Development of a 1 MJ cryocooler-cooled split magnet with Ag-sheathed Bi2223 tapes for Si single-crystal growth applications

A project to develop a high-temperature superconducting split magnet for Si single-crystal growth applications began in October 1997 and is scheduled to be completed for three years. The project is being executed on the basis of collaboration between Toshiba Corp., Sumitomo Electric Industries Ltd. and Shin-Etsu Handotai Co. Ltd., and is partially funded by Ministry of International Trade and Industry (MITI) of Japan. The purpose of this project is to confirm the energy-saving performance and high reliability of a large HTS split magnet (1 MJ) using Bi2223 tapes. This split coil system is composed of 2 coils, each consisting of 18 pancakes, and the total length of HTS tapes is approximately 80 km. The magnet is to be cooled to below 20 K by a highly efficient GM-type cryocooler in order to make overall current density of the magnet close to the density of metal superconducting magnets. In the first year of this project, a conceptual design was established and R&D of the fragile HTS tapes was carried out. In the second year, the design, fabrication, testing and evaluation of an experimental magnet, incorporating pancake coils of the same size as those of the actual magnet, has been accomplished. This work will contribute to the improvement of the design and fabrication of the full-scale magnet in the final year of this project.