The interchange and geodesic acoustic type modes in two-fluid theory

Interchange and geodesic acoustic type modes are considered within the unified approach of two-fluid theory. It is assumed that electrons are in the adiabatic, $\omega <>k_\parallel v_{Ti} $. Appropriate moment equations are used for both components taking into account the the magnetic field curvature, which is modeled by the addition of the constant gravity forces, as well as electromagnetic effects. Both electron and ion drift effects are taken into account including the finite Larmor radius (FLR) effects for ions due to gyroviscosity. Within this approach , ion temperature gradient, interchange, and geodesic acoustic modes are recovered. It is shown that geodesic acoustic modes are intrinsically related to interchange modes. Both types of modes occur as a result of the essential balance between the radial diamagnetic and inertial (polarization) currents. It is shown that coupling of drift and geodesic curvature effects leads to the destabilization of geodesic acoustic modes.