Abstract
Abstract A numerical method providing the optimal laser intensity profiles for a direct-drive inertial confinement fusion scheme has been developed. The method provides an alternative approach to phase-space optimization studies, which can prove computationally expensive. The method applies to a generic irradiation configuration characterized by an arbitrary number $N_{B}$ of laser beams provided that they irradiate the whole target surface, and thus goes beyond previous analyses limited to symmetric configurations. The calculated laser intensity profiles optimize the illumination of a spherical target. This paper focuses on description of the method, which uses two steps: first, the target irradiation is calculated for initial trial laser intensities, and then in a second step the optimal laser intensities are obtained by correcting the trial intensities using the calculated illumination. A limited number of example applications to direct drive on the Laser MegaJoule (LMJ) are described.
Highlights
In the direct-drive (DD) inertial confinement fusion (ICF)[1, 2] context a spherical capsule containing the deuterium– tritium (DT) nuclear fuel is irradiated by laser beams
The method can be used for any DD laser configuration accounting for a general number NB of laser beams, provided that the beams irradiate the whole target surface
In some sense this is a kind of predictor–corrector method that consists of two steps: firstly, initialized by a set of NB trial laser intensity profiles, the imperfect surface irradiation is calculated; the beam profiles are recalculated in order to correct the previously estimated nonuniform illumination
Summary
In the direct-drive (DD) inertial confinement fusion (ICF)[1, 2] context a spherical capsule containing the deuterium– tritium (DT) nuclear fuel is irradiated by laser beams. The external shell of the capsule absorbs a fraction of the incoming laser energy producing a plasma; the plasma temperature (≈keV) increase provides the outward expansion of the low-density corona and launches a series of inward shock waves. These shock waves compress the DT payload in a high-density shell that implodes and reaches stagnation. MegaJoule (LMJ)[11] or the smaller Orion[12] facility where the locations of the beams are optimized for the indirectdrive[13] ICF scheme In these latter cases the optimal laser intensity profiles must be adapted to the laser configuration. The laser intensity profiles are not necessarily equal to each other or axially symmetric
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