Development of Nb44wt%Ti 25wt%Ta based superconducting conductors for LHC magnets

A trial cable for LHC dipole inner layers made up of the Nb ternary alloy Nb44wt%Ti 25wt%Ta has been manufactured by GEC Alstrom Intermagnetics within the framework of a CERN development program. This cable is composed of 28 strands of 1.065 mm in diameter. The purpose of the study is: (i) to improve the superconducting behaviour of LHC cables at 1.9 K, the operating temperature of the Large Hadron Collider (LHC), and (ii) to evaluate the cabling feasibility of wires made with this alloy. Ic tests performed on wire samples before and after cabling at 4.2 K and 1.8 K show that at 4.2 K NbTi25wt%Ta wires exhibit lower Jc than those of the conventional binary alloy Nb47wt%Ti or those of a ternary alloy with only 15wt%Ta. But they have a larger magnetic field shift when cooled down from 4.2 to 1.8 K (about 1 T). The cabling of NbTi25wt%Ta wires presented no particular problem. Jc degradations due to cabling and evaluated on extracted strands are comparable to those observed on NbTi material. The performances achieved are reported and discussed in this paper.<>