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

Abstract

The axial strain dependence of the critical current I_c and effective upper critical field B_c2* 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 B_c2* 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 I_c and B_c2* data fit the strain scaling law well. The results are also consistent with earlier-published T_c vs. strain data for Nb₃Sn at compressive strain as large as -0.85% and with I_c vs. strain data for stainless-steel reinforced Nb₃Sn superconductors at compressive strain as large as -0.65%. The data contradict, however, recently reported B_c2* 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.