Is nuclear fusion finally poised to deliver?

“We are standing on the ground that could change the future of energy,” says engineer Laurent Pattison, deep in the reactor pit of the world’s biggest nuclear fusion project.

Around him is a vast construction site, all aimed at creating temperatures of 150mC on this spot and finally bringing the power of the sun down to Earth. The €18bn (£14.3bn) Iter project, now rising fast from the ground under the bright blue skies of Provence, France, is the first capable of achieving a critical breakthrough: getting more energy out of the intense fusion reactions than is put in.

“It is a bet that is very important for humanity,” says Johannes Schwemmer, the director of Fusion for Energy, the EU partner in the international Iter collaboration. “We need to get this energy once and for all.”

The long allure of nuclear fusion is simple: clean, safe, limitless energy for a world that will soon house 10bn energy-hungry citizens. But despite 60 years of research and billions of dollars, the results to date are also simple: it has not delivered.

Fusion is in danger of following its atomic cousin, conventional fission nuclear power, in over-promising – “electricity too cheap to meter” – and under-delivering. The Iter project itself, which stems from a cold war Reagan-Gorbachev summit in 1985, has seen years of turmoil. The US pulled out entirely between 1998-2003 and in 2008, Iter had to treble its budget and shift its deadline back a decade.

But leaders representing half the world’s population – through the Iter partners, the EU, China, Russia, US, India, Japan and South Korea – are now making the €18bn wager that fusion can deliver and have radically overhauled Iter’s management to fix the mistakes of the past.

The goal is to trap a plasma in a huge magnetic ring and force heavy hydrogen isotopes to fuse together to release prodigious amounts of energy – four times more than the splitting of uranium atoms produces in conventional fission reactors.

“We are convinced we can deliver hundreds of megawatts through Iter,” up to 10 times more energy than is put in, says David Campbell, the director of science and operations at Iter (which means “the way” in Latin).

To achieve that breakthrough, Iter will use a donut-shaped magnetic cage called a tokamak to trap the plasma. More than 200 smaller tokamaks have been built around the world and Campbell says the decades of physics and engineering that Iter is building on is a strong guarantee of success.

But nothing has ever been attempted on the scale of Iter. The world record for fusion power – 16MW – was set in 1997 at the JET reactor in the UK. The longest fusion run – six minutes and 30 seconds – was achieved at France’s Tore Supra in 2003. Iter is aiming for 500MW and 50-minute runs.

The site is a cathedral to the fusion dream: it spans the equivalent of 60 football fields and the reactor building will weigh 320,000 tonnes, all resting on rubber bearings in case of an unlikely, but not impossible, earthquake. The reactor itself will weigh 23,000 tonnes, three times more than the Eiffel Tower. It is the most complex engineering project in history.

More than 2,800 tonnes of superconducting magnets, some heavier than a jumbo jet, will be connected by 200km of superconducting cables, all kept at -269C by the world’s largest cryogenic plant, which will pump 12,000 litres per hour of liquid helium.

Millions of precision components will be shipped in from the seven partners to be assembled by thousands of workers. This is all aimed at keeping just two grammes of plasma hot enough and stable enough in the 30m-diameter tokamak for fusion to take place.

Iter’s schedule is to create the first plasma in 2025, then start firing tiny 5mm frozen pellets of heavy hydrogen – deuterium and tritium – into the plasma and generating energy. Deuterium is easily refined from seawater and fuses with tritium, which is harvested from fission reactors but could be self-generated in Iter in future. The aim is to reach its maximum power output by 2035 and, if so, Iter will be the foundation of the first fusion power plants.

Bernard Bigot, the director general of Iter, is certain it will produce plentiful power, “but what is not granted so far is that this technology will be simple and efficient enough that it could be industrialised,” he says.

The point of Iter is finding out, says Bigot: “The world needs to know if this technology is available or not. Fusion could help deliver the energy supplies of the world for a very long time, maybe forever.”