Thermally induced pre-stress and critical current density of PbMo6S8wires

Powder-metallurgical processed PbMo
6
S
8
monofilamentary wires with a molybdenum-matrix suffer under a tensile pre-stress on the superconducting core which is due to a difference in the thermal expansion coefficient of the constituents. In this case the observed critical current densities may be up to two orders of magnitude smaller compared to bulk samples. We have now improved considerably the critical current density of PbMo
6
S
8
monofilamentary wires by a compressive pre-stress on the superconductor. This was achieved by developing a new hot extrusion and drawing technology based on a molybdenum stainless-steel matrix. J
c
is now in the range of 1×10
⁸
A/m
²
at 14 T and 4.2 K, which corresponds approximately to the value observed in PbMo
6
S
8
bulk samples. Lengths of up to 1 km of these wires have already been manufactured.