Theory for toroidal momentum pinch and flow reversal in tokamaks

It is demonstrated that besides the well-known toroidal momentum diffusion Bur there is a pinchlike Aux in the fluctuation-induced toroidal stress. A toroidal Row profile is determined up to a constant, e.g., the value of the Row at the magnetic axis, by balancing these two fluxes. The remaining residual toroidal stress determines the value of the flow at the axis. It is illustrated that the direction of the Row at the axis can change after plasma confinement is improved. The theory is applied to explain the toroidal Row reversal in tokamak experiments.