Modelling of the edge plasma of MAST in the presence of resonant magnetic perturbations

Abstract

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.

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

“…On the other hand additional electron heat transport in the stochastic magnetic field leads to the temperature reduction. As a result there is no temperature drop in the pedestal region when RMPs are switched on; on the contrary modest rise of the temperature is observed both in the modeling and in the experiments [85,87].…”

“…Note that according to [87] in low density regimes the observed pump-out effect could not be explained by the additional convective flux and was likely caused by increase of turbulent diffusion during RMPs.…”

“…(13) into the code and calculate radial electric field from ambipolarity condition, [85], [87][88][89]. Example of change of the radial electric field in the presence of RMPs in the MAST L-mode [87] is shown in Fig.…”

“…This additional positive particle convective flux is of the order of the neoclassical particle flux with neoclassical diffusivity replaced by the ion heat conductivity. This flux can compete with the turbulent particle flux thus being sufficient to produce pronounced pump out effect [85,87,90]. The temperature change during RMPs is determined by two factors.…”

“…Several results of the modeling both with transport code B2SOLPS5.2 [85], [87] and with the kinetic code [88][89] demonstrated that to match the observed radial electric field and pump out effect it is necessary to reduce significantly the perturbed magnetic field with respect to the vacuum value, especially in the H-mode discharges. In other words significant screening of the perturbed magnetic field might take place.…”