Final optics for laser-driven inertial fusion reactors

A promising concept for the final optics of a baseline laser-driven ICF (inertial confinement fusion) reactor is described. It addresses the problem of long-term survival of the final optics with respect to neutron damage. The use of refractive optics is considered. A baseline design consists of two wedges of fused silica, which put a dogleg into the beam and thus remove optics further upstream from direct sight of the reactor. If the closest optic were located 40 m from the center of a 3-GWt reactor, it would be subject to an average 14-MeV neutron flux of ≈5×10¹² n/s-cm² with a peak flux of ≈6×10¹⁸ n/s-cm². A major question to be answered is: What duration of reactor operation can this optic withstand? To answer this question, the literature bearing on radiation-induced optical damage in fused silica was reviewed to assess its implications for reactor operation with the baseline final optics scheme. It appears possible to continuously anneal the neutron damage in the silica by keeping the wedge at a modestly elevated temperature. The literature review indicates that the proposed final optic material-fused silica-is structurally resistant to radiation damage and that if operated at a temperature of about 300°C will remain optically clear