United Kingdom lights up its unusual fusion reactor
The United Kingdom’s revamped fusion reactor, known as the Mega Amp Spherical Tokamak (MAST) Upgrade, powered up for the first time yesterday after a 7-year build. The £55 million device will be a testbed for technologies critical to all future fusion reactors, and may provide a stepping stone to a new design of energy-producing facility.
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. (ITER, a gigantic tokamak under construction in France, is a major focus of global efforts to realize fusion power.)
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. A parallel effort at the Princeton Plasma Physics Laboratory, called the National Spherical Torus Experiment (NSTX), was similarly upgraded. Soon after restarting in 2016, however, NSTX suffered a magnet failure and is now being rebuilt.