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Superconductivity Revolution

World's First "Yttrium-based Oxide Superconducting Wires" Development Story

Phase.5 Develop equipment and step into the future

With more original and innovative technologies than anybody else, Fujikura, a frontrunner in the world of superconducting wires, starts demonstrating its capability.

As yttrium-based superconducting wires have a high critical current characteristic in magnetic fields, they can be used for any applications. They are regarded as the best, above all, for use in equipment (such as linear motor cars, diagnostic MRI equipment, and energy storage systems) that uses a magnetic field in particular. A magnet in the coil form of the superconducting wire is used for these sets of equipment. When the wire is processed into a coil, a strain such as bend or tension will work when winding it. In addition, the electromagnetic force will also work when electricity is applied. The application in equipment was expected to experience various problems, such as a need for balancing with a cooling system and the events that could occur at the time of a failure, which were not known at the level of wire materials. Consequently, there were many considerations to be examined before using the superconducting wires for equipment applications, and we needed to feed the information back to the wire production process.

Liquid Nitrogen Cooling Magnet
Liquid Nitrogen Cooling Magnet
For this reason, Fujikura repeated verifications on various assumptions such as examining the operational characteristics of a magnet in the coil form of the superconducting wire, testing the energization of the magnet when applying current exceeding the critical current value to it, and checking the change of temperatures when it was in liquid nitrogen, including investigating the superconductive property when the superconducting wire was bent.
In reality, the verifications proceeded smoothly even if the magnet was energized. We then applied current greater than the critical current value, and the magnet started to become slightly displaced to normal conduction and a voltage was observed. When we continued to increase the energizing current, the voltage increased, but the temperature gauge attached to the magnet did not show even the slightest movement. This meant that a set of equipment in which yttrium-based superconducting wires were applied would operate more stably than conventional sets of metal-based superconducting equipment.

Cryocooler-cooled Magnet
Cryocooler-cooled Magnet
In addition, we produced a cryocooler-cooled magnet in 2006 to understand the excitation characteristic of a magnet at temperatures lower than the liquid nitrogen temperature of 70 k. We examined the excitation characteristic in the temperature range of 30 to 70 k by using the magnet. The result clarified that it was possible to energize the magnet at lower temperatures than the liquid nitrogen temperature as stably as that in liquid nitrogen.
In response to these results, we produced the first motor that used yttrium-based superconducting wires. The motor, intended for use in ships, had a rated rpm of 360 and a rated output of 15 kW, and it used the yttrium-based superconducting wires in field coils. It was semi-superconducting, and the armature used copper wires. After they passed motor rotation tests, we attached a screw to the motor to further test the characteristics of the motor for ships and tested it under water. The test results were good, which boosted the momentum to commercialize the yttrium-based superconducting wires.

As described above in this article, we have attained the level where we can produce yttrium-based superconducting wires having a length of 500 m or longer. We have also reached the stage where the critical current exceeds 500 A at the liquid nitrogen temperature. While we further improve the characteristics of the superconducting wires at the same time we are refining technologies with which we can produce the longer wires at lower cost, we intend to examine every case where the yttrium-based superconducting wires can be applied to various sets of superconducting equipment in the future. We also intend to continue to take the approach of providing them to the world as early as possible. To succeed as a business, we are approaching the critical period. With more original and innovative technologies than anyone else, Fujikura, a frontrunner in the world of superconducting wires, has started demonstrating its capability.

Note that most of the research results that have been explained above in this article are based on the research and development results from "Superconducting Electric Power Applied Technology Development" (1987 to 1998), "Research and Development of Basic Technologies for Superconductivity Applications (Phase I)" (1999 to 2002), and " Research and Development of Basic Technologies for Superconductivity Applications (Phase II)" (2003 to 2007), in which The New Energy and Industrial Technology Development Organization (NEDO) commissioned Fujikura to conduct research and development.

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