The research on the impact of compaction and twisting on the critical current performance of six-around-one copper-reinforced REBCO cable-in-conduit conductors

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Abstract Rare-earth barium copper oxide (REBCO) superconductors are recognized for their excellent electrical conductivity and thermal stability, making them promising candidates for high-current applications in future fusion reactors. However, their unique structure and anisotropic properties challenge stable operation in low-temperature (4.2 K) and high-field (20 T). To address these issues, the Institute of Plasma Physics, Chinese Academy of Sciences has developed a six-around-one copper-reinforced cable-in-conduit conductor (CICC) configuration using highly flexible REBCO cables (HFRC) for the central solenoid coil in next-generation fusion reactors. This study introduces an optimized design for a six-around-one copper-reinforced CICC and evaluates the feasibility of its compaction and twisting processes. Initially, considering factors such as the CICC’s and sub-cable’s geometric configuration and dimensions, a statistical analysis was conducted on experimental data concerning variations in outer diameter, inner diameter, and wall thickness of four different copper tube specifications after compaction. The results indicated that the copper tube with an outer diameter of 12.5 mm and a wall thickness of 0.9 mm exhibited minimal deformation during the compaction process by compaction equipment. Consequently, this specification is preferable for sub-cable compaction. Subsequently, three HFRC cables and two conductor-on-round-core cables were compacted within this copper tube, resulting in an outer diameter of 10.86 ± 0.06 mm after compaction. Following this, the wires underwent a six-around-one twisting process with a pitch of 550 mm. The twisting experiments were performed on CICC prototypes wound with sub-cable and dummy copper tubes. Meanwhile, critical current ( I C ) tests were conducted on the conductor before and after compaction and twisting at 77 K under self-field conditions. The results show that the I C of all samples remains above 98% before and after compaction and twisting, which verifies the feasibility and reliability of the compaction and twisting technology. This research provides valuable insights and a theoretical basis for designing and applying high-performance CICC conductors in fusion reactors.

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