A pivotal step in the march towards fusion power, the ‘Holy Grail’ of sustainable clean energy, could be taken this year.

Scientists in the US are preparing for the dramatic moment when the world's most powerful laser unleashes the nuclear force that lights up the Sun and achieves “ignition”.

At that moment, 192 laser beams housed in a building the size of three football pitches will focus on a target the size of a peppercorn to trigger a self-sustaining fusion reaction.

If all goes according to plan, this could be achieved in October.

Scientists have spent decades chasing the dream of fusion power, which holds out the promise of producing unlimited amounts of clean energy from hydrogen, the most abundant element in the universe. Nuclear fusion happens when the nuclei of atoms are driven together so hard that they fuse to form a heavier particle. A self-sustaining chain reaction occurs as more atomic nuclei collide, releasing huge amounts of energy in the process.