A pioneering nuclear fusion experiment based in Oxfordshire has been switched on for the first time.
Mast Upgrade could clear some of the hurdles to delivering clean, limitless energy for the grid.
Fusion differs from fission, the technology used by existing nuclear power plants, because it could release vast amounts of energy with little associated radioactivity.
The £55m machine has taken seven years to build.
Current nuclear energy relies on fission, where a heavy chemical element is split to produce lighter ones.
But nuclear fusion works by combining two light elements to make a heavier one. It’s an attempt to replicate the processes of the Sun here on Earth.
Unlike fission, it produces no long-lived radioactive waste and could transform the way we source our power – tackling the climate crisis at the same time.
Mast (Mega Amp Spherical Tokamak) Upgrade will use an innovative design known as a spherical tokamak.
The tokamak is a fusion device that uses magnetic fields to confine the plasma – hot, ionised gas – inside a vessel. This plasma allows the light elements to fuse and yield energy.
Most tokamaks are shaped like a doughnut. But in Mast Upgrade, the size of the doughnut’s hole has been reduced as much as possible, giving the plasma an almost spherical profile.
Prof Ian Chapman, chief executive of the UK Atomic Energy Authority (UKAEA), said the switch-on was “a really momentous occasion”.
The first plasma in the machine marks the start for this trailblazing effort to move the UK closer to building a fusion power plant. It’s one thing to control a plasma and perform fusion. But it’s another to generate more energy out of the reaction than the experiment puts in.