Production and qualification of 40 km of Al-stabilized NbTi cable for the ATLAS experiment at CERN

The production of the conductor for the superconducting toroids of the ATLAS experiment at LHC (CERN) is now in progress. The toroid system, composed of one barrel toroid (BT) and two end cap toroids (ECTs), exploits aluminum-clad Rutherford-type NbTi conductors of large size (57 × 12 mm for BT, 42 × 12 mm for ECTs) and high critical current (Ic) (58 kA for BT and 60 kA for ECTs @ 4.2 K, 5 T). Some 55 km of conductor are required for the BT and 26 km for the ECTs, respectively. An Italian-Swiss (ETH Zurich and INFN) consortium is in charge of the delivery of half of the whole amount. This paper describes the results of this production with particular emphasis to the quality control system developed to monitor the production with both on-line controls and the post-production quality assessment protocols. The main result is the confirmation that the technologies selected and the whole process are reliable and reproducible over large production quantities. The overall degradation due to the cabling and the co-extrusion, was rather moderate, 34% in total, and did not change significantly along the production. An ultrasonic system was developed to assess the quality of the bonding between the Rutherford and the aluminum matrix over the whole length, and its results were combined with the quantitative results from pull-out tests at the conductor´s extremities: in all the cases the 20 MPa limit for the BT and 15 MPa for the ECTs, respectively was largely exceeded, and no relevant change was detected among the lengths.