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

Superconducting and mechanical performance and the strain effect, the influence of mechanical strain on the critical current ( I c ), are investigated for a commercially available MgB 2 multifilamentary tape. The conductor was made through the ex situ route and has 14 filaments in nickel matrix with copper stabilizer. I c was measured as a function of magnetic field ( B ) at 4.2, 15, 20, and 25 K and we determined the irreversibility fields ( B irr ) using I c –B curves at each temperature. I c , measured as a function of field angle at 4.2 K and 4 T, shows an anisotropic behaviour. We also measured I c 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 I c –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 I c ( I cm ) at 0.57% tension. Although d ( I c / I cm )/d (strain), the slope of the linear I c –strain relation in the reversible regime, depends on both temperature and magnetic field, the relations between d ( I c / I cm )/d (strain) and B / B irr fall on a universal line independently of temperature.