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An internal-tin route Nb3Sn superconducting wire that has both remarkably low hysteresis loss (Qh) and high critical current density (Jc) was developed according to a new design idea. The wire was constructed by arranging the filaments in a radial layout, enlarging the outer filaments along the radial direction, intentionally narrowing the filament spacing in the radial direction, and enlarging the filament spacing in the tangential direction. Thus, the electromagnetic coupling among the filaments in the tangential direction due to the bridging and/or proximity effect was suppressed without decreasing the volume fraction of Nb. As a result, excellent properties such as Jc(12 T) = 1.15 × 10³ A/mm², Qh = 301 mJ/cm³ (for 1 cycle of B = ±3 T), Tc = 17.3 K, and Bc2 = 24.1 T were obtained. Scanning electron microscope observations confirmed that the cause of experimental Qh values being lower than expected is that the majority of the filaments in the second and outermost rows were not completely combined. Electron probe micro-analyses confirmed that the good Tc and Bc2 values resulted from the qualitative improvement of the Nb3Sn compound. This wire is promising for use with conduction-cooled high-field magnets and for the strands of fusion coils. [ABSTRACT FROM AUTHOR]

Abstract: An internal-tin route Nb3Sn superconducting wire that has both remarkably low hysteresis loss (Q h) and high critical current density (J c) was developed according to a new design idea. The wire was constructed by arranging the filaments in a radial layout, enlarging the outer filaments along the radial direction, narrowing the filament spacing in the radial direction intentionally and enlarging the filament spacing in tangential direction. Thus, the electromagnetic coupling among the filaments in tangential direction due to the bridging and/or proximity effect was suppressed without decreasing the volume fraction of Nb. As a result, excellent properties such as J c(12T)=1.15×103 A/mm2 and Q h =301mJ/cm3 (for 1cycle of B =±3T) were obtained. We also evaluated the transition temperature (T c) and upper critical field (B c2) of the wire. The values for T c and B c2 were 17.3K and 24.1T, respectively, which were much better than those of usual internal-tin route wires. Moreover, electron probe micro-analyses confirmed that the good T c and B c2 were the result of the qualitative improvement of the Nb3Sn compound based on the effects of arranging the Nb filaments radially, increasing the ratio of Sn-to-Nb and shortening the diffusion length for Sn. This wire is promising for use with conduction-cooled high-field magnets, in which there is a need to decrease the load of the cryocooler, and also for the strands of fusion coils. [Copyright &y& Elsevier]