The world’s largest nuclear fusion project has entered its five-year assembly phase.
Once this is complete, the facility will be able to start generating the superheated “plasma” required for the fusion power.
The £ 18.2bn (€ 20bn; $ 23.5bn) facility has been under construction in Saint-Paul-lez-Durance, southern France.
Proponents say the merger could be a clean, unlimited source of energy that would help tackle the climate crisis.
Iter is a collaboration between China, the European Union, India, Japan, South Korea, Russia and the United States. All members share the cost of construction.
Nuclear power today depends on fission, where a heavy chemical element breaks down to produce lighter ones.
Nuclear fusion, on the other hand, works by combining two light elements to make a heavier one.
This releases large amounts of energy with very little radioactivity.
Iter will confine the hot plasma within a structure called a tokamak to control fusion reactions.
The project will aim to help demonstrate whether the merger can be commercially viable. French President Emmanuel Macron said the effort would unite countries around a common good.
The facility could see plasma generated on the machine, a theoretical start to operations, shortly after the assembly phase ends in 2025.
President Macron said: “Iter is clearly an act of confidence in the future. The greatest advances in history have always been the product of daring bets, of trips loaded with difficulties.”
“At first it always seems that the obstacles will be greater than the will to create and progress. Iter belongs to this spirit of discovery, of ambition, with the idea that, thanks to science, tomorrow can be better than yesterday.”
But fusion power has its skeptics. Making it commercially viable has been difficult because scientists have struggled to get enough energy from the reactions.
Proponents believe Iter can overcome technical hurdles and that, given the planetary challenges it faces, the merger is worth the expense and effort.
The UK is a member of the Iter project, but it is slated to fall, because the British government withdrew from a key treaty as part of Brexit. The UK could be left alone if a new way to maintain its stake is found at the end of the Brexit transition.
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