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Title: Indirectly driven, high-convergence implosions (HEP1)

Abstract

High-gain inertial confinement fusion will most readily be achieved with hot-spot ignition, in which a relatively small mass of gaseous fuel at the center of the target is heated to 5-10 keV, igniting a larger surrounding mass of approximately isobaric fuel at higher density but lower temperature. Existing lasers are too low in energy to achieve thermonuclear gain, but hydrodynamically equivalent implosions using these lasers can demonstrate that the important, scalable parameters of ignition capsules are scientifically and technologically achievable. The experiments described in this article used gas-filled glass shells driven by x rays produced in a surrounding cavity, or hohlraum. These implosions achieved convergence ratios (initial capsule radius/ final fuel radius) high enough to fall in the range required for ignition-scale capsules, and they produced an imploded configuration (high-density glass with hot gas fill) that is equivalent to the hot-spot configuration of an ignition-scale capsule. Other recent laser-driven implosions have achieved high shell density but at lower convergences and without a well defined hot spot. Still other experiments have used very-low-density gas fill to reach high convergence with unshaped drive, but that approach results in a relatively low shell density. Moreover, even at the highest convergence ratios the implosionsmore » described here had neutron yields averaging 8% of that calculated for an idealized, clean, spherically symmetric implosion - much higher than previous high-convergence experiments.« less

Authors:
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Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (United States)
OSTI Identifier:
376959
Report Number(s):
UCRL-LR-105820-95
ON: DE96013181; TRN: 96:004685-0025
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Jun 1996; Related Information: Is Part Of Inertial confinement fusion. 1995 ICF annual report, October 1994--September 1995; PB: 407 p.
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; LASER TARGETS; INDIRECT DRIVE LASER IMPLOSION; PROGRESS REPORT

Citation Formats

Hatchett, S.P., Cable, M.D., and Caird, J.A.. Indirectly driven, high-convergence implosions (HEP1). United States: N. p., 1996. Web. doi:10.2172/376959.
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Hatchett, S.P., Cable, M.D., & Caird, J.A.. Indirectly driven, high-convergence implosions (HEP1). United States. doi:10.2172/376959.
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Hatchett, S.P., Cable, M.D., and Caird, J.A.. Sat . "Indirectly driven, high-convergence implosions (HEP1)". United States. doi:10.2172/376959. https://www.osti.gov/servlets/purl/376959.
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@article{osti_376959,
title = {Indirectly driven, high-convergence implosions (HEP1)},
author = {Hatchett, S.P. and Cable, M.D. and Caird, J.A.},
abstractNote = {High-gain inertial confinement fusion will most readily be achieved with hot-spot ignition, in which a relatively small mass of gaseous fuel at the center of the target is heated to 5-10 keV, igniting a larger surrounding mass of approximately isobaric fuel at higher density but lower temperature. Existing lasers are too low in energy to achieve thermonuclear gain, but hydrodynamically equivalent implosions using these lasers can demonstrate that the important, scalable parameters of ignition capsules are scientifically and technologically achievable. The experiments described in this article used gas-filled glass shells driven by x rays produced in a surrounding cavity, or hohlraum. These implosions achieved convergence ratios (initial capsule radius/ final fuel radius) high enough to fall in the range required for ignition-scale capsules, and they produced an imploded configuration (high-density glass with hot gas fill) that is equivalent to the hot-spot configuration of an ignition-scale capsule. Other recent laser-driven implosions have achieved high shell density but at lower convergences and without a well defined hot spot. Still other experiments have used very-low-density gas fill to reach high convergence with unshaped drive, but that approach results in a relatively low shell density. Moreover, even at the highest convergence ratios the implosions described here had neutron yields averaging 8% of that calculated for an idealized, clean, spherically symmetric implosion - much higher than previous high-convergence experiments.},
doi = {10.2172/376959},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Jun 01 00:00:00 EDT 1996},
month = {Sat Jun 01 00:00:00 EDT 1996}
}
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Technical Report:
View Technical Report (69.79 MB)
DOI:  10.2172/376959
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  • ; ; ; ... - Physics of Plasmas
    In this study, we present the results of high-resolution simulations of the implosion of high-convergence layered indirect-drive inertial confinement fusion capsules of the type fielded on the National Ignition Facility using the xRAGE radiation-hydrodynamics code. In order to evaluate the suitability of xRAGE to model such experiments, we benchmark simulation results against available experimental data, including shock-timing, shock-velocity, and shell trajectory data, as well as hydrodynamic instability growth rates. We discuss the code improvements that were necessary in order to achieve favorable comparisons with these data. Due to its use of adaptive mesh refinement and Eulerian hydrodynamics, xRAGE is particularlymore » well suited for high-resolution study of multi-scale engineering features such as the capsule support tent and fill tube, which are known to impact the performance of high-convergence capsule implosions. High-resolution two-dimensional (2D) simulations including accurate and well-resolved models for the capsule fill tube, support tent, drive asymmetry, and capsule surface roughness are presented. These asymmetry seeds are isolated in order to study their relative importance and the resolution of the simulations enables the observation of details that have not been previously reported. We analyze simulation results to determine how the different asymmetries affect hotspot reactivity, confinement, and confinement time and how these combine to degrade yield. Yield degradation associated with the tent occurs largely through decreased reactivity due to the escape of hot fuel mass from the hotspot. Drive asymmetries and the fill tube, however, degrade yield primarily via burn truncation, as associated instability growth accelerates the disassembly of the hotspot. Finally, modeling all of these asymmetries together in 2D leads to improved agreement with experiment but falls short of explaining the experimentally observed yield degradation, consistent with previous 2D simulations of such capsules.« less
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  • ; ; ; ... - Physical Review Letters; (United States)
    A series of high convergence indirectly driven implosions has been done with the Nova Laser Fusion facility. These implosions were well characterized by a variety of measurements; computer models are in good agreement. The imploded fuel areal density was measured using a technique based on secondary neutron spectroscopy. At capsule convergences of 24:1, comparable to what is required for the hot spot of ignition scale capsules, these capsules achieved fuel densities of 19 g/cm[sup 3]. Independent measurements of density, burn duration, and ion temperature gave [ital n][tau][theta]=1.7[plus minus]0.9[times]10[sup 14] keV s/cm[sup 3].

  • ; ;
    A key issue for inertial confinement fusion (ICF) is the hydrodynamic stability of the imploding capsule. Imperfections on the capsule surface can grow into large perturbations that degrade capsule performance. Understanding this process is crucial if the authors are to successfully predict requirements for future high-gain ICF capsules. Experiments on the Nova laser at Lawrence Livermore National Laboratory have directly measured perturbation growth on planar foils, and three experimental groups have investigated backlit perturbation growth using imploding spheres. In addition to these efforts, which concentrate on indirectly driven implosions, is work investigating the hydrodynamic stability of directly driven ICF capsules.more » In these direct-drive experiments the laser light shines directly on the capsules, causing the implosion and providing the seed for perturbation growth. This article reports measurement, via emission from spectroscopic tracers, of the full process of perturbation growth leading to pusher-fuel mix in spherical implosions, and shows perturbation growth dependence on initial perturbation amplitude and wavelength. In contrast to the cited direct-drive work, the authors have in this experiment separated the drive from the perturbation seed.« less

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