Nonlocal analysis of the excitation of the geodesic acoustic mode by drift waves

The geodesic acoustic modes (GAMs) are typically observed in the edge region of toroidal plasmas. Drift waves have been identified as a possible cause of excitation of GAMs by a resonant three wave parametric process. A nonlocal theory of excitation of these modes in inhomogeneous plasmas typical of the edge region of tokamaks is presented in this paper. The continuum GAM modes with coupling to the drift waves can create discrete ''global'' unstable eigenmodes localized in the edge 'pedestal' region of the plasma. Multiple resonantly driven unstable radial eigenmodes can coexist on the edge pedestal.