Suppressive effects of diamagnetic drift on neoclassical double tearing modes based on four-field reduced MHD model

Abstract

The explosive behavior of neo-classical double tearing mode (NDTM) is numerically investigated by a reduced four-field-drift-magnetohydrodynamic code [Ye et al., Nuclear Fusion 59, 096044 (2019)] with the bootstrap current effect. It is numerically observed that the explosive burst of NDTM can be absolutely suppressed by diamagnetic drift flow. The dependence of the critical value of diamagnetic drift flow V0*c for avoiding the explosion on typical plasma parameters is numerically studied in detail. It is found that V0*c decreases with increasing Δrs, while it increases with an increasing bootstrap current fraction. The plasma viscosity and resistivity can raise the threshold through their effects on the rotation of magnetic islands and the instability of system, respectively. Furthermore, the perpendicular transport and parallel transport, which are significant to the driven effects of the bootstrap current, have the opposite effects on V0*c. The underlying mechanisms are discussed.

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

“…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.…”