Tape stacks enable tough magnet conductor
Putting together superconducting tapes to fabricate a large-scale magnet conductor appropriate for the fusion reactor led to the achievement of an electrical current of 100kA—billed as the highest in the world—by researchers The National Institute for Fusion Science (NIFS), of the National Institutes of Natural Sciences in Japan.
The researchers used yttrium-based high-temperature superconducting tapes developed and produced in Japan. For the conductor joints, NIFS designed a low-resistance joint technology through collaborative research with Tohoku University.
Figure 1: The cross-section of the conductor sample. Source: NIFS
There were 54 tapes in total, each measuring 10mm in width and 0.2mm in thickness. Together with the substrate used for this type of tape that was exceptional in strength and flexibility, a copper jacket and a stainless steel jacket were used to surround the stack—making for a construction of an extremely strong conductor.
The electrical current flows only through the stack of tapes, induced by magnetic induction. As a result of the prototype conductor test, at the absolute temperature of -253°Celsius, the electrical current exceeded 100kA. The overall current density surpassed 40A/mm2 including the jackets, and this value is of practical use for manufacturing large-scale fusion reactor magnets.
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.
Further, 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. Ripple effects are anticipated in the future.
Figure 2: The whole set of the conductor. Source: NIFS
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