Prebending effects in bronze route Nb₃Sn wires

Abstract

Control and optimization of the residual strain are one of the most important issues in the development of Nb3Sn superconducting magnets. We found that the repeated bending loads at room temperature change the prestrain of Nb3Sn wires and result in the enhancement of Jc, Bc 2 and Tc. We call this repeated bending strain ‘prebending strain’. In order to understand the prebending effect, superconducting properties were measured as functions of temperature, field, axial tensile stress and strain. In addition, the three-dimensional strain state was also evaluated by the neutron diffraction. Those obtained results strongly suggest that the prebending process changes the radial residual strain as well as the axial one independently. Hence, it is considered that the prebending effect is effective for the control and optimization of the three-dimensional strain state on the react and wind process.

Application of Prebending Effect to Triplet Cables Using Bronze-Route ${\rm Nb}_{3}{\rm Sn}$ Strands

“…The enhancement effect is larger in the case of strand. It is in agreement with the previous results [6]. The short sample test result indicates that the react-and-twist cabling process does not deteriorate .…”

The $I_{C}$ Irreversible Strain of Some ITER High $J_{C}$${\rm Nb}_{3}{\rm Sn}$ Wires

“…This effect of increase after a load-unload cycle at low temperatures has been observed by other research groups in both intrinsic tensile and compressive regions [7]. It seems to be analogous to the increases after repeated prebending of reacted at room temperature [8]. In that case, the effect is believed to be due to the release of both axial and transverse pre-strain.…”

Feasibility Study of React-and-Wind Method for Helical Coils Wound from Cable-in-Conduit Conductors

“…In the case of the LHD helical coil, a special winding machine was developed for forming NbTi conductors plastically into helical shape with a shaping head. Since the plastic deformation of the wires is not allowed for Nb 3 Sn or Nb 3 Al conductors, the allowable strain after heat treatment is considered to be within the range of 0.5% [7,8]. A proposed winding method is as follows: 1) CIC conductors are heated for reaction of the A15 phase on a bobbin, the circumference of which is the same as the length of one pitch of the helical coil.…”