NEOCLASSICAL TRANSPORT AND POLOIDAL ROTATION AT THE L-H TRANSITION

We address the question of establishing if, and under what physical an d boundary conditions, the neoclassical transport is quantitatively ca pable of establishing high gradients in a narrow layer at the edge of an auxiliary heated tokamak plasma, and of driving poloidal rotation i n the absence of external momentum input and vanishing parallel viscou s stress, in a time scale of a few milliseconds. We observe that a tor que for poloidal and toroidal acceleration with constant parallel flow is provided by the displacement current at third order of the adiabat ic expansion. Combining neoclassical transport with a model of anomalo us transport suppression we show the development, during a few millise conds, of strong gradients in temperature, radial electric field and p oloidal rotation at the edge, that are consistent in magnitude nd sign with observations.