Modelling of the radial electric field in the ASDEX upgrade Ohmic shots

Several ASDEX-Upgrade Ohmic shots with different densities and temperatures corresponding to different collisionality regimes at the separatrix were simulated with transport code B2SOLPS5.0. The expression for the parallel viscosity was extended to be consistent with the neoclassical electric field in all collisionality regimes including plateau and banana regimes. It is demonstrated that for all shots in the core region deeper than the viscous layer (of the order of 1cm inside the separatrix) the relation between the radial electric field, parallel velocity, density and temperature gradients is close to the neoclassical one. This is consistent with the results of many simulations performed earlier for the collisional regimes. The contribution from the toroidal velocity, which is generated in the SOL and transported further to the core, to the radial electric field profile is found to be modest and comparable with density and temperature gradient contribution. The simulation results do not reproduce the dependence of the poloidal velocity of the turbulence on the collisionality deep inside the core. On the other hand, the shape of the radial electric field in the separatrix vicinity both inside and outside the separatrix is consistent with the measured poloidal rotation velocity of the turbulence. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)