Modeling of the Edge Plasma of MAST in the Presence of Resonant Magnetic Perturbations

Full text: The impact of resonant magnetic perturbations (RMP) on the edge plasma of MAST has been studied using the B2SOLPS5.2 transport code. The effect of RMP is taken into account by adding an electron current along a stochastic magnetic field to the current continuity equation solved in the code. From analytical models it is known that the radial ion current which is generated to compensate the electron current changes the radial electric field in the separatrix vicinity and accelerates the plasma toroidally in the co-current direction. The additional particle flux which is proportional to the ion current might lead to the density drop near the separatrix -the pump out effect. Simulations were performed for three L-mode shots with different densities with and without RMP. It was found that the electric field at the core side of the separatrix becomes less negative and plasma is accelerated in the co-current directions in all the cases with RMP. The variations in the electric field and in the toroidal rotation are consistent with those measured in these shots. A H-mode shot where more frequent type III ELMs are triggered by the application of the coils has been simulated as well. For this discharge it was demonstrated that the additional particle flux in the barrier region might explain the pump out effect and the rise of the pedestal electron temperature. For the L-mode shots the additional particle flux is not sufficient to cause a significant pump out effect. It was demonstrated by the simulations that the transport coefficients in the L-mode shots with RMP are significantly bigger than in the shots without RMP. The effect is more pronounced for the low density cases. The rise of the transport coefficients correlates with the increase of the amplitude of ion saturation current fluctuations observed in the L-mode. It was shown that the level of the magnetic field perturbations required matching the pump-out effect in the H-mode and variation of the radial electric field and toroidal rotation in the L-mode is significantly smaller than the vacuum magnetic field, i.e. significant screening of the perturbed magnetic field is predicted. The mechanisms of screening are analyzed. (author)