Analysis of Internal-Tin Nb3Sn Conductors for ITER Central Solenoid

Japan Atomic Energy Agency (JAEA) is procuring 100% of the ITER Central Solenoid (CS) conductors. The CS conductor is required to maintain the performance under 60000 pulsed electromagnetic cycles. JAEA tested two internal-tin Nb3Sn conductors for the CS at the SULTAN test facility. As a result of destructive examination, the twist pitches of both of the cables satisfied requirements of the ITER Organization (IO). The current sharing temperatures Tcs of each sample were 6.6 and 6.8 K before cyclic operation, and the Tcs values were 6.8 and 6.9 K after 9700 electromagnetic cycles, including three warm-up/cooldowns, respectively. The Tcs performance of both samples satisfied the IO requirement. The ac losses of CSKO1-C and CSKO1-D were approximately half of typical bronze-route CS conductors at 2 and 9 T. The ac loss at 45.1 kA after the cycling was 1.5 times higher than that without the transport current. An almost constant strain of the jacket was observed after the test as a result of the residual strain measurement. Therefore, the deformation of the cable might have been homogeneous along the conductor axis. Because of the higher Tcs of CSKO1-D than CSKO1-C, JAEA started the manufacturing of the CS conductor with the same specification as CSKO1-D.