Numerical Analysis of the Electrical Interconnections Between LHC Superconducting Magnets

The wire production aims at manufacturing continuous lengths of several tens of kilometers with good and reproducible critical current characteristic. The wire thickness must be kept within a tolerance of a few m, the inclusion of metallic chips or dirt during production must be strictly avoided and the NbTi must be produced with high purity and with a variation in titanium contents of 1% or less. For that reason the multi lamentary superconducting wires are fabricated in a multistep process. Round bars with a diameter of about 150 mm and a length of 500 to 750 mm are manufactured from the high homogeneity material. Then they are wrapped with a nobium foil which serves as a di usion barrier to prevent the formation of CuTi compounds during high temperature heat treatments. Those coated bars are inserted in a thick walled can of pure copper, RRR > 100, of about 200 mm outer diameter, closed at the ends by electron-beam welded caps. After evacuation the can is compressed and extruded at 600-700 C to a composite of 30-50 mm diameter. At this point a multiple process of drawing and compaction is performed and a long hexagonal cross section bar of 3.5 mm width is obtained. The bar is now cut in short pieces 0.50 mm long, well cleaned and stacked again into another 300 mm diameter thick walled copper tube, with a central copper rod. Besides the superconductor properties in fact, the wire has to be exible and bendable around small corners without degradation. The intent of the multi-lamentary structure of NbTi in a copper matrix and the central copper core of the strands facilitate the deformation needed in cable production. Then compaction, hot extrusion and a high number of drawing steps follow, with heat treatments in between, in order to optimize the current carrying capacity.