ENHANCEMENT OF THE CRITICAL-CURRENT DENSITY IN CHEVREL-PHASE SUPERCONDUCTING WIRES

The critical current densities J(c) of Chevrel phase wires with niobiu m as an antidiffusion barrier were measured in magnetic fields up to 2 4 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% superco nducting cross section has been successfully drawn and its overall cri tical current density J(c)(ov) exceeds 100 A/mm(2) at 1.9 K up to a ma gnetic field slightly above 20 T. This demonstrates the ability of Che vrel phase wires to be used in high magnetic field applications. Moreo ver, 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 effe ctive upper critical field mu(0)H(c2), deduced from the magnetic fiel d 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 s urfaces, J(c)(ov) should be higher than 100 A/mm(2) up to at least 30 T. (C) 1997 American Institute of Physics.