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The effects of misalignment of modular coils on various physical properties in the Chinese first quasi-axisymmetric Stellarator (CFQS) are discussed in this study. To estimate the effects quantitatively, simple assumptions are made regarding the structure of coil displacement. We consider the following three cases: displacement in radial direction (Case A), displacement in the vertical direction (Case B), and displacement by tilting (Case C). In all cases, we assume that the displacement structure has a stellarator symmetry. These assumptions are employed to calculate the change in the magnetic surfaces, rotational transform profile, magnetic well depth profile, and the effective helical ripple. Calculation results show that if the magnitude of displacement is less than 10 mm, the effects on these physical properties are small, and the good neoclassical transport property is retained.

The Chinese First Quasi-axisymmetric Stellarator (CFQS) is a joint project of international collaboration. It is designed and fabricated by Southwest Jiaotong University (SWJTU) in China and National Institute for Fusion Science (NIFS) in Japan. In this work, a plasma boundary and modular-coil system for the CFQS have been designed and optimized via scan of the magnetic configurations with various aspect ratios. The present target parameters of the CFQS are as follows: toroidal periodic number, aspect ratio, magnetic field strength and major radius are 2, 4.0, 1.0 T, and 1.0 m, respectively. The VMEC and NESCOIL codes are employed to obtain the optimum coil design via minimizing the normal component of the magnetic field on the target plasma boundary surface generated by the modular coils. In order to estimate the accuracy of the filament coils, the shape of the plasma boundary, rotational transform, depth of magnetic well and main Fourier components of magnetic field strength produced by the modular-coil system are compared with the target plasma boundary, rotational transform, depth of magnetic well and main Fourier components, correspondingly. This comparison between properties of the coil induced configuration and the target configuration shows a good agreement.