Influence of shear flows on dynamic evolutions of double tearing modes

In this paper, we investigate the influences of shear flows on dynamic evolutions of them/n= 2/1 double tearing mode (DTM), using three-dimensional, toroidal, and nonlinear resistive magnetohydrodynamic code CLT. It is found that weak shear flows can lead to the decoupling of tearing modes on the two resonant surfaces, reducing the linear growth rate of DTMs. When the two tearing modes grow to large amplitudes at the nonlinear stage, they start to lock with each other. Consequently, DTMs with weak shear flows exhibit almost the same behavior as those without shear flows, i.e. weak shear flow can significantly reduce the linear growth rate of the DTM and delay a pressure crash, but has almost no influence on the time and the amplitude of the pressure crash. It is also found that the linear growth rates of the modes can become even larger than those without shear flows when the shear flow exceeds a critical value, due to Kelvin-Helmholtz (KH)-like instability. This KH-like instability can broaden the spectrum of the modes and then form a broad region with stochastic magnetic fields. Therefore, strong shear flows might be even more destructive in relation to plasma confinement.