Shear Formation by a Poloidal Chain of Magnetic Islands

We estimate the electron angular velocity shear ∂rωθo, which can be formed by plasma heating near the low-order rational surface with a poloidal chain of magnetic islands. We suppose that the plasma is heated sufficiently that its electrons start to miss the magnetic islands during their radial collisional shift and movement along the toroidal surface. This provides an ion volume charge in some regions of magnetic islands, which leads to shear formation. The time taken for shear formation is short. The conditions for magnetic island width leading to the shear are derived. It is shown that even narrow magnetic islands can lead to the shear. The shear can damp instabilities with a growth rate smaller than the ion cyclotron frequency. The spatial structures of convective vortical cells are described. We derive inverse dependences of the radial width of excited vortices on ∂rωθo and radial gradient of plasma density ∂rn0e. Amplitude of electron radial oscillations is smaller for larger ∂rωθo and ∂rn0e. These dependences promote a steep radial distribution of the plasma density and internal transport barrier.