April 12, 2012


How to build an artificial star on Earth (Celeste Biever, 4/10/12, New Scientist)

THE sun beats down through a cloudless sky as we weave between concrete blocks, each about as tall a person. Hundreds of the blocks are arranged in lines that fan out from a central point, like a child's drawing of the sun, cast at the bottom of a huge limestone pit in southern France. It is as if I'm standing in a shrine to our closest star, and in a way I am. If all goes well, the space above my head will one day rage with humanity's first self-sustaining fusion reaction, an artificial sun ten times hotter than the one that gives our planet life.

The blocks - each fitted with an elastomeric top to absorb vibrations - are seismic plinths, designed to shield the building that will rise above from damage in the event of an earthquake. Together they form the bowels of ITER, the International Thermonuclear Experimental Reactor, an ambitious and unusual collaboration between seven of the world's biggest powers: China, the European Union, India, Japan, South Korea, Russia and the US. Their goal is to build the first energy-producing fusion reactor - harnessing the process that powers the sun and most other stars. At extremely high temperatures, hydrogen nuclei will fuse to form helium, spitting out more energy than the process consumes, something that has never yet been achieved by a human-made device.

With many advantages over its more toxic cousin, fission, it has long been clear that nuclear fusion could be a wonder energy source. Only now - following major budget cuts in the 1990s and years of bitter political wrangling to determine its location - are the formidable structures and devices that will make ITER a reality starting to take shape. "This is one of the most complicated things you could possibly imagine building," says Richard Pitts, leader of ITER's plasma-wall interactions group. "It is a truly massive scientific endeavour."

The 60-metre-high building that will one day stand above me will be the centrepiece of a 39-building compound, and will house the burning, doughnut-shaped hydrogen-helium mixture at ITER's heart. At a fiercely hot 150 million °C, deuterium, an isotope of hydrogen with one extra neutron, and tritium, with two, will form a state of matter known as a plasma, in which their nuclei fuse to form helium. When they achieve "plasma burn", they will spit out power in the form of a highly energetic neutron that will be used to heat the walls of the reactor, and in future reactors, would be used to drive a turbine.
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Posted by at April 12, 2012 6:33 AM

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