67 research outputs found
MHD stability in X-point geometry:simulation of ELMs
A non-linear MHD code, named JOREK, is under development with the aim of
studying the non-linear evolution of the MHD instabilities thought to be
responsible for edge localized modes (ELMs): external kink (peeling) and
medium-n ballooning modes. The full toroidal X-point geometry is taken
into account including the separatrix, open and closed field lines.
Analysis of the influence of the separatrix shows a strong stabilization
of the ideal and resistive MHD external kink/peeling modes. One
instability remains unstable in the presence of the X-point,
characterized by a combination of a tearing and a peeling mode. The
so-called peeling-tearing mode shows a much weaker dependence on
the edge q. Non-linearly the n = 1 peeling-tearing mode saturates
at a constant amplitude yielding a mostly kink-like perturbation of the
boundary with an island-like structure close to the X-point. The
non-linear evolution of a medium-n ballooning mode shows the formation
of density filaments. The density filaments are sheared off from the
main plasma by an n = 0 flow non-linearly induced by the Maxwell stress.
The amplitude of the ballooning mode is limited by this n = 0 flow and
multiple (in time) density filaments can develop to bring the plasma
below the stability boundary
Magnetohydrodynamics modelling of H-mode plasma response to external resonant magnetic perturbations
The response of an H-mode plasma to Resonant Magnetic Perturbations
(RMPs) generated by so-called I-coils in DIII-D experiments on type I
edge localized modes suppression is modelled using the nonlinear reduced
magnetohydrodynamics (with zero-β, i.e. zero plasma temperature, in
the version used here) code JOREK in X-point geometry. JOREK
self-consistently advances in time the magnetic flux, vorticity, and
plasma density in the presence of the RMPs. Without any toroidal
rotation, the magnetic response from the plasma does not significantly
modify the islands widths. A radial convective E⃗×B⃗ plasma
transport is observed to occur in the presence of the RMPs. The
possibility that this mechanism could explain the enhanced density
transport observed experimentally in DIII-D is discussed. Simulations
with a rigid-body-like rotation at a fixed velocity shows evidence of a
screening of the RMPs. The extension of our results to realistic
parameters is discussed
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