Science magazine takes us inside the Mega Amp Spherical Tokamak (MAST) Upgrade, an experimental fusion reactor which has been switched on after a 7-year build and revamping. Ultimately, it should provide pointers to a future source of abundant, cheap, clean energy – if we can get the containment fields right:
Tokamaks are the frontrunners in the decadeslong effort to generate energy by fusing light elements together. These doughnut-shaped vessels contain a superhot ionized gas—or plasma—of hydrogen isotopes that is constrained with powerful magnets and heated by microwaves and particle beams….
MAST is a variation on the standard tokamak; it is shaped more like a cored apple than a doughnut. Researchers believe that shape can confer greater stability in the roiling plasma than a doughnut-shaped tokamak, but it is less well understood than the traditional design. MAST first tested the concept on a large scale starting in 1999 and has now been upgraded with extra heating power, new technology for extracting heat from the plasma, and other improvements.