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28/09/2009
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Thermal cycling can be used to magnetise high temperature superconducting magnets to 17 Tesla, opening up applications in much more compact MRIs and large motors.
 Dr Timothy Coombs, founder of University of Cambridge spinout Magnifye, told us that while yttrium barium copper oxide was found able to superconduct at liquid nitrogen temperatures back in 1987, there has until now been no simple way known to induce circulating currents inside it sufficient to make it function as a powerful magnet. This would be a particular problem if it came up to room temperature through some mishap, losing its magnetisation.
What has now been discovered is a method by which magnetisation from a relatively low power magnet – neodymium iron boron - can be used to induce a much higher magnetisation in the superconducting magnet. The trick is to have a disk of gadolinium between the two magnets, with a heater round its edge. The disk is then heated to near its Curie temperature, where its permeability changes rapidly with temperature. Dr Coombs said that cycling the temperature of the gadolinium works like stroking an iron nail with a magnet, pumping up the field in the superconducting magnet.
The target market is MRI machines, where it allows the magnets to be made very much smaller, since it would replace three Tesla magnets with 17 Tesla devices. Dr Coombs said: "Scanners could be made smaller and the opening for the patient made larger – MRI could even be incorporated into a hand held want for quick imaging in A&E departments or even in the field. We did a survey for a major Japanese car maker last year and we are talking to various people who make compact motors. It reduces their sizes by a factor of ten. And, if the hydrogen economy takes off, the next stage from storing hydrogen in pressure vessels would be to use liquid hydrogen at 20 deg K which makes superconductors work even better."
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Author
Tom Shelley
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