Fiber Bragg Grating Cryo-Sensors for Superconducting Accelerator Magnets

The design, fabrication and tests of the new generation of superconducting magnets for the High Luminosity upgrade of the Large Hadron Collider (HL - LHC) require the support of an adequate sensing technology able to assure the integrity of the strain sensitive and brittle superconducting cables through the whole service life of the magnet: assembly up to 150 MPa, cool down to 1.9 K and powering up to about 16 kA. A precise temperature monitoring is also needed in order to guarantee the safe working condition of the superconducting cables in the power transmission lines (SC - Link) designed to feed the magnet over long distance. Temperature and strain FBGs based monitoring systems have been implemented in the first SC-Link prototype and in two subscale dipole magnets and tested in the cryogenic test facility at CERN at 30 K, 77 K and 1.9 K.