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

Abstract 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 10 14 n/cm 2 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.