Research Study for the Construction of a Superconducting Large Helical Device

大型螺旋装置将具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，大型超导装置的低温装置技术的现场研究已作为联合研究计划进行。研究的国家是美国、独联体（旧称：苏联）、德国和法国。主要研究领域分为以下5大类。(1)对独联体T-15超导托卡马克装置和德国HERA超导对撞机等大型超导装置的总体系统进行了研究。并对操作系统进行了讨论。(2)由于铲运机极向线圈将采用强制流型超导体，螺旋线圈将采用池沸腾型超导体，因此研究了强制流型超导体和池沸腾型超导体的发展现状。在国外，强制流型超导体主要计划应用于大型超导装置，因为它的电绝缘更容易，并且可以预期高强度。但与此同时，很明显，还有许多问题需要开发，如绝缘机制，减少热输入和组成材料，以支持超导体抵抗大的电磁力。(3)对法国TORE-SUPRA大型低温系统进行了研究，该系统采用了超流氦冷却系统。并对元件技术等多项内容进行了讨论。(4)对低温材料和结构进行了研究。铲运机可选用奥氏体不锈钢，但必须保证焊接件的力学性能，特别是断裂韧性。(5)大型低温系统的长期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初始故障大多发生在运行后的2年内。

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.