(BBC News) Researchers at a US lab have passed a crucial milestone on the way to their ultimate goal of achieving self-sustaining nuclear fusion.

Harnessing fusion – the process that powers the Sun – could provide an unlimited and cheap source of energy.

But to be viable, fusion power plants would have to produce more energy than they consume, which has proven elusive.

Now, a breakthrough by scientists at the National Ignition Facility (NIF) could boost hopes of scaling up fusion.

Note: Read our discussion guidelines before commenting.