Neutron irradiation of flint glasses for optics in ITER

Abstract

Radiation-resistant optics, which is necessary to transfer light from plasma to detectors in ITER, will be exposed to neutron fluxes at D-T stage. Achromatic lenses located in the interspace and in the port cell areas must have a sufficient optical radiation hardness to sustain a neutron irradiation without significant degradation of transmittance in as wide spectral range as possible. They will be made of two types of glass: KU1 fused silica and a flint glass. The radiation hardness of the candidate flint glasses under neutron irradiation to ITER-relevant doses has to be investigated.Six types of the commercial Ce-doped flint glasses have been irradiated in a nuclear reactor up to fluencies of the fast neutrons (E > 0.1 MeV) within the range of 1012 − 1016 n/cm2. F108 and TF200 types have demonstrated the most prominent results. F108 type has a high transmittance in the visible region and a sufficient radiation hardness to be recommended for use in the port cell. TF200 type has a limited spectral range, but it has shown the best radiation hardness at a fluence of 1016 n/cm2. It can be used in the interspace area if a low transmittance in the violet-blue region is not an issue. Keywords: Flint glass, Radiation hardness, Neutron irradiation, ITER