Finite Element Design and Magnetization Issues of Ring-Shaped Cryo-Permanent Magnets

Trapped peak magnetic fields beyond 15 T obtained for melt-textured 123-High-Temperature Superconductor (HTS) bulk cylinders, make these materials highly attractive for cryo-permanent magnets (CPM). However, to in-situ magnetize such HTS bulk parts using pulsed copper coils, and, in particular to reduce the required peak magnetic field, is a key issue for turning the proven material performances into practical magnetic devices. Novel concepts like the injection-current assisted pulsed magnetization of ring-shaped CPM's are needed. Based on the modeling of the superconducting HTS bulk properties and finite element designs this approach is investigated semi-quantitatively. A still simple but very compact design taking into account all components of the resonant structure, has been chosen. Time evolutions of magnetic field profiles are presented. The results reflect the complexity of such highly dynamic and nonlinear magnetization processes. Comparisons are made for two different multi-pulse sequences without and with current injection. The latter obviously always leads to a higher trapped magnetic flux. Thus the presented model calculations gives confidence that based on further optimizations even trapped magnetic field profiles of les 5 T over ges 10 cm can be achieved with pulsed copper coils