Multifilament Nb3Sn superconductors produced by the E.C.N. technique

Multifilament Nb
3
Sn conductors are produced by reduction of composites containing bundles of niobium tubes filled with NbSn
2
-powder and surrounded by pure copper. Heat treatment at temperatures between 575 and 675°C after final reduction causes the tin from the NbSn
2
-powder to diffuse into the niobium tubes, which results in a final Nb
3
Sn-layer at the inner side of the tube. Two types of experimental wire are produced, the first type consisting of 4 bundles of 9 tubular filaments, the powder cores having diameters of about 35 micron, the outer size of the wire being 1 mm square. The second type consists of 4 bundles of 45 tubular filaments. This type is fabricated in 3 sizes: round φ 2.3 and square 1.4 and 1.0 mm, corresponding with powder core diameters of 26,18 and 13 microns respectively. Critical current densities in the Nb
3
Sn-layers reach values of about 4 - 6 × 10
⁹
A/m
²
at 8 Tesla and 1,6 - 2,4 × 10
⁹
A/m
²
at 12 Tesla. Maximum critical temperatures are about 18.1 K with a ΔT
c
of 0.3 K.