NONEXPONENTIAL DECREASE OF CRITICAL-CURRENT WITH FIELD IN BI-2223 AG SUPERCONDUCTING TAPES AT ELEVATED FIELDS/

Non-exponential decrease of critical current (I-c) with magnetic field (H) was studied for a variety of Bi-2223/Ag superconducting tapes, Th e measurements were performed by a four-probe d.c, method using I-mu V /cm criterion. The field dependence of I-c at elevated fields was desc ribed as: I-c-I(c0)exp[-(H/H)(a+1)/(a+1)], where H* is the field of t he peak of the pinning force density and a is a positive parameter res ponsible for the non-exponential behaviour. Values for both, H and a were obtained from experimental data, It was shown that a decreases wi th improvement of the texture of the grains and the quality of the lin ks between the grains, but increases with flux pinning, The former fac tor influences a more strongly than the latter, Experimental results g ive support to flux entanglement as a source of the non-exponential be haviour.