Losses in 2G Tapes Wound Close Together: Comparison With Similar 1G Tape Configurations

In multilayer and magnetically coupled coils made from tape, the loss in each segment of tape in a coil depends on the parallel segments in the adjacent layers. In the case of a single multilayer coil, the current in all the layers is the same, but in magnetically coupled coils, the current in adjacent layer from different coils can be different both in amplitude and phase-usually 180 degrees out of phase one with respect to the other. In previous work, we have studied the influence of the proximity between tapes by considering the total loss in a segment as the sum of three components: the transport current in it, the global magnetic field due to the complete coil (or coils), and the local magnetic field due to the current in the tape wound just over or under the segment in question. To measure the last component, an experimental method has been proposed and carried out with Bi-2223 tape, showing that the loss in the tape can be increased or reduced by the proximity of another tape, depending on the current, if any, that the latter carries. By means of the loss variation, we have shown how the variation of transport currents (and, therefore, of the associated magnetic fields) influences the practical critical current of the tape under test. Advances in YBCO tape (2G tape) fabrication have led to increases in the field tolerance of the tape, and the dependences of loss and practical critical current on the proximity of an adjacent tape needed to be revised. In the present work, we study the behavior of the loss in 2G tapes under the influence of other tapes carrying zero or different currents. A comparison between Bi-2223 and YBCO tapes is shown.