A global partnership of scientists is building the first prototype nuclear fusion reactor in southeast France.
At a cost of at least $24bn, the project could be the answer to the world’s clean energy needs when it is switched on - but that won't be for another 17 years.
Engineers say the project is so complex and expensive that they fear delays could cause countries to withdraw funding.
Al Jazeera's Natacha Butler reports from Cadarache.
