Radiation hardness of passive fiber optic components for the future thermonuclear fusion reactor instrumentation links

The future thermonuclear fusion reactor ITER will require remote-handled equipment to monitor its operation and to allow hazard-free manipulations during its frequent maintenance periods. Heavy shielded umbilicals will be required to connect the sensors and the actuators with their instrumentation. Multiplexing sensor signals turns out to be essential to ease the umbilical management. We are considering fibre optic technology, with its intrinsic wavelength multiplexing (WDM) capabilities, to handle these ITER multiplexing issues. We propose a new analog data link design for low-bandwidth sensors and actuators based on commercial-off-the-shelf (COTS) fiber optic components. We rely on passive components such as WDM couplers and fibre Bragg gratings (FBG) to build a radiation-resistant analog data link. WDM couplers remain operational up to a 13 MGy gamma total dose. A radiation-induced channel drift is observed. The refractive index change under ionizing radiation is proposed as the degradation mechanism. FBG filters continue to operate satisfactorily up to a 150 MGy total gamma dose and a neutron fluence of about 1015 n/cm2. Our results on these COTS all-fibre passive components open perspectives to build a radiation-tolerant analog optical data link compatible with the ITER requirements.

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