High performance tokamak operation regimes

Many tokamak plasma regimes have been developed which exhibit improved plasma stability and energy confinement compared with the ELMy H-mode which has been used for some time as the baseline for reactor design. In particular, transient high performance has been achieved in experiments with low or reversed magnetic shear ( s = r / q ( dq / sr )) and substantial progress is now being made to extend these plasmas towards steady state. The achievements with regime in several tokamak devices are presented and outstanding issues for the further exploitation of this scenario are discussed.