The hottest place in our solar system is not the Sun, as you might think, but a machine near a south Oxfordshire village called Culham. Housed inside a vast hangar, it’s a nuclear fusion experiment called JET, or Joint European Torus. When operating, temperatures here can reach 150 million degrees Celsius – ten times hotter than the centre of the Sun. On December 21st 2021, JET set a new record by producing 59 megajoules of sustained energy through a process known as nuclear fusion.

59 megajoules isn’t a huge amount; just enough to power three domestic tumble dryer cycles. Nevertheless, as far as humanity is concerned, proof that nuclear fusion works is a very big deal indeed. Fusion produces energy by fusing atomic nuclei together, the opposite of what happens in all nuclear power stations, where atomic nuclei are split through nuclear fission. Once harnessed on a commercial scale, fusion could produce so much energy from so little raw material, that it may solve all of humanity’s energy problems in one fell swoop – amongst many other things. 

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Professor Stephen Hawking was once famously asked which problem he hoped scientists might solve before the end of the 21st century. “I would like nuclear fusion to become a practical power source,” he replied. “It would provide an inexhaustible supply of energy, without pollution or global warming.”

Right now, though, JET requires more energy to operate than it produces. Net energy gain – the holy grail of nuclear fusion since that would release more energy than it consumes – still eludes the scientists at JET; and indeed every other scientist working in this field. 

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Star in a jar

Up close, JET is truly awesome. While the experts at the Culham Centre for Fusion Energy (overseen by the UK Atomic Energy Authority) are familiar with every inch of this huge machine, to the untrained eye it’s a bewildering, asymmetrical jumble of steel bars, joists, cages, ladders, wires, cables, pipes, ducts, switches, monitors, valves, plugs, scaffolding, catwalks and steel runners.

On the outside it’s 12 metres tall with a diameter of over seven metres. The entire machine weighs 2,800 tonnes. Hidden somewhere in the centre is the doughnut-shaped (or toroidal) vessel called a tokamak. (Based on early Soviet designs from the 1950s, ‘tokamak’ is an acronym derived from Russian phrases meaning ‘toroidal chamber’ and ‘magnetic coil’.)

Although nuclear fusion reactors are far safer than nuclear power stations (more of that later), the security and safety at Culham is understandably tight. JET itself is housed behind one-metre-thick, 20-metre-tall concrete barriers, which close during operation, primarily to contain dangerous neutrons produced by the fusion reaction. Entry is through a security turnstile, with each visitor measured by a dosimeter for radiation levels on entry and exit.

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The tokamak hall at Culham. 

First operational in 1983, JET has produced nuclear fusion pulses on tens of thousands of separate occasions. At the end of next year, after 40 years of service, it will make its swan-song before eventually being decommissioned. The scientific understanding and much of the technology it has proven will be used in the next generation of tokamak fusion projects. Currently being constructed near Marseille, in the south of France, is the International Thermonuclear Experimental Reactor, or ITER – a collaboration of 35 nations, including the UK. There are also plans for a British project called Spherical Tokamak for Energy Production, or STEP. On 3 October its location was confirmed as the site of the West Burton power station in Nottinghamshire. 

The man in charge of JET is the UK Atomic Energy Authority’s CEO, Professor Ian Chapman. He predicts that ITER will start achieving net energy gain by the late 2040s. Ask him when nuclear fusion might produce cost-effective energy on a commercial scale, and he’s less precise.

“That’s an imponderable question and depends so much on energy dynamics, government policy, and what’s going on with carbon pricing,” he tells National Geographic UK. “I never answer the question. I always quote Lev Artsimovich, one of the founding fathers of the tokamak. He was asked this question at a press conference in the Soviet Union in the 1970s, and his answer was: ‘When mankind needs it, maybe a short time before that.’ I think that’s still true.”

Fusion futures

With the fuel crisis currently dominating UK headlines, Chapman points out how the energy we generate using current methods will eventually become so expensive that governments and private companies will be impelled into investing further and taking more risks to harness nuclear fusion. He explains how original investment for JET started in the late 1970s, in the aftermath of the global oil crisis. Now, energy insecurity fomented by the war in Ukraine might prove to be a similar catalyst for nuclear fusion.

“Energy policy happens on decadal timeframes,” he adds. “No parliaments anywhere in the world work on decadal timeframes so, unfortunately, it’s shocks to the market which generally stimulate action in energy.”

Even with massive investment, there are very high hurdles still to overcome: technical challenges such as fuel performance and reactor maintenance; political challenges, too, although the Americans, the Europeans, the Russians, the Chinese, the Japanese and the Australians have all warmed to the idea.

As have Britons. In October 2021, the Department for Business, Energy & Industrial Strategy published its strategy on nuclear fusion. This form of energy, it notes, will be abundant, efficient, carbon-free, safe, and will produce radioactive waste much shorter-lived than that of current nuclear power stations. 

Arthur Turrell is a former plasma physicist at Imperial College London, and author of a 2021 book, The Star Builders: Nuclear Fusion & the Race to Power the Planet. He says that “controlling fusion to produce energy is the biggest technological challenge we’ve ever taken on as a species”. He explains how fusion reactors, or “star machines”, are indescribably complex, with tens of millions of individual parts. 

