Status of instrumentation and diagnostics using fiber optic sensors for superconductors
Abstract: In the framework of HL-LHC, FCC and the HTS program, fiber optic sensors have been integrated into several magnets and superconducting cables to monitor strain and temperature. A single optical fiber can replace tens of traditional single-point resistive sensors, providing a significant reduction in installation, calibration, and maintenance costs allowing monitoring assets. The fragility of the optical fibres and the high-stress environment in a superconducting magnet makes the integration of the fibres still very demanding. FBG sensors, equipped with a functionalized coating material to improve temperature sensitivity have been calibrated and integrated into a 20-meter long cryostat for 18 kA MgB2 Superconducting Link for temperature monitoring. FBG sensors have been integrated in four different Nb3Sn HL-LHC magnet models for monitoring the mechanical behaviour from its assembly to its operation in cryogenic conditions. FBG sensors, embedded during cable winding and coil assembly steps makes it possible to monitor the resin impregnation process by providing information on the uniformity of the process. Feather-M2, designed to test Roebel type HTS cable, has been equipped with FBG sensors and a distributed optical fiber sensing based on Rayleigh scattering. Implementation in magnets was successful in 91% of cases, with 44 FBG sensors working. The presentation will give an overview of the recent advances in the FOS development for cryogenic applications and results of the sensors integration, with an introduction to the dedicated fiber laboratory that has been set up at SM18 for FOS characterization.