Superconducting strand properties at each production stage of the CMS solenoid conductor manufacturing

The Compact Muon Solenoid (CMS) detector is one of the general-purpose particle detectors presently being built for the LHC project at CERN. The superconducting CMS solenoid will produce a magnetic field of 4 T in a bore 6 m in diameter and 12.5 m long. The coil is wound from 20 high purity aluminum-stabilized NbTi conductors with a total length of 45 km. The main part of the structural integrity of the CMS coil is ensured by aluminum-alloy reinforcement welded to the high purity aluminum stabilizer of the conductor. The Rutherford type superconducting cable within the stabilizer consists of 32 copper-stabilized multifilamentary NbTi strands each with Nb barrier. The strands are optimized with respect to a high critical current density (> 3000 A/mm² at 5 T, 4.2 K). Approximately 1950 km of superconducting strand has been produced from 148 extrusion billets and cabled in unit lengths of 2.65 km. All strands within a cable can unambiguously be identified by distinctive patterns of the NbTi filaments. The statistics of I_c measurements, n-value, copper RRR and (Cu + Nb)/NbTi ratio are presented. Since the strands are subjected to potentially dangerous high temperatures and mechanical strain during the different conductor production steps it was important to trace the critical current properties of the strand as it progressed through the conductor fabrication process. The paper presents results of I_c measurements, which were performed on all individual strands extracted from conductor samples taken at each step of the manufacturing process. The comparison among the measurements assured accurate quality control during the whole process of conductor production. In addition, I_c measurements in fields up to 6 T on the complete CMS conductors using the MaRiSA test facility are reported.