High Compressive Axial Strain Effect on the Critical Current and Field of Nb3Sn Superconductor Wire

Abstract

The axial strain dependence of the critical current Ic and effective upper critical field Bc2* have been measured on a series of Nb3Sn wire superconductors having initial compressive strain as large as -0.95% arising from thermal contraction of the conductor matrix. Results include data for binary Nb3Sn and ternary Nb3Sn with Ti additions. The effective upper critical field Bc2* is obtained using a general form of the pinning expression, since the data show that the Kramer method is not generally applicable to ternary Nb3Sn superconductors. The Ic and Bc2* data fit the strain scaling law well. The results are also consistent with earlier-published Tc vs. strain data for Nb3Sn at compressive strain as large as -0.85% and with Ic vs. strain data for stainless-steel reinforced Nb3Sn superconductors at compressive strain as large as -0.65%. The data contradict, however, recently reported Bc2* data obtained on multifilamentary Nb3Sn wires where high compressive strain was applied by soldering the wires to a bending beam and then flexing the beam.