H-mode operation in the START spherical tokamak

H-mode operation has been achieved in high current (I-p > 200 kA) plasmas in the START spherical tokamak for both neutral-beam-injection-heated and Ohmic discharges. The transition to H mode features the development of well-defined edge pedestals in density and temperature, which signifies the formation of an edge-transport barrier, and associated edge-localized modes. Recent operation at plasma currents exceeding 250 kA shows that these features are accompanied by increases in energy confinement time. This is the fil st clear demonstration of the H-mode regime in a spherical tokamak. PACS numbers: 52.55.Fa.