Development And Performance Study Of MgB₂ Cable-in-conduit Conductor

Fully superconducting tokamak is a promising route to controlled fusion energy utilization and resolve the global energy crisis.Tokamaks are comprised of superconducting magnets as their central components.Primarily,they are utilized to excite and contain the high-temperature fusion plasma.Due to their sturdy support,low AC loss,and forced flow cooling,Cable-In-Conduit Conductors（CICCs）are an excellent option for fusion superconducting magnets.In addition,MgB₂ superconductors have a higher critical temperature and lower material cost than NbTi and Nb3Sn and are potential candidates for developing tokamak poloidal field（PF）magnets and correction coils（CC）.To promote the use of MgB₂ CICCs magnets in future fusion experimental devices,eight academic institutions,including the University of Twente and the Institute of Plasma Physics of the Chinese Academy of Sciences（ASIPP）,formed the International Collaboration for Advancement of Magnesiumdiboride Applications（ICAMS）.The ASIPP is responsible for designing,producing,and testing MgB₂ CICCs in ICAMS.The research was conducted in response to the demand for MgB₂ CICC development.The performance of MgB₂ wires were evaluated.The structure of conductors was designed.The processes of cabling,compaction,and heat treatment were optimized.The conductor’s performance was evaluated at low temperatures using the first domestic MgB₂ CICCs.Based on the flux pinning theory of non-ideal type Ⅱ superconductors,the scaling laws of MgB₂ wires were established.The critical performance of MgB₂ wires in various temperatures and fields has been studied,and the results follow the scaling law.Furthermore,the tensile performance of MgB₂ wire at various temperatures was evaluated,the stress-strain functions of superconducting wires were created,and the allowable axial stress of MgB₂ wires was specified.It lays the groundwork for developing and analyzing the stability of MgB₂ CICCs.Then,the MgB₂ CICC design was completed.The full back-twist cabling method with a small forming angle is proposed,and the superconducting cable’s structural integrity and surface regularity are ensured.In addition,a method of dimension control based on the axial extension law of the jacket has been proposed,eliminating the need to cut conductor samples after forming.Finally,two sub-size MgB₂ CICC samples were manufactured successfully.The present method for wire heat treatment cannot be utilized for CICC heat treatment due to its rapid heating rate and short reaction time.Therefore,two kinds of heat treatment methods with multiple plateaus suited for MgB₂ CICCs are proposed.Thermal inertia and hysteresis are eliminated from the conductor heat treatment process.Experiments confirmed the dependability and stability of the new conductor heat treatment methods.The MgB₂ CICCs were heat treated with a temperature difference of less than 5℃.The performance of MgB₂ CICCs at low temperatures was also investigated.The conductors’ critical current in various fields was characterized,and no degradation was observed.The AC losses of the conductors were evaluated.Finally,electromagnetic cyclic load tests evaluated the conductor’s performance under transverse loads.The research results on MgB₂ CICCs provided the good basis for the future development of full-size MgB₂ CICCs and large magnets.