Impact of Localized Radiative Loss on Inertial Confinement Fusion Implosions

A. Pak, L. Divol, C. R. Weber, L. F. Berzak Hopkins, D. S. Clark, E. L. Dewald, D. N. Fittinghoff, V. Geppert-Kleinrath, M. Hohenberger, S. Le Pape, T. Ma, A. G. MacPhee, D. A. Mariscal, E. Marley, A. S. Moore, L. A. Pickworth, P. L. Volegov, C. Wilde, O. A. Hurricane, and P. K. Patel

Phys. Rev. Lett. 124, 145001 – Published 6 April 2020

Abstract

The impact to fusion energy production due to the radiative loss from a localized mix in inertial confinement implosions using high density carbon capsule targets has been quantified. The radiative loss from the localized mix and local cooling of the reacting plasma conditions was quantified using neutron and x-ray images to reconstruct the hot spot conditions during thermonuclear burn. Such localized features arise from ablator material that is injected into the hot spot from the Rayleigh-Taylor growth of capsule surface perturbations, particularly the tube used to fill the capsule with deuterium and tritium fuel. Observations, consistent with analytic estimates, show the degradation to fusion energy production to be linearly proportional to the fraction of the total emission that is associated with injected ablator material and that this radiative loss has been the primary source of variations, of up to 1.6 times, in observed fusion energy production. Reducing the fill tube diameter has increased the ignition metric $χ_{no α}$ from 0.49 to 0.72, 92% of that required to achieve a burning hot spot.

Received 21 June 2019
Revised 18 February 2020
Accepted 18 March 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.145001

Physics Subject Headings (PhySH)

High-energy-density plasmas Indirect drive

Plasma Physics

Authors & Affiliations

A. Pak ¹, L. Divol¹, C. R. Weber¹, L. F. Berzak Hopkins¹, D. S. Clark¹, E. L. Dewald¹, D. N. Fittinghoff ¹, V. Geppert-Kleinrath ², M. Hohenberger¹, S. Le Pape¹, T. Ma¹, A. G. MacPhee¹, D. A. Mariscal¹, E. Marley¹, A. S. Moore¹, L. A. Pickworth¹, P. L. Volegov², C. Wilde², O. A. Hurricane¹, and P. K. Patel¹

¹Lawrence Livermore National Laboratory, Livermore, California 94550, USA
²Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

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Vol. 124, Iss. 14 — 10 April 2020

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Images

Figure 1
(a) Experimental setup showing the hohlraum and capsule target. X-ray and neutron images are taken along three and two lines of sight, respectively [19, 20]. The polar and azimuthal angle for each detector are denoted. The fill tube enters the capsule at an angle of 90-07 as indicated by the green line. (b) Illustration and radiograph of the initial capsule with dimensions given in $μ m$ . The light and dark gray regions denote the undoped, doped with an atomic fraction of 0.33% of tungsten layers of the HDC ablator, respectively. The blue region denotes the DT ice layer. (c),(d) Observed x-ray emission along the 00-00 line of sight at stagnation integrated over $\sim 125 ps$ for experiments conducted with a 10 and $5 μ m$ fill tube, respectively. The green arrow indicates the initial orientation of the fill tube. (e) 3D reconstruction of the hot spot temperature ( $> 2 keV$ ) for N170601 produced using two temporally integrated neutron emission measurements (outlined in red). Using three x-ray images (outlined in black) the region of localized mix within the hot spot can be reconstructed and is shown by the green contour.
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Figure 2
(a),(b) Profiles of hot spot temperature for experiments N170821 and N170601 conducted with a 10 and $5 μ m$ fill tube, respectively. The shaded region indicates the region of fill tube mix. The dashed and solid lines indicate the direction along which the temperature profile in (c) are taken. The over-plotted dashed and solid green lines denote the location of the mixed material.
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Figure 3
(a) Yield vs observed emission mix fraction for five experiments with same drive conditions. The fill tube diameter was 2 and $5 μ m$ for the blue and red data, respectively. Open black squares are the observed emission mix fractions of simulated x-ray images from implosions with increasing fill tube diameters (0, 2, 5, 10, 15, $20 μ m$ ). The solid line represents the best linear fit to the data. Images of the x-ray emission with energies $> 10 keV$ for the different observed mix fractions are also shown. (b) Observed yield vs expected yield using Eq. (2), with and without taking into account the impact of radiative loss shown by the black circles and red squares, respectively. (c) Inferred yield amplification vs $χ_{no α}$ with regions of burning hot spot and plasma denoted as defined by [30]. Green and red circles indicate experiments N170821 and N170601 conducted with a 10 and $5 μ m$ fill tube, respectively. The red and blue diamonds denote experiments shown in Fig. 3. Higher yield amplifications can be obtained in simulations of implosions of similar adiabat (2.9 vs 3), without drive asymmetries and with 1.15 times larger capsules that absorb $\sim 1.15$ times more energy and obtain a velocity 1.09 times larger than experiments reported here.
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