The separate structure of two branches of the sheared slab imode near the minimum-qmagnetic surface is analysed and the effects of plasma rotation shears are considered in the weak magnetic shear region. Results show that the separation condition depends on the non-monotonous qprofile and the deviation of rational surface from the minimum-qsurface. Furthermore, it is found that the diamagnetic rotation shear may suppress the perturbation of the sheared slab imode at one side of the minimum-qsurface, the poloidal rotation shear from the sheared × flow has a similar role to the slab mode structure when it possesses a direction same as the diamagnetic shear. A plausible interrelation between the separate structures of the two branches of the sheared slab mode and the discontinuity or gap of the radially global structure of the drift wave near the minimum-qsurface observed in the toroidal particle simulation (Kishimoto Y et al1998 Plasma Phys. Control. Fusion40A663) is discussed. It seems to support such a viewpoint: the double or/and global branches of the sheared slab imode near the minimum-qsurface may become a bridge to connect the radially global structures of the drift wave at two sides of the minimum-qsurface and the discontinuity may originate from the separate structures of these slab modes for a flatter qprofile.
The performance of equilibrium radial electric field shear on microturbulence with different magnetic shears in tokamak plasmas