During its lifetime, START was upgraded several times to improve its performance and the experimental programme produced many important results. However the challenge for the future is to prove that the theoretical and experimental advantages seen in START can be realised in larger machines.

The successor to START at Culham is MAST (Mega Amp Spherical Tokamak). Its objective is to test physics at tight aspect ratio in sustained high current plasmas with additional heating. Unlike START, MAST is a custom-built machine with a stainless steel vacuum tank and modern power supplies.

MAST will add to the existing data on conventional tokamaks, so extending the fusion community's database of results, and providing an increased understanding of the behaviour of toroidal plasmas. Much of this research will be of relevance to the Next Step fusion device, ITER, and so increase Europe's contribution to the ITER partnership.

START is being retained as a test facility, for example for the neutral beam injectors now installed on MAST.