# Geodesic Acoustic Mode

The Geodesic Acoustic Mode (GAM) is a plasma oscillation occurring in toroidal confinement devices with the following properties: [1] [2] [3]

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

The GAM frequency is, approximately:[2]

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

## References

1. N. Winsor, J.L. Johnson and J.M. Dawson, Geodesic Acoustic Waves in Hydromagnetic Systems, Phys. Fluids 11 (1968) 2448
2. K.J. Zhao et al., Toroidal Symmetry of the Geodesic Acoustic Mode Zonal Flow in a Tokamak Plasma, Phys. Rev. Lett. 96 (2006) 255004
3. Z. Gao, Collisional damping of the geodesic acoustic mode, Phys. Plasmas 20 (2013) 032501