Small Tight Aspect Ratio Tokamak

The Small Tight Aspect Ratio Tokamak, or START was a nuclear fusion experiment that used magnetic confinement to hold plasma. START was the first full-sized machine to use the spherical tokamak design, which aimed to greatly reduce the aspect ratio of the traditional tokamak design.

The experiment began at the Culham Science Centre in the United Kingdom in 1990 and was retired in 1998. It was built as a low cost design, largely using parts already available to the START team. The START experiment revolutionized the tokamak by changing the previous toroidal shape into a tighter, almost spherical, doughnut shape. The new shape increased efficiency by reducing the cost over the conventional design, while the field required to maintain a stable plasma was a factor of 10 less.