Reduction of screening-current induced strain in REBCO coils via preferential generation of perpendicular field during charging

Abstract The screening-current effect presents a crucial challenge in developing high-field high-temperature-superconducting (HTS) magnets. The concentrated screening-current induced strain (SCS) is a significant cause of mechanical damage in high-field REBCO magnets. In this work, we conducted an experimental study focusing on SCS differences under various background field charging sequences, demonstrating the SCS reduction effect of a perpendicular-field-first charging (PEFC) sequence. A 10-turn REBCO test coil was placed near a 4.35 T HTS magnet within a 10 T LTS external magnet. The HTS magnet generated a perpendicular background field on the REBCO test coil, while the LTS external magnet provided a parallel background field. When the perpendicular field was first charged, the peak hoop strain at the upper edge of the test coil was both calculated and measured to be smaller at the target field. The measured axial field near the test coil also showed a lower value with the PEFC sequence. The primary mechanism of this SCS reduction was local demagnetization at the edges of REBCO tapes. This study demonstrates the effectiveness of the PEFC method in reducing the peak SCS in REBCO insert coils and provides experimental references for mitigating strain-related issues in high-field HTS magnets.