 MAST followed the highly successful Small Tight Aspect Ratio Tokamak (START) experiment (1991-1998) and used the same innovative spherical tokamak design as START.Spherical tokamaks have been shown to be more efficient in use of the magnetic field than the more conventional toroidal design, adopted by Joint European Torus (JET) and ITER.START proved to exceed even the most optimistic predictions and MAST confirmed the results of its forerunner on a larger, more purpose-built experiment.