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 opera tion, control of heat Bur to lower the divertor heat load, and control of the transport barrier for further improvement of confinement and M HD stability. Control of ELM activity is extremely important for densi ty control in the H-mode. Some examples of controlling ELMs are discus sed. The remote radiative cooling of the main plasma and the divertor plasma is necessary to lower the divertor heat load. Since the heat fl ux 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 trans port barrier with plasma shaping has been demonstrated. The toroidal f ield dependence of the threshold power for an internal transport barri er (ITB) formation of the high-beta(p) mode is significantly different from that for an edge transport barrier formation in the H-mode, indi cating the transition physics might be different. Formation of an ITB was successfully demonstrated by ion Bernstein wave resonant heating a nd by negative magnetic shear.