An evaluation of multilayer mirrors for the soft x ray and extreme ultraviolet wavelength range that were irradiated with neutrons

The Plasma Spectroscopy Group at the Johns Hopkins University develops high photon throughput multilayer mirror (MLM) based soft x ray and extreme ultraviolet (XUV 10 Angstrom <λ<304 Angstrom) spectroscopic diagnostics for magnetically confined fusion plasmas. The D-T reactions in large fusion reactor type devices such as the International Thermonuclear Experimental Reactor will produce neutrons at a rate as high as 5x1019 ns-1. The MLMs, which are used as dispersive and focusing optics, will not be shielded from these neutrons. In an effort to assess the potential radiation damage, four MLMs (No. 1: Mo/Si, d=87.8 Angstrom, Zerodur substrate with 50 cm concave spherical curvature; No. 2: W/B4C, d=22.75 Angstrom, Si wafer substrate; No. 3: W/C, d=25.3 Angstrom, Si wafer substrate; and No. 4: Mo/Si, d=186.6 Angstrom, Si wafer substrate) were irradiated with fast neutrons at the Los Alamos Spallation Radiation Effects Facility (LASREF). The neutron beam at LASREF has an energy distribution that peaks at 1 endash 2 MeV with a tail that extends out to 100 MeV. The MLMs were irradiated to a fast neutron fluence of 1.1x1019 ncm-2 at 270 endash 300 degree C. A comparison between the dispersive and reflective characteristics of the irradiated MLMs and the corresponding qualities of control samples will be given. copyright 1997 American Institute of Physics