Protection System for the Superconducting Outsert Coils of the HFML 45 T Hybrid Magnet

The High Field Magnet Laboratory of the Radboud University Nijmegen is developing a 45 T hybrid magnet consisting of a 33 T resistive insert magnet and a 12 T, all Nb₃Sn-Cu Cable-In-Conduit Conductor (CICC) based superconducting outsert magnet. Standard quench protection of the outsert coils is achieved with a permanently connected external dump resistor parallel to the coils. A major challenge is to prevent a quench of the outsert magnet during spurious trips of the insert circuit that may occur. Such an event is characterized by a fast decay of the insert current generating field changes at the windings of the outsert coils of a few T/s. Without precautions, the resulting AC losses in the superconducting strands would quench the inner windings. Here we present a model to analyse the effectiveness of an adapted protection scheme in terms of system and component characteristics and the required AC loss properties of the proposed CICC design.