As yttrium-based superconducting wire has an extremely high critical current density per unit cross-sectional area, it can produce superconducting wire through which the largest current can be passed. It also features a high critical current in a magnetic field in the neighborhood of the liquid-nitrogen temperature. Since superconducting devices can be commercialized with low-cost liquid nitrogen as the cooling agent, it is expected to be used in a wide range of applications.
Because the yttrium-based superconducting material is required to have a precisely textured crystal structure over its long length to transport as high current as its own intrinsic Ic performance, the production of long wires from the material has in the past been regarded as quite difficult. However, Fujikura successfully produced the world's first 100-meter length of superconducting wire in 2004, and we have poured our efforts into further improvements since then. In February 2008, we finally developed superconducting wire with a length of 500 m and a capacity of 300A, which are regarded as requirements for practical use. But since this is likely to lead to the deployment of a wide range of applications, it had been regarded as desirable to develop a 1000-m class wire.
In our latest accomplishment, we succeeded in developing an 816.4 m superconducting wire with a critical current of 872A. We had previously lost the top position in August 2009 with the announcement of 300,330 Am as the value of Ic·L (the product of critical current and length (L)), by Super Power in the US. We regained the leading position in October 2010 by setting a world Ic·L record of 374,535 Am when we developed a superconducting wire with a length of 615 m and a capacity of 609 A. We have now beaten our own record by developing a wire with the Ic·L value of 466,981 Am.
In this development, Fujikura has exercised ingenuity in achieving uniform characteristics over the entire length by making further improvements to the IBAD buffer layer and the PLD method superconducting layer. In particular, we have succeeded in dramatically stabilizing the temperature control over the growing surface of the superconducting film by developing a new "hot-wall heating system" with the pulsed laser deposition (PLD) process forming a superconducting layer. The above efforts have enabled us to produce a high yield of wires that maintain high qualities over their entire length. In October 2010, we succeeded in producing superconducting wire not only of 615 m x 609 A and 100 m x 706 A, but also of 816.4 m x 572 A.
Fujikura intends to achieve 1,000,000 Am for the value of Ic·L in 2012 as a rough target, with the aim of producing much longer superconducting wire with higher performance at a lower cost and to endeavor to supply 1000 m class yttrium-based superconducting wire to accelerate the further commercialization of a wide range of superconducting devices including power equipment.
This accomplishment is one of the deliverables resulting from the "Technological Development of Yttrium-based Superconducting Power Equipment" project Fujikura carried out in response to a commission from the New Energy and Industrial Technology Development Organization (NEDO) and will also contribute to research and development in the "Rare Metal Substitute Materials Development Project (Development of Yttrium-based Complex Materials)" commissioned by the organization.