ITER niobium-tin strands reacted under model coil heat-treatment conditions

Heat-treatment conditions were studied for ITER Central Solenoid model coils wound with Nb/sub 3/Sn cables jacketed in Incoloy-908 conduits. The heat treatments recommended by the strand manufacturers had to be modified to meet various requirements for the large coils and to prevent Stress Accelerated Grain Boundary Oxidation (SAGBO) of Incoloy 908. Single-strand tests of ITER wires produced by Vacuumschmelze, IGC, Furukawa and Mitsubishi were carried out prior to the model coil heat treatments to verify the heat-treatment conditions. The modified heat treatments improved the performance of all four wires. Especially, critical currents of Furukawa wire were improved significantly. Test results of the witness samples co-reacted with ITER CS coils indicate that the heat treatments of all 10 layers of the inner module were successfully completed.