An analysis of grazing incidence metal mirrors in a laser ICF reactor driver
Abstract
Grazing incidence metal mirrors (GIMM's) are 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-ms pulse, irradiated mirrors made of Al, Al alloys, or Mg were found to have calculated laser damage limits of 0.3-2.3 J/cm(exp 2) of beam energy and neutron lifetime fluence limits of over 5 x 10(exp 20) 14 MeV n/cm(exp 2) when used at grazing incidence 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 m(exp 2) each. This chapter includes calculations of damage limits for GIMM's and discusses critical issues relevant to the integrity and lifetime of such mirrors in a reactor environment. The reflectivities of various metals are calculated from measured optical constants at room temperature and at cryogenic temperatures for 250- to 500-nm light at both normal and grazing incidence. Then, for the mirrors in a representative system, the thermal absorption and conduction rates of the best candidate metals are used with the maximum allowable cyclic thermal stress to give the maximum allowed surface-temperature rise and surface thermal load. The allowed surface thermal load and surface reflectivity give the maximum beam energy density and the minimum size for each mirror. For mirrors made of aluminum alloy 7475 and initially operated at room temperature, the resulting optical damage threshold and allowable temperature rise give a required mirror size for each final mirror. Critical issues relevant to the integrity and lifetime of such mirrors in a reactor environment are briefly discussed.
- Publication:
-
Unknown
- Pub Date:
- July 1991
- Bibcode:
- 1991agim.book.....B
- Keywords:
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- Fusion Reactors;
- Grazing Incidence;
- Inertial Confinement Fusion;
- Laser Damage;
- Laser Fusion;
- Mirrors;
- Reactor Design;
- Aluminum;
- Aluminum Alloys;
- Laser Beams;
- Magnesium;
- Metal Surfaces;
- Plasma Physics