The National Ignition Facility (NIF) uses a powerful laser to heat and compress hydrogen fuel, initiating fusion.

An experiment suggests the goal of "ignition", where the energy released by fusion exceeds that delivered by the laser, is now within touching distance.

Harnessing fusion, the process that powers the Sun, could provide a limitless, clean energy source.

In a process called inertial confinement fusion, 192 beams from NIF's laser - the highest-energy example in the world - are directed towards a peppercorn-sized capsule containing deuterium and tritium, which are different forms of the element hydrogen.

This compresses the fuel to 100 times the density of lead and heats it to 100 million degrees Celsius - hotter than the centre of the Sun. These conditions help kickstart thermonuclear fusion.

An experiment carried out on 8 August yielded 1.35 megajoules (MJ) of energy - around 70% of the laser energy delivered to the fuel capsule. Reaching ignition means getting a fusion yield that's greater than the 1.9 MJ put in by the laser.

"This is a huge advance for fusion and for the entire fusion community," Debbie Callahan, a physicist at the Lawrence Livermore National Laboratory, which hosts NIF, told BBC News.

As a measure of progress, the yield from this month's experiment is eight times NIF's previous record, established in Spring 2021, and 25 times the yield from experiments carried out in 2018.

"The pace of improvement in energy output has been rapid, suggesting we may soon reach more energy milestones, such as exceeding the energy input from the lasers used to kick-start the process," said Prof Jeremy Chittenden, co-director of the Centre for Inertial Fusion Studies at Imperial College London.

But building commercially viable fusion facilities that can provide energy to the grid will require another giant leap.

"Turning this concept into a renewable source of electrical energy is likely to be a long process and will involve overcoming substantial technical challenges, such as being able to re-create this experiment several times a second to produce a steady source of power," said Prof Chittenden.

18/08/2021
By Paul Rincon
Science editor, BBC News website

https://www.bbc.com/news/science-environment-58252784