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Newsletter "SEI NEWS" 2011

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[Newsletter "SEI NEWS" Vol.405]

Bright Future for Superconductivity

Superconducting cable

High-temperature oxide superconductors were the focus of much industrial attention some 20 years ago, as you may know. They grabbed newspaper headlines for a few years at that time. However, interested companies pulled out one after another due to manufacturing difficulties. Yet, finally, usable and economically viable oxide superconducting wires have become available. This year marks the 100th year anniversary of the discovery of superconductivity. In commemoration of that discovery, this issue features superconductivity, which is now the focus of renewed attention.

100-Year History of Superconductivity

1911

Heike Kamerlingh Onnes (Leiden University, the Netherlands) discovers superconductivity.

1957

John Bardeen, Leon Cooper and John Robert Schrieffer explain the basic mechanism of superconductivity with their BCS theory*.

1963

Sumitomo Electric commences research in superconductivity.

1986

Johannes Georg Bednorz and Karl Alexander Muller discover a high-temperature superconductor.

1987

Paul Chu (University of Houston) and others discover an yttrium-based superconductor.

Superconductivity attracts a great deal of industrial attention.
2000

Jun Akimitsu (Aoyama Gakuin University) and others discover a magnesium diboride superconductor.

2006

An in-service transmission line in the U.S. incorporates Sumitomo Electric’s high-temperature superconducting cables.

2008

Hideo Hosono (Tokyo Institute of Technology) and others discover an iron-based superconductor.

Even today, 100 years after the discovery of superconductivity, research on the subject is actively promoted, searching for materials that enter a superconducting state at yet higher temperatures.

* BCS Theory:
A theory that explains how superconductivity occurs. Starting from the assumption that, in the superconducting state, electron pairing (known as the Cooper pair) occurs, BCS theory explains zero resistivity and the Meissner effect.

 

Future Applications of Superconductivity

Bismuth-based superconducting wire

With such features as zero resistivity and high current density, superconductivity provides low-loss operation and high magnetic field, features inconceivable with normal conductivity. Accordingly, expectations are high that superconductivity will improve the performance of electrical appliances.

The superconducting state occurs within limited temperature, magnetic field and current density ranges. Thanks to the discovery of oxide superconductors of high critical temperatures*1 and the increased critical current density*2 of superconducting wires made from them, superconductivity is expected to be used in a broader range of commercial fields.

 

Note:
*1 Critical temperature
In a superconductor, the electrical resistance drops abruptly to zero when the material is cooled to a certain temperature. This temperature is referred to as the critical temperature.
*2 Critical current density
The maximum current per unit cross-sectional area of a superconductor below which the superconductor has zero resistivity.

 
 Superconducting Cable

When a superconducting wire and a copper wire have the same cross-sectional area, the former carries approximately 200 times more electricity than the latter. This indicates the possibility of downsized power cable by incorporating superconductors. Meanwhile, as a consequence of the recent great earthquake, radical increase in the use of renewable energy has attracted public interest. As a compensating solution for the fluctuating nature of renewable energy, expectations are high for the massive introduction of superconducting cables, since they can be made small for low-voltage, DC and high-current applications and are free from the issue of voltage drop. There are plans to first apply superconducting cables to urban and suburban railways, which use DC, and then to expand their applications.

Comparison of superconducting and conventional cables

 
■ Superconducting Magnet/Coil

Superconducting magnets and coils are used in various industrial products, since they create massive force using only a small power supply, though they require cooling to be given the nature of superconductivity.

Using superconducting coils, Sumitomo Electric has created high-temperature superconducting test apparatuses.

The Superconducting Inductive Floating Object (SIFO) is used to explain the principle of superconducting inductive magnetic levitation. The Hanarete Motor* creates a very strong magnetic field away from itself. These are highly popular as test apparatuses for students.

* The Hanarete Motor is also known as Remotor.

 
Superconducting Levitation Demonstration

This demonstration apparatus comprises a stack of two disc-shaped superconducting coils placed around an iron core. The lower coil is connected to a power supply. The upper coil is short-circuited. When the lower coil is powered, a reverse current is induced in the upper coil and a massive repulsive force is created between the two coils.

Once a current is passed through the coil, the current continues to flow permanently, due to zero resistivity in the coil. It can potentially carry current densities over 100 times the capability of copper wires. The resulting extremely strong magnet can lift a person. The required power supply is only a single 1.2 V nickel-hydrogen battery. No normal conductors can carry such a high current at such a low voltage and create a force sufficient to lift a person. Maglev vehicles run on the same principle, though differing in construction and scale.

 

 
 Applications of Superconductivity

Apart from the aforementioned applications, we envision various innovative industrial uses of superconductivity including marine motors, electric vehicles and maglev vehicles in the transport sector.

Sumitomo Electric will intensify its research and development efforts to make this year-the 100th year anniversary of the discovery of superconductivity-a year that marks the beginning of full practical use of high-temperature superconductivity.

 

- SIFO and Hanarete Motors are trademarks or registered trademarks of Sumitomo Electric Industries, Ltd.

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