France's experimental fusion reactor would work like the sun
6 August 2013 Last updated at 18:39 BST
The world's most ambitious attempt to harness fusion as a source of power is taking shape in the south of France.
Fusion is the process that drives the sun - atoms are forced together to release energy - and repeating it here on Earth could in theory offer an almost endless supply of electricity.
The construction of a vast experimental reactor has now entered a key phase.
Science editor David Shukman was given special access to explain how the reactor would work.