A new B2SOLPS5.2 transport code has been developed and implemented for the simulation of H-mode shots. A new equation system is proposed, which is equivalent to the system which was used in B2SOLPS5.0 previously. The main idea is to replace the major part of the large radial ∇B driven convective fluxes by poloidal fluxes with the same divergence both in the particle balance and in the energy balance equations. This is of special importance for the H-mode where the diffusion coefficient is strongly reduced inside the barrier and large radial convective flows are strongly undesirable from the numerical point of view. The H-mode shots of ASDEX-Upgrade and MAST have been simulated with the new version with reasonable time steps and convergence. It is demonstrated that the radial electric field inside the edge transport barrier and in the pedestal region is close to the neoclassical electric field as in previous simulations of Ohmic shots. The toroidal rotation is co-current directed as in L-mode but is significantly larger in absolute value. It is shown that the shear of the poloidal drift at the inner side of the barrier is close to the value of the shear before the transition, while inside the barrier the value of the shear is significantly bigger. This fact determines self-consistently the width of the edge transport barrier. It is demonstrated that to match the experimental density and temperature radial profiles the drop in the diffusion coefficient within the barrier needs to be significantly larger than the drop in the electron heat conductivity coefficient. For the H-mode the pedestal region usually corresponds to the collisionless regime, so several corrections were introduced into the transport coefficients to extend the applicability of the code to the plateau and banana regimes in the inner regions of the simulation domain.

The impact of resonant magnetic perturbations (RMPs) on the structure of the edge transport barrier has been studied. A model for the density pump-out mechanism during the stochastization of the plasma edge is proposed. The observed phenomena are explained as a result of the impact of the ambipolar electric field, which is modified during RMP, on the particle fluxes in the pedestal region. It is demonstrated that the rise of the particle fluxes inside the transport barrier leads to the pump-out effect on density, while the pedestal temperature increases in spite of the big electron heat conductivity in the stochastic magnetic field. The latter is not sufficient to change significantly turbulent heat conductivity in the barrier region and only compensates the rise of the pedestal temperature caused by the density drop for constant heating power. The analytical approach is supported by results of simulations with the B2SOLPS5.2 2D transport code which uses a full description of particle sources and transport phenomena in the pedestal region. Simulations are performed for ASDEX-Upgrade and MAST configurations for various values of electron stochastic conductivity. The radial electric field with RMPs is predicted to be less negative than without RMP. The density drop and temperature rise in the pedestal region are observed in accordance with the experimental results. Generation of toroidal rotation in the co-current direction is predicted. Extrapolations to ITER are discussed.

A systematical study of drift and parallel current effects is reported based on the analysis of the simulations by the B2SOLPS5.2 transport code. It is demonstrated that divertor asymmetry is caused or amplified by the poloidal drift and parallel thermal current.

The transport code B2SOLPS5.2 was used to simulate L and H-mode discharges on MAST with and without resonant magnetic perturbations (RMP). The simulated variation of the radial electric field (less negative for RMP) and toroidal rotation (spin-up in the co-current direction for RMP) is in agreement with experiment. The pump-out effect in the L-modes with high and medium plasma density and in the H-mode is caused by the additional neoclassical radial plasma flow in the electric field modified due to the electron loss along the stochastic field lines. The pump-out in the low density L-mode can be reproduced only by a significant rise of the turbulent transport coefficients. The modeling suggests strong RMP screening. An analytical model for RMP screening is proposed.