Bigger and better superconducting magnets

March 6, 2003
Magnets are used in many important industrial applications, everything from medical MRI to removing impurities from clay for whiter ceramics and paper.

Superconducting (SC) magnets, such as the 900-MHz version designed by Oxford Instruments, in the U.K. (www.oxinst.com), bring several advantages. Permanent magnets are limited in strength to 2 Tesla (1T=10,000 Gauss), and electromagnets top out at 35 T. But SC magnets can be rigged to generate 45 T. And SC magnets use much less power, take up less space, and are easier to keep stable with low drift rates and consistent field strengths than comparably powered electromagnets. SC magnets do have drawbacks. They need to be kept extremely cold, commonly done with liquid helium. They also need SC wire, which is relatively expensive compared to copper. And in case of failure, the unit has to quickly dissipate 17 MJ of energy. At Oxford Instruments, they use heaters that warm the magnet's coils, making them resistive in case of failure. This disperses the energy safely.

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