Plasma in spherical tokamak MAST. (Source: Wikipedia.org)

Tokamak with a low aspect ratio and a round plasma in a shape resembling a cored apple. While a conventional tokamak has a more donut-like shape with a central hole, a spherical tokamak minimizes this hole to achieve a higher compactness. A single common conductor runs through the centre of the tokamak, to which toroidal magnets in the shape of semicircles are connected. Due to its more compact shape, the spherical tokamak achieves the same plasma parameters as a conventional tokamak with a lower magnetic field. This allows it to be smaller and cheaper. Typical spherical tokamaks are the Small Tight Aspect Ratio Tokamak (START) or the Mega Ampere Spherical Tokamak (MAST).