MAGNETIC-FIELD HYSTERESIS OF CRITICAL CURRENTS IN BI(2223) AG TAPES AND A WAY TO OVERCOME IT/

Experiments showing hysteresis of critical currents versus the externa l magnetic field I-c(B-e) were performed with two multifilamentary Bi( 2223)/Ag tapes. The I-c(B-e) hysteresis is observable in the transvers al as well as in the longitudinal orientation of the long axis of the tape with respect to the magnetic field. Based on the idea that the hy steresis is the effect of trapped flux in a network of well-connected current paths, a way to overcome this effect has been proposed and exp erimentally verified. The induced frozen-in screening currents are spl it into several parallel current patterns by cycling the external magn etic field around the adjusted value. Using the proposed method, the ' neutral' I-c(B-e) characteristics have been found. Approximate calcula tions of the penetration depth of the trapped flux show that the netwo rk of well-connected current paths could be formed by several disk-sha ped grains (approximate to Phi 8 x 0.4 mu m) stacked into more or less axially ordered (quasi cylindrical) colonies of average dimensions es timated to approximate to Phi 8 x 4 mu m. (C) 1998 Elsevier Science Lt d.