THEORY OF ENHANCED REVERSED SHEAR MODE IN TOKAMAKS

It is shown that toroidal-magnetic-field ripple-induced particle flux can drive poloidal E x B speed to bifurcate over the local maximum of the nonlinear poloidal (or parallel) viscosity. Here, E is the electri c field, and B is the magnetic field. This mechanism, together with th e turbulence suppression due to the radial gradient of the E x B and d iamagnetic angular velocity, is employed to explain the enhanced rever sed shear mode observed in the core region of tokamaks.