Drift effects on geodesic acoustic modes

We present a fluid model for geodesic acoustic modes including diamagnetic effects due to inhomogeneous plasma density and temperature. Effects of ion parallel viscosity (pressure anisotropy), which allows to recover exactly the adiabatic index obtained in kinetic theory are considered. We show that diamagnetic effects lead to the positive up-shift of the GAM frequency and appearance of the second (lower frequency) branch related to the drift frequency. The latter is a result of modification of the degenerate (zero frequency) zonal flow branch which acquires a finite frequency or becomes unstable in regions of high temperature gradients.

► We present a comprehensive two fluid model to investigate diamagnetic effects on geodesic acoustic modes. ► An instability due to temperature gradients was found in regions with high safety factor regions. ► When diamagnetic effects is considered the frequencies is non-degenerated and, consequently, an extra solution is found. ► We compare the effects of density and temperature gradients with equilibrium rotation.