Evaluation of Jc-compressive Strain Properties for Nb3Sn Wires

To clarify the Jc-compressive strain properties of Nb3Sn superconducting wires fabricated using the internal-tin process, an evaluation of the properties has been carried out by applying pre-compressive strain to the wires. The strain was induced by clothing the wires in stainless steel that has large thermal contraction and then subjecting the wires to a heat-treatment process. We succeeded in shifting the peak strain from 0.3% to 0.7- 0.8% and grasping the Jc-compressive strain properties. These experimental values agree well with the stress analysis results. We also examined the differences in Jc-strain properties including the compressive strain between internal-tin processed wires and bronze wires. As a result, it was found that Jc-strain properties are different between them; however when both wires are clothed in stainless steel, they show almost the similar strain-sensitivity. Using these data, the specification value on Jc for the strand wire of the ITER TF coils was examined. It was concluded that 9.7% higher Jc is needed for internal-tin processed wires as compared to bronze route Nb3Sn wires at T=4.2 K and B=12 T, assuming that both wires have the same Jc at T=6 K and B=11.8T.