Development of Nb3Al superconductors for International Thermonuclear Experimental Reactor (ITER)

A fabrication technique of a Nb3Al strand using mass-production billets was developed for the framework of International Thermonuclear Experimental Reactor (ITER) Engineering Design Activity (EDA). The weight of a multifilament billet is about 70 kg, which corresponds to the total length of the wire of about 16 000 m. The critical current density is over 600 A mm(-2) at 4.2 K, 12 T, and the hysteresis loss for the field parallel to the wire axis is lower than 600 mJ cm(-3) at +/- 3 T. The residual resistivity of the chrome-plated wire is drastically improved to be lower than 1.6 x 10(-10) Omega m with setting the large copper area at the centre, which reduces the chrome diffused into the copper. The yield of the superconducting strand has been improved, resulting in a yield of 70% for wire longer than 1500 m. The total volume of fabricated Nb,AI superconducting strand for ITER Nb3Al insert coil, which is fabricated in the ITER-Central Solenoid (CS) model coil program, is about 210 000 m, i.e. 1000 kg. This is the first experience of mass-production for Nb3Al superconductors in the world. (C) 1999 Elsevier Science Ltd. All rights reserved.