Phase.3　Development of superconductivity

Fujikura establishes a succession of new records in approaches to improving film deposition speed and critical current density, and producing longer wires.

In the days when the IBAD approach was discovered, Fujikura examined the operating principal of the approach with a set of small static equipment. We could only produce intermediate layer wires having a length of a few centimeters with the approach due to the restrictions of the equipment. Following that, we moved on to design and manufacture the first equipment that was capable of depositing a film on a base material tape as we were moving it. To show the world that they could function as superconducting wires, we studied the ion sources in terms of what ion sources should be selected, how they should be placed and the like so that meter-class wires could be produced. When actually manufacturing the equipment, we tried to commission the task to a heavy electric manufacturer good at ion implantation technologies, but the manufacturer at first declined our request because of cost. However, it eventually accepted our request at a considerably low cost based on the assumption that it would be compensated when we succeeded in our project. That was the birth of the equipment at the end of fiscal year 1992. The equipment took so long for orientation processes that wire was produced at a rate of only 10 cm per hour. Due to this fact, it took a few days of 24-hour continuous operation to produce intermediate layer wires having a length of a few meters.

Following that, as a result of further improvements, equipment that was capable of producing intermediate layer wires at a rate of 1 m per hour was developed. We finally succeeded in producing an intermediate layer wire with a length of 100 m. In addition, in an yttrium-based wire development project started in fiscal year 2003, we increased the ion source to 4 times larger than before, from 60 x 8 cm to 110 x 15 cm, so that an intermediate layer wire with a length of 500 m could be produced at a rate of 5 m/h. At the end of fiscal year 2007, we were successful in producing 504-m-long superconducting wires with an average critical current of 440 A with this equipment.

In addition, we carry out research and development on intermediate layer materials and ion irradiation methods to improve the film deposition speed, and we will soon achieve a film deposition speed of several 10 m/h to 100 m/h.

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  Development of "Large Reeling IBAD Equipment"

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  500 m-class IBAD Film Deposition Equipment

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  1.1 x 0.15 m Ion Source

When the temperature was too high, only low critical current films could be produced due to reasons such as the decomposition of a film deposited with the superconductor. We took countermeasures such as increasing the laser output and improving the temperature control method, and consequently we could produce long wires with a critical current density of not less than 1,000,000 A/cm² by around 2005, in contrast to the wires that had a critical current density of approximately 500,000 A/cm² in the mid-1990s. We further improved the critical current density to 2,000,000 A/cm² in 2007, and we can now produce wires that have a critical current density of not less than 3,000,000 A/cm².