No abstract

Cuprate high-temperature superconductors (HTS), such as RE-Ba 2 Cu 3 O 7−δ (REBCO, RE = rare earth), (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10−x and Bi 2 Sr 2 CaCu 2 O 8−x , have enabled the development of high-field superconducting magnets capable of generating magnetic fields far exceeding 20 T. The brittle nature of HTS requires elaborate means to protect them against the high stresses and strains associated with high-field magnet operation, and so far, has prevented reliable high-field HTS magnets from becoming a reality. Here we report a more than tenfold increase in the irreversible strain limit under axial tension (ε irr ) to over 7% in optimized high-current conductor on round core (CORC ® ) conductors, compared to the REBCO tapes from which the CORC ® conductor is wound. Minimizing the tape winding pitch of the helical wind mechanically decouples the brittle REBCO film from the overall conductor. The REBCO tapes behave as springs, limiting the rate at which applied strain is transferred to the ceramic film. In addition, high-strength alloy cores allow the critical stress (ε crit ) under axial tension at which initial degradation of CORC ® conductors occurs to exceed 600 MPa, making them one of the strongest superconductors available. Mechanically decoupling the ceramic REBCO films from the overall CORC ® conductor allows effective protection against the high operating stresses in high-field magnets. This breakthrough presents a monumental shift for HTS magnet technology, bringing reliable high-field superconducting magnets for compact fusion machines, the next generation of particle accelerators, and 40-60 T research solenoids within reach.