EXTERNALLY-DRIVEN H-MODE STUDIES IN CCT

Test particle E x B radial flux surface excursions are reduced during the H-mode. Particle transport is reduced by a factor of 10 in the H-m ode, but energy confinement increases are small. In the H-mode the evo lution of poloidally resolved turbulent statistics are not explained b y published theory. Turbulent momentum transport leads to a concentrat ion of poloidal momentum within the transport barrier, and compressibi lity leads to poloidal shock-like phenomena. The electron distribution functions may be modified by this shock, leading to kinetic instabili ties. A physics-based understanding of the H-mode must therefore inclu de toroidal effects combined with an adequate treatment of particle or bits, plasma compressibility and associated kinetic effects, and at le ast a two-species model of turbulent transport. The results suggest th at rapid poloidal core-plasma rotation could form core transport barri ers without reliance on fluid shear or reversed magnetic shear effects .