Two-fluid Analysis of the Geodesic Acoustic Mode in Tokamaks

In most analysis reported so far on the geodesic acoustic mode (GAM) in tokamaks, the current along the magnetic field has been assumed to vanish, J∥ = 0. The parallel electron current associated with low frequency modes in tokamaks is large even in electrostatic limit and tends to short-circuit the cross-field electric field. The collisionless electrostatic GAM as predicted in the original work (Winsor, et al.) does not exist. The GAM only modifies the Alfven frequency. The finding in this study suggests that electrostatic GAM should be confined at the edge where the electron collision frequency is high