Active control of H-mode

The present status of investigations concerning active control of the H-mode is discussed, including density control for steady H-mode operation, control of heat flux to lower the divertor heat load, and control of the transport barrier for further improvement of confinement and MHD stability. Control of ELM activity is extremely important for density control in the H-mode. Some examples of controlling ELMs are discussed. The remote radiative cooling of the main plasma and the divertor plasma is necessary to lower the divertor heat load. Since the heat flux across the separatrix to keep the H-mode has to be higher than the threshold power for the HL transition, the feasibility of cooling the H-mode plasma with the main radiation loss depends on the ratio of the threshold power to the total heating power. Control of the edge transport barrier with plasma shaping has been demonstrated. The toroidal field dependence of the threshold power for an internal transport barrier (ITB) formation of the high-βp mode is significantly different from that for an edge transport barrier formation in the H-mode, indicating the transition physics might be different. Formation of an ITB was successfully demonstrated by ion Bernstein wave resonant heating and by negative magnetic shear. (author)