CRITICAL CURRENTS THROUGH STRONG LINKS IN AG BI-SR-CA-CU-O SUPERCONDUCTING TAPES/

Transport critical currents were measured on Ag-sheathed Bi-based supe rconducting tapes at 77 K, with the field H parallel and perpendicular to the tape plane. A transition field from flux creep to flux flow re gime of about 350 mT was obtained from the change of the curvature of the V-I characteristics. The critical current conducted via strong lin ks (I-c(s)) was extracted from the total I-c. An empirical expression for I-c(s) versus H in the flux creep regime was found: I-c(s) = I(c0) (s)exp[-(H/H-0)(a+1)], with 0 less than or equal to a less than or equ al to 1. log(I-c) versus H has a downward (negative) curvature in this regime, which is often mistakenly ascribed to the transition to flux flow. This curvature is defined by the values of a and H-0. In the flu x flow regime, I-c decreases with positive curvature. Using the measur ed values of I-c0(s), we estimate J(c) would increase 2-3 orders of ma gnitude by turning all the weak links into strong ones. This shows the re is still a great capacity for improvement of J(c) by still betterin g the links between the grains.