In situ transmissivity measurements of KU1 quartz in the UV range under 14 MeV neutron irradiation

The transmissivity of KU-1 quartz which is a candidate of the window material for UV and visible spectroscopy in ITER was measured under the irradiation of 14 MeV neutrons up to the fluence of 7.4×1019 n/m2 in the UV range (200–400 nm). Significant transmission loss was observed in the wavelength range of 200–300 nm. Two absorption peaks were identified: an E′-center at 215 nm and Si(III) defects at 245 nm. The E′-center absorption is much larger than the Si(III) defect absorption. The transmission loss increased with the neutron fluence, decreased during the irradiation breaks and returned almost to the same level as before when the irradiation resumed. This phenomenon indicates that an absorption induced by the neutron irradiation is caused by stable scattering and short lifetime centers.