Radial-build design and support system for the helical DEMO reactor FFHR-d1

A conceptual design for the helical DEMO reactor FFHR-d1 is under development at the National Institute for Fusion Science. In the large helical device (LHD)-type configuration of FFHR-d1, the space between the plasma boundary and the helical coil is limited. Many components are required to be installed at definite geometric positions within this space. The position of each component changes owing to variations in the surrounding conditions, such as temperature, electromagnetic forces, and support methods. This paper proposes a radial-build design concept; the application of this concept ensures constant geometric positions of the components and the gaps between them during normal operation and the construction/maintenance phase. On the other hand, large apertures are required for the coil support structure for the maintenance of blanket and divertor systems. This paper presents a structural design procedure for the coil support structure with large apertures and an LHD-type gravity support post. The analytic results show that the stress level of the structure is lower than the permissible limit.