Superconducting and mechanical performance and the strain effects of a multifilamentary MgB₂/Ni tape

Abstract

Superconducting and mechanical performance and the strain effect, the influence of mechanical strain on the critical current (Ic), are investigated for a commercially available MgB2 multifilamentary tape. The conductor was made through the ex situ route and has 14 filaments in nickel matrix with copper stabilizer. Ic was measured as a function of magnetic field (B) at 4.2, 15, 20, and 25 K and we determined the irreversibility fields (Birr) using Ic–B curves at each temperature. Ic, measured as a function of field angle at 4.2 K and 4 T, shows an anisotropic behaviour. We also measured Ic as a function of temperature in 0–5 T. The stress–strain relation was tested at 296 and 113 K. The strain effect was examined in magnetic fields at 4.2, 15, and 20 K using a U-shape rig made of stainless steel (SUS304). The Ic–strain relation is linear and reversible in the window of external strain between −0.5% (compression) and 0.5% (tension). With increasing strain, large and irreversible degradation occurs after the maximum of Ic (Icm) at 0.57% tension. Although d (Ic/Icm)/d (strain), the slope of the linear Ic–strain relation in the reversible regime, depends on both temperature and magnetic field, the relations between d (Ic/Icm)/d (strain) and B/Birr fall on a universal line independently of temperature.