Stress Analysis of Winding Process, Cooling Down, and Excitation in a 10.7 T REBCO HTS Magnet

A 25.7-T, 32-mm cold bore HTS/LTS superconducting magnet has been fabricated and tested at Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS). The REBCO HTS insert experienced large stress state while it was energized up to the target field, which is harmful for the protection of the HTS insert. In this paper, to understand the stress distributions in the HTS insert clearly, a simulation model was proposed, in which the analysis was divided into three stages, i.e., winding process, cooling down, and excitation. The effects of winding tension, band wound over the HTS insert were considered while the HTS insert is fabricated. The residual thermal stress caused by the thermal contraction differences of the coil, mandrel, and band was analyzed during the cooling down process. The final stress state was compared with the stress induced only by the electromagnetic force, which shows a large difference. The experiments conducted after the HTS insert quenched at 25.7 T proves that is not mechanical damage in the HTS magnet and the analysis results are believable.