Design And Manufacture Of The Hybrid Solenoidal High-field Full Superconducting Magnet

High-field superconducting magnets provide the necessary strong magnetic field conditions for a series of low-temperature scientific research,such as superconducting material performance testing,with promoting the application of superconducting technology in scientific research.CRAFT is one of the priority large scientific device construction projects in the 13th Five-Year Plan of China.The project aims to accelerate the engineering design of CFETR and the experimental testing of its key systems,and will become a comprehensive research platform with the highest parameters and most complete functions in the field of fusion after completion.The CRAFT material comprehensive performance research platform is aimed at developing a hybrid solenoidal backfield magnet system with larger aperture and higher magnetic field to fulfill the critical performance research of superconducting materials under complex working conditions.To meet the needs of comprehensive material performance research platform,the design and key process researches of hybrid solenoid-type high-field superconducting magnets are carried out in this paper.The key process technologies such as the realtime visual imaging turn pitch detection and forewarning,the precise control of prestress in constant tension wound coils and the vacuum pressure impregnation with speed-controlled,constant temperature and pressure are developed.A prototype of 15 T-80 mm aperture hybrid solenoid-type high-field superconducting magnet is successfully developed,which provides important theoretical support and practice for the next design and preparation of 15 T-150-250 mm aperture hybrid solenoid-type high-field superconducting magnets and future domestic 19 T-80-150 mm aperture ultra-high-field full superconducting magnets.To optimize the performance utilization of superconducting wires,the concentric co-axial nested magnet structure with optimized hierarchical configuration of wires is used,according to the different critical performance of superconducting strands.The design parameters of the magnet are determined by using the parameter equation of the hybrid solenoidal coil to minimize the volume of the coil.The parameters of the closewound structure and the parameter relationship equation of the orthogonal parity winding type are used to minimize the amount of superconducting wires and the difficulty of coil winding.The electromagnetic and structural analysis models of magnets are established to evaluate the field strength,stress and its distribution characteristics of magnet coils.The insulation treatment processes of NbTi and Nb3Sn coil skeletons are explored for the insulation requirements of spiral coil skeletons,with the insulation treatment specifications for different types of coils formed.The winding process of compact coils are explored by using the constant tension automatic wire arrangement winding machine,which combined with the real-time visual imaging turn pitch detection and prewarning system to realize real-time detection of micron-level turn pitch and prewarning of overrun as well as high-precision detection of coil flatness.By using Fuji pressure-sensitive film and image analysis technology,the experimental study on the relationship between winding tension and coil pre-stress is carried out,which provides the key reference basis for further improving the comprehensive stress analysis model of hybrid magnet and realizing the accurate loading of pre-stress.With reference to the basic theory of close-wound solenoid coil impregnation,a speed-controlled constant temperature and pressure vacuum impregnation system is designed and built to achieve a high degree of filling of micron-sized voids in solenoid coils under vacuum,constant temperature and constant pressure using the principle of a linker.Based on the theoretical design method and development process of the magnet above,the design and fabrication of the hybrid magnet prototype with 15 T-80 mm aperture are carried out.Combined with the diode group section passive quench protection scheme,the low-temperature excitation and long-time operation stability experiments of the prototype are conducted in the 4.2 K temperature region.The feasibility of the design and preparation technology of hybrid solenoid-type high-field superconducting magnets and the reliability of the segmental quench detection and passive quench protection scheme are further verified,laying the foundation for the localization process of larger aperture high-field magnets in the future.