Since the discovery in 2001, MgB
2 has gained much interests as a new hope of superconductors for its applicability at temperatures of liquid H
2 (~20 K) or liquid Ne (~27 K). Then large efforts have been dedicated to the processing of MgB
2 wires.
Ex situ and
in situ techniques are two major techniques for the fabrication of MgB
2 wires. The
ex situ process uses previously reacted MgB
2 powders filled into appropriate sheath tubes which are then fabricated into a wire. In the
in situ process a mixture of Mg and B powders is encased in a sheath tube, and after the wire fabrication, the MgB
2 core is synthesized
in situ by the heat treatment. C or SiC nano-powders are effective dopants to enhance the high-field performance of MgB
2 wires. Wires a few kilometers long have been produced via both processes. The diffusion process starting from a composite of Mg rod or pipe and B powder is another promising process in MgB
2 wire fabrication. The connectivity of MgB
2 grains is still poor due to the insufficient packing factor of powders, voids caused by the volume contraction during MgB
2 formation, and the envelope of MgO and other insulating phase around MgB
2 grains. This poor connectivity reduces the critical current density of MgB
2 wires. Improved powder quality, fabrication techniques, and dopants may appreciably improve the performance of MgB
2 wires. Presently, the main target of MgB
2 wire application is direct-current use at 20 K, such as for MRI magnets. In this article, material aspects, fabrication process, superconducting performance and future possibilities of MgB
2 wires are briefly surveyed.
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