P ROVENCE, 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).

It may, however, have emerged from its long, dark teatime of the soul. Bernard Bigot, a physicist who used to run France’s Atomic Energy Commission, and who has been director-general of the project since 2015, has shaken things up. The site at the Cadarache nuclear facility near St-Paul-lez-Durance is now busy with cranes and concrete-pouring lorries (see picture), and Dr Bigot says Iter is 60% of the way to the 2025 startup goal.

Those first experiments, whenever they actually happen, will study the physics of deuterium-tritium plasmas in the reactor—these two isotopes of hydrogen being the front-running candidates as the fuel mixture for nuclear fusion. Only after a decade of such work will fusion experiments proper begin. The aim is to return at least ten times as much energy from nuclear reactions as is used to heat the plasma up in the first place. By 2045, Dr Bigot hopes, engineers will be able to start designing power stations based on Iter’s results.

Faced with competition from firms that reckon they can build commercial fusion reactors well before then (see article) Dr Bigot says he is energised by these rivals, but has no concern about Iter becoming an also-ran. He says Iter will be true to its retrofitted name by being the one that shows the world the path to grid-scale fusion electricity.

That, he says, is because it will work on problems that most of the private companies will not. It will, for example, develop new materials to withstand the extreme temperatures of the plasma. And it will develop and test ways to make tritium efficiently and safely on site at a power plant—for tritium, unlike deuterium, is radioactive and exists only transiently in nature.

That Iter is based in France, the home of grands projets, has a certain appropriateness. Iter has grand scale and grand objectives. France is also, though, a country for whose soul dirigisme and laissez-faire are in constant struggle. Iter is dirigisme par excellence. But this is a battle that laissez-faire might win.