Comparative Study of the Continuous and Batch Thermal Processing of MgB2 Wires

The last stage of the manufacturing process requires complex reactive diffusion formation process of MgB2 in the presence of SiC nanoparticles. Continuous thermal processing was adopted to produce long length MgB2 in situ wires with a homogeneous mixture of micron-sized Mg, nanosized B, as well as SiC dopant powders. This process has enabled the formation of MgB2 superconducting compound in a relatively short time. Traditional superconductor batch processing requires the wire batch to be heat treated in dedicated large furnaces. Additionally, such a batch process requires controllable slow heating-up, dwelling, and cooling down procedures to ensure uniformity of the superconducting properties along the wire length. Such a prolonged reactive diffusion process does require lower dwelling temperature and can potentially prevent full utilization of the doping materials, resulting in less effective pinning centers formation. On the other hand, continuous wire thermal processing enables rapid formation of the doped MgB2 with full utilization of the dopant. Also, in the continuous process, the moving thermal front brings complex dynamics to Mg-B, C-B, Mg-Si interaction during MgB2 formation processes. The manuscript presents a comparative study of the reactive diffusion kinetics, the microstructural formation of the doped MgB2 compound, and their Jc(B, T) characteristics

Composite superconducting MgB2 wires made by continuous process

Previously developed manufacturing technology of a low-cost composite single core MgB2 superconductive wires has been investigated in details using monel sheath and titanium diffusion barrier. In this process Mg and nano-sized B as well as SiC dopant powders were fed continuously to a "U" shaped me-tallic sheath titanium, and subsequently monel sheath. Resulting wires were assembled in "6+1" configuration cable constructed from six 0.75 mm Monel/Titanium/(MgB2+10 wt%SiC) and Monel/Titanium/MgB2 wires and one central copper wire with two twist pitch arrangements: 13 mm and 26 mm. Undoped and SiC doped wires were compared in respect of their Ic(B,T) characteristic. Wires were sintered at 700°C for different times and subsequently have been initially tested in a dedicated helium force vapour cooling system at temperatures 20-35K at 1 T. Systematic and statistic Ic(B,T) measurements of the wires and cables in LHe were conducted at high external magnetic flux density up to 9T. It was shown that wire feeding, sealing, reduction and forming technology enable virtually unlimited conductor lengths as well as in-line processing control simultaneously ensuring a high degree of reproducibility and consistent quality of the MgB2 superconductor. Such generic single core MgB2 conductors enable manufacture of multifilamentary MgB2 conductors with desired configurations (e.g. twist pitch for transient losses and AC applications)