Study on the degradation of current-carrying performance of YBCO multi-filamentary tapes prepared by reel-to-reel ultraviolet picosecond laser cutting under pure torsion mode

YBCO multi-filamentary tapes’ current-carrying performance is susceptible to torsional stress during cable and magnet fabrication. In this study, commercial YBCO tapes from Shanghai Superconductor Technology Co., Ltd. were cut using a reel-to-reel ultraviolet picosecond laser cutting device developed by our group to fabricate 2-filament, 6-filament, and 10-filament multi-filamentary tapes. Additionally, some of the multi-filamentary tapes were encapsulated using the copper-plating re-encapsulation process developed by our group. The current-carrying performance degradation behavior of non-striated tapes, unencapsulated multi-filamentary tapes, and re-encapsulated copper-plated multi-filamentary tapes under pure torsion mode was systematically analyzed. The results show that the degradation behavior of multi-filamentary tapes is strongly dependent on the number of filaments. Specifically, the critical current degradation rates of unencapsulated non-striated tapes and unencapsulated 2-filament tapes are 12.11 % and 12.43 % respectively when the shear strain reaches 0.4125 %. In contrast, unencapsulated 6-filament and unencapsulated 10-filament tapes exhibit degradation rates of 11.69 % and 20.96 % respectively at a lower strain (0.375 %). For samples subjected to single-side copper-plated re-encapsulation with a thickness of 10 μm, the pattern of performance degradation is essentially consistent with that of the samples before copper-plated re-encapsulation, but their overall ability to withstand shear strain is improved by approximately 0.1 %. Macroscopic observations indicate that the surface of the tapes remains smooth without delamination after torsion; however, the “triangular” deformation feature reveals uneven internal stress distribution, suggesting that the superconducting layer may have incurred microscopic damage.​.