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The so-called fast ignition mode is one way to ignite
the thermonuclear fuel in systems of inertial fusion and decrease
of the necessary energy of the driver. In the present work the
second stage of the process—the heating, the thermonuclear
burning initiation under the influence of a powerful ion pulse,
and distribution of the burning all over the rest of the
cylindrical system—is studied. The main purpose of the
presented calculations was to determine the threshold of the
fast ignition of the cylindrical DT cord by a heavy ion beam.
Experiments carried out at the ISKRA-5 facility
have demonstrated high (not worse than 3%) symmetry of
the X-ray radiation flux inside a spherical case (hohlraum).
This fact gave us an opportunity for investigating into
compression of the targets with the initial nonspherical
geometry. The asymmetry affects both the total neutron
yield and the moment of neutrons generation. In this paper
we present the simulation results of the asymmetric targets
dynamics which were carried out by means of the 2D MIMOZA-ND
code. This code allows to take into account effects of
nonstationary, nonequilibrium, spectral transfer of X-ray
radiation. Comparison between simulation results and experimental
data was made. It was demonstrated that one could observe
a satisfactory agreement between experimental data and
the total neutron yield, as well as the time delay of the
moment of neutrons generation.
The first experiments to study the shell's
controlled asymmetry of capsule with DT-fuel in a highly
symmetrical X-ray field, which is obtained inside a spherical
hohlraum, were implemented. The asymmetry results from
the coating of one hemisphere with the additional layer
of material. The main goal of the experiment was to define
the value of the capsule asymmetry, allowing us to experimentally
obtain the neutron yield, which would be very different
from the yield obtained in the experiment with the spherically
symmetrical shell having the same mass as the asymmetrical
one. It was shown that the shell asymmetry of ∼50%
leads to the ∼(2–4) times reduction of the neutron
yield as compared with the symmetrical shell. 2D calculations
of the asymmetric capsule compression, using the MIMOZA-ND
code, were conducted. The calculations demonstrated that
the compression of targets, when exploding pusher regime
occurs has a complicated character. The computational neutron
yield, and the delay of the neutron generation time are
in good agreement with the experimental data.
The properties of heavy-ion induced fusion targets with two-sided illumination and with the converters placed completely inside the Hohlraum have been investigated using integrated simulations based on the SATURN and MIMOZA code packages in order to check the results obtained with the view-factor method in previous work, which is briefly reviewed. Separate converter simulations show the importance of an accurate treatment of radiation transport but also demonstrate that a converter efficiency of 40–80% can be achieved easily depending on the detailed converter material and geometry. For the complete target, a gas fill is shown to be necessary, and it turned out to be very important to allow some of the radiation shields to become partially transparent during the evolution. In the most favorable case, an asymmetry in the temperature on the capsule of about 5% was achieved, leading to a reduction of the neutron yield by a factor of 7 compared to an ideally symmetric situation.
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