Engineering Perspective of the CFQS Quasi-Axisymmetric Stellarator and its Upgrade Status Toward the 1 Tesla Experiment

抄録

The National Institute for Fusion Science in Japan and Southwest Jiatong University in China are proceeding with the CFQS quasi-axisymmetric stellarator project since 2017. CFQS principal physical properties are as follows: toroidal periodic number N_p = 2, aspect ratio A_p = 4, and major radius R₀ = 1 m. Sixteen modular coils are employed to produce the quasi-axisymmetric magnetic field configuration. Its upgrade from the 0.1 T operation as the CFQS-TEST, hereafter called CFQS-T to the 1 T operation as the CFQS is ongoing. In this report, the finalized engineering design, R&D, established essential component manufacturing, and assembly of the CFQS-T are described. Subsequently, the upgrade status toward the CFQS is given, focusing on the further improved design of a support structure that can withstand the complex and enormous electromagnetic forces acting on the modular coils at the 1 T operation. Iterative design and validation using the finite element method revealed a rational support structure with low-cost, good port accessibility, and manufacturability even under a packed configuration of the CFQS main body due to its low-aspect ratio. The engineering knowledge obtained through the CFQS project, particularly regarding the improved support structure design, would contribute to developing next-generation advanced stellarators.