L-H transport barrier formation: Self-consistent simulation and comparison with ASDEX upgrade experiments

Monte Carlo ion simulation based on neoclassical radial current balance near edge in a divertor tokamak geometry gives a stationary sheared E~ ×B~ flow. The neoclassical radial electric field Er shows no bifurcation in contrast with earlier orbit loss models, but the shear in Er reaches values at which a transition to enhanced confinement has been observed. Also, MHD turbulence analysis shows that a smooth transition can occur through the neoclassical E~ × B~ flow shear suppression. The parameter scaling of threshold temperature for suppression of turbulence agrees with the H-mode threshold scaling in ASDEX Upgrade.