Design and Quench Protection Analysis of a 9 T NbTi Superconducting Magnet for a Large-Bore EMPS

A 9 T NbTi superconducting magnet with a large bore is designed and will be fabricated for an EMPS (electro-magnetic property measurement system) whose sample space is 50 mm in diameter. To match the large sample space of the system, the winding bore of the magnet should exceed 89 mm in diameter. Because the winding diameter is much larger than a conventional 9 T class NbTi superconducting magnets, wire selection and magnet design are very important and difficult in this research. An optimal design process with a genetic algorithm considering the critical current, magnetic stress, thermal stability and field uniformity is carried out to develop the 9 T large bore NbTi EMPS magnet. The design algorithm calculates the structure and dimensions of the magnet to minimize the total volume while satisfying the constraints related to the stability of the magnet [Jang et al. (2018)]. To evaluate the thermal stability of the magnet with a protection circuit, a quench analysis is also implemented considering the two boundaries among three adjacent coaxial NbTi coils. The maximum hot spot temperature of the magnet is calculated based on the quench analysis model via a numerical analysis and an electrical circuit simulation. After the optimized design is created, fabrication of the 9 T large bore NbTi magnet will be conducted for its application to the large bore EMPS.