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 pining 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 temperature 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.
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