Study of color centers in optical fibers to be used for ITER plasma diagnostics

The paper presents a comparative study, by off-line measurements of the irradiation induced optical attenuation in several large diameter (600 μm) optical fibers subjected to gamma-rays and neutron irradiation. The optical fiber samples fall into two categories: optical fibers with an enhanced UV transmission (high OH content core) and solarization resistant optical fibers. The irradiation conditions were as follows: a) gamma irradiation at a 60Co source, with a dose rate of 0.33 kGy/h +/- 5%, up to the maximum total irradiation dose of 313 kGy; b) neutron irradiation (mean energy 5.2 MeV) using a deuteron beam (13 MeV) and a thick beryllium target, for a total fluence of 6x1012 n.cm-2. Electron paramagnetic resonance measurements have been carried out to further investigate the radiation sensitivity of the considered fibers and to identify irradiation induced paramagnetic point defects.