Geodesic mode instability driven by the electron current in tokamak plasmas

• Effect of the electron current and diamagnetic drift on geodesic modes is analyzed.
• The effect is treated by kinetic theory using shifted Maxwell electron distribution.
• Found instability occurs due to cross term of the electron current with the ion drift.
• The threshold electron velocity have to be larger the parallel GAM phase velocity.

Effect of the parallel electron current on Geodesic Acoustic Modes (GAM) in a tokamak is analyzed by kinetic theory taking into the account the ion Landau damping and diamagnetic drifts. It is shown that the electron current modeled by shifted Maxwell distribution may overcome the phase velocity threshold and ion Landau damping thus resulting in the GAM instability when the parallel electron current velocity is larger than the effective parallel GAM phase velocity Rqω. The instability occurs due to its cross term of the current with the ion diamagnetic drift. Possible applications to tokamak experiments are discussed.