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Making a small superconducting bar.

Making a small superconducting bar

To date, the ability of high temperature superconductors to carry high currents has waned as the physical dimensions of the samples waxed. In the May 24 NATURE, physicist Paul Chu and his colleagues at the University of Houston report processing the ceramic yttrium-barium-copper oxide into a small superconducting bar (5.2 centimeter x .5cm x .3cm) that maintains encouraging current-carrying capacity. The process appears adaptable for continuous manufacturing of superconducting plates, rods, wires, ribbons and thick coatings.

Although researchers have processed the same superconducting ceramic into tiny single crystals or extremely thin films that carry enough current for specialty electronic devices and detectors, no one has made bulkier samples that carry enough current for larger-scale uses. Random alignment of the samples' crystalline grains, poor electrical contact between these grains and meandering regions of resistance-creating magnetic flux have frustrated attempts.

By using a tubular furnace with different temperatures at different locations within its interior, and by controlling the speed at which a bar of sintered precursor yttrium-barium copper oxide powder moves through the furnace, the scientists have made superconducting bars with fewer of these defects. Pieces of one bar carried currents as high as 30,000 amps/cm2, but the presence of magnetic fields reduces the pieces' capacity. Though preliminary tests seem promising, the researchers have yet to determine exactly how much current an intact bar can carry, notes Ruling L. Meng, a materials scientist working in the group. The work "brings practical applications for high-temperature superconductors closer to realization," notes Neil Alford of ICI Advanced Materials in Runcorn, England, in an accompanying commentary.
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Publication:Science News
Date:Jun 9, 1990
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