Modulation behaviour and possible existence criterion of geodesic acoustic modes in tokamak devices

Abstract Geodesic acoustic modes (GAMs) represent the oscillating counterpart of zonal flow in tokamak plasma and can affect transport due to their interaction with turbulence eddies. GAMs have been observed many experiments modelled under different conditions, but because variety characteristics, we do not yet a complete picture dynamics. It has demonstrated that optical methods be efficiently used describe predict several characteristics GAM radial structures interpreted as ‘waves’ propagating space-time. We exploit complex eikonal theories investigate behavior are commonly experiments, find periodic modulation intermittency explained by properties equilibrium temperature profile. Theoretical results obtained this work supported gyrokinetic simulations for equilibria. Implications existence criteria dynamics conditions discussed, particular attention edge low high confinement modes.