Application of the prebending strain effect onCuNb/Nb3Sn superconducting coils fabricated by a react-and-wind method

Abstract

We have found that prebending treatment, which is repeated bending load at room temperature,greatly enhances the critical current, upper critical field and critical temperature of practicalNb3Sn superconducting wires. In this paper, we focus on the application of the prebending straineffect to practical superconducting coils fabricated by a react-and-wind method.To demonstrate the prebending strain effect on the react-and-wind coil, we prepared two kinds ofCuNb /Nb3Sn superconducting monolayer coils. For one of the coils, the superconducting wire of 1.0 mmdiameter was repeatedly bent by using ten fixed pulleys before the winding process,resulting in a prebending strain value of 1.0%. The final winding diameter of both coils was200 mm and the number of turns was 49.In the compressive stress condition, the critical current of the coil with 1.0% prebendingstrain was 296 A at 11 T, which was larger than that of the coil with 0% prebending strain.These values were much larger than the critical current of the witness sample. Theresults indicate that the prebending treatment enhanced the coil critical current.In the case of the hoop stress condition, the coil critical currents were approximately 230 Aat 11 T for both coils. The maximum electromagnetic hoop stress was calculated to be360 MPa. The short sample tensile test results qualitatively explained the critical currentdeterioration of the coil. Furthermore, the 360 MPa hoop stress did not deteriorate thecritical current irreversibly.