Copper sheath MgB 2 wires fabricated by an in situ PIT method

Abstract

We investigated the applicability of Cu as sheath materials for MgB 2 wires prepared by in situ PIT (powder-in-tube) method in comparison with stainless steal. Since the critical current density of MgB 2 increases with TiH 2 doping, we prepared TiH 2 doped MgB 2 Cu sheath wires 40 m in length and ∅ 1.0 mm or 0.5 × 1.0 mm 2 in cross section by rotary swaging, drawing, and two-axial rolling under cold working. We then annealed the samples at 600–850 °C for 1–2 h in Ar gas atmosphere. The critical current of TiH 2 (6%) doped MgB 2/Cu short sample annealed at 650 °C reached 208 A ( J c=230 kA/cm 2) at 4.2 K and self-field. We also fabricated several coils using these wires. The I c value was ∼100 A at 4.2 K for a coil prepared with use of a 5 m length wire. These results suggest that it is possible to fabricate Cu sheathed MgB 2 wires with good performance by using the in situ PIT method.