Is turbulence indeed reduced in the tokamak edge pedestal? Mysteries of PEDESTAL poloidal ASYMMETRIES revealed

It has been suggested that the sudden transition between states of low and high confinement involves the reduction of turbulence by sheared radial electric fields. For H-mode pedestals, the amount of turbulence may be only large enough to affect high order phenomena, such as heat transport. Neoclassical collisional theory may thus be expected to properly treat low order phenomena, such as flows. However, H-mode edge pedestals on Alcator C-Mod exhibit significantly stronger poloidal asymmetry than predicted by the most comprehensive neoclassical models developed to date. We propose a novel self-consistent neoclassical theoretical model that allows us to explain these poloidal asymmetries. First, impurity temperature asymmetries can be driven by inertial effects, which are significant when impurities are allowed to reach sonic speeds. Second, a much stronger impurity density in-out asymmetry than given by just the magnetic field can be introduced by the poloidally varying impurity diamagnetic drift. This is achieved by allowing the diamagnetic drift contribution to be comparable to the poloidal and toroidal flows used to measure the radial electric field. We thus provide a more realistic predictive model for pedestal observations without the need of invoking anomalous transport.