Influence of Excitation Sequences on Screening-Current Induced Strain in a 36 T Ultra-High-Field Magnet: Numerical Analysis and Discussion

The screening-current induced strain (SCS) increase the risk of mechanical degradation during the operation of REBCO insert magnets. In this work, we focused on a 36 T all-superconducting magnet and conducted a numerical analysis to study the influence of excitation sequences on the SCS in a representative REBCO single pancake (Coil 1 SP 1). We compared several typical sequences, including External-First (EF), where the initial step is to ramp up the external field to 20 T first, followed by the 16 T insert, and Insert-First (IF), which requires ramping up the insert field to 16 T first, followed by the external field. The SCS results significantly differed between these two cases. When the magnet reached a center field of 36 T, the maximum SCS in Coil 1 SP 1 was significantly lower in the IF case compared to EF. We discussed the probable mechanism behind this phenomenon and presented the calculated SCS results for EF and IF cases without considering the tilting effect. These results revealed that the existence of tilting angle was probably the reason for the differing SCS distribution.