Relation between tokamak temperature profiles and localized instabilities

Three types of tokamak instabilities which depend on temperature profiles and which affect energy confinement have been examined. In the central region of the plasma, where density and temperature gradients are small, a poloidal rotation instability has been found whose properties resemble the observed sawtooth disruptions. In the presence of auxiliary ion heating, the turbulence resulting from unstable ion pressure-gradient-driven drift waves is found to give an anomalous ion thermal conductivity which is consistent with recent experimental results. Unless the electrons are deep into the banana regime, electron temperature-gradient-driven tearing modes are found to be unstable because of the response of electrons near the trapped/untrapped boundary in velocity space. (author)