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Cryogenics for English Majors
By Kristen Coyne
Helium, helium, everywhere,
Nor any drop to drink.
Our apologies to Samuel Taylor Coleridge, but this twist on the famous line from “The Rime of the Ancient Mariner” seemed a fitting start to a discussion of cryogenics – the art and science of keeping things frigid.
That’s because helium – the most important cryogen used in science – is both abundant and hard to come by (a riddle we’ll clarify in a bit). We don’t think Coleridge would begrudge us a little artistic license, especially since our story, like his mariner’s tale set in the Antarctic, takes place in extreme cold.
Cryogenics isn’t just about helium. By definition, it’s the study of very low temperatures (colder than any place on Earth), how to produce and exploit them, and how materials behave at those temperatures. But helium is of special interest. Thanks to its unique properties, it can be used to make other stuff really cold. It is the ultimate deep freezer: At the Magnet Lab it keeps our powerful superconducting magnets at the extremely low temperatures they need in order to function.
PHYSICS FACTOID: Helium – less soluble in human blood than nitrogen – is combined with oxygen to create a nitrogen-free atmosphere in decompression chambers for deep sea divers so that they don’t get the bends.
Looking at these incredible magnets from the outside, all you see is a metal cylinder, perhaps several scientists tall. You may not realize that most of what you see is not the magnet itself, but the insulating chambers filled with liquid helium and another important cryogen, liquid nitrogen. Take a look below to see one of these machines exposed.
The MagLab uses about 100,000 cubic feet of helium every week. That’s gas helium. To be of any use, though, it must be turned into elusive, precious “drops,” as in Coleridge’s poem. But before we get into that mystical transformation, let’s take a few minutes to consider liquid and the other states of matter … and revisit Coleridge’s gruesome ballad. The British bard will, in fact, accompany us throughout our story, a reminder that science and art need not always seem so far apart...
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