Propagation and stochastic dynamics of ion-temperature-gradient driven fluctuations

The drift dynamics of ion-temperature-gradient (ITG) driven fluctuations in the plane perpendicular to a guiding magnetic field is investigated by mapping its governing equation into a Schrödinger-type equation. First, we separate the parallel dynamics and the perpendicular dynamics. The parallel dynamics can coherently couple with the perpendicular dynamics, leading to the growth of a coherent, localized ITG eigenmode. The E × B flow plays a dominant role for the fluctuation propagation dynamics and impact on the radial redistribution of fluctuations. Another attractive finding is that the ITG wave packet can penetrate a strong yet narrow E × B shear layer through “tunneling.” When the parallel dynamics becomes stochastic, non-eigenmode peaks can emerge in the fluctuation power spectrum and an estimate of the saturated spectrum intensity of the ITG fluctuations can be obtained.