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Electrical Engineering, Measurement and Control Technology
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 Å〈λ〈304 Å) 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 5×1019 n s−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 Å, Zerodur substrate with 50 cm concave spherical curvature; No. 2: W/B4C, d=22.75 Å, Si wafer substrate; No. 3: W/C, d=25.3 Å, Si wafer substrate; and No. 4: Mo/Si, d=186.6 Å, 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 1–2 MeV with a tail that extends out to 100 MeV. The MLMs were irradiated to a fast neutron fluence of 1.1×1019 n cm−2 at 270–300 °C. A comparison between the dispersive and reflective characteristics of the irradiated MLMs and the corresponding qualities of control samples will be given. © 1997 American Institute of Physics.
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