February 22, 2011

Thin superconducting cables for stronger magnets and overhead wire

A researcher at the National Institute of Standards and Technology (NIST) has invented a method of making high-temperature superconducting (HTS) cables that are thinner and more flexible than demonstration HTS cables now installed in the electric power grid while carrying the same or more current. The new thin superconducting cables are light enough to be used as overhead wire instead of being buried underground. The thin superconducting wire can also be used to make magnets stronger than 25 tesla.

Today's superconducting magnets contain niobium-titanium wires wound into coils that can provide at most 25 Tesla magnetic fields. Magnets made using the new high-temperature superconducting cables could give higher fields while potentially requiring less power for cooling. Such compact, high-field magnets could be used for proton cancer treatment and high-energy physics

Researchers at CERN (the European Organization for Nuclear Research) in Switzerland are also interested in using the thin cables to feed the several thousands of amperes of current to the magnets used at the Large Hadron Collider.

The low weight and flexibility are especially appealing to the military as a replacement for the bulky copper cables that carry large amounts of power from generators to weapons and devices on board aircraft and ships. "If you look at replacing standard copper cables on a Navy ship, you have to be able to pull the cable through existing conduits with many sharp bends," van der Laan says. He is now making a demonstration cable for the U.S. military.

Superconducting cables have recently been used in small power grid demonstrations. A bismuth-based cable was installed at a utility substation in Columbus, Ohio, in 2006, for instance. It has a diameter of seven centimeters and can carry 3,000 amperes.

In comparison, van der Laan has made a cable 7.5 millimeters wide that can carry 2,800 amperes. Another is 6.5 millimeters in diameter and can carry 1,200 amperes. The cables can be bent around a cable with a diameter of less than a quarter of a meter.

Van der Laan starts with a core made of multiple copper strands sheathed in nylon insulation. Then he winds gadolinium barium cuprate superconducting tapes in alternating directions around the core.

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