Development of structural materials of superconducting coil for fusion experimental reactor

The Japan Atomic Energy Research Institute has carried out the development of superconducting coils for tokamak nuclear fusion devices. So far, large achievement has been obtained in LCT project, cluster project and so on, and the importance of the problem on the structural strength of superconducting coils was pointed out in the manufacture and experiment of these coils. Since very large electromagnetic force acts on them, the coil frames and supporting structures must withstand it. The JAERI started the development of the structural materials of the superconducting coils for the fusion experimental reactor in 1982, which is planned next to JT-60. The effect of carbon and nitrogen contents on the strength and toughness of 304 and 316 austenitic stainless steel has been clarified. In this paper, on the development of the structural materials of superconducting coils for the FER, the target of development, the method of development, the method of material testing at 4.2 K, and some results obtained so far are explained. The material with yield stress higher than 1200 MPa and fracture toughness of 200 MPa √m at 4.2 K is aimed at, and the test is in progress. (Kako, I.)