High- performance of the START spherical tokamak

Using additional heating provided by neutral-beam injection, the START spherical tokamak at UKAEA Fusion Culham has achieved high- (ratio of volume average plasma pressure to vacuum magnetic-field pressure) values of , more than twice the value previously obtained in a tokamak. These plasmas reach normalized beta values of at values of auxiliary heating power comparable to the ohmic power. Operation at high normalized current is observed, so that the plasma current exceeds the central rod toroidal-field current for the first time in a hot tokamak.