Fluctuations in the JET boundary plasma (from the scrape-off layer up to 1.5 cm inside the last closed flux surface) have been investigated using a multi-pin reciprocating Langmuir probe system. Coherent electrostatic fluctuations consistent with the geodesic acoustic mode (GAM) are observed in the edge plasma. The GAM properties and structure have been investigated and experimental evidence is presented suggesting an interaction between GAMs and the ambient turbulence.
Observation of geodesic acoustic modes (GAMs) and their radial propagation at the edge of the TEXTOR tokamak