Researchers at the US National Ignition Facility (NIF) in California confirmed the nuclear community’s worst-kept secret on Tuesday (13 December) – that fusion experiments had released more energy than was pumped in by the lab’s enormous, high-powered lasers, a landmark achievement known as ignition or energy gain.

The technology is far from ready to turn into viable power plants – and is not about to solve the climate crisis – but scientists hailed the breakthrough as evidence that the power of the stars can be harnessed on Earth.

Researchers from NIF used the world’s most energetic laser to fire 2.05 megajoules (MJ) of energy into a capsule of hydrogen fuel about the size of a peppercorn. Reaching temperatures many times those found in the sun’s core and pressures 300 billion times those normally experienced on Earth, a wave of nuclear reactions ripped through the fusion fuel, releasing 3.15 MJ of fusion energy – 1.1 MJ more than was put in – over a few tens of nanoseconds.

This is significant not because of the absolute energy released – that was a small amount, only enough to boil two or three kettles. It’s significant because it’s the first scientific proof that fusion can produce more energy out than is put in.