POLOIDAL SPIN-UP AND ELECTRIC-FIELD GENERATION RELATED TO DISPLACEMENT CURRENT AND NEOCLASSICAL TRANSPORT

In accordance with the conventional orderings of neoclassical theory, poloidal and toroidal accelerations with constant parallel flow can be driven by heat transport in the absence of external momentum input an d with vanishing parallel viscous stress. In a transient phase in whic h the heat transport is the primary source of the time dependence, the torque generating the rotation is provided at third order in the adia batic expansion by the surface-averaged (non-ambipolar) displacement c urrent, which is also responsible for charge build-up and for the radi al electric field. The heat transport equation has been solved in a na rrow layer interfaced with the intensely heated plasma core through he at flux continuity, assuming neoclassical multicollisional coefficient s with self-consistent suppression mechanism of anomalous transport. S tarting from low temperature in the edge layer, a strong temperature g radient, a mass poloidal rotation in the ion direction and a strongly negative sheared radial electric field can be generated, in agreement with the observations, and reach a stationary state after a displaceme nt current-dominated triggering phase (intrinsically non-ambipolar) la sting few milliseconds. Momentum input becomes important on longer tim e scale and is responsible for the toroidal rotation, decoupled from t emperature gradient and for a further development of the radial electr ic field. The results show the ability of edge transport processes to adapt flexibly to a high temperature imposed on the inner side of the edge layer and support the view that the edge processes are an integra l part of a more fundamental global process involving possibly an inte rnal bifurcation of state.