Iter, a reactor in France, may deliver fusion power as early as 2045

PROVENCE, IN south-east France, is known for its pleasant weather, ratatouille and thickly wooded mountainsides. But it is also the site of what will be, if and when finished, one of the most complicated machines ever built. Iter (originally, “International Thermonuclear Experimental Reactor”, but now rebranded as Latin, thus meaning “journey”, “path” or “method”) will be a giant fusion reactor of a type called a tokamak. It will have over 1m components. Its main vessel will weigh more than 23,000 tonnes—three times the Eiffel tower. And it will cost at least $20bn.For the optimistic, Iter is an example of how people from around the world (35 countries are involved) can collaborate to achieve a lofty long-term ambition. For cynics, it is a boondoggle plagued by delays (it began in 2007 and was supposed to begin experiments in 2016, but this will not now happen until 2025), questionable management and ballooning costs (double the original estimate).