The shocked state of superconductors.
Blasting crystals of a high-temperature, oxide superconductor with a shock wave can substantially increase the material's capacity to carry electrical current, reports a research team led by William J. Nellis of the Lawrence Livermore (Calif.) National Laboratory.
The team uses a gas-powered gun to fire lightweight, plastic projectiles at small samples of bismuth strontium calcium copper oxide in powder form. The resulting shock wave deforms the material, apparently creating tiny defects in its crystal structure. Those defects help anchor lines of magnetic flux, which penetrate the material when it's immersed in a magnetic field. Normally, even a modest electric current can shunt the flux lines aside, and the material loses its superconducting properties (SN: 2/10/90, p.95). Measurements of the magnetic characteristics of the shocked crystals confirm they can carry larger superconducting currents than unshocked samples. The researchers are also trying the technique on yttrium barium copper oxide.
Shock-wave processing has several advantages over other recently investigated techniques for creating defects to pin flux lines and increase the current superconductors can carry, Nellis says. Irradiating materials with neutrons, for instance, is impractical on an industrial scale, whereas the use of shock-wave techniques based on relatively simple, conventional explosives for the large-scale processing of high-temperature superconductors seems feasible.
Ivars Peterson reports from Anaheim, Calif., at an American Physical Society meeting
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|Date:||Mar 31, 1990|
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