Ignition Capsules with Aerogel-Supported Liquid DT Fuel For The National Ignition Facility Page: 4 of 6
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(3) Carbon atoms in aerogel absorbs radiation and raises fuel entropy.
(4) Carbon in aerogel increases radiation loss during fuel assembly.
Optimizing the capsule performance, based on the understanding of these advantages and
disadvantages, is described in the following section.
3. A systematic approach to optimize wetted-aerogel capsules
We started with the NIF-scale, pure-DT capsule with plastic ablator (see Fig. 1). The NIF pure-DT
capsule has an outer radius of 1.108 mm ("ref. radius"), absorbs 167 kJ, and has a yield of 19.4 MJ.
----- r: H hter 1 J7 c
Si doped 15 at IS 1d im
Si doped 3 at % 55prn
Si doped. 1 5 at . 3 pr
DT 0255 gcc
DT gas 0 3 rlgcc
outer radius = 1.108 mm
ablator thickness = 192 vm
fuel thickness = 72.2 pm
fuel mass = 0.17 mg
Fig 1. Configuration of the NIF scale pure-DT capsule with plastic ablator.
This pure-DT capsule has good low-mode (t < 30) behavior as shown in Fig. 2. It is also robust
to high-mode (t < 1000) mix at the ablator-fuel interface, e.g. the clean fuel fraction is 83% at peak
velocity. Since the dominant perturbation at the ablator-fuel interface is around mode 60 and there is
only a 1 - 2 % difference in the clean fuel fraction between simulations with maximum mode of 200
and mode 1000, we will rely on simulations that include only low and intermediate modes, i.e.,
mode numbers up to 200, to estimate the amount of mix at the ablator-fuel interface.
If we replace the pure-DT fuel in this capsule by a wetted-aerogel with an aerogel density of 20
mg/cm3, at the same payload mass (mass of liquid DT + foam mass) and same DT gas density, then
the yield drops by more than 10%. Even worse, the wetted-aerogel capsule has considerably less
low-mode robustness than the pure-DT capsule as shown in Fig. 2. This figure also indicates that the
low-mode robustness deteriorates rapidly as aerogel density increases. For this reason, the focus of
our study will be based on an aerogel with density at 20 mg/cm3 (the density of liquid DT + aerogel
at 20 mg/cm3 is 0.2405 g/cm3).
liq. DT + 0.02 g/cc
liq. DT + 0.03 g/cc
2 3 4
ice-surface perturbation multiplier
Fig 2. Low-mode robustness of NIF scale pure-DT vs wetted-aerogel capsules with same outer radius.
To recovery from the lose yield and the reduced implosion velocity, we increase the wetted-
aerogel capsule radius by 2.4% from the ref. radius to 1.135 mm while maintaining the same fuel
mass of 0.17 mg. With the presence of the 20 mg/cm3 aerogel, the payload mass is increased to 0.184
mg. To ensure that there is enough ablator mass remaining and enough clean mass fraction at the
time of peak velocity, the ablator and the heavily doped layer thicknesses are also increased to 195
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Ho, D D; Salmonson, J D; Clark, D S; Lindl, J D; Haan, S W; Amendt, P et al. Ignition Capsules with Aerogel-Supported Liquid DT Fuel For The National Ignition Facility, article, October 25, 2011; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc838135/m1/4/: accessed November 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.