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Strain Has Major Effect On High-Temp Superconductors
Boulder CO (SPX) Feb 22, 2007 Just a little mechanical strain can cause a large drop in the maximum current carried by high-temperature superconductors, according to novel measurements carried out by the National Institute of Standards and Technology (NIST). The effect, which is reversible, adds a new dimension to designing superconducting systems-particularly for electric power applications-and it also provides a new tool that will help scientists probe the fundamental mechanism behind why these materials carry current with no resistance. The measurements, reported in Applied Physics Letters,* revealed a 40 percent reduction in critical current, the point at which superconductivity breaks down, at just 1 percent compressive strain. This effect can be readily accommodated in the engineering design of practical applications, NIST project leader Jack Ekin says, but knowing about it ahead of time will be important to the success of many large-scale devices. The effect was measured in three types of yttrium-barium-copper-oxide (YBCO), a brittle ceramic considered the best prospect for making low-cost, high-current, superconducting wires. The researchers developed a "four point" bend technique that enables studies of superconducting properties over a wide range of uniform strain at high current levels. The superconductor is soldered on top of a flexible metal beam, which is then bent up or down at both ends while the critical current is measured. The discovery is the first major reversible strain effect found in practical high-temperature superconductors, which generally have been tested under smaller tensile strains only, or at strains so high they caused the material to break down permanently. The newly discovered effect is totally reversible and symmetric for both compressive and tensile (pushing and pulling) strains, suggesting it is intrinsic to the fundamental mechanism of superconductivity in YBCO. The NIST team is now pursuing the possibility of using the effect as a new tool for probing the elusive mechanism underlying high-temperature superconductivity. The next step is to investigate how magnetic fields affect the strain effect, and several collaborations are under way with universities and other research organizations to study the interplay of the effect with other factors affecting high-temperature superconductivity. The research described in the new paper was supported in part by the U.S. Department of Energy. * D.C. van der Laan and J.W. Ekin. Large intrinsic effect of axial strain on the critical current of high-temperature superconductors for electric power applications. Applied Physics Letters, 90, 052506, 2006. Posted online Jan. 31. Related Links Powering The World in the 21st Century at Energy-Daily.com Our Polluted World and Cleaning It Up China News From SinoDaily.com Global Trade News The Economy All About Solar Energy at SolarDaily.com Civil Nuclear Energy Science, Technology and News Powering The World in the 21st Century at Energy-Daily.com
Tiny High-Frequency Cryocooler Is Cold And Efficient
Washington DC (SPX) Feb 21, 2007A new cryogenic refrigerator has been demonstrated at the National Institute of Standards and Technology (NIST) that operates at twice the usual frequency, achieving a long-sought combination of small size, rapid cooling, low temperatures and high efficiency. The cryocooler could be used to chill instruments for space and military applications, and is a significant step toward even smaller, higher-frequency versions for integrated circuits and microelectromechanical (MEM) systems. |
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