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Thursday, September 9, 1999 Published at 23:09 GMT 00:09 UK


A step closer to fusion power

Magnets twist and turn to confine the superhot plasma

By BBC News Online Science Editor Dr David Whitehouse

At 5:15 PM on Tuesday, 31 August, a cheer echoed through the HSX Plasma Laboratory at the University of Wisconsin-Madison. The occasion was the so-called "first plasma" for the innovative HSX plasma machine.

Plasma has been called the fourth state of matter after solid, liquid and gas. In fact, most of the known material in the Universe is in the form of a plasma. It is achieved by heating matter to intensely high temperatures, creating a glowing, gas-like state that can conduct electricity.

[ image: The Sun: Made of plasma and powered by fusion]
The Sun: Made of plasma and powered by fusion
Plasmas on Earth include neon signs and the Northern Lights. But many scientists are interested in them because they are essential to get at fusion energy, a possible source of virtually unlimited power - if only we had the technology to exploit it.

"Making a 'first plasma' is a momentous occasion," says Joseph Talmadge, a co-investigator in HSX, who admits that the elation is combined with "tremendous relief."

HSX, or the Helically Symmetric Experiment, is a new type of fusion experiment that combines the best attributes of existing technologies. It brings together two existing styles of plasma containment experiments known as tokamaks and stellarators.

Quality and stability

Tokamaks have achieved the best results so far, but they have their drawbacks in requiring a strong current in the plasma itself. Stellarators do not need that current, making them potentially more attractive to some scientists. But they do not produce the high-quality magnetic field that confines plasmas and allows them to reach the very high temperatures required.

HSX solves that problem by achieving symmetry in the magnetic field through its oddly-shaped and complex magnet coils. The plasma-confining energy is located in coils outside of the plasma itself, making it a more stable and attractive as a reactor.

The device will confine plasmas in a magnetic field, at temperatures of up 10 million degrees. It is an experimental device designed to investigate the properties of plasmas and ways to exploit them.

"The 'first plasma' really marks the line between the construction and the research phase," says Joseph Talmadge.

Fusion holds tremendous promise as an alternative energy source. The same way the sun creates energy, fusion is achieved by melding atomic nuclei of two elements under extremely high temperatures, which releases energy.

A fusion reactor could be fuelled by the Hydrogen in seawater with one gallon producing the equivalent energy of 300 gallons of petrol.

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