Temperature and magnetic field dependence of the critical current density for a mass-produced NbAl multifilamentary strand fabricated by a jelly-roll method

Takahashi, Yoshikazu; Koizumi, Norikiyo; Nunoya, Yoshihiko; Takaya, Yoshiyuki*; Tsuji, Hiroshi

JAERI has been developing jelly-roll processed multifilamentary NbAl/Cu strands for the Toroidal Field (TF) coils of fusion tokamak machines since 1986, in cooperation with industries. One ton of mass-produced strands were successfully manufactured for the 13T-46kA NbAl insert which will be tested using the ITER Central Solenoid model coil. The critical current of the Nb3Al strand developed for the ITER project was measured in temperatures from 4.2 K to 15 K and in applied magnetic fields up to 16 T. An empirical equation for the critical current density was devised using these data and the pinning force scaling method. Good agreement between this equation and the measured data is obtained in the operating condition of the ITER machine. The equation is useful in evaluating the performance of the full-size conductor that consists of 1,152 strands and in establishing the optimum design criteria for the conductor in fusion machines.