This week, researchers at the US National Ignition Facility in California achieved a major breakthrough in nuclear fusion. For the first time, humans have harnessed the process that powers the stars to generate more energy from a fusion reaction than was used to start it — otherwise known as ‘ignition’. But how close are we to moving this from laboratories to power plants, and will it become the clean, safe, and abundant source of energy the world so desperately needs? Ian Sample speaks to Alain Bécoulet about what’s being called ‘one of the most impressive scientific feats of the 21st century’. Help support our independent journalism at theguardian.com/sciencepod