Local transport in multi-filamentary superconductors: longitudinal versus transverse dissipation

Abstract

Little is known on the electrical properties of superconducting tapes and coatings in the direction transverse to the long dimension of the composite. However, transverse dissipation can eventually determine the fate of a transmission line in the case of failure due to the presence of transversal cracks, and is also crucial in the AC regime. In this paper we present a detailed experimental study of the electrical transport properties along the transverse direction of Bi 2 Sr 2 Ca 2 Cu 3 O 10+x -Ag tapes, and compare them with those measured along the long axis of the material. We study in detail the influence of the tape's microstructure on electrical properties along both directions by using sliding electrodes. Our measurements suggest that there is always dissipation in the transverse direction for any value of the current. We also demonstrate that the local dissipation in the transverse direction has a nontrivial correlation with the local density of superconducting filaments.

Modeling transport properties of inhomogeneous superconductor-metal composites

“…Figure 4(a) shows raw hEi À I curves in the transverse direction-notice that, since the distribution of the superconducting and metal components is almost constant along the length of the tape, hEi À I curves measured on transverse bridges cut at different positions along the tape are repeatable, provided that the voltage probes are at the same positions within the bridge. As reported earlier by us, 22 due to the inter-filament silver in the way of the current as it percolates through the transversal bridge, dissipation is present even at low applied currents.…”

“…This anisotropy, fundamental to AC losses 15 and to the ability to circumvent transverse cracks 16,17 by redistributing currents among different filaments, 18 has been rarely studied in tapes. [19][20][21][22] In this paper, we introduce a model to describe the dissipation characteristics of inhomogeneous superconductormetal composites. The approach is based on a differential equivalent circuit representing the material, combined with real data from 2D image analysis of the samples.…”

“…In order to test the model, we use experimental curves published in a previous paper by our group 22 as well as some extra data obtained under similar experimental conditions, briefly described here. Samples were prepared from a silversheathed 61-filament Bi 2 Sr 2 Ca 2 Cu 3 O 10þx tape (BSCCO-Ag), measuring 4.32 mm in width and 0.23 mm in thickness.…”

“…Narrow bridges with 0.30 mm of width were cut from the tape using a laser technique. 22,26 Current-voltage curves were measured using the four-probe technique. The current contacts were attached outside the narrow bridges and far from the voltage contacts, i.e., on the wider areas shown in Figs.…”

Inverted anisotropy in the in-plane dissipation of BSCCO tapes: preliminary results

“…Later on, a clear anisotropy in the dissipation associated to transport currents in the longitudinal vs. transverse directions have been found and studied in detail by our group by cutting longitudinal and transversal bridges using a laser technique [25][26][27][28].…”