| dc.description |
The intrinsic limits of J<sub>c</sub> in composite Bi(Pb)-2223 multifilamentary tapes due to the reduction of the effective cross section and the enlargement of the twisted filaments have been analysed. A simple model of the twisted filaments as elliptic helices grouped in concentric shells have been used to derived analytical results for the intrinsic variation of J<sub>c</sub> with the twist pitch, t<sub>p</sub>. In tapes with high thickness to width aspect ratios and large t<sub>p</sub> values, this model predicts a linear dependence of J<sub>c</sub> with 1/t<sub>p</sub>, when the shape and superconducting filling factor of the tapes are constant. The J<sub>c</sub>(t<sub>p</sub>) values depend on a set of parameters that define the helices, which may be derived from the analysis of the morphology of the filaments inside the tapes. To assess the model we have compared the predictions with the results here reported on Ag and Ag<sub>0.94</sub>Au<sub>0.06</sub> alloy sheathed tapes with 19 and 37 twisted filaments, respectively. In tapes with high J<sub>c</sub>, we have found a good agreement between the variation of J<sub>c</sub> with t<sub>p</sub> experimentally measured and the intrinsic limits imposed by the filament geometry. |
