title: Neoclassical radial current balance in tokamaks and transition to the H mode
abstract: Monte Carlo ion simulation based on neoclassical radial current balance in a divertor tokamak gives a stationary sheared E-->xB--> flow. The neoclassical radial electric field E(r) shows no bifurcation in contrast with earlier orbit loss models, but the shear in E(r) 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-->xB--> flow shear suppression. The parameter scaling of threshold temperature for strong turbulence shear suppression agrees with the H-mode threshold scaling in ASDEX Upgrade.
authors.affiliation: VTT, Euratom-TEKES Association, FIN-02044 VTT, Espoo, Finland.
authors.initials: JA
authors.lastname: Heikkinen
authors.initials: TP
authors.lastname: Kiviniemi
authors.initials: AG
authors.lastname: Peeters