Transport properties of multifilamentary,in situroute, Cu-stabilized MgB2strands: one metre segments and theJc(B,T) dependence of short samples

The transport critical current density (Jc) was measured at 4.2 K for MgB2 monofilamentary and 7-, 19-, and 37-stack multifilamentary strands. Simple, one-step heat treatments (HT) were used, with temperatures of 675 and 700 °C, and times from 10–40 min. Most measurements were performed on 1 m segments of strands wound onto barrel holders. Transport properties of monofilament, 7-, 19-, and 37-stack strands were compared, and the influence of CuNi and monel outer sheaths was investigated. HT optimization studies were performed on various strands. Transport Jcs of 0.8 mm OD strands reached 2 × 105 A cm−2 at 4 T and 4.2 K (1 µV cm−1), and 1.15 × 106 A cm−2 at 4.2 K and zero field. Smaller 10-filament wires with ODs as small as 0.25 mm (40 µm filaments) exhibited good performance in some cases. The temperature and field dependences of the transport Jc were also measured; a typical example was 2 × 104 A cm−2 at 4 K, 20 T.