCID "0000-0003-4054-6967"

Landen, O. L.  ^[1];

• Search DOE PAGES for author "Landen, O. L."
• Search DOE PAGES for ORCID "0000-0002-1499-8217"

Salmonson, J. ^[1]; Masse, L.  ^[1];

• Search DOE PAGES for author "Masse, L."
• Search DOE PAGES for ORCID "0000-0002-3587-9671"

Tabak, M. ^[1]; Smalyuk, V. A. ^[1]; Schiaffino, S. ^[1]; Heredia, R. ^[1]; Schneider, M.  ^[1];

• Search DOE PAGES for author "Schneider, M."
• Search DOE PAGES for ORCID "0000-0001-9706-8308"

Nikroo, A.  ^[1]

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• Search DOE PAGES for ORCID "0000-0002-8855-0378"

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+ Show Author Affiliations

1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:

Wed Dec 16 00:00:00 EST 2020

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1764324

Alternate Identifier(s):

OSTI ID: 1765923

Report Number(s):

LLNL-JRNL-813556
Journal ID: ISSN 1070-664X; 1021432; TRN: US2206166

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 27; Journal Issue: 12; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; x-ray fluorescence; time resolved imaging; plasma confinement; laser fusion; radiation physics; radiative flux; x-rays