Inter-strand coupling losses in Bi-2212 Rutherford cables

Inter-strand coupling loss measurements were carried out in liquid helium for Bi-2212 Rutherford cables composed of 30 non-twisted strands. Short, straight samples composed of three stuck cables were set in a uniform field space inside the NbTi magnet of race-track and split type. Frequency characteristics of coupling losses were observed for transverse ac magnetic field, both perpendicular and parallel to the flat face of cables. An additional measurement of ac losses was carried out in order to clarify properties of hysteresis losses and intra-strand coupling losses. The obtained effective filament diameter describing the hysteresis loss property indicated that almost all filaments in strands were strongly connected to each other. From both this result and the frequency characteristics of coupling losses for the perpendicular field case, the inter-strand coupling time-constant was given in the order of 10 m. Moreover, the effective contact resistance between crossover strands in the cable was also given in the order of 10(-10) Omega m(2), which was the same order as that for the NbTi Rutherford cable composed of Cu matrix strands.