Stability of ion-temperature-gradient-driven modes in the presence of sheared poloidal flows

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Abstract
The linear theory of the sonic ion-temperature-gradient-driven mode in the presence of sheared poloidal rotation is discussed in the context of a hydrodynamic model. Analytical and numerical calculations show that the growth rate increases for weak shear, but then decreases when the shearing frequency exceeds the mode frequency. This trend is a consequence of the coupling of radial eigenmodes induced by the asymmetric effective potential and the absorption and damping due to resonance between the wave frequency and shearing frequency. The former dominates at weak shear, resulting in destabilization, while the latter dominates for strong shear, resulting in stabilization. Mixing length estimates of the turbulent diffusivity are given, and a novel bifurcation scenario for the L→H transition is discussed.