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The Chinese first quasi-axisymmetric stellarator (CFQS), which will be the first quasi-axisymmetric (QA) stellarator in the world, is now under construction. The primary task of the CFQS project is to realize a QA configuration and to examine its physical properties. Based on this task, two important issues were investigated in this work in order to estimate the robustness of the CFQS design from a physical perspective. One was the toroidal field (TF) ripple due to the discreteness of modular coils (MCs) which could potentially degrade the charged particle confinement in the CFQS configuration. The other was a possible MC misalignment in the assembly that would affect the magnetic field and charged particle confinement in the CFQS. Moreover, since the stellarator symmetry might be broken by the MC misalignment, such a case was also investigated in this work. By performing a magnetic field line tracing and charged particle orbit tracing calculation, it was found that the TF ripple does not affect the confinement property significantly and the magnetohydrodynamics equilibrium was robust against possible MC misalignments. These results are helpful in defining the reasonable tolerance of assembly accuracy., source:Guozhen Xiong et al 2023 Plasma Phys. Control. Fusion 65 035020, source:https://doi.org/10.1088/1361-6587/acb5c1, identifier:0000-0002-5601-7106

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., source:https://doi.org/10.1585/pfr.14.3403151, identifier:0000-0003-3764-3184

The world's newest quasi-axisymmetric stellarator CFQS is constructed as a joint project of the National Institute for Fusion Science, Japan and Southwest Jiaotong University, the People's Republic of China. The project is named “NSJP for CFQS”. The CFQS has a major radius of 1 m, toroidal periods of 2, and aspect ratio of 4. The toroidal magnetic field strength will be increased up to 1 T. The CFQS equilibrium is characterized by low-aspect ratio and quasi-axisymmetry, having both natures of two-dimensional tokamak and three-dimensional stellarator. The CFQS offers new opportunities and fields to increase understanding of toroidal fusion plasmas., source:https://doi.org/10.1585/pfr.14.3402074, identifier:0000-0002-3572-1882

The Chinese First Quasi-axisymmetric Stellarator (CFQS) is a new quasi-axisymmetric experimental device planned for construction at South West Jiaotong University (SWJTU), China. This is a joint project of the National Institute for Fusion Science (NIFS) and the SWJTU. The present paper discusses the equilibrium configuration of the CFQS with a major radius of 1.0m, a toroidal magnetic field strength of 1.0 T, and an aspect ratio of 4.0. As the CFQS is a quasi-axisymmetric stellarator, a tokamak-like bootstrap current is expected. The magnitude of the bootstrap current was estimated by BOOTSJ code. Next, the effects of the bootstrap current on the quasi-axisymmetric property and the neoclassical diffusion coefficient were estimated. The bootstrap current little affected the quasi-axisymmetric property, and a good neoclassical transport property was maintained., source:https://doi.org/10.1585/pfr.13.3403123 Details, identifier:0000-0003-3764-3184

The Chinese First Quasi-axisymmetric Stellarator (CFQS) is now under design and construction. It will be the first quasi-axisymmetric (QA) configuration device to be operated in the world. The main parameters of the CFQS are as follows: the toroidal periodic number Np = 2, major radius R = 1.0 m, aspect ratio Ap = 4.0 and magnetic field strength Bt = 1.0 T. The low Ap makes it quite challenging to design a supporting structure because of the limited space and strong electromagnetic (EM) force. In this paper, a cage-like supporting structure is proposed for the CFQS modular coil (MC) system to sustain the EM force and the weight of entire device. A finite element analysis is carried out for ensuring the reliability of the supporting structure. The analysis results of the CFQS global model indicate that the cage-like supporting structure can basically satisfy the requirement., source:https://doi.org/10.1016/j.fusengdes.2020.112021, identifier:0000-0002-5601-7106

To date, almost all coil-design codes, e.g. NESCOIL, COILOPT, FOCUS codes, etc, have been primarily attributed to the optimization of filament coils for stellarators. However, evolving to a practical/finite-sized coil from a filament coil, the finite-size effect of coils significantly constrains the fabrication tolerances of a coil system. This paper presents a novel approach that emphasizes the optimization of practical modular coils to reduce sensitivity to fabrication tolerances and to achieve the expected magnetic configurations precisely. A new evaluation parameter, surface twist, is defined in this paper and applied to the optimization sequence in addition to the practical coil line torsion and curvature. The approach has been applied to the framework of the filament coil scheme in the Chinese first quasi-axisymmetric stellarator. This practical coil system without surface twists has been accomplished. Compared to the original finite-sized coil design, the new result is a more considerable simplification of coil shapes, such that in a certain direction view each finite-sized coil becomes a planar-like one. Moreover, this method can also be implemented for the estimation of stochastic deviations of practical coils during the fabrication and assembly of the coil system., source:Yangbo Li et al 2020 Plasma Phys. Control. Fusion 62 125004, source:https://doi.org/10.1088/1361-6587/abb9fb, identifier:0000-0002-7635-2905

source:27th IAEA Fusion Energy Conference (FEC 2018), source:22–27 October 2018, Gandhinagar (nearest Airport: Ahmedabad), India, source:https://conferences.iaea.org/event/151/contributions/5632/contribution.pdf

source:45th EPS Conference on Plasma Physics P1.1039, source:https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwinseqI9eD5AhUXfnAKHZcfBTEQFnoECAkQAQ&url=http%3A%2F%2Focs.ciemat.es%2FEPS2018PAP%2Fpdf%2FP1.1039.pdf&usg=AOvVaw2rgr7BFi9NuK3ssVKWL9z2

source:45th EPS Conference on Plasma Physics P1.1053, source:https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjI-Zno_uD5AhUUCt4KHVIaBMYQFnoECBgQAQ&url=http%3A%2F%2Focs.ciemat.es%2FEPS2018PAP%2Fpdf%2FP1.1053.pdf&usg=AOvVaw3lPS8YqjRFXeIdV3XayqRc, identifier:0000-0003-3764-3184

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., source:https://doi.org/10.1585/pfr.13.3405067

The transition of trapped-particle orbit topologies has been investigated in quasi-axisymmetric (QA) configurations, such as the Chinese First Quasi-axisymmetric Stellarator (CFQS). It is found that the axisymmetry-breaking phenomenon in QA configurations is of great significance at some specific locations, which could easily induce blocked particles to transit into localized particles. A novel aspect is presented to interpret the transition mechanism of trapped-particle orbit topologies in this paper, i.e., as the amplitudes of non-axisymmetric field increase along the radius direction, the region of large toroidal inhomogeneity is gradually generated, which makes the length of the trapped-particle trajectory substantially short, and hence, may restrict particles to a single helical field period. Meanwhile, at such locations the "pseudo-axisymmetric" field results in coupling of the maximum radial drift and the minimum poloidal drift, which enables the transition of trapped-particle orbit topologies considerably and forms specific loss channels, degrading plasma confinement. These results may shed light on the optimization of QA configurations via avoidance of such coupling with respect to energetic particle confinement. Moreover, this work is also relevant to the generation of inhomogeneity of particle flux deposition on the devertor plates., source:Lang Yang et al 2020 EPL 129 35001, source:https://doi.org/10.1209/0295-5075/129/35001