Control of neo-classical double tearing modes by differential poloidal rotation in reversed magnetic shear tokamak plasmas

摘要

The control of neo-classical tearing modes (NTMs) by the differential rotation in the reversed magnetic shear (RMS) configuration with different separations Ar_s between two rational surfaces is numerically studied by means of reduced magnetohydrodynamic (MHD) simulations. It is found that the differential rotation with a strong shear at the outer resonant surface can effectively suppress the explosive burst of double tearing modes (DTMs)/NTMs. Critical values of the strength of rotation to suppress the burst are also presented for different bootstrap current fractions f_b. Furthermore, a couple of measurable parameters (δ, k), corresponding respectively to the triangularity and elongation of the magnetic islands at the outer resonant surface, are introduced to characterize the deformation of islands in the nonlinear phase. It is found that the triangularity 6 is more likely to precisely predict the onset of burst than the island width w and elongation k. For a given Ar_s, the critical value of triangularity δ_crit is obtained by scanning different plasma parameters. Establishing such a database of (6, k) is helpful to effectively control the development of NTMs in the RMS experimental discharges.