Application prospects of MgB$_2$ in view of its basic properties

TL;DR

This paper reviews the fundamental properties of MgB$_2$ superconductors, analyzing their current transport, critical fields, and potential for high-field applications, highlighting areas for further enhancement.

Contribution

It provides a comprehensive overview of MgB$_2$'s basic properties and discusses how these can be optimized for improved superconducting performance in practical applications.

Findings

High upper critical fields can be achieved through impurity scattering.

Grain boundary pinning is near the theoretical limit in polycrystalline MgB$_2$.

Connectivity between grains remains a limiting factor for critical current density.

Abstract

Seven years after the discovery of superconductivity in magnesium diboride, the fundamental superconducting properties of this compound are well known and the peculiar current transport in polycrystalline materials is essentially understood. Based on this knowledge the ultimate performance of wires or tapes at high magnetic fields will be predicted and compared to state-of-the-art materials and to other superconductors. The key parameter for high field applications is the upper critical field, which can be strongly enhanced by impurity scattering. This fundamental property might be further optimized in bulk materials, since higher values were reported for thin films. The MgB$_2$ grains are usually very small, if prepared by the in-situ technique. The resulting high density of grain boundaries leads to strong pinning, close to the theoretical limit. On the other hand, the connectivity between the grains is still rather poor and strongly reduces the achievable critical currents, thus leaving room for further improvements.