Research Study for the Construction of a Superconducting Large Helical Device

大型螺旋装置将有超导螺旋线圈和极向线圈，并在低温下运行。为了设计和制造LHD，开展了大型超导装置低温装置技术的现场研究作为联合研究计划。研究的国家有美国、独联体(旧名：苏联)、德国和法国。主要研究内容如下：(1)对独联体超导托卡马克装置(T-15)和德国超导对撞机(HERA)等大型超导装置的总体系统进行了研究。研究了强流型超导体和池沸腾型超导体在铲运机中的发展现状，其中极向线圈将采用强迫流型超导体，螺旋线圈将采用池沸腾型超导体。在国外，强迫流型超导体主要计划应用在大型超导设施上，因为它的电气绝缘更容易，而且可以预期到高强度。但与此同时，超流氦冷却系统在超流氦冷却系统运行的法国Tore-Supra大型低温系统进行了研究，在超流氦冷却系统的运行过程中，超流氦冷却系统在绝缘机理、减少热输入和材料组成等方面还有待进一步研究。并对元件技术等方面进行了探讨。(4)低温材料和结构研究。铲运机可以使用奥氏体不锈钢，但必须保证焊件的力学性能，特别是断裂韧性。(5)大型低温系统的远程运行记录在世界上很少。橡树岭国家实验室和费米国家实验室的大部分初始故障都是在运行后的两年内观察到的。

The Large Helical Device will have superconducting helical coils and poloidal coils and operated at cryogenic temperature. In order to design and fabricate the LHD, the field research of a cryogenic device technology for large superconducting apparatus has been carried out as a joint research program. The countries researched are USA, CIS (Old name : USSR), Germany and France. The main research field has been classified into the following 5 large groups.(1) The total systems of large superconducting facilities such as Superconducting Tokamak Device (T-15) in CIS and Superconducting Collider (HERA) in Germany were researched. And the operation system was discussed.(2) The development status in the forced flow type and pool boiling type superconductors were researched, because the forced flow type superconductor will be used for poloidal coils and pool boiling type will be done for helical coils in the LHD. In foreign countries, the forced flow type superconductors are mainly planned to apply on large superconducting facilities, because its electric insulation is easier and the high strength can be expected. But at the same time, it is clear that there are many problems to be developed such as the insulation mechanism, reducing the heat input and consist materials to support the superconductors against large electro-magnetic force.(3) The large cryogenic system of TORE-SUPRA in France was researched, where the super fluid helium cooling system was in operation. And many items including the element technology was discussed.(4) The cryogenic materials and structures are researched. The austenitic stainless steel is available for the LHD, but the mechanical properties of weldments, especially the fracture toughness, must be ensured.(5) The long range operation records of large cryogenic systems are very few in the world. Most of the initial troubles in Oak Ridge National Laboratory and Fermi National Laboratory have been observed during 2 years after being in operation.