The defence company’s announcement that it is working on a fusion reactor that could fit on the back of a truck was greeted with surprise. It says it could change the future of the planet, but some are sceptical. Daniel Clery reports.
Lockheed Martin, the US defence company behind stealth aircraft, is known for working on futuristic projects. Even so, its announcement earlier this month surprised many people. The company revealed it is working on a fusion reactor that it says could power a small city but will be compact enough to fit on the back of a truck. At a press conference last week, Lockheed team leader Tom McGuire talked about fusion-powered ships and even aircraft. “We have an idea that makes us very excited,” he said. Fusion researchers have reacted with some scepticism, especially to the claim that the reactor could be ready for commercial use in 10 years.
Fusion is a nuclear reaction in which small nuclei are melded together to make larger ones – the opposite of what happens in the fission reaction of today’s nuclear power plants. Both types of reaction release large amounts of energy, but fusion doesn’t produce harmful and long-lived radioactive waste. And its fuel – two types of heavy hydrogen – is plentiful and cheap.
The difficulty with fusion is that atomic nuclei, being positively charged, repel each other, so getting them close enough to fuse is challenging. It requires heating the hydrogen to a plasma – a gas of nuclei and electrons – and beyond, to more than 100 million degrees Celsius. At this temperature nuclei collide with enough force to overcome their electrical repulsion. Mainstream attempts to create these conditions have led to the building of huge and expensive machines, such as the €20 billion ITER reactor being built in France, and the $4 billion National Ignition Facility (NIF) now being tested in the US without great success.
Frustration with the slow pace of these massive projects has led to a number of small privately funded efforts to find a faster and cheaper way to achieve fusion. Lockheed Martin’s “compact fusion reactor” is the latest, and perhaps the only one that is being worked on by a major corporation.
Different approaches to fusion involve juggling three parameters: temperature, density and confinement time (the length of time the plasma lasts). Mainstream “tokamak” reactors such as ITER hold the plasma within magnetic fields for a confinement time of at least one second, but at a low density. Laser fusion facilities such as NIF go to the other extreme, using powerful lasers to crush the plasma to enormous densities in shots that last only nanoseconds.
Most of the new private efforts, including Lockheed’s, fall somewhere between the two extremes.
Many fusion approaches have appeared promising at small scale or in simulation only to become much more complicated once they are scaled up.
At last week's press conference McGuire said Lockheed’s approach combined the best parts of several existing methods for confining plasma. The first of these, known as cusp confinement, uses ring-shaped electromagnets to encircle the plasma. These produce magnetic fields that bulge inwards towards the enclosed plasma, producing a sort of padded cell for charged particles. When a particle in the centre of the device tries to move outwards the magnetic fields exert a force to push it back. The further a particle strays from the centre, the stronger the force pushing it in again.
Scientists studied cusp confinement in the 1960s and 1970s but found it leaky – gaps between the magnetic fields allowed particles to escape so it proved impossible to reach high enough temperatures. McGuire said Lockheed’s solution has been to encapsulate the cusp confinement inside a mirror machine, a cylindrical device that uses a straight magnetic field to confine particles to moving along its axis and additional strong fields at the ends – magnetic mirrors – to prevent particles escaping. Mirror machines were extensively studied last century but also proved leaky.
With a magnetic mirror, charged particles bounce back from the high field region, so containing the plasma between the coils. Some particles still escape from the ends.Credit: Anton Banulski
For particles that do slip through both layers of encapsulation, McGuire revealed another innovation – recirculating escaped particles. “We recapture the flow and route it back into the device,” he said.
McGuire said he and five to 10 researchers have been working for four years and have built their first experimental device. They carried out 200 test shots while commissioning it. He declined to say what temperature, density or confinement time they had achieved but he said the plasma appeared stable and they had heated it with up to one kilowatt of power. To reach fusion temperatures, tens of megawatts of heating are typically needed.
With no hard information about its performance, fusion researchers are taking Lockheed’s claims with a pinch of salt. Many fusion approaches have appeared promising at small scale or in simulation only to become much more complicated once they are scaled up.
“Lockheed Martin has a reputation to lose,” said Steven Cowley, director of the Culham Centre for Fusion Energy in the United Kingdom, adding that the furore surrounding Lockheed’s announcement was reminiscent of that around cold fusion in the 1980s. “If they have put in only one kilowatt of power then they are at such a small level that it is really hard to know how it will extrapolate to reactor scales,” said Greg Hammett of the Princeton Plasma Physics Laboratory.
“We’re not naïve,” Ray Johnson, Lockheed’s chief technology officer, said at the press conference. In such frontier science “unexpected challenges come up, in fusion in particular”, he said. McGuire acknowledged that they were “very early in the scientific process” and their reasons for going public were to build up his team and develop partnerships with others working in this area. Experimental results, he said, would be published next year. They will be eagerly awaited.
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