3-1 Start of Manufacture of the Superconductors for the ITER Magnets

－Development of Exacting Quality Assurance Techniques－

Fig.3-2　ITER superconducting magnet system

Fig.3-2　ITER superconducting magnet system

The system consists of 18 toroidal field (TF) Coils, 6 central solenoid coils and 6 poloidal field coils.

 

Fig.3-3　Structure of TF coils and their superconductor

Fig.3-3　Structure of TF coils and their superconductor

A circular, multistage superconducting cable, consisting of around 1000 superconducting strands, is inserted into a circular stainless steel jacket. The superconductor is subsequently inserted into the groove of a radial plate.

Fig.3-4　Fabrication process of the TF conductor

This Picture(286KB)

Fig.3-4　Fabrication process of the TF conductor

Jackets with a length of 13 m are butt-welded by an automatic welding machine to create a jacket whose total length is 760 m. The superconducting cable is inserted into the jacket. The jacket is then compacted to a diameter of 43.7 mm.

The ITER device being constructed by Japan, China, the EU, India, Korea, Russia and the US, will have a field of 10 T in order to confine and control a very high temperature plasma. Huge superconducting coils are necessary for this purpose (Fig.3-2). The height, width and weight of a toroidal f ield (TF) coil, which generate the magnetic field, are 14 m, 9 m and about 300 tons, respectively (Fig.3-3). Japan is procuring 9 TF coils and 25% of all TF superconductors, and is the first to begin manufacturing the TF conductors.

A circular superconducting cable, consisting of around 1000 superconducting strands, is inserted into a circular stainless steel jacket (Fig.3-4). The jacket is composed of tubes, each 13 m in length, that are butt-welded by an a utomatic welding machine to create a single length of 760 m. The gap between the cable and the jacket is approximately 2 mm. The pulling force on the cable is approximately 4 tons. Following cable insertion, the jacket is compacted to the specified diameter in a single step. After welding, a helium leak test, radiographic inspection and a dye penetrant test are carried out on the welds. Following the c ompaction, outer diameter tolerances of 0.2 mm, corresponding to 0.5% of the outer diameter (43.7 mm), are confirmed through continuous laser measurement. The conductor is wound as a one-layer solenoid with a diameter of 4 m, and a helium leak test is carried out in a vacuum tank. Demanding specifications have required the development of exacting quality assurance techniques. These techniques were confirmed as valid during the fabrication of a 760 m Cu dummy conductor, as a result of which we have started fabrication of actual superconductors at the rate of approximately one conductor per month.

Reference
Nabara, Y., Takahashi, Y. et al., Procurement of Nb3Sn Superconducting Conductors in ITER, Journal of Plasma and Fusion Research SERIES, vol.9, 2010, p.270-275.

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