Grazing Incidence Metal Mirrors as the Final Elements in a Laser Driver for Inertial Confinement Fusion

Grazing incidence metal mirrors (GIMMs) have been examined to replace dielectric mirrors for the final elements in a laser beam line for an inertial confinement fusion reactor. For a laser driver with a wavelength from 250 to 500 nm in a 10-ns pulse, irradiated mirrors made of Al, Al alloys, or Mg were found to have calculated laser damage limits of 0.3–2.3 J/cm² of beam energy and neutron lifetime fluence limits of over 5 × 10²⁰ 14 MeV n/cm² (or 2.4 full power years when used in a 1,000-MW reactor) when used at grazing incidence (an angle of incidence of 85 degrees) and operated at room temperature or at 77 K. A final focusing system including mirrors made of Al alloy 7475 at room temperature or at liquid nitrogen temperatures used with a driver which delivers 5 MJ of beam energy in 32 beams would require 32 mirrors of roughly 10 m² each. This paper briefly reviews the methods used in calculating the damage limits for GIMMs and discusses critical issues relevant to the integrity and lifetime of such mirrors in a reactor environment.