Influence of the heat treatment of internal tin Nb3Sn strands on the critical current and the magnetization losses

Internal tin strands for the ITER Toroidal Field Model Coil have been syste matically heat treated to form Nb3Sn. Resulting superconducting cross-secti ons and elementary distribution were monitored by SEM and EDX. Variations o f the heat treatments with respect to annealing conditions were reflected i n the field dependence of the critical current values I-c(B). Measurements were performed in fields up to 12 T at 4.2 K. Also hysteresis and coupling losses of the same wires have been measured at 4.2 K and ramp rates up to 5 00 mT/s. From these data variations of various critical parameters (1(c0), B-c2) as well as of the effective time constant m of the strand could be de duced. (C) 2001 Elsevier Science B.V. All rights reserved.