For the cooling of high-temperature superconductivity applications (HTS applications), G-M, Stirling and pulse-tube cryocoolers are used. However; those coolers were developed for other applications; in other words, they are not suited for adaptation to HTS applications. Cryocoolers for HTS applications are described and the requirements of cryocoolers are explained. A new refrigerator required for HTS applications is presented and explained.
In the past decade, there has been significant progress in the production and application of metallic superconductors. The production of Nb-Ti wires for LHC facilities, totaling approximately 7,000 km in length, has been completed. The fabrication of NB3Sn wires for ITER facilities, totaling some 500 t in weight, is underway. The high-field performance of Nb3Sn wires has been appreciably enhanced, facilitating the generation of 20 T at 4.2 K. Today, Nb3Al wires that are fabricated using an improved process are approaching practical use. Newly developed MgB2 wires are also being developed with the aim of applications at 20K. In the present course, the recent status of these metallic superconductors will be described. As an introduction, this article outlines the chronological progress of metallic superconductors. Progress has been made through basic research on electromagnetic and material aspects, as well as through the development of new fabrication processes. A personal comment regarding the development of metallic superconductors is also briefly mentioned in this article.