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The optimization of the heat treatment of \Nb3\Sn conductors for toroidal field coils in ITER was attempted to improve the current sharing temperatures (Tcs). Using the strand, we chose the pattern at 570  ^\circ\C for 250 h and 650  ^\circ\C for 100 h as the best, which increased the critical current and maintained the residual resistivity ratio higher than 100. The behavior of the critical current of the strand vs. the magnetic field, temperature, and strain was also improved. This pattern was used on two conductors, and their performances were tested. Tcs was evaluated over 1000 electromagnetic cycles and one thermal cycle. A sharp Tcs degradation occurred at 50 cycles. Then Tcs decreased linearly. Although this tendency was similar to the conductors that were heat treated with the original pattern, the degradation rates were improved. The ac losses (Q) before cycling were approximately 10% lower than those of the original pattern. Q after cycling became almost equivalent between two patterns. The conductor was inspected after the test, which showed that the conductor under the high-magnetic-field zone had contracted by approximately 600 ppm during the test. Some clearly deformed strands were observed under the high-magnetic-field zone, which could degrade Tcs. [ABSTRACT FROM PUBLISHER]

The performance of four \Nb3\Sn conductors for the ITER central solenoids was tested. The current sharing temperatures (Tcs) were measured over approximately 9000 electromagnetic cycles, including two or three thermal cycles between 4.2 K and room temperature. Tcs increased and became almost constant through the cycling. The gradient of the electric field against the temperature gradually decreased against cycling. The degradations caused by the electromagnetic force of the short twist pitch conductors were smaller than that of the original twist pitch conductor. The ac losses of short twist pitch conductors were several times higher than that of original twist pitch conductor. The dents and the removals of the Cr plating on the strands, which were formed during cabling, decreased the electric resistance between strands, which may cause the observed high ac loss. Inspection of the cable showed neither a clear bias of cable in the cross-sectional surface nor distorted strands in the lateral face. The high rigidity of the short twist pitch cable could prevent these plastic deformations, caused by the Lorentz force. [ABSTRACT FROM PUBLISHER]

The performances of six Nb3Sn conductors for the ITER Toroidal Field coils were tested. Four of them showed similar degradation rates of their current sharing temperatures Tcs over 1,000 electromagnetic cycles. By contrast, two of them showed sharp Tcs degradations at 50 cycles, after which their slopes became similar to those of the other four conductors. These two cables seemed to shrink under high magnetic fields during the first 50 cycles, which caused the sharp Tcs degradation. This shrinkage might arise from a decline in cable rigidity due to, for example, the deformation of strands or the breakage of the Nb3Sn filaments. The four mass-produced conductors had roughly the same AC loss before cycling. After 1,000 cycles, the AC losses of all the conductors decreased markedly to less than half of those before cycling, and the values became approximately the same. After the test campaign, the destructive inspection of two of the conductors made it clear that the conductor had shrunk by about 520 ppm under the high magnetic field during the test. It was also clarified that some strands were visibly deformed under the high magnetic field, whereas those under the low magnetic field did not look distorted. This plastic deformation of the strands could be one of the major reasons for the Tcs degradation with cyclic operation. [ABSTRACT FROM PUBLISHER]

Japan Atomic Energy Agency (JAEA) was the first to start the mass production of the TF conductors (jacketing) in March 2010 among the 6 parties who are procuring TF conductors in the ITER project. [ABSTRACT FROM PUBLISHER]

The Nb3 Sn cable-in-conduit conductors for the ITER TF coils are fabricated using the latest high performance strands. The strands made by bronze and internal-tin methods are used for the conductors with a void fraction of 29% and 33%, respectively. Superconducting performance of the conductors was measured at the operating condition of the TF coils. The measured current sharing temperatures Tcs are 6.3-6.6 K for the bronze and 5.6-6.1 K for the internal-tin. The Tcs of the conductor with void fraction of 29% is 0.1-0.3 K higher than the conductor with a void fraction of 33%. It is shown from the results that the strain on the cable is between -0.7% and -0.75% and the n-values are between 4 and 6, much smaller than the n-values of strands. [ABSTRACT FROM AUTHOR]