Anomalous transport arising from nonlinear resistive pressure-drive modes in a plasma

Anomalous transport caused by fluctuations of resistive pressure-driven modes is discussed. The nonlinear reduced equations describing fluctuations localized near a particular magnetic field line are derived for tokamak and reversed-field pinch (RFP) plasmas, taking into account nonzero viscosity and heat conductivity. Based on the reduced equations, the relationship between the dynamo effect, or the electric field caused by the fluctuations, and the anomalous heat transport is obtained. For an ideally stable but resistively slightly unstable plasma, the anomalous transport is caused particularly by convective motions. The convection is studied as bifurcation from the linearly unstable equilibrium, and the expression of the anomalous transport in a tokamak plasma is obtained as a function of the mean pressure gradient near the critical point. In order to evaluate the effects of the convection on the anomalous transport under various conditions, the reduced equations are also solved numerically. It is found that the Nusselt number, that is, the ratio of the total heat transport including the anomalous heat transport to the classical collisional heat conduction, is significantly large under some conditions