Resistive electrostatic instabilities

The appropriate toroidal equations governing the stability properties of resistive electrostatic instabilities are derived and analyzed. These equations include the influence of impurity gradients and are valid for both strongly collisional and semicollisional regimes. Analytic and numerical solutions have been obtained in the sheared slab limit with toroidal curvature effects approximated with the familiar constant gravity model. The results indicate that for relevant experimental conditions, the resistivity-gradient-driven class of electrostatic modes is difficult to excite. Hence, with the possible exception of the very edge, these instabilities do not appear to be a likely candidate to account for the large thermal transport observed in the exterior region of most tokamak plasmas.