Screening-current-induced mechanical strains in REBCO insert coils

In recent years, remarkable progresses have been made in the R&D efforts for high temperature superconducting (HTS) high-field magnets. The screening-current-induced magnetic field and mechanical stress/strain in rare-earth barium-copper-oxide (REBCO) coils are raising growing concerns. This paper presents experimental and theoretical analyses on the effects of screening-current-induced mechanical strains in a REBCO insert setup without transport currents. Strain measurements on two REBCO coils, with and without over-banding structures, were carried out in an low temperature superconducting (LTS) background field magnet. Electromagnetic-mechanical models were developed, coupling the tilting angles of the superconducting tapes and the strain dependency of the critical current. The discrete-coupled model with turn-to-turn contacts, the discrete-sequential model and the block model were implemented and compared against the measured hoop strains. Combining experimental data with simulation models, it is shown that moderate over-banding structures are effective in providing reinforcements for the superconductors. A new method of edge-bonding was proposed and tested, which could reduce hoop strains in low applied fields but failed in higher fields. This work could be useful for the design and analysis of future high-field REBCO magnets.