Irradiation test of fiber optics for H-alpha diagnostics in ITER

•Three silica fibers (high OH, high OH+H2, low OH+H2) have been irradiated at the Co-60 gamma source up to 15 kGy.•Relative transmittance of the fiber samples was measured during irradiation test.•There are no practically transmittance changing of the H2 doped fibers.•The best radiation resistance was demonstrated by the high OH+H2 silica fiber. The reliability of the optical diagnostics in ITER critically depends on a radiation resistance of the fiber optics for a transmission of the plasma light to remote detectors. The design of the H-alpha diagnostics includes the fiber bundles 60 m long, the first 10 m of that run through the gamma-neutron fields. This part of the bundle will accumulate the absorbed dose of no more than 10 kGy (for silica) and the total neutron fluence of 1014 n/cm2 in the ITER lifetime. The modern types of the radiation resistant silica-based fibers can be applicable in the visible range under such condition. The convenient way to select the fiber type is in-situ gamma irradiation test. The test has to be performed at a dose rate comparable to the radiation conditions in the ITER facility. The report is devoted to the irradiation tests of three types of the silica based fibers in the Co-60 gamma source at the dose rate of 0.015 Gy/s. The transmittance losses of the fibers were measured in-situ in the spectral range of 450–700 nm. The conclusion was made about the applicability of the tested fibers for the H-alpha diagnostics in ITER.