Effect of resonant magnetic perturbations on local plasma current density gradients and neoclassical tearing modes. (22nd February 2021)

• Record Type: Journal Article
• Authors: Yu, Q.; Günter, S.; Lackner, K.
• Is Part Of: Nuclear fusion. Volume 61:Number 3(2021)
• Publication Date: 2021-02-22
• Subjects: weakly three-dimensional equilibrium -- resonant magnetic perturbation -- error field -- plasma current density gradient -- magnetic island -- neoclassical tearing mode -- two-fluid physics; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/abd197
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: The effect of externally applied resonant magnetic perturbations (RMPs) on the local equilibrium plasma current density profile is studied numerically based on two-fluid equations in simplified cylindrical geometry. It is found that a moderate RMP below its penetration threshold, via non-linear mode coupling, induces a parallel electric field around its rational surface that can significantly change the local flux-surface-averaged current density gradient. At a given RMP amplitude, the modification of the current density profile increases with increasing electron temperature, and it significantly depends on the bi-normal electron fluid velocity at the resonant surface. The effect of this modification on the magnetic island growth is demonstrated by the example of small m / n = 2/1 islands ( m / n being the poloidal/toroidal mode numbers), driven by an unfavorable plasma current density profile and bootstrap current perturbation. The 2/1 mode growth is stabilized by moderate static 4/2 or 6/3 RMPs if the local electron fluid velocity is in the ion drift direction or sufficiently large in the electron drift direction. These results reveal that a weakly three-dimensional equilibrium, containing a moderate 4/2 RMP and the associated shielding current, can be more stable against the 2/1 mode, which often causes tokamak plasma major disruptions.