Magnets are the biggest market for superconducting wire, and the favored wire for generating high fields is round and contains multiple filaments. The round geometry enables flexible conductor designs that support high magnetic stresses and can be wound in complex patterns to precisely shape the field. Although wires made from YBa2Cu3O7−x (YBCO) and other high-temperature cuprate superconductors offer the allure of high current densities, that goal has been realized primarily only in broad, flat, single-filament “tape” geometries that reduce the prevalence of current-limiting misalignments between crystal grains (see the article by Alex Malozemoff, Jochen Mannhart, and Doug Scalapino, Physics Today, April 2005, page 41, and also January 2008, page 30). Now David Larbalestier (National High Magnetic Field Laboratory) and colleagues have found a way to make round, multifilament wire out of the superconductor Bi2Sr2Ca1Cu2...

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