BEHAVIOR OF OPTICAL FIBERS UNDER HEAVY IRRADIATION

Several kinds of optical diagnostics are planned in a fusion reactor. Complicated optical systems such as periscopes are thought to be prima ry candidates for optical measurements, especially for visible wavelen gths. However, optical fibers have several advantages over such optica l systems. Also, the optical fibers could be a far better transmission line for signals under a high electromagnetic field. However, they ha ve been considered vulnerable to heavy irradiation. In this study, sev eral kinds of optical fibers were irradiated in the Japan Material Tes ting Reactor (JMTR). The optical transmissivity in fibers was measured in situ during fast neutron and gamma irradiation, up to doses of 2x1 0(24)n m(-2) and 5 x 10(9) Gy, respectively. The irradiation temperatu re ranged from 300 to 700 K. For pure ionizing irradiation environment s, some methods for improving the radiation resistance of optical fibe rs were indicated. The results showed that effects of the irradiation associated with fast neutrons would be different from the effects of p ure ionizing irradiation. Some fibers were found to withstand the heav y irradiation, especially in an infrared wavelength range. (C) 1998 Pu blished by Elsevier Science S.A. All rights reserved.