Mechanical and electromagnetic characteristics of MgB₂ wires & Cable-in-Conduit Conductors for fusion magnet application

A study on a 4-stage sub-size MgB ₂ Cable-in-Conduit Conductor (CICC), tested at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), revealed a 20% degradation in critical current at 4.2 K compared to single-strand data. To address this issue, the mechanical properties of MgB ₂ wires from Hyper Tech and WST were investigated, and two sub-size CICCs were manufactured using a “close-to-1-ratio” Twente design with smaller diameter wires. These cables demonstrated no significant degradation in critical current after cabling and compaction, nor after electromagnetic load cycling. The results indicate that the close-to-1-ratio cable design is optimal for brittle superconducting materials such as MgB ₂, Nb₃Sn, and BSCCO, as it minimizes mechanical stress and preserves superconducting properties. This design shows significant potential for the application of MgB ₂ in next-generation fusion reactors, particularly in Poloidal Field (PF) coils, Correction Coils (CC), and feeders.