Quench Protection Analysis of 20 T Hybrid Accelerator Dipole Magnets

The US Magnet Development Program is leading an effort to design and manufacture a 20 T accelerator dipole magnet. Various designs are under development featuring cos-theta, block-coil, or common-coil geometries. To achieve the target field while maintaining cost-effectiveness the magnet cross-section includes high-temperature superconductor (HTS) inner coils and Nb3Sn outer coils, which are all powered in series. The quench protection of this class of high-field accelerator magnets is extremely challenging due to the high energy density, high current density, slow quench propagation, in particular in the HTS coils, and highly inhomogeneous thermal properties of HTS and Nb3Sn coils. The magnet quench discharge is simulated with the STEAM-LEDET program as coupled electro-magnetic and thermal transients. The peak temperature and voltage to ground in the magnet coils during the transient are presented. The performance of a CLIQ-based quench protection system applied to 1 m long model magnets in terms of peak temperature and voltage to ground is investigated. Furthermore, the scalability of the proposed solution to full-scale, 15 m long magnets is discussed.