Screening of resonant magnetic perturbations by flows in tokamaks

Abstract

The non-linear reduced four-field RMHD model in cylindrical geometry was extended to include plasma rotation, neoclassical poloidal viscosity and two fluid diamagnetic effects. Interaction of the static resonant magnetic perturbations (RMPs) with the rotating plasmas in tokamaks was studied. The self-consistent evolution of equilibrium electric field due to RMP penetration is taken into account in the model. It is demonstrated that in the pedestal region with steep pressure gradients, mean flows perpendicular to the magnetic field, which includes E × B and electron diamagnetic components plays an essential role in RMP screening by plasma. Generally, the screening effect increases for lower resistivity, stronger rotation and smaller RMP amplitude. Strong screening of central islands was observed limiting RMP penetration to the narrow region near the separatrix. However, at certain plasma parameters and due to the non-linear evolution of the radial electric field produced by RMPs, the E × B rotation can be compensated by electron diamagnetic rotation locally. In this case, RMPs can penetrate and form magnetic islands. Typical plasma parameters and RMPs spectra on DIII-D, JET and ITER were used in modelling examples presented in the paper.

Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations

“…and k i = −1 [12] are used. In the MAST case, the neoclassical friction is not included in the model.…”

“…Indeed, the total suppression of the type-I ELMs by RMPs was demonstrated in DIII-D [2,3] and later in ASDEX upgrade [4] and KSTAR [5]; the strong mitigation of the ELM size was also obtained in the JET [6], MAST [7] and NSTX [8] tokamaks, motivating the use of this method in ITER [2,9]. The non-linear MHD theory and modeling made significant progress to refine the understanding of the RMP interaction with the plasma [10][11][12][13][14][15]. In particular, it was demonstrated that the penetration of the RMPs in the plasma is conditioned by the rotating plasma response [11][12][13][14][15].…”

“…The non-linear MHD theory and modeling made significant progress to refine the understanding of the RMP interaction with the plasma [10][11][12][13][14][15]. In particular, it was demonstrated that the penetration of the RMPs in the plasma is conditioned by the rotating plasma response [11][12][13][14][15]. The generation of current perturbations on the rational surfaces in the plasma can prevent magnetic reconnection, leading to the screening of RMPs.…”

“…However, at certain plasma parameters, RMPs can on the contrary be amplified [16]. Non-linear MHD modeling of the rotating plasma response to RMPs in cylindrical geometry [11,12] demonstrated that the poloidal plasma rotation, including the E × B and diamagnetic rotations, both perpendicular to the magnetic field, are particularly important in the pedestal region and are likely to screen the RMPs. The aim of the present work is to extend the previous RMP modeling [12] to the more realistic toroidal geometry of the tokamak, including the X-point and the Scrape-Off Layer (SOL).…”

Flux-driven simulations of turbulence collapse

“…(1) (l neo : neoclassical friction coefficient) is obtained from the radial force balance equation linking the radial electric field, pressure gradient, and poloidal velocity (detailed derivation can be found, for example, in Ref. 22). This term gives rise to mean E Â B flow generation due to pressure curvature.…”