Title: Effects of thermal conductivity of liquid layer in NIF wetted foam experiments

Abstract

Numerical simulation of inertial confinement fusion (ICF) capsule implosion experiments needs many plasma parameters corresponding to different materials and their mixtures for a wide range of densities and temperatures. Thermal conduction plays a crucial role in coupling energy to the capsule, is one of the primary mechanisms of energy loss during implosion, has a significant effect on hot-spot formation, and impacts the growth of hydrodynamic instabilities. The determination of accurate thermal conductivity of ICF relevant materials is thus important for understanding capsule performance. Analytic models such as Spitzer or Lee-More models have been extensively used in simulations due to the limited availability of experimental data. First principles calculations have shown that these analytic models tend to underestimate electron thermal conductivity in the warm dense plasma regime for ICF related materials. Here, we numerically investigate the effects of different models for the electron heat conductivity coefficients, including both analytic and Quantum Molecular Dynamics (QMD)-based models, for mixed materials in ICF. We also investigate the impact of how conductivities are calculated in mixed cells from constituent material conductivities. We apply this to the modeling of recent wetted foam capsule implosions on the National Ignition Facility, in which a foam layer on themore » inside of the capsule is wetted with deuterium-tritium (DT) liquid. We have found that electron heat conductivity affects the initial hot-spot formation and its evolution. Strikingly, we observe that capsule performance is more sensitive to the method used to mix material conductivities in mixed cells than how individual material conductivity coefficients are calculated. Furthermore, we have found that using the first principles QMD-based conductivity model along with an appropriate model for mixed-cell conductivities yields better agreement with experimental results compared to the established modeling strategies. We also investigate the impact of mixed material conductivity modeling on the process of ablator material mixing with DT ice in a plastic ice-layer capsule. In our simulations, the heat conductivity model affects the calculated mix widths at the fuel-ablator interface, particularly near the tent scar. Additional mixing between the DT fuel and the ablator in turn increases the implosion adiabat, which results in a lower hot-spot pressure.« less

Authors:

Dhakal, Tilak Raj ^[1]; Haines, Brian Michael  ^[1];

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Olson, Richard Edward  ^[1]

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• Search DOE PAGES for ORCID "0000-0001-5471-1404"
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+ Show Author Affiliations

1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:

2019-09-12

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1571621

Alternate Identifier(s):

OSTI ID: 1561388

Report Number(s):

LA-UR-19-23692
Journal ID: ISSN 1070-664X; TRN: US2100341

Grant/Contract Number:  

89233218CNA000001

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 26; Journal Issue: 9; 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