Fundamental Research in High Energy Density Science (2023) / Chapter Skim
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Appendix A: Approaches to Inertial Confinement Fusion
Appendix A: Approaches to Inertial Confinement Fusion
Pages 101-110
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From page 101... ...
With laser indirect drive (LID) , as seen in Figure A-1, lasers are directed onto the inner walls of a cylindrical cavity called a hohlraum, at the center of which sits the spherical, fuel-filled implosion capsule.
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From page 102... ...
long enough to trap the energetic fusion reaction products from these initial reactions, it can return their energy to the dense fuel layer as additional heat. If the confinement time is sufficient, this self-heating can increase temperatures to 20,000 eV, exponentially increasing both the participating fuel volume and rate of fusion reactions, leading to an explosive release of energy called ignition.
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From page 103... ...
While this improved symmetry control, the low gas fills led to a faster filling of the hohlraum with plasma. Significant progress was made on reducing effects of engineering features; for example, the fill tube size was reduced five-fold.
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From page 104... ...
The spherical concentric layers of a LDD ICF target typically consist of a central region of DT vapor surrounded by a cryogenic DT-fuel layer and a thin, nominally plastic layer, called the ablator. The incident laser drive is designed to be as spa tially uniform as possible on the outer surface of the capsule, using multiple laser beams with a peak, overlapped intensity of <1015 watts/cm2.
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From page 105... ...
:110501, https://doi.org/10.1063/1.4934714. As the DT-fuel layer decelerates, the initial DT vapor and the fuel mass that was thermally ablated from the inner surface of the DT-ice layer are compressed and form a central hot-spot plasma having a pressure of ~100 Gbar, in which fusion reactions occur for a few tenths of a nanosecond around stagnation.
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From page 106... ...
Low-mode implosion asymmetry has been studied using X-ray imagers and nuclear diagnostics with multiple lines of sight, characterizing the in-flight shell asymmetry and the hot-spot flow velocity at stagnation. FIGURE A-3 Extrapolated fusion yield at 2 MJ of laser energy for spherical direct drive OMEGA DT cryogenic implosions performed at 0.03 MJ plotted as a function of the energy-scaled generalized Lawson parameter (hot-spot pressure × hot-spot confinement time)
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From page 107... ...
MAGNETIC DIRECT DRIVE AND MAGNETO-INERTIAL FUSION Magnetic direct drive (MDD) fusion is distinct from the two laser fusion concepts in that the implosive force is provided by the interaction of direct current through a cylindrical target with its own self-generated magnetic field, rather than by photons.
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From page 108... ...
The magnetic field inhibits radial heat conduction, keeping the fuel hot during the implosion. Right: an increasing current drives a relatively slow, 100 km/s cylindrical implosion, increasing the fuel tempera ture to ~3-4 keV, compressing the fuel to ~0.3 g/cm3, and flux-compressing the axial field to ~10-20 kT, producing a stagnating plasma that generates 1013 DD fusion neutrons (2kJ DT equivalent)
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From page 109... ...
Introducing an external axial magnetic field before the implosion solves both of these problems: the magnetic field inhibits radial conduction losses, keeping the fuel hot during the implosion, and the initial magnetic field is flux compressed by the implosion to such a degree that it effectively traps and confines charged fusion products that are emitted in the radial direction. In the axial direction, MDD has sufficient areal density to inertially confine charged fusion products.
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From page 110... ...
These experiments include novel diagnostics that can detect mix from various target com ponents (mix is a concern for MIF because, unlike conductive heat losses, radiative heat losses from high-Z impurities in the hot fuel are not inhibited by the external magnetic field)
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