Unstable spectra of double tearing modes with anti-symmetric shear flow

The linear properties of both even and odd double tearing modes (DTMs) in the presence of plasma shear flow are studied based on a reduced resistive MHD model in slab geometry. It is found that for the anti-symmetric shear flow, the linear growth rates γ ( k y ) of the even (odd) eigenmode of DTMs decrease (increase) with increasing the strength of shear flow. Indeed, in the small wavenumber k y regime, γ ( k y ) of the even eigenmode is larger than that of the odd eigenmode, while γ ( k y ) of two kinds of eigen states coalesce with each other (the same growth rate and opposite frequencies) when the wavenumber k y exceeds a critical value k y C. It is demonstrated that k y C decreases with decreasing η for a fixed separation between two resonant surfaces x s, while decreasing x s increases the critical value of k y C for a fixed shear velocity. In the nonlinear regime for a low value of resistivity, it is observed that by increasing the strength of anti-symmetric shear flow, in the early phase of the abrupt regime a monster plasmoid and subsidary small plasmoids are generated, and later they are ejected from the DTM current sheet and merged with the main DTM islands.