Magnets from Mini to Mighty
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Superconducting Magnets: Power Unplugged
Superconductivity is a very cool phenomenon in which electrical resistance is overcome with the help of very cold temperatures – colder than anything this side of Pluto!
You could think of it this way: In a superconducting current, the atoms that make up the conducting material stay the heck out of the way of the electrons that make up the current: They’re just too cold to make any trouble! It’s easy street for those electrons; once you get ‘em started, they’ll chug along well after you’ve unplugged the thing, as long as you keep things chilly.
PHYSICS FACTOID: Most superconducting magnets are made using an alloy called niobium-titanium – "Ni-Ti" for short.
Superconducting magnets are powered this way, rather than by conventional electricity. While you save on the electric bill, these magnets are more expensive to build, and you need a constant supply of cryogens – liquid helium and liquid nitrogen to keep them good and cold. In fact, if you look at a superconducting magnet (such as the one pictured below), you’ll notice that most of it is made up of the materials devoted to keeping it cold.
Superconductivity is an awesomely powerful phenomenon, one that scientists have only just begun to exploit. For years doctors have used it in the powerful superconducting magnets of MRI machines, which take noninvasive pictures of their patients’ insides. Researchers are also aggressively studying how superconducting magnets can be used in levitating trains.
The Magnet Lab is home to one of the most powerful superconducting magnets on the planet, a 900-megahertz machine used for nuclear magnetic resonance (NMR) studies that delivers a field of 21 tesla. At Japan’s National Institute for Materials Science, a slightly more powerful superconducting magnet is in operation. Magnet designers continue to push the envelope, struggling to overcome problems with critical fields, the point at which superconducting materials cease to superconduct. At the Magnet Lab, scientists are working on superconducting magnets with fields upwards of 38 tesla; they have already demonstrated the technology to make these magnets.
Let’s see. We’ve learned that the highest fixed field created by a superconducting magnet is about 21.6 tesla, and the highest field created by a resistive electromagnet is 35 tesla.
So you can’t get any higher with a steady magnetic field?
Sure you can. You just need to do a little math!
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