Spherical Tokamak

A spherical tokamak is a fusion device built on the same magnetic confinement principles as a conventional tokamak but with a much narrower aspect ratio, shrinking the donut-shaped hole at the middle of a traditional tokamak until the plasma forms an almost spherical shape often compared to a cored apple, which is why the design is also called a spherical torus, or ST for short. Martin Peng of Oak Ridge National Laboratory proposed the design in 1984, using a single central conductor with magnet coils wired as half-rings to reach aspect ratios as low as 1.2, far tighter than a conventional tokamak achieves. Major experimental spherical tokamaks have included START and MAST in the United Kingdom, NSTX-U in the United States, and Globus-M in Russia, and researchers have studied whether the design offers a route to lower-cost fusion reactors, though the spherical tokamak program remains roughly one generation of development behind conventional tokamak efforts such as JET. Even without reaching commercial power generation, spherical tokamaks remain valuable for studying plasma physics and as sources of neutrons for other research.