Observations on the formation and control of transport barriers

Internal and edge transport barriers are widely observed in a number of devices, including tokamak and helical systems, with various heatings. The E × B flow shear suppression of turbulence seems to explain formation and subsequent propagation of transport barriers in many cases. However, the role of the safety factor profile has not been clearly understood. Moreover, electron transport still remains a major issue. Tokamak research is challenging the active control of transport barriers. Steady or quasisteady performance of H-modes with internal barriers has been gradually improving and stable sets of profiles close to the steady-state solution have been demonstrated at high β.