Hunting the holy grail of fusion

2007年9月にTIMES ONLINEにて紹介された記事

Jonathan Leake and Elizabeth Gibney

The mighty Zeta: limitless fuel for millions of years” trumpeted the newspapers. It was January 25, 1958 and Britain’s media were alive with the news that the nation’s scientists had created the world’s first controlled fusion reaction. It was, they promised, the dawn of a new era, when power would be both limitless and free. 


Alongside the stories were photographs of a giant machine, codenamed Zeta, whose existence had been one of the nation’s most closely guarded secrets, alongside the triumphant young scientists who had built it. The fanfare followed a news conference called the day before by Sir John Cockcroft, the Nobel prize-winning director of the government’s Harwell research laboratories and one of our most respected scientists. 


His machine, he told the assembled media, had achieved temperatures of 5,000,000C – generating the world’s first controlled nuclear fusion reaction. “To Britain this discovery is greater than the Russian sput-nik,” he declared, promising a commercial fusion reactor within 20 years.


That was 49 years ago. Just a few months later Cockcroft quietly issued a press release. His researchers had, it seemed, been mistaken. Zeta had never achieved fusion. It had not even achieved temperatures of 5mC. The machine was a dud.


Cockcroft’s blunder was, however, far from the last. Over the years, fusion’s lure of limitless energy has tempted many more scientists and politicians into the same trap of wishful thinking. In 2002 one set of researchers announced that they had achieved bubble fusion, while in 1989 another group announced that they had achieved cold fusion. All have ended in retractions, recrimination and humiliation.


What, then, are we to make of a new announcement last week, again from Harwell, that Britain could once more be on the road to achieving nuclear fusion?


Professor Mike Dunne, of the Rutherford Appleton laboratory, is seeking a £500m grant from the European Union to build a machine that will, he hopes, finally achieve fusion. Last week he got the green light to start designing the machine and finding a site for it. Dunne was far more cautious that Cockcroft, warning that success will take many years and that it was far from guaranteed. Underneath it, however, lay the same hope: that Britain could lead the world into a new era where nuclear fusion provided almost limitless and very cheap energy.


“The problems are huge,” said Dunne. “But if we can solve it we will have a way of tackling climate change. The prize is too great to ignore.”


So, as £500m of taxpayers’ money heads towards yet another attempt at fusion, is there really a chance that scientists could harness the power of the sun or are they, like Cockcroft, simply deluded by hope? On the face of it, Dunne’s plans could seem just as fantastic as Cockcroft’s. His machine, called Hiper, would work by firing tiny pellets of hydrogen across a steel vacuum chamber. At a critical point along its trajectory, each pellet would be hit by laser light. The beams would be so powerful the pellet would be simultaneously crushed and heated, achieving temperatures of around 100,000,000C, about 10 times hotter than the sun.


At such temperatures the atoms that make up all matter are ripped apart. The outer electrons are stripped away and the hydrogen nuclei fly around at such fantastic speeds that when they collide they fuse. As they fuse, some of their mass is destroyed and converted into large amounts of energy in the form of heat, light and radiation. It is this energy that Dunne hopes to capture and turn into electricity.


“Fusion is basically nature’s solution to the energy problem,” said Dunne. “It’s how the sun and the stars work. If we can control it here on Earth then we really will have limitless energy.”


The principles of fusion have been known ever since Einstein showed the power locked up in atoms with his famous equation, . It showed that annihilating just a tiny amount of matter would release vast amounts of heat, light and radiation.


In 1952 the Americans used this to build the first hydrogen fusion bomb. The explosion wiped out an entire Pacific atoll using the energy liberated from destroying a few hundred grams of hydrogen. That event inspired other scientists who immediately realised fusion’s potential in both peace and war – and led to some extraordinary research.


Dunne’s project is, for example, partly inspired by a US military programme from the 1980s when researchers successfully started a fusion reaction in a pellet of hydrogen by blasting it with x-rays. But their method had a flaw for peaceful power generation, because the only way they could get powerful enough x-rays was by detonating an atomic bomb nearby – hardly sustainable.


Dunne’s calculations show that a powerful laser could do the same job. Designing such a machine is among the biggest hurdles that his team faces.


“The laser would be the most powerful ever built,” said Dunne. “It would generate pressure of around a billion atmospheres within the hydrogen pellet. That’s equivalent to 10 aircraft carriers sitting on your thumb. A large part of our research will be working out how to build such a machine.”


Dunne’s approach is realistic enough to have been endorsed by peer reviewers for the European commission. They have looked closely at the global advances in laser technology and concluded that Dunne’s machine could be feasible.


It is not just new technology which is opening doors for Dunne. His proposal also comes at just the right time with the twin threats of climate change and energy insecurity prompting renewed global interest in fusion as a potential source of power.


The European Union is, for example, already backing ITER, a much larger project under construction in France, which is also supported by Japan and America. It will attempt fusion by a completely different approach, using powerful magnetic fields to heat and contain the fusion fuel. The Americans are also going it alone with their National Ignition Facility under construction in California, which will use some of the world’s largest lasers for fusion research. Dunne hopes to use its work as a basis for his own.


“What we are seeing is a radical shift in the politics of energy,” said Malcolm Grim-ston, an expert in energy policy based at Chatham House, the think tank.


“In the 1990s, Europe and especially Britain had plentiful energy in the form of coal and North Sea oil and gas, so the interest in fusion research waned. In the past few years, however, climate change and the realisation that we are running out of oil and gas are promoting a longer-term view.


Fusion research has benefited from that.”


Studies by the International Energy Agency (IEA) illustrate the need. They show that the world consumed energy equivalent to 11.4 billion barrels of oil in 2004 and that this will rise to a predicted 17.1 billion barrels by 2030.


The IEA warns that one consequence will be a 55% increase in the amount of carbon dioxide emitted from energy production – at a time when climate change is becoming one of the most pressing global issues. “Fusion should never be seen as a way of guaranteeing energy security or as an excuse to shirk our responsibilities on cutting climate change emissions,” said Dunne.


“We don’t know how or when we will find it. For me it is a bit like the holy grail.”

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