Modelling of the Edge Plasma with Account of Self-Consistent Electric Fields

Abstract

Recent results on the simulation of the edge plasma parameters are discussed with emphasis on the role of self-consistent electric fields. It is demonstrated that simulation with B2SOLPS5.0 code as well as with the other codes is consistent with the neoclassical nature of the radial electric field in the core region 1-2 cm inside the separatrix. Near the separatrix the viscous layer exists, where the impact of the parallel fluxes of the SOL is important and electric field deviates from the neoclassical value. It is shown that the experimental dependence of the L-H transition threshold on the local and global plasma parameters might be explained on the basis of the simulations. The impact of the geometrical factors on the radial electric field structure is discussed. It is shown that the change of the parallel fluxes in the scrape-off layer, which are transported through the separatrix due to turbulent viscosity and diffusivity, should result in variation of the radial electric field. The parallel (toroidal) fluxes in the SOL and mechanisms of their formation are analyzed for different geometry and directions of the magnetic field. Currents in the SOL and in the core region are analyzed and compared with the analytical predictions.

Modelling of the Radial Electric Field in the ASDEX Upgrade Ohmic Shots

“…In all simulations dependence of the radial electric field on the parallel velocity, density and temperature gradients is close to the neoclassical one Eq. (3) with exception of a dip in the separatrix vicinity, as in the previous simulations, [4]- [5]. Example of comparison is shown in Fig.3.…”

“…(3) due to anomalous terms. This however, as was discussed in detail in [4]- [5] takes place only in the very narrow viscous layer at the separatrix.…”

Drifts, Currents, and Radial Electric Field in the Edge Plasma with Impact on Pedestal, Divertor Asymmetry and RMP Consequences

“…Others considered the poloidal drifts as the main source of additional divertor asymmetries [30,53]. Simulations [16,37,28,53] were not able to give an unambiguous answer to this problem since the role of the drifts was masked by the usual LFS -HFS asymmetry. The parallel current flowing in the divertor adds to the complexity of the problem.…”

“…The parallel velocity within this layer is transported from the SOL to the core while the electric field here is different from the neoclassical value. This might explain the larger negative electric field when the ion ∇B drift is directed towards the X-point in a single-null configuration and other geometrical effects [15,37].…”

“…The role of drifts and parallel currents was discussed in several publications, see e.g. [50,37,16,51,41]. One possibility is that the radial E × B drifts play the main role due to the radial flows from LFS divertor to the HFS one (for single null divertor configuration), see [50,52].…”