The effect of shape and deformation in ex situ MgB_2-W/Fe composite wires

Addition of tungsten metallic particles has led to an improvement of the current carrying capacity of ex situ MgB2 wires, due to an improved internal stability. The best performance was observed for 5–10 wt% of W addition and therefore this content was also used for multi-core wires made by the rectangular wire-in-tube technique (RWIT). Transport current measurements show how the variable wire shape (rectangular, circular or tape) as well as additional mechanical deformations (twisting, bending and axial stresses) influence the critical current density of four-filament MgB2–W/Fe wires in external magnetic fields ranging up to 11 T. Critical current degradation by twisting, bending at room temperature and axial stresses at 4.2 K are discussed. It was found that the addition of W particles has no effect on the value of the irreversible strain limit.