A review on high performance MgB2 wires: From material science to practical application

• This review provides a systematic overview on PIT and IMD MgB 2 wires/tapes, critically assessing their respective advantages and limitations. • This review gives a summary of method aiming at improving superconducting performance of MgB 2 wires, including advanced chemical doping and process optimization techniques. • This review highlights the promising potential of MgB 2 helium-free superconducting applications such as high-current cables and large-scale magnets. MgB 2 has more than 2 decades of development since the discovery of its superconductivity. Thanks to its high transition temperature ( T c ), low anisotropy, and absence of weak links at grain boundaries, etc., MgB 2 was considered as a promising material for superconducting applications at 20 K, low-field. This review gives a brief history of MgB 2 wires and tapes, covering key advancements up to the latest progress. The fundamental properties of MgB 2 are introduced at the beginning, including its crystal structure, superconducting characteristics, and notably its unique two-gap superconductivity. Then, an overview towards the development of high-performance MgB 2 wires and tapes is provided. First, it includes an introduction to the 1st-generation powder-in-tube (PIT) method and the second-generation internal magnesium diffusion (IMD) method, highlighting their respective advantages and limitations. Second, various strategies are summarized, which are proposed by different research groups worldwide to enhance J c and J e of MgB 2 wires and tapes, such as chemical doping (e.g., C, SiC, or Dy 2 O 3 doping) and process optimizations (e.g., ball milling, deformation, or heat treatment). Finally, the progress in long PIT and IMD wires, as well as the development of MgB 2 superconducting joints, are being discussed. In terms of practical applications, numerous MgB 2 -based products developed by companies in the U.S., China, Europe, etc. have been introduced. These include high-current MgB 2 cables (e.g., Superconducting Links - SC Links), or large-scale MgB 2 magnets (e.g., Magnetic Resonance Imaging - MRI). We believe that, in the near future, MgB 2 can partially replace NbTi wires in scalable applications, especially for helium-free superconducting magnets or cables.