Processing Coated Conductors

Superconductors are a class of materials with extremely important properties. One of their most emblematic applications is CERN's LHC (Large Hadron Collider), which led to the discovery of the Higgs boson in 2013. Without superconductors and the power of the magnets they enable, CERN's ring would be 100 km long, rather than the current 27 km; the construction of ITER (CEA-Cadarache France), which aims to harness energy production through nuclear fusion, would not be feasible.

Superconductivity has been known for a century, and research into superconducting materials has always been very active in applying these "magical" physical properties. Materials physicists and chemists have succeeded in developing metal alloys in wire form that take advantage of so-called classical superconductors (such as NbTi or Nb ₃ Sn alloys, for example) whose critical temperature remains below 20 °K. They require liquid helium cryogenics, which is well-known but expensive. In 1986, the high-T revolution _c (or HTS for High Temperature Superconductor) through the discovery of superconductivity above the temperature of liquid nitrogen turned this field on its head. Not only are the new cuprate-based materials, of which YBa ₂ Cu ₃ O ₇ is the best known, no longer metals in the material sense of the term, but ceramics, and their critical temperature reaches 93 °K and even 120 °K in some compounds (the latter are not very exploitable, however). The interest in this new family is enormous, but so is the effort required to take advantage of it. How do you manufacture a cable several kilometers long using ceramics? Such is the challenge posed by these new materials. Thanks to the joint efforts of physicists and chemists, a new class of materials is about to emerge.

Initially, the researchers exploited a variety of cuprates, suitable for shaping close to that of conventional superconductors; they succeeded in inserting BiSrCaCuO aggregates or powders (Bi ₂ Sr ₂ CaCu ₂ O _x : Bi2212 or Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x : Bi2223) in silver sheaths and turn them into superconducting ceramics. Industrialists were able to transform these wires into superconducting cables, the most high-profile...