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