Prospects for MgB₂superconductors for magnet application

Abstract

Superconducting magnets have a variety of industrial, medical and research applications. This review discusses the prospects for MgB2 superconductor for practical magnet applications vis-à-vis the intermetallic low (LTS) and high temperature superconductor (HTS) cuprates. It has high TC (39 K), high JC (105–106 A cm−2 at 4.2 K and in the self-field) and HC2 (15–20 T at 4.2 K) in wire/tape geometry, with great scope for further improvement in the coming years, making it a promising candidate for practical applications. The superconducting properties of MgB2 differ from those of LTS and HTS in many ways. Besides the unusually high TC, MgB2 has a large coherence length, low anisotropy and transparent grain boundaries. The most important difference between MgB2 and other practical superconductors is that it has two superconducting gaps originating from two different bands. Tuning the scattering rates between the two bands improves the superconducting properties and the practical applicability of MgB2. The different methods of fabrication of MgB2 conductors are described and compared. Fabrication of long length MgB2 conductors is relatively easy and less expensive as compared to HTS and the method allows the use of a variety of sheath materials with suitable barriers or reinforcement. The conductors have much better mechanical properties for practical applications. The critical issues and the challenges to be addressed for realization of MgB2 superconductors as the first choice for high field magnet applications are discussed. At present MgB2 is most suited for 20–25 K operation in fields of 1–2 T.

Intergrain connectivity of MgB2 ceramics studied by impedance analysis

“…2 However, the strong field-dependent critical current density ͑J C ͒ represents one of the main stumbling blocks in realizing this potential application. It is clear that J C is determined not only by the electrical intergrain connectivity, but also by the flux pinning strength of the grain boundaries.…”

“…Their results indicate that the low packing factor and poor connectivity strongly restrict J C in MgB 2 . Many experimental methods, such as Campbell's method, 10 magneto-optical and electromagnetic studies, 11 magnetoresistance and radio frequency penetration depth techniques 12 have been used to investigate the intergrain connectivity of MgB 2 .…”

A new approach to MgB2superconducting magnet fabrication

“…MgB 2 has the highest T c among intermetallic superconductors (T c = 39 K) [4]. The H c2 at 4.2 K of SiC-doped MgB 2 is 33 T [9], which is much higher than those of either NbTi or Nb 3 Sn [10]. MgB 2 is a promising material for superconducting magnets generating high steady magnetic fields.…”

EFFECTS of DUAL DOPING OF C AND TiC NANOPARTICLES ON SUPERCONDUCTING PROPERTIES OF Fe-SHEATHED MgB[sub 2] TAPES

“…Compared with the low-temperature superconductors commercially available, the main obstacle of MgB 2 for its practical applications at high magnetic field is its lack of flux pinning [9]. Adding nano-scale dopants has been proved a very effective way for introducing pinning centers into MgB 2 [10].…”