Critical Current Test Facilities for LHC Superconducting NbTi Cable Strands

The Rutherford-type superconducting Cu/NbTi cables of the LHC accelerator are currently mass-produced by a few industrial firms. As a part of the acceptance tests, the critical current of superconducting multifilamentary wires is systematically measured on virgin strands to qualify the wires and on extracted strands to qualify the cables. For this purpose, four test stations are in operation at CERN to measure the critical current of strands at both 4.2 K and 1.9 K in magnetic fields in the 6-11 T range. The measurement setup and procedures of these facilities are reported in this article. The quality of the critical current test is guaranteed by supervising the SPC (Statistical Process Control) charts of a reference sample. The measurement repeatability and reproducibility of the stations are found to be excellent. Moreover, the measured critical current of a strand is found to be almost independent of the test station in which the measurement is performed.