Ac-loss measurement of small superconducting Bi-2223 test coils wound with multifilament barrier type conductors

Internally assembled ring-bundle-barrier Bi-2223 tapes with a Rutherford type stranded structure were optimised with respect to low coupling losses. They had resistive barriers of a mixture of SrCO₃ and SrZrO₃ around the strands and around the central Ag core. From these tapes small test coils were wound and the ac losses were measured with a sinusoidal ac transport current at 77 K. The loss measurement was performed by the standard magnetization technique. A calorimetric calibration yielded the correct absolute values of the losses. The results show that the main loss component is hysteretic, and coupling losses do not contribute significantly to the total losses. The suppression of coupling losses due to the resistive barriers leads however to a small critical current of the tapes and further optimisation with respect to losses and critical current is necessary.