According to the assumed specification of the Nb3Sn for the accelerator magnets of the FCC (Future Circular Collider), it is required to achieve both extremely high Jc, which is unprecedented, and high RRR and low effective filament diameter (deff).
We have developed high performance Nb3Sn wire via DT (Distributed Tin) method, which is a type of internal Sn method with single barrier. So far, Non-Cu JC of 1,100 A/mm2 at 16 T, 4.2 K has been achieved by reducing Sn diffusion length and optimizing Ti content. Effective filament diameter of the samples were about 30 to 60 μm. The values of RRR were about 350, and RRR after 10% rolling assuming deformation of the cabling were 150 to 200, and no decrease in Jc was observed.
From these results, we believe that the DT method has very high potential as a candidate of Nb3Sn wire for FCC. We will continue to improve Jc by further increasing Nb ratio and optimizing for the Sn diffusion distance, ternary additive elements and heat treatment, etc., for targeting the FCC's specification.
Acknowledgments: This work was supported by the CERN and KEK under contract. Appendix 19 to the Agreement on Collaborative Work between CERN and KEK (ICA-JP-0103)