NIFS-SWJTU joint project for CFQS. Physics and engineering design. Ver. 3.1

The National Institute for Fusion Science (NIFS) and Southwest Jiaotong University (SWJTU) concluded an agreement for international academic cooperation to promote cooperative research in helical fusion plasma research on July 3, 2017. Since then, NIFS and SWJTU have continued the design study of the quasi-axisymmetric stellarator CFQS as a joint project. NIFS and SWJTU have organized the steering committee to manage this joint project. This document summarizes achievements of physical and engineering design study of the CFQS up to the 3rd steering committee meeting, which was held on November 12, 2020 online, due to the effect of COVID-19. Principal parameters of the CFQS is as follows: the major radius is 1 m, the magnetic field strength is 1 T, the aspect ratio is 4, and the number of toroidal period is 2. Magnetic field configuration is designed based on that of CHS-qa. Good MHD stability is confirmed. Good confinement property in the context of neoclassical theory is achieved by its quasi-axisymmetric configuration. Magnetic field coil system is designed for the CFQS, which consists of 16 modular coils. Supporting system is designed to withstand strong electro-magnetic force under 1 T operation, and it is improved to obtain wider space for heating and diagnostic systems. Analysis by using finite element method shows that the stress in the supporting structure is less than allowable level. Layout of main components, e.g. CFQS itself, diagnostic system, heating system, power supply in the torus hall is designed. For one of modular coils, mock up coil was constructed in the factory of Hefei Keye Electro Physical Equipment Manufacturing Co. Ltd., and various tests, such as heat run test and voltage isolation test were performed. Details are reported in this document. (author)