Enhancement of the critical current density in Chevrel phase superconducting wires

Abstract

The critical current densities Jc of Chevrel phase wires with niobium as an antidiffusion barrier were measured in magnetic fields up to 24 T. At 20 T and 1.9 K, Jc reaches 5.4×108 A/m2 and decreases slightly down to 3.1×108 A/m2 at 24 T. A wire with a 20% superconducting cross section has been successfully drawn and its overall critical current density Jcov exceeds 100 A/mm2 at 1.9 K up to a magnetic field slightly above 20 T. This demonstrates the ability of Chevrel phase wires to be used in high magnetic field applications. Moreover, some parts of the coil have certainly higher Jc, since Jc is very often limited by a thermal excursion of the entire coil. The effective upper critical field μ0Hc2*, deduced from the magnetic field dependence of Jc, is too low compared to the expected bulk value, indicating that superconducting properties at the grain boundaries are still degraded. If the bulk μ0Hc2 can be restored at the grain surfaces, Jcov should be higher than 100 A/mm2 up to at least 30 T.