Masamitsu Ichihara

Multifilament niobium-tin conductors

A new Nb 3 Sn wire fabrication method has been developed, improving wire drawing workability and superconducting properties, such as stability and ac losses. A cross section of the single filament wire consists of a niobium tube with a copper sheathed tin rod inside and high conductivity copper tube outside. These constituents show scarcely any workhardening. Wires with 54 to 295 filaments were drawn down to 0.2 mm to 1.0 mm diameter. Heat-treatment conditions to obtain the highest critical current were clarified as a function of the tin content inside the niobium tube. The effect of bend strain in Nb 3 Sn on the critical current was also examined for samples with different wire diameters and Nb 3 Sn layer thickness. Losses were measured for twisted and non-twisted samples by means of magnetization experiments. Results were compared with calculated values. It was found that the effective resistivity between Nb 3 Sn filaments was one order of magnitude higher than that of pure copper. A coil was constructed using a 1 km long Nb 3 Sn composite having 258 filaments with 1 × 2 mm cross section. The maximum field obtained was 10.65T at 236A in the 6T backing field by NbTi solenoid.

Development of Cu-Ag alloys conductor for high field magnet

Highly conductive materials with high strength have been required for the development of high field magnets such as the pulsed magnet. Compared with Cu-Al/sub 2/O/sub 3/, Cu-Be, Cu-Cr and Cu-Nb alloys, Cu-Ag alloys are very useful because of easiness in melting and casting. In addition, the alloys exhibit high strength, high conductivity and uniform characteristics by the proper combination of cold-working and heat-treatment. We manufactured the Cu-Ag alloys conductor (4/spl times/6 mm in cross section). The conductor has a tensile strength of 1000 MPa and an electrical conductivity of 80% IACS at room temperature, and this conductor is suitable for the high field pulsed magnet. It is also easy to handle the conductor in making a coil with a diameter of about /spl phi/20 mm. >

Properties and performance of the multifilamentary Nb 3 Sn with Ti addition processed by the Nb tube method

MF Nb 3 Sn conductors made by titanium added niobium tube process have been developed for use in high fields. Composites, consisting of Nb-1. Owt.%Ti tube with a copper sheathed tin core inside and a high conductivity copper tube outside, were stacked together up to 264 filaments, then drawn to the final sizes without any intermediate annealings. As workability was further improved by the titanium addition, it was possible to decrease the Cu/SC ratio for the conductor down to 0.67 and to increase the tin concentration up to 30 wt.% in Cu-Sn inside the filament. An enhanced layer growth rate and a slightly increased grain size of Nb 3 Sn were observed in the titanium added conductors. compared with those made by use of pure Nb tube. The critical current density at high fields, which was more sensitive for heat-treatment condition, was superior to that of the other conventional processed conductors. Especially, the conductors with 30 % tin content have high critical current density for Nb 3 Sn layer and an excellent field dependence of critical current density without copper: 1550 A/mm2at 10 T, 600 A/mm2at 15 T and 350 A/mm2at 17 T. The critical current was also measured in the temperature range 1.88 - 4.2 K. A coil, aiming at 14 T, was fabricated using the conductor with .25 % tin to assure high level performance in practical situations.

Development of a forced-cooled Nb 3 Sn bundle conductor

Forced flow cable conductors using Nb 3 Sn superconductors have been developed. In manufacturing the cable-in-conduit type conductors, some problems are considered. Initial phase of investigations of these problems have been carried out. Some results of the investigations are discussed and described in this paper. Using a roll-forming method, the reliable manufacture of the long length cable-in-conduit type conductors has been achieved. By forming the Cu 2 O+ Cu2S film on the surface of strands, there was no adhesion between strands after the heat treatment at high temperature for a long time. Both Nb 3 Sn superconductors by the bronze process and the tube method have achieved a critical current density in the non copper area of more than 400A/mm2at 12T, 4.2K.