Preliminary structure design and stress analysis of preload structure of DC magnet for Super-X test facility

https://doi.org/10.1016/j.fusengdes.2020.111916Get rights and content

Highlights

  • Preload structure of DC magnet for Super-X test facility is design.

  • Preloaded rod and Pre-tightening screw are used to provide pretension.

  • Through finite element analysis to determine to meet design requirements.

Abstract

Super-X test facility can simulate the electromagnetic performances of a superconducting conductor under fusion reactor operating conditions, in which DC magnets are a core assemble. The DC test magnet provides 15 T central magnetic field. The field homogeneity of test area is more than or equal to 98 %. The magnet comprises three pairs of Nb3Sn coils (i.e., high-field, mid-field and low-field.). Included in the magnet assembly are a preload structure, joints, cooling pipe, etc. The preload structure includes preloaded rods, pre-tightening screws, end plates, an intermediate connection flange, buffer layers and shims between coils. The main function of the preload structure is to maintain registration of the coils under magnetic loads, and, secondarily, to support gravity so that they will not separate. It also provides axial preload compression on the coils. Orthotropic equivalent properties of the coil regions are calculated based on generalized Hook’s law and ANSYS software, the superconducting coils are modelled with equivalent orthotropic properties of winding to simplify the finite element model (FEM). A quarter FEM of the simplified DC magnet is established with the coupling solver, and the finite element analysis has verified the design satisfies appropriate design limits base on the ASME Code.

Introduction

Many large-scale superconducting conductors and testing facilities have been designed and built to carry out research on superconductor performance, and many advanced superconducting technologies have been established using these facilities. SULTAN [1,2] conductor test facility provides performance testing services for cable-in-conduit conductors (CICC) developed by ITER, which handles most worldwide testing tasks. After the large-scale superconducting test facility SSTF [3] is completed, it can meet the performance testing requirements of high-field superconducting strands, high-performance CICC superconductors and KSTAR [4,5] device PF and TF coils. The DC magnetic field provided by ITER central solenoid (CS) model coil (CSMC), it can be utilized as a superconducting coil performance test platform [6]. Performance tests have been conducted on Japan's Nb3Sn interpolated coils, Russian TF interpolated coils, and Nb3Al interpolated coils [7,8]. These facilities have provided important test platforms for the development of large superconducting magnet technologies. However, because testing must develop rapidly toward large-scale high-field capacities, existing superconducting test facilities will soon not meet the needs of users. The Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) plans to establish the Super-X test facility to test the performances of conductors (e.g., CFETR CS and TF) in which the DC magnet will provide a test magnetic field of 15 T, which has not been achieved before [9,10]. The DC magnet is the core of Super-X test facility and is installed using three pairs of Nb3Sn coils through a preload structure, as shown in Fig. 1.

The DC magnet will withstand huge electromagnetic forces and will endure low temperatures during operation. Therefore, mechanical analysis is necessary to evaluate the preload structure design. The design purpose of the preload structure is to axially fix these coils, support the joints and other components, and provide friction to overcome the coil gravity. ITER’s Magnet Department has analyzed the stress distribution of the ITER CS coil structure under various load conditions, and the results have shown that the design of the coil preload structure is reasonable. ASIPP has completed the stress and deformation distribution of CFETR CSMC [11,12] under gravity, preload stress, thermal load, and electromagnetic load [13]. These studies provide the bases for the research of this paper. The base includes elasticity theory, electromagnetic and thermal analysis, and finite element simulation to evaluate the mechanical properties of preload structure. This will also lead to the production of a technical guide and support for the final manufactured DC magnet.

Section snippets

Structure design and analysis process of preload structure

Fig. 2 shows the preload structure of the DC magnet, which includes preloaded rods, pre-tightening screws, end plates having a thickness of 40 mm, an intermediate connection flange, buffer layers, and shims between the coils. The size of the preload structure is 3.2 × 3.6 × 3.2 m, and its main function is to overcome the gravity of the coils so that they will not separate. It also provides axial contraction to the coils. Preloaded rods and pre-tightening screws composed of 316 L N provide the

Results

The results of the analyses using combined loading cases on the preloaded DC magnet are discussed in the following sections including contour plots of stresses.

Conclusions

The 3D structure of the Super-X test facility DC magnet was established. We focused on the material selection and design rationality of the preload structure and conductor under various conditions. For the preload structure, the most dangerous moment occurred during installation. Considering the economics and structural safety of coils manufacturing, 316 L N is used to manufacture all 316 L N components. Furthermore, the stress distribution of 316 L N components met the design requirements.

CRediT authorship contribution statement

Wenbiao Zhu: Conceptualization, Methodology, Formal analysis, Investigation, Writing - original draft. Ke Chen: Supervision. Yu Wu: Funding acquisition. Yi Shi: Project administration, Funding acquisition. Hongmei Zheng: Validation, Formal analysis, Investigation, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This work was supported by Comprehensive Research Facility for Fusion Technology Program of China (Contract No. 2018-000052-73-01-001228).

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