Absorption and fluorescence phenomena of optical fibers under heavy neutron irradiation

For applying to optical diagnostics for fusion reactor, two types of radiation-resistant optical fibers have been fabricated and their optical phenomena were examined in the JMTR. The optical absorption due to radiation-induced defects and formation of color centers, is concentrated in the wavelengths less than 700 nm. By contrast, the absorption was quite low in the wavelength range from 700 to 1500 nm. The optical fibers appeared to have good radiation resistance and survived neutron irradiation up to 2 x 1024 n/m2. During JMTR irradiation, strong optical emission from 400 to 1400 nm with a sharp peak intensity at 1270 nm was observed. The peak value at 1270 nm is directly proportional to the reactor power. The results of absorption and fluorescence phenomena suggest the possibility of multi-parameter sensing for fusion reactor diagnostics. (orig.)