Initial results from a UK experiment could help clear a hurdle to achieving commercial power based on nuclear fusion

The researchers believe they now have a better way to remove the excess heat produced by fusion reactions.

This intense heat can melt materials used inside a reactor, limiting the amount of time it can operate for.

The system, which has been likened to a car exhaust, resulted in a tenfold reduction in the heat.

The tests were carried out at the Mast (Mega Amp Spherical Tokamak) Upgrade nuclear fusion experiment at Culham in Oxfordshire. The £55m device began operating in October last year, after a seven-year build.

Mast Upgrade is one attempt to come up with a template for more compact, cheaper fusion reactors. It makes use of an innovative design known as a spherical tokamak to squeeze the fuel into a 4.4m-tall, 4m-wide space. By comparison, the containment vessel Iter will use to control its fusion reactions is 11.4m tall and 19.4m wide.

But Mast Upgrade's bijou dimensions come at a price: "You're making something that's hotter than the Sun... in a smaller volume. How you then get the heat out becomes a big challenge," said Prof Chapman.

The core of the plasma within the tokamak reaches temperatures of 100 million C. Without an exhaust system that can handle this unimaginable heat, materials in the design would have to be regularly replaced - significantly affecting the amount of time a power plant could operate for.

The new exhaust system being trialled at Culham is known as a Super-X divertor. This would allow components in future commercial tokamaks to last for much longer; greatly increasing the power plant's availability, improving its economic viability and reducing the cost of fusion electricity.

Tests at Mast Upgrade have shown at least a tenfold reduction in the heat on materials with the Super-X system.

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