Screening effect of plasma flow on the resonant magnetic perturbation penetration in tokamaks based on two-fluid model

Abstract

Numerical simulation on the resonant magnetic perturbation penetration is carried out by the newly-updated initial value code MDC (MHD@Dalian Code). Based on a set of two-fluid four-field equations, the bootstrap current, parallel, and perpendicular transport effects are included appropriately. Taking into account the bootstrap current, a mode penetration-like phenomenon is found, which is essentially different from the classical tearing mode model. To reveal the influence of the plasma flow on the mode penetration process, E × B drift flow and diamagnetic drift flow are separately applied to compare their effects. Numerical results show that a sufficiently large diamagnetic drift flow can drive a strong stabilizing effect on the neoclassical tearing mode. Furthermore, an oscillation phenomenon of island width is discovered. By analyzing it in depth, it is found that this oscillation phenomenon is due to the negative feedback regulation of pressure on the magnetic island. This physical mechanism is verified again by key parameter scanning.

Effects of diamagnetic drift on nonlinear interaction between multi-helicity neoclassical tearing modes

“…( 2) and the magnetic island width. [45] Figure 2(b) gives the dependence of average saturated magnetic island width on δ . In this context, "average" refers to the mean value of the magnetic island width during the saturation phase, considering the periodic oscillations observed in the magnetic island width.…”

“…For instance, the simulation results are adopted to explain experimental observations in ASDEX-U [34] and DIII-D. [56] In simulations related to two-fluid dynamics, cylindrical geometry has also been extensively employed. [42,44,45,57] Simulation results have demonstrated the ability to elucidate certain phenomena observed in experiments. Paz-Soldan et al found alignment between simulation results by TM1 code, a nonlinear two-fluid MHD model with cylindrical geometry, and experimental island healing.…”

“…[39,40] Hence, there has been an increasing focus on research related to two-fluid effects in recent years. For example, studies have been carried out on the control of NTMs by resonant magnetic perturbations, [41][42][43] on the suppression of the onset of neoclassical double tearing modes by diamagnetic drift, [44] on the systematic numerical simulation of the mode penetration in NTMs, [45] on the influence of Hall effect on TMs [46,47] and on the influence of diamagnetic drift on MHD stability in DIII-D experiments. [48] Despite great progress having been made in two-fluid studies, further research is still required to simulate multi-helicity NTMs based on two-fluid theory.…”