Geodesic acoustic modes in the tokamaks

Geodesic Acoustic Modes (GAMs) are important for understanding transport in plasma and hence for thermonuclear fusion development. GAMs are investigated worldwide on the bunch of devices, such as ASDEX-U, TCV, HL-2A, DIII-D etc.
This work represents a short review of experimental results obtained on different devices with several diagnostics. These results are compared with results obtained on T-10 tokamak with Heavy Ion Beam Probe (HIBP).
Many characteristic GAM features studied on different devices complement and confirm each other reciprocally. There are controversial results about GAM radial structure. This may point to different nature of GAM at various conditions (global and nonglobal one).