High transport currents in mechanically reinforced MgB[sub 2] wires

Abstract

Monofilamentary PIT-MgB 2 -wires with a mechanically reinforced sheath were developed. The two kinds of prepared PIT-wires had different precursors, commercial MgB 2 powder or a Mg/B metallic powder mixture. Both wires were heat treated to get a dense filament. We observed a significantly different behavior of the superconducting properties. In wires with the metallic Mg/B precursors, the highest transport critical current densities of J c =10 5 Acm -2 (4.2 K/0 T) were measured. The maximum of pinning was found at low fields of B = 1 T and the critical current drops close to zero at fields of B = 5-6 T. In wires from MgB 2 powders, a significantly different transport current behavior was observed. At B = 0 T, J c = 65000 Acm -2 is about 35% reduced, but towards higher fields the J c degradation was smaller and the pinning force maximum shifts to approx. 3.5 T. A similar but much weaker behavior was observed changing the first wall in the sheath from Nb to Ta for in-situ-wires. This result shows that pinning and the superconducting performance at higher fields can be influenced and improved by the preparation route and the design of the wire composite. At temperatures close to T c (38.4 K, midpoint), also high transport currents were found, J c exceeds 23000 Acm -2 for T < 30 K and 52000 Acm -2 at T < 20 K, B = 0 T. The reproducibility of the current carrying capacity of all wires was excellent, indicating dense filaments through a very successful mechanical reinforcement.