Formation of the radial electric field profile in the scrape-off layer of the tokamak in the outer midplane is analyzed on the basis of SOLPS-ITER modeling for various regimes of ASDEX-Upgrade and ITER. The radial electric field is a result of the interplay of different contributions to the electron parallel momentum balance equation and the sheath potential drop at the plate, all of the same order. The relative role of these contributions is analyzed for semi-detached and attached divertor conditions. It is demonstrated that in the conduction-limited regime the electric field is positive, while in the semi-detached regime it decreases in absolute value in the major part of SOL and even becomes negative at the separatrix.
Calculation of the radial electric field with RF sheath boundary conditions in divertor geometry