Enhancement of the critical current density in Chevrel phase superconducting wires

The critical current densities J(c) 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, J(c) reaches 5.4 x 10(8) A/m(2) and decreases slightly down to 3.1 x 10(8) A/m(2) at 24 T. A wire with a 20% superconducting cross section has been successfully drawn and its overall critical current density J(c)(ov) exceeds 100 A/mm(2) 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 J(c), since J(c) is very often limited by a thermal excursion of the entire coil. The effective upper critical field mu(0)H(c2)*, deduced from the magnetic field dependence of J(c), is too low compared to the expected bulk value, indicating that superconducting properties at the grain boundaries are still degraded. If the bulk mu(0)H(c2) can be restored at the grain surfaces, J(c)(ov) should be higher than 100 A/mm(2) up to at least 30 T. (C) 1997 American Institute of Physics.