The science bit

So just how does nuclear fusion work? It is the fusing of light nuclei to form a heavier nucleus, at the same time releasing huge amounts of energy. It’s what happens in the middle of stars like our Sun, providing the power that drives the universe. Crucially, it’s the opposite of nuclear fission, the process used in nuclear power stations whereby huge amounts of energy are released when nuclei are split apart to form smaller nuclei.

The Sun notwithstanding, humans are currently experimenting with two main methods of fusion. JET, for example, uses what’s known as magnetic confinement fusion: two isotopes of hydrogen – deuterium and tritium – are heated to temperatures up to 150 million degrees Celsius, becoming an electrically-charged gas called plasma, which is confined in the doughnut-shaped tokamak, and controlled with strong magnetic fields. The deuterium and tritium fuses together to produce helium and high-speed neutrons, releasing vast amounts of energy in the process – 10 million times more energy per kg of fuel than that released by burning fossil fuels. As Turrell neatly explains, the mass of deuterium-tritium fuel equivalent to an Olympic swimming pool of water would contain more energy than the entire planet uses in a year. 

The other fusion method is called inertial confinement fusion, using powerful lasers to heat and compress deuterium and tritium inside a capsule. One of the leading developments in this is at the National Ignition Facility (NIF) in California.

Of course, proving that nuclear fusion works is not the same as harnessing it on a commercial scale. There used to be a common quip traded between nuclear physicists, something along these lines: “Nuclear fusion is 30 years away; and always will be.”

That old quip is starting to lose power just as nuclear fusion is starting to gain it. All over the world there are fusion pioneers on Promethean missions to steal the Sun’s energy production process, and replicate it here on Earth. It’s estimated that, currently, there are over 100 experimental fusion reactors worldwide, some under construction, others already operating. As Turrell explains: “Public and private, big and small, star machines are taking off.”

In the UK alone, there are four major facilities – all currently in Oxfordshire: in addition to JET, there is Tokamak Energy, First Light Fusion, and General Fusion.

Ultimately, they are all striving for net energy gain. Ask Turrell where he believes this might first occur, and his eye is drawn to the National Ignition Facility in California where, already, they have achieved 70 per cent of net energy gain. He suggests they are “a small tweak away” from reaching 100 per cent.

Chapman delights in all this competition. “This is all good for the community,” he says. “We all want nuclear fusion to happen. We should try a diverse range of different options. Spend more money, take more risks.”

He compares this noble endeavour to the space race between the United States and the Soviet Union in the 1960s. “When Kennedy made his speech, it was inconceivable that, seven years later, man would walk on the Moon. If you have the political imperative to go really fast and spend money then you can achieve incredible things. The US was spending over four per cent of GDP on the space race.”

Fans of fusion suggest this sustainable form of energy may eventually replace all our nuclear fission power stations. There are a number of clear benefits.

Firstly, the fuel supply is abundant. “Deuterium is outrageously common,” Turrell writes in his book. “Tritium… can be made from another element that is extremely plentiful: lithium. Perfecting power from nuclear fusion could provide humanity with millions, perhaps billions, of years of clean energy.”

Chapman concurs: “For the rest of my life, all the fuel I’d need is the water that would fit in a bathtub and the lithium that would fit in two laptop batteries. That’s all I’d need, for 60 years.” However, some critics point out that the Earth’s supplies of tritium won’t be sufficient. One solution, which ITER is exploring, is to manufacture tritium from lithium using what they call breeding blankets. These would form part of the reactor wall and cause neutrons to react with lithium in the blanket to produce further tritium. If it works, power plants could end up being self-sufficient in tritium.

Tackling fear

Inevitably, mere mention of the word “nuclear” fills many energy consumers with dread. Chapman understands why but quickly rebuts the thought, stressing how fusion is virtually risk-free in comparison to fission. This is the second clear benefit.

“In a fission plant, there’s enough fuel in there for two or three weeks,” he says. “If a really off-normal thing happens, like a tidal wave or an earthquake, that fuel will keep going for two or three weeks. You’ve got no control over it. In fusion, there’s enough fuel inside the machine for about ten seconds, so if you want it to stop, it just stops. It’s physically impossible to have a chain reaction process. I’ve spent my 20-year career trying to keep the bloody thing going.”

While those working in nuclear fusion are clearly biased, they all agree that this form of energy will be vital in an energy-greedy world. Renewable energy will still play an important part, but renewables may not provide enough. 

“We want to make the world a better place and allow everyone access to sustainable energy,” Chapman says. “We should do renewables everywhere we can. But they just don’t work everywhere – if you don’t have access to sun or wind, for example. Fusion works everywhere and the fuel is readily available. It stops energy poverty; it gives us energy equality; it means we stop having wars over energy. It would be such a massive revolution and such an important part of the future portfolio of energy.”

He believes nuclear fusion will change the world as radically as the Industrial Revolution did. Turrell goes one step further, suggesting this form of energy could end up powering the spaceships that eventually transport humans on interstellar journeys. “Fusion rockets are humanity’s best hope for travelling across the vast distances of space,” he told National Geographic UK.

Back in the hangar at Culham, JET sits idle, waiting for its next experiment. Before it is eventually decommissioned in late 2023, it will conduct several further fusion experiments, mainly on behalf of the new ITER plant.

Meanwhile it lies like a sleeping dragon. Once it wakes, you’d be wise to keep your distance. When this dragon breathes fire, it burns at 150 million degrees.

Dominic Bliss is a freelance journalist based in London. Follow him on Twitter.