Geodesic Acoustic Mode

The Geodesic Acoustic Mode (GAM) is a plasma oscillation occurring in toroidal confinement devices with the following properties:

• Radially localized
• Axisymmetric (n=0)
• Poloidally symmetric potential (m=0) and asymmetric density (m=1) perturbations

The GAM frequency is, approximately:

$f_{GAM}\sim (1+1/2q^2)\frac{\sqrt{(T_e+T_i)/M_i}}{2\pi R}$