Mechanical Stress Analysis of RE-Ba-Cu-O Bulk Superconductors for the HTS Undulator During Assembly, Cool down and Field-Cooled Magnetization

The bulk high-temperature superconducting undulator can produce an on-axis magnetic field of up to 2.1 T for a period as short as 10 mm, outperforming current permanent magnet and low-temperature superconducting undulators. This paper presents a comprehensive analysis of the electromagnetic-mechanical coupling in RE-Ba-Cu-O (REBCO) bulk superconductors within the HTS undulator during the assembly, cool down and field-cooled magnetization processes. It is calculated that the compressive stress exerted by the copper disk upon cooling to 77 K significantly exceeds the pre-stress from the shrink-fit assembly. This indicates that the interference amount between the REBCO bulk and the copper disk can be minimized, allowing for a small degree of interference amount to facilitate shrink-fit assembly while ensuring effective thermal contact for enhanced heat conduction efficiency. It is observed that the maximum first principal stress in the REBCO bulk superconductor after field-cooled magnetization from 7 T is reduced to below 50 MPa when accounting for the pre-stress induced by the copper disk. To validate these computational findings, we developed a strain measurement system to assess the mechanical stress in the REBCO bulk superconductor after cooling to 77 K. The experimental results demonstrated good agreement with the simulation results.