Study of geodesic acoustic and Alfvгén modes in toroidal fusion devices (brief review)

Geodesic acoustic modes, Alfvén eigenmodes, stationary and oscillating components of the electric field, and their relations to plasma confinement have been studied. Theoretical concepts of the interaction of geodesic acoustic modes with other types of plasma turbulence have been tested. Concomitant problems such as the effect of heating methods on the plasma confinement and turbulence, as well as the properties of impurities and scrape-off layer have also been discussed. Key diagnostics such as heavy ion beam probe, correlation reflectometry, and multipurpose optical diagnostic complex have been described. The main experiments have been performed at the T-10 tokamak, which has a high-power electron cyclotron resonance heating system. The supporting experiments have been performed at the TJ-II stellarator in Spain, the COMPASS tokamak in Czech Republic, and the STOR-M tokamak in Canada. The results of the experiments have been compared with the analytical and numerical calculations.