Gyrokinetic study of ion temperature gradient instability in vicinity of flux surfaces with reversed magnetic shear

Ion temperature gradient (ITG) driven instability is investigated in the vicinity of a flux surface where the magnetic shear reverses. The generic properties of the profile of the magnetic shear are taken into account with gyrokinetic stability theory in the local sheared slab geometry integral equation. The stability analysis shows that there are four distinct unstable ITG branches with significantly different eigenvalues and mode structures existing simultaneously in the vicinity of the minimum q layer. The variation of eigenmode structures with magnetic shear is investigated in detail. The mixing length estimation of the induced plasma transport is performed. Detailed numerical results are presented and general correlations with simulations and experiments are noted. (C) 2001 American Institute of Physics. [DOI: 10.1063/1.1326060].