Results of thermal Strain and Conductor Elongation upon Heat Treatment for Nb3Sn Cable-in-Conduit Conductors

The change of length upon heat treatment of steel jacketed, Nb3Sn cable-in-conduit conductors (CICC) is driven by the difference of coefficient of thermal expansion between Nb3Sn and the other components. The cold work of the steel jacket also plays an important role. During the preparation of CICC samples for test in the SULTAN facility, the change in length has been systematically measured for 16 sections of CICC. The broad range of changes, from elongation to shrinkage, is a concern for the manufacture of the ITER toroidal field (TF) coils, where the shape/length of the conductor after heat treatment must be exactly predicted to fit into the radial plates.