Transverse resistivities in untwisted HTSC tapes at 4.2, 30, and 60 K

Using vibrating sample magnetometry eddy-current loss was measured on unbri dged Bi:2223/Ag tapes. After taking the tape's aspect ratio, alb, into acco unt the transverse resistivity, rho (perpendicular to), obtained was still very much greater than that obtained using the effective-medium prescriptio n, in this case (1 + lambda)/(1 - lambda)rho (Ag,bulk) at 4.2 K. Moreover, rho (perpendicular to) was found to be proportional to alb. Temperature dep endence measurements verified that the apparently enhanced resistivity was seated within the interfilamentary matrix, and not asssociated with any T- and H-independent filament/matrix barrier. It was concluded that the eddy-c urrent loss was occurring within a relatively small volume fraction of the filamentary region and that appropriate volume normalization would in fact return a rho (perpendicular to) closer to expectation. This has important i mplications in terms of low AC-loss strand design. The above results were b ased on 4.2 and 30 K measurements. At 60 K where intrafilament flux flow mi ght be expected especially at higher fields, the apparently large rho (perp endicular to) becomes further enhanced by an additional resistivity compone nt. This is a dynamic resistance that the dH/dt-driven eddy-currents encoun ter as they circulate along the filamentary segment of their path under flu x flow. (C) 2001 Elsevier Science B.V. All rights reserved.