Current distribution in superconducting parallel conductors wound into pancake coils

We made a preliminary investigation of the applicability of high-T_c superconducting parallel conductors to pancake coils. For the sake of a uniform current distribution and low ac loss, the constituent strands need to be transposed so as to be inductively equivalent with each other. We adopted an interdisk transposition where the strands are not transposed inside a single-pancake coil but only at the joint between the pancake coils. The fabrication process is simple. We have only to fabricate the same double-pancake coils and connect the strands individually with transposition outside the winding. We searched theoretically for the optimum transposition in the case of 3-strand and verified the theoretical result by using small test coils wound with NbTi 3-strand parallel conductors for convenience.