An inertial confinement fusion capsule directly driven by laser beams has been considered. A ray-tracing package is used to evaluate the uniformity of the energy deposition and the absorption efficiency provided by the direct irradiation of the capsule. Two distinct configurations with a single laser beam or a bundle of nine laser beams associated to 32 directions of irradiation are considered. Assuming a beam-to-beam power imbalance of 5% and a super-Gaussian spatial profile of the beams intensity, is found that the configuration using the bundles provides better irradiation uniformity. The laser beams of each bundle have been divided in two groups of four and five beams with associated different focal spots in order to increase the laser-capsule coupling efficiency. A configuration saving 16% of the laser energy and limiting the irradiation nonuniformity to less than 1% has been individuated.
One of the biggest challenges the HiPER project is facing is to identify a laser architecture that meets all the demanding requirements. Among those are high wall-plug efficiency (15 to 20%) and repetition rate (5 to 10 Hz). In order to perform this task, four teams from the co-authors' institutions are working together and exploring several approaches described here.
The uniformity of the illumination of a spherical capsule directly driven by laser beams has been assessed numerically. Two schemes characterized by 32 and 48 directions of irradiation with associated a single laser beam or a bundle of laser beams characterized by a super-Gaussian intensity profile are considered. The calculations take into account beam imperfections as power imbalance and pointing errors. It is found that the optimum laser intensity profile, which minimizes the illumination uniformity, depends on the beams’ imperfections. A comparison between both schemes shows that the 48 beams configuration allows better illumination uniformity than the 32 beams’ configuration.
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