Fig. 2-21 Status of the development on the superconducting coil scale

Fig. 2-22 Schematic of the ITER model coil cross section The windings of 8 layers and the buffer spacers were impregnated with epoxy resin to increase stiffness. FRP: Fiber reinforced plastic.

Fig. 2-23 Outside view of the finished model coil

Because a superconducting coil has zero electrical resistance, we can maintain the magnetic field only by operating a refrigerator. A superconducting coil is used as the primary winding coil to induce plasma current in the fusion experimental reactor, ITER. Figure 2-21 shows the status of generated magnetic fields and the currents of superconductors. We have manufactured the model coil required by ITER as a test. The conductor consists of an Incoloy jacket of 46 x 46 mm and 1,080 superconducting strands. The heat treatment of the superconductors is made after its winding formation in the case of large coils. Because Incoloy cracks under heat treatment with oxygen, we need to take special care for the gas evacuation in the heat treatment. Another key point is the development of a joint structure with smaller energy loss. We used our expertise for the insulation structures and its processing to withstand thermal deformation. Figure 2-22 shows the ITER model coil cross section. We have established the manufacturing process of the coil overcoming many issues involving choices of the materials and their arrangement. The outside of the coil is shown in Fig. 2-23. This technology is indispensable for the steady state operation of a fusion reactor.

Reference H. Nakajima et al., Central Solenoid Model Coil Outer Module: Design and Fabrication, Proc. 15th Int. Conf. on Magnet Technol., 361 (1998).

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