Plasma in the MAST reactor. Note the almost circular outer profile of the plasma. The extensions off the top and bottom are plasma flowing to the ring diverters, a key feature of modern tokamak designs.
The Mega Ampere Spherical Tokamak, or MAST experiment is a nuclear fusion experiment in operation at Culham, Oxfordshire, United Kingdom since December 1999. It follows the highly successful START experiment (1991 - 1998). MAST uses the same innovative spherical tokamak design as START, which has shown itself to be more efficient than the conventional toroidal design, adopted by JET and ITER. START proved to exceed even the most optimistic predictions and the purpose of MAST is to confirm the results of its forerunner by using a larger more purpose-built experiment.
It was fully commissioned by EURATOM/UKAEA and took two years to design and a further two years to construct. It includes a neutral beam injector similar to that used on START and uses the same merging compression technique instead of the conventional direct induction. Merging compression provides a valuable saving of central solenoid flux, which can then be used to further ramp up the plasma current and/or maintain the required current flat-top.
The device is presently planning a major upgrade to significantly enhance its capabilities to address its primary objectives (listed below).