  The energy input and frequency shift of geodesic acoustic modes (GAMs) due to
turbulence in tokamak edge plasmas are investigated in numerical two-fluid
turbulence studies. Surprisingly, the turbulent GAM dispersion relation is
qualitatively equivalent to the linear GAM dispersion but can have drastically
enhanced group velocities. In up-down asymmetric geometry the energy input due
to turbulent transport may favor the excitation of GAMs with one particular
sign of the radial phase velocity relative to the magnetic drifts and may lead
to pulsed GAM activity.

Plasma Physics