LLNL Poster Symposium 2015

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  • Fokker-Planck Modeling of Heat Conduction in NIF Hohlraums

    We use the Vlasov-Fokker-Planck code OSHUN to model electron heat conduction in a realistic plasma profile for a NIF rugby-shaped hohlraum. Please attend my talk on 25 August 2015 to see NIF results.

    Andrew H. Dublin1,2, David J. Strozzi1, Adam Tableman3, Benjamin Winjum3 Lawrence Livermore National Laboratory1 | University of Rochester2 | University of California at Los Angeles3

    Results:

    Introduction: Methods: Electron heat conduction is a key process in inertial fusion

    targets, like NIF hohlraums. Radiation-hydrodynamics codes routinely use the collisional

    Spitzer-Harm model, with an ad-hoc flux limit to match data. Kinetic and non-local effects can sometimes be important.

    The code OSHUN (Tzoufras et. al, Phys. Plasmas 2013), developed at UCLA, solves the Vlasov-Fokker-Planck equation:

    OSHUN uses the spherical harmonic expansion:

    Spherical coordinates: Electron-ion collision operator (electron-electron is more complicated)

    Thermal conductivity :

    Spitzer-Hrm, local collisional result (Zi >>1):

    We ran OSHUN on the 1-D green path from above: Z=2 helium We compare OSHUN results with Spitzer-Hrm theory.

    LLNL-POST-675603 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

    Lasnex simulation of NIF hohlraum. We study heat conduction along the green path.

    Gold wall

    Capsule: ablator and fusion fuel Helium plasma

    electron-electron collisions

    electron-ion collisions

    fe(r,p,t) = electron distribution

    Discussion: OSHUN displays non-local reduction in thermal conductivity for

    large temperature gradients. Future work: 2D simulations, mobile ions, and gold wall

    conditions.

    Spitzer-Hrm Result

    Non-local reduction in

    0 = mean free path

    1-D NIF profile for OSHUN 4.5 0.12

    ne

    Te

    0 0

    0.05 Non-locality Parameter

    0