LAUSR

For the application of Re₁Ba₂Cu₃O_7-δ (REBCO: RE such as Y, Gd, and Eu) superconducting tapes to large-scale magnets, an enhancement of current capacity is required for magnet protection. In this study, a configuration of parallel conductors were introduced, and the current-sharing properties of three-strand parallel conductors wound into a pancake coil were investigated. An equivalent resistance exists even for a much smaller current than the critical current I_c. This should influence the current sharing among the tapes even if inductances are balanced by transposition. Uneven current sharing could lead to a fatal problem in the uniformity of a produced magnetic field, which is usually on the order of ppm. In this paper, every branch current was evaluated by numerically solving the circuit equation. As a result, it is shown that, in the case where the constituent tapes are different in I_c and n values, this should influence the current sharing among the tapes even if both the inductances and joint resistances are balanced among the tapes. An unbalance is serious when the difference in I_c and the n value is large. In addition, an unbalance increases as frequency decreases. The results suggest that uniformity in I_c and the n value of the REBCO tapes is important for the development of MRI magnets.