Final Optic Protection Designs for ICF Containment Chambers

Abstract

The output from a laser-driven high-gain ICF target in the laboratory microfusion facility (LMF) target chamber could produce enough x-rays, shrapnel, and debris to severely damage the laser’s final optics. If the final optics were left unprotected, the replacement and reinstallation costs for each beam would exceed $40K. Assuming the laser has 68 beams, the replacement costs for each shot could reach $2.7M. To avoid these excessive costs, we must design a reliable optics protection system. This requires that we define the hazardous environment to which the optics are exposed.Thegeometrical layout for the 68 beams of the 10 megajoule laser shows the final optics placed at 25 meters from the target (see Fig. 1). The final optic will be a 2–5 cm thick debris shield ($40K each) which will be placed in front of a $200K focussing lens. Each of the 68 beams will deliver 150 kJ of 0.35 µm (3ω) light and will consist of either a 4×4 or a 2×8 array of beamlets, with each beamlet aperture having dimensions of 29 cm × 29 cm. This produces a 3ω energy density at the final optic of 12 J/cm2 average and 225-30 J/cm2 peak.