Fine-filamentary in situ MgB2 wires

Nineteen-filament MgB2/Ti/Cu/SS composites have been made by an in situ approach using only drawing deformation to a filament size of 16.6--58 mu m. Circular cables containing 133 filaments were assembled from 1 + 6 strands of diameter 0.25 mm and 0.375 mm. All wires and cables were heat treated at 800 degree C/0.5 h in pure Ar atmosphere. The critical current densities Jc of the different wire sizes were measured and EDX element mapping was done for some of them. It was found that the critical current density decreases with reduced filament size, especially below the filament diameter of 27 mu m due to copper penetration through the thin Ti barrier ( 104 A cm - 2 was measured at 4.2 K and field 5.5 T for the thinnest 16.6 mu m filaments published up to now.