NOTCHED VELOCITY PROFILES AND THE RADIAL ELECTRIC-FIELD IN HIGH ION TEMPERATURE PLASMAS IN THE TOKAMAK FUSION TEST REACTOR

A large ''notch,'' or non-monotonic feature, appears in measured toroi dal velocity profiles of the carbon impurity in the Tokamak Fusion Tes t Reactor (TFTR) [Plasma Phys. Controlled Fusion 26, 11 (1984)], cente red near the radius of strongest ion temperature gradient. This is exp lained as a consequence of radial momentum transport dominated by anom alous diffusion together with parallel heat friction on the impurity i ons arising from the hydrogenic neoclassical parallel heat flow. The t oroidal velocity profile of the hydrogenic species is predicted to be monotonic, from measurements of the impurity toroidal velocity, consis tent with the anomalous radial diffusion of toroidal momentum. This su pports a neoclassical calculation of the radial electric field for nea r-balanced beam injection. In supershot plasmas [Phys. Rev. Lett. 58, 1004 (1987)], a well structure in the radial electric field profile is found in the enhanced confinement region. An associated shear layer s eparates the core, where the local confinement trends are favorable, f rom the degraded outer region. This provides a mechanism for the nonli near coupling of the ion temperature gradient, ion thermal confinement , and the radial electric field, which may help explain the favorable core confinement trends of very high temperature supershot plasmas. (C ) 1998 American Institute of Physics.