Superconducting Properties of Wires With Radially Arranged Filaments

An internal-tin route superconducting wire that has both remarkably low hysteresis loss and high crit- ical current density was developed according to a new de- sign idea. The wire was constructed by arranging the filaments in a radial layout, enlarging the outer filaments along the radial di- rection, intentionally narrowing the filament spacing in the radial direction, and enlarging the filament spacing in the tangential di- rection. 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 , (for 1 cycle of ), , and were obtained. Scanning elec- tron microscope observations confirmed that the cause of experi- mental values being lower than expected is that the majority of the filaments in the second and outermost rows were not com- pletely combined. Electron probe micro-analyses confirmed that the good and values resulted from the qualitative improve- ment of the compound. This wire is promising for use with conduction-cooled high-field magnets and for the strands of fusion coils.