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R&D: Nuclear fusion may be worth the long wait
By Clive Cookson
Financial Times (U.K.)

Friday, January 15, 2010

Capturing the sun’s energy, by redirecting solar heat or using photovoltaic devices, is one of the most active fields of research. An entirely different approach is to recreate on Earth the nuclear fusion that powers the Sun.

Although some optimistic scientists continue to work on small-scale fusion devices – successors of the largely discredited “cold fusion” experiment by Martin Fleischmann and Stanley Pons 20 years ago – the main action is taking place on a far grander scale.

Most experts believe that to obtain useful power through controlled fusion, extreme temperatures and/or pressures are needed to force atomic nuclei to join together and release immense amounts of energy – as occurs in the sun and (uncontrollably) in the hydrogen bomb.

Research is concentrating on two “big science” approaches, both costing billions of dollars. One is magnetic fusion: heating hydrogen ions, which are held inside a doughnut-shaped reactor with ultra-strong magnets, to more than 100m°C. The other is “inertial confinement” or laser fusion: shooting a small pellet of solid hydrogen fuel with an array of lasers so powerful that they trigger nuclear fusion.

The centrepiece of magnetic fusion research is Iter. Its name was originally an acronym for International Thermonuclear Energy Reactor but is now defined as the Latin for “the way”.

Iter is a partnership between the European Union, China, Japan, South Korea, the US, Russia and India. As host of the project, which is located at Cadarache in the south of France, the EU pays 45 per cent of what is turning out to be a rapidly escalating bill.

When Iter was formally set up in 2006 – 20 years after the project was first proposed – the estimated cost was about $5bn for construction, plus a further $5bn to run the reactor for 20 to 30 years. But that was based on a provisional 2001 design for an unspecified location.

It became clear during last year that the real construction cost will be closer to $10bn. The partners agreed to keep going but more slowly than previously planned, with a more simple reactor. A new schedule is likely to be approved next month, as building work starts, with a start-up date in 2018 and full-scale operation in 2026.

Meanwhile, smaller magnetic fusion reactors continue to operate in member countries, such as KStar in Korea and Jet in the UK, gathering data that will be useful in building and operating Iter.

The latter will have a reactor 10 metres tall in which a plasma of two hydrogen isotopes, deuterium and tritium, will be contained with superconducting magnets. At temperatures measured in hundreds of millions of degrees, the atomic nuclei will fuse to form helium while ejecting neutrons and generating enormous heat.

While Iter will eventually produce a “burning plasma”, with a self-sustaining fusion reaction lasting at least 10 minutes and generating 500MW of energy, it is not designed to be a power station. The task of demonstrating sustained large-scale power generation from fusion will fall to Iter’s successor, called Demo. On the most optimistic timescale, Demo would come into operation in the 2030s and feed power into the grid around 2040.

But widespread commercialisation would take much longer. Iter itself talks of the world entering the age of fusion “when mankind covers a significant part of its energy needs with an inexhaustible, environmentally benign and universally available resource” by the last quarter of this century.

The alternative approach, laser fusion, is unlikely to be any quicker. Its showcase is the National Ignition Facility at the Lawrence Livermore National Laboratory in California.

NIF has been built by the US government during the past 10 years at a cost of about $4bn. It is a dual-purpose facility, offering a means of testing nuclear weapons without actually detonating a bomb, as well as energy generation.

The world’s most powerful laser system will have 192 X-ray beams focusing all of their energy on a small pellet of frozen hydrogen which – if all goes well – will burn for a short while like a miniature star.

Laser testing at NIF is going well and the first hydrogen targets may be introduced later this year. A European fusion experiment called High Power Laser Energy Research facility or HiPER, operating on similar principles but not designed for weapons testing – and therefore less costly than NIF – has been proposed, with construction due to start in the middle of this decade and operation in the early 2020s.

But it will be a long engineering step from igniting miniature stars in a laser facility to building a commercial fusion power station. There is no good reason to assume that lasers would be any quicker than magnets to come to fruition, although it seems reasonable for the world not to put all its fusion eggs in one basket.

Doubters have long scoffed at fusion for being a power source that always lies 50 years ahead. Whichever route is eventually chosen, it is likely to be more than half a century before fusion energy becomes routine.

But our grandchildren may find that it is worth the wait.

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