The use of the in-field critical current density, Jc(0.1 T), as a better descriptor of (Bi, Pb)2Sr2Ca2Cu3Ox/Ag tape performance

Abstract

Extended voltage-current characteristics of 13 optimized ͑Bi, Pb͒ 2 Sr 2 Ca 2 Cu 3 O x /Ag multifilamentary tapes from four different manufacturers were extensively evaluated so as to extract the field-dependent J c (H), the characteristic field H p obtained from the relation J c ϳexp (ϪH/H p ), and the irreversibility field H*. Values of the self-field critical current density J c (0 T, 77 K) ranged from 12 to 63 kA/cm 2 , I c (0 T,77 K) from 11 to 139 A, H p from 128 to 204 mT, and H* from 163 to 369 mT, this range thus being representative of present optimized composites. Self-field can strongly dominate J c (H) in fields below 20 mT; thus, J c (0 T,77 K) is a flawed parameter for characterizing tapes because of its very heavy dependence on self-field. We propose that a much better descriptor of tape performance is J c (0.1 T,77 K), because it lies outside the self-field and weak-link-destruction regimes and clearly within the flux-pinning-controlled domain where the connectivity-determined active cross-section carrying current is constant.

Critical current limiting factors in post annealed (Bi; Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ tapes

“…A strong correlation between and is found. As reported previously [12], the curves of Bi-2223 tape exhibit an exponential form above the self-field and weak-link dominated region, , where the characteristic field characterizes the in-field performance. As listed in Table I, increased from 126 mT for TA-3 to 183 mT for TA-5.…”

“…Measurements of critical current ( ) were made in liquid nitrogen in a 1 Tesla electromagnet with the magnetic field applied perpendicular to the broad tape surface, making nominally parallel to the axis [12]. The criterion for is 1 V cm and was defined as , where is the average of two or three Bi-2223 cross-section measurements.…”

Irreversibility fields of Bi-2223 at 30-77 K

“…For Bi-2223 tapes there is also a region from about 50 mT to 150 mT for which is proportional to [3]. We report this decrement field, , as a second benchmark of tape quality.…”

“…Careful study of tapes from multiple sources by transport has shown that (77 K) as measured by can vary significantly from 160 to 370 mT [3]. In principle, a higher is taken to be evidence of stronger flux pinning, a highly desirable property that would be even more valuable in the 25-50 K range where Tesla-strength magnetic field applications for 2223 can be considered.…”

Improving the critical current density in Bi-2223 wires via a reduction of the secondary phase content

“…Because the self-field significantly suppresses the of highcurrent Bi-2223 tapes at 77 K [6], [7], performance levels are now quantitatively measured in an applied field of 0.1 T (//c) to determine intrinsic material performance. The value of 22 100 A cm at 77 K and 0.1 T (//c) from the new experimental wire reported here is 10 higher than the level obtained last year [2], 30% higher than the estimated 0.1 T value for AMSC's self-field record tape (74 kA cm , 77 K, made in 1998) [4], and represents a new level of performance for MFC wires.…”