Superconducting properties of MgB 2 tapes and wires

• Published in: Physica. C, Superconductivity Vol. 385; no. 1; pp. 286 - 305
• Main Authors: Flükiger, R., Suo, H.L., Musolino, N., Beneduce, C., Toulemonde, P., Lezza, P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-03-2003
• Subjects: Anisotropy; Critical current; Fabrication of wires and tapes; Irreversibility line; Powder in tube process; Upper critical field; 74.60.Ec; Critical current; Powder in tube process; Anisotropy; 74.70.Ad; Upper critical field; Irreversibility line; Fabrication of wires and tapes
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/S0921-4534(02)02307-9

An overview of the current state of development of MgB
2 wires and tapes prepared by several techniques is presented, based on the known literature data and our own results. We focus on the powder-in-tube processing method, using pre-reacted MgB
2 powders surrounded by an Fe sheath (ex situ processing route). The study of the effect of the initial MgB
2 particle size shows that after reducing the initial particles by ball milling to sizes of the order of 3 μm, the degree of texturing and the upper critical field,
B
c2, remain unchanged, while both the critical current density,
J
c, and the irreversibility field,
B
irr, show a considerable increase, followed by a decrease after longer milling times. After various recrystallization times and temperatures we show that a critical amount of impurities introduced during the particle reduction process is responsible for the observed maximum of
J
c and
B
irr. Our analysis indicates that this is a grain boundary effect, thus pointing the way for further improvement of the transport properties. A preferential orientation along the
c-axis has been observed in Fe/MgB
2 tapes by X-ray diffraction. An anisotropy ratio of 1.3 for both
B
c2 and
B
irr was found. The Fe/MgB
2 tapes exhibit a very high
n factor, which opens up the possibility for a persistent mode operation at 4.2 K and moderate fields. Transport
J
c values above 10
4 A/cm
2 are obtained in monofilamentary Fe/MgB
2 tapes at 4.2 K and 6.5 T and at 25 K and 2.25 T. Multifilamentary tapes were found to exhibit lower
J
c values due to the presently used deformation process yielding a lower density with respect to monofilaments. In all measured tapes, quenching was observed at the lowest applied fields. Improvement of the thermal stability of MgB
2 tapes will be one of the major challenges in future developments.