Study of interactions between GAMs and broadband turbulence in the T-10 tokamak

New findings in study of geodesic acoustic modes (GAMs) on the T-10 tokamak since the last IAