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Hail the Artificial Suns
By James Morgan
The Herald (UK)

Tuesday, May 30, 2006

A generation from now, our planet could be powered by the heat from artificial suns. Last week the world's richest nations agreed to invest £10bn in a prototype nuclear-fusion reactor, which they hope will be the gateway to a virtually limitless supply of clean energy.

The International Thermonuclear Experimental Reactor, known as Iter, which is Latin for "the way", will be built in Cadarache, southern France. Inside its core, a doughnut-shaped vacuum vessel, radioactive hydrogen atoms will be fused together at temperatures 10 times hotter than the centre of the sun.

A ball of plasma will form, spitting out high-energy particles on to the reactor's lithium wall, creating heat that can be captured to make electricity.

The fusion reaction is so efficient, say physicists, that a bathtub full of water and the lithium from a household battery would be enough to supply your energy needs for 30 years. And fusion power has many other advantages. Fusion fuel is abundant in nature. Deuterium - a type of hydrogen isotope - is found in seawater at one part in 600. Its waste product - helium gas - is harmless and commercially useful, and the fusion reaction does not emit CO2. There is some solid radioactive waste, but unlike conventional nuclear waste, it will be safe and recyclable within 50 years.

No wonder, then, that the EU and the governments of Japan, China, South Korea, India and the USA, have seen fit to stump up the cash for Iter. Although the reactor will not provide electricity to the grid, it will be the first full-scale model of a working fusion power plant. At present, there are 28 smaller fusion research facilities, the biggest of which, Jet - the Joint European Torus - is in Culham, Oxfordshire. Jet spokesman, Chris Carpenter, says: "Fusion is not a pipe dream. With this financial backing, we will have a working fusion power plant here in the UK within 30 years. We are confident that there will be no showstoppers."

Carpenter can afford to be cocky because, also last week, San Diego scientists announced they had overcome one of the final major hurdles to building Iter and the first generation of power stations. Physicists feared that, in an industrial-scale fusion reactor such as Iter, high pressures would force turbulent plasma to pulse out of the reactor's core and damage the wall so badly it would need to be replaced every two years.

The solution, proposed by Todd Evans, of General Atomics, San Diego, is an ingenious reconfiguration of the powerful magnetic fields which hold the plasma within the chamber in such a way that excess heat can be "drained off" at special points in the wall.

This would extend Iter's working life to 15 years at least, though a working fusion power plant might last 50 to 100 years, he says.

On a scale of one to 10, Evans says his discovery is "right up there at the highest. Probably eight or nine. We don't need any more now to make the machine work. The remaining breakthroughs, which relate to efficiency, are the frosting on the cake".

Efficiency, or rather inefficiency, has been the bane of these "artificial suns" ever since the first experiments began in the 1950s. It takes enormous amounts of heat - 100,000,000oC - to force repellent hydrogen ions together and release their atomic energy. So while Jet has yielded as much as 18.2MW of power output, it took even more power in - 25MW - to trigger the reaction.

"I know it doesn't sound very promising," says Carpenter, "but with fusion, efficiency is all to do with size. The bigger the reactor, the more efficient it becomes. Iter is twice the size of Jet and will get 10 times the energy you put in to heat the fuel."

Work is already under way to design the UK's first fusion power plant, once the data from Iter has been inputted to calibrate it.

The plant, Demo, short for demonstration, is expected to produce 2.5GW, as much a large coal-fired power station.

"You could build a larger one," says Carpenter, "but it's not wise to have all your eggs in one basket, just in case something goes wrong."

Fortunately, if something did go wrong in a fusion reactor, no matter how powerful, there is no risk of a Chernobyl-style meltdown.

Carpenter says: "Unlike conventional nuclear power plants, which utilise fission, nuclear fusion reactions simply cannot get out of control. There's only a tiny amount of fuel in there at one time, and if you stop putting fuel in, it goes out instantly. It's a bit like a gas boiler. If you stop putting fuel in, it goes out."

He admits that fusion will result in some residual radioactive waste material - the reactor's wall. "But if we choose the material carefully," he explains, "the whole of the power station wall could be recycled within 50 to 100 years."

There are other "clean energy" hopes, such as cold fusion, where water releases energy when electricity is passed through it. But Todd Evans is convinced fusion is the leading contender. "Things like solar, geothermal, tidal, and wind are very attractive from the point of view that they can be distributed as local sources. But to power the major industrial cities and major residential areas you're going to need large generating stations such as fusion.

"We need simultaneously to develop all of these clean resources. The economy is going to demand it."

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