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Floating magnet may yield clean energy.

Who: An experiment at the Massachusetts Institute of Technology aimed at reproducing the magnetic fields of the Earth and other planets has yielded its first significant results, potentially leading to new ways of creating a power-producing plant based on nuclear fusion--the process that generates the sun's energy.

Technology: The results come from the levitated dipole experiment (LDX) which uses a half-tonne doughnut-shaped magnet made of superconducting wire coiled inside a stainless steel vessel. The magnet is suspended by an electromagnetic field and is used to control the motion of the electrically charged gas, or plasma, at temperatures of 10 million degrees contained in a 16ft-diameter outer chamber.

The results confirm the counter-intuitive prediction that inside the device's magnetic chamber, random turbulence causes the plasma to become more densely concentrated--a crucial step to getting atoms to fuse together--instead of becoming more spread out, as usually happens with turbulence. This "turbulent pinching" of the plasma has been observed in the way plasmas in space interact with the Earth's and Jupiter's magnetic fields but has never before been recreated in the laboratory.

Most experiments in fusion around the world use one of two methods: tokamaks, which use a collection of coiled magnets surrounding a doughnut-shaped chamber to confine the plasma, or inertial fusion, using high-powered lasers to blast a tiny pellet of fuel at the device's centre. But LDX takes a different approach. "It's the first experiment of its kind," says Jay Kesner, MIT's physics research group leader for LDX.

When operating, the LDX magnet is supported by the magnetic field from an electromagnet overhead, which is controlled continuously by a computer based on precision monitoring of its position using eight laser beams and detectors. The position of the magnet, which carries a current of one million amperes can be maintained in this way to within half a millimetre. A cone-shaped support with springs is positioned under the magnet to catch it safely if anything goes wrong with the control system.

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Levitation is crucial because the magnetic field used to confine the plasma would be disturbed by any objects in its way, such as supports to hold the magnet in place. In the experimental runs, MIT researchers recreated the same conditions with and without the support system and confirmed that the confinement of the plasma was dramatically increased in the levitated mode with the supports removed. With the magnet levitated, the central peak of plasma density developed within a few hundredths of a second, and closely resembled those observed in planetary magnetospheres.

Application: The results of the experiment show that this approach "could produce an alternative path to fusion," Kesner says, although more research would be needed to determine whether it would be practical. For example, though researchers have measured the plasma's high density, new equipment needs to be installed to measure its temperature, and ultimately a much larger version would have to be built and tested.

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Title Annotation:Nuclear fusion research
Publication:Professional Engineering Magazine
Geographic Code:1USA
Date:Feb 10, 2010
Words:486
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