Undeterred by taunts that fusion always seems to lie 50 years in the future as a commercial energy source, a growing programme of research is aimed at taming the nuclear reaction that powers the sun and the H-bomb. It releases energy by combining light elements, in contrast to the atom-splitting fission process that drives current nuclear power stations.

Fusion research falls into three different camps. One is the traditional “big science” approach — exemplified by ITER, a project to build an experimental fusion reactor at Cadarache in France.

Second is a wave of start-ups whose ambition is to deliver power more quickly and less expensively than the big public projects. These companies are using the same hot fusion approach, forcing atomic nuclei together at extreme temperatures and pressures.

The ITER cryostat
The ITER cryostat, designed to house super-conducting magnets and deliver a super-cool fusion environment

Lurking out in left field is a third way — utterly different in that it claims to release fusion energy in much more moderate conditions, close to room temperature. This approach, a successor to the “cold fusion” experiments carried out by Stanley Pons and Martin Fleischmann in 1989 and now usually called “low energy nuclear reaction” or LENR, is ignored by the scientific mainstream but making progress according to devotees in labs around the world.

All three techniques offer the long-term promise of virtually limitless carbon-free energy with much less radioactive waste than nuclear fission.

Hot fusion projects use various techniques to sustain the reaction. Leading the way is “magnetic confinement”. Here a powerful magnetic field keeps the reactants, a plasma of hydrogen isotopes heated to 100m degrees centigrade, inside the reactor. If they touch the vessel’s walls, the reaction stops.

The most popular magnetic reactor is the doughnut-shaped tokamak, invented in the 1950s Soviet Union. Its largest manifestation will be ITER, a partnership between the EU, China, Japan, South Korea, US, Russia and India, which is building a tokamak 10 metres high surrounded by superconducting magnets. When ITER was set up in 2006, it was expected it should have started up this year. Now completion is expected in 2025 and the estimated cost has soared above $20bn.

An alternative configuration for magnetic confinement is the stellarator, which has a more sinuous twisted shape. The world’s most ambitious stellarator, the €370m Wendelstein 7-X in Germany, starts up this year.

Radically different is “inertial confinement”. More than 150 ultra-powerful lasers focus their energy simultaneously on a pellet of hydrogen fuel, triggering fusion. Two publicly funded facilities are taking this approach: the National Ignition Facility in California and Laser Mégajoule in France.

The new wave of privately funded fusion companies in Europe and North America is using both inertial and magnetic confinement. Among them is First Light Fusion, an Oxford university spinout that raised £22.7m last August.

Another UK fusion start-up Tokamak Energy is aiming for commercial energy from magnetic confinement, based on a miniature version of the technology used at ITER. “Compact fusion power is no longer a pipe dream,” says David Kingham, Tokamak chief executive. “We are aiming for that ‘Wright Brothers’ moment of take-off for fusion energy within 10 years.”

If so there will be considerable competition from well-funded North American companies focusing on magnetic confinement. Leading fusion start-ups there include General Fusion in Canada and Tri Alpha Energy and Helion Energy in the US. At least one large company, Lockheed Martin, is also active in the field.

While there is considerable interaction between scientists working on hot fusion, cold fusion research takes place in a world of its own. Many mainstream scientists will not touch LENR which they see as tainted by the cold fusion fiasco of 1989, when Profs Fleischmann and Pons claimed to have achieved fusion on a lab bench — an experiment that others could not reproduce. However, after more than 25 years of experimentation, several research groups have built up evidence that real nuclear reactions lay behind the pair’s results. The problem according to Professor Huw Price, a philosopher of science at Cambridge university, is that cold fusion became a “reputation trap” which most researchers avoid because they know the scientific world will not take their work seriously.

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