The National Institute for Fusion Science (NIFS), of the National Institutes of Natural Sciences (NINS) in Japan, has achieved an electrical current of 100,000 amperes, which is by far the highest that has yet been produced.
NIFS is undertaking the development of a high-temperature superconducting coil that is appropriate for the fusion reactor magnet. State-of-the-art yttrium-based high-temperature superconducting tapes, developed and produced in Japan on the basis of a new approach that simply stacks the tapes, have been employed by NIFS to form a conductor of exceptional mechanical strength. For the conductor joints, which are important for the production of the large-scale coils, NIFS developed low-resistance joint technology through collaborative research with Tohoku University. As a result of the prototype conductor test, at the absolute temperature of 20 degrees Kelvin (-253 C) the electrical current exceeds 100,000 A. The overall current density exceeds 40 A/mm2 including the jackets.
This value is of practical use for manufacturing large-scale fusion reactor magnets. In all, 54 yttrium-based high-temperature superconducting tapes were used to produce the magnet. Each tape is 10 mm in width and 0.2 mm in thickness, and the electrical current flows only through this area. Together with an exceptionally strong and flexible substrate, this conducting area was surrounded by a copper jacket and a stainless steel jacket The current was induced by magnetic induction.
The revolutionary method by which the helical fusion reactor's massive magnet is manufactured by sequentially connecting the short high-temperature superconductors has received much attention, say researchers at NIFS. Further, they add, the large current-capacity high-temperature superconductor with simple stacking of yttrium-based tapes and the so-called "joint winding method" have also impacted the development of high-temperature superconducting magnets used in medical instruments and power-electric devices.
Additional citation: "Feasibility of HTS magnet option for fusion reactors", Plasma and Fusion Research, Vol.9 (2014) p. 1405013.