Improvement of Critical Current Density of Bronze Processed Nb3Sn Superconducting Wire

Materials for classical and high- superconducting tapes and wires at 4.2 K

“…The highest magnetic field value produced by an Nb 3 Sn magnet is actually 21.8 T at T = 1.8 K. Various methods are used for the industrial fabrication of Nb 3 Sn multifilamentary wires: (a) bronze route, by VAC (Germany) [1], Kobe Steel (Japan) [2], Hitachi (Japan) [3], Furukawa (Japan) [4] and Kurchatov Institute, (b) internal Sn route (separate filaments), by IGC (USA) [7], Alsthom (France) and Eurometalli (Italy) [8], (c) internal Sn route (jelly roll), by TWC (USA)/Oxford (USA) [6], (d) Nb tube technique, by Showa (Japan) [9], (e) NbSn 2 route, by SMI (Netherlands) [10] and (f) Nb 6 Sn 5 compound route (Tokai University, Japan) [11]. The observed difference in j c for the various methods is essentially due to the total amount of Sn in the wire, which varies from 13.5 wt% (bronze route) to >30 wt.% (NbSn 2 route), as indicated in table 1.…”

“…It was found that B c2 of Nb 3 Sn can be enhanced by ≈4 T after adding Ta or Ti, due to the enhancement of the normal state resistivity ρ n [11,12]. A further enhancement of j c at B > 18 T was later obtained by simultaneously adding Ta (to Nb) and Ti (either to Nb or to the Cu bronze) [1][2][3][4]. The effect of various additives on j c is shown in figure 1.…”

“…The effect of various additives on j c is shown in figure 1. At 4.2 K and 20 T, the known j c values are 100-130 A mm −2 for the bronze route [1][2][3]7], 150-180 A mm −2 for the internal Sn route [6][7][8], 230 A mm −2 for the Nb tube route [9], >230 A mm −2 for the NbSn 2 route [10] and 320 A mm −2 for the Nb 6 Sn 5 route [11], j c scaling with the total Sn content.…”

“…However, this production route has the smallest Sn content (table 1), due to the binary Cu-Sn phase diagram. Earlier, Cu bronzes with 13.5 wt% Sn were used, but the appropriate technologies have been now developed to work with >14 wt% Sn [1][2][3][4][5]. Very high non-Cu j c values, 1.0 × 10 4 A cm −2 , have been reported at 22 T and 1.8 K [2], which is considered as sufficient for producing this field in a magnet.…”

“…Earlier, Cu bronzes with 13.5 wt% Sn were used, but the appropriate technologies have been now developed to work with >14 wt% Sn [1][2][3][4][5]. Very high non-Cu j c values, 1.0 × 10 4 A cm −2 , have been reported at 22 T and 1.8 K [2], which is considered as sufficient for producing this field in a magnet. Recently, the Osprey method has been used for melting homogeneous bronzes with 15.2 wt.% Sn [5], and a new processing route was developed for fabricating 10 000-filament Nb 3 Sn wires with high Nb/bronze ratios and high non-Cu j c values [5].…”