Title: Application of cross-beam energy transfer to control drive symmetry in ICF implosions in low gas fill Hohlraums at the National Ignition Facility

Abstract

Cross beam energy transfer (CBET), invoked by setting a wavelength difference, Δλ, between inner and outer beam cones, can be used to increase the drive on the waist in indirectly driven inertial confinement fusion experiments at the National Ignition Facility (NIF). Historically, hot spot symmetry control in capsule implosions in high (≥0.9 mg/cm^{3 4}He) gas fill Hohlraums was enabled by substantial CBET. However, these implosion designs suffered from inflight symmetry swings, high SRS backscatter on the inner cones, and significant hot electron generation posing a threat to DT fuel preheat. Subsequent experiments in larger, low (≤0.6 mg/cm^{3 4}He) gas fill Hohlraums demonstrated round implosions by varying the inner cone fraction throughout the laser drive at Δλ = 0 Å while keeping backscatter and hot electron generation very low. To enable driving larger capsules at a given Hohlraum size, additional tools for implosion symmetry control are required. With this goal in mind, here we present a detailed experimental study of using CBET in low gas fill Hohlraums near NIF's current peak power capability. We find a ~2.5× higher sensitivity of the P₂ Legendre mode with respect to Δλ changes compared to that of high gas fill designs. We attribute this observationmore » to the fact that backscatter remains very low and that CBET remains in a linear regime, as suggested by simulations. As a result, a much smaller Δλ of order 1 Å is sufficient for sustaining implosion symmetry while keeping laser-to-Hohlraum coupling high and hot electron generation very low. While this study used plastic ablator capsules, our findings can be generalized to other ablator materials and, hence, show great promise for using wavelength detuning as a strong lever for implosion symmetry control in future low gas fill designs that require smaller case to capsule ratios in order to increase the energy coupled to the capsule.« less

Authors:

Pickworth, L. A.  ^[1];

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Döppner, T.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-5703-7125"

Hinkel, D. E.  ^[1];

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Ralph, J. E.  ^[1];

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Bachmann, B.  ^[1];

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Masse, L. P.  ^[1];

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Divol, L. ^[1]; Benedetti, L. R.  ^[1];

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Celliers, P. M.  ^[1];

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Chen, H.  ^[1];

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Hohenberger, M.  ^[1];

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Khan, S. F.  ^[1];

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Landen, O. L.  ^[1];

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Lemos, N.  ^[1];

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MacGowan, B. J. ^[1]; Mariscal, D. A.  ^[1];

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Michel, P. A. ^[1]; Millot, M.  ^[1];

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Moore, A. S.  ^[1];

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Park, J.  ^[1]

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more »; Schneider, M. B.  ^[1];

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Callahan, D. A.  ^[1];

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Hurricane, O. A.  ^[1]

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• Search DOE PAGES for ORCID "0000-0002-8600-5448"

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+ Show Author Affiliations

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

Publication Date:

Thu Oct 01 00:00:00 EDT 2020

Research Org.:

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

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1769081

Alternate Identifier(s):

OSTI ID: 1669182

Report Number(s):

LLNL-JRNL-804567
Journal ID: ISSN 1070-664X; 1008728; TRN: US2206706

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 27; Journal Issue: 10; 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; crossed beam scattering; deuterium; x-ray imaging; radiography; fusion experiments; plasma waves; plasma confinement; tritium