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 T > 30%, more than twice the value previously obtained in a tokamak. These plasmas reach normalized beta values of ND %=.I=aB/ 4 at values of auxiliary heating power comparable to the ohmic power. Operation at high normalized current IND Ip=aBT 8 is observed, so that the plasma current exceeds the central rod toroidal-field current for the first time in a hot tokamak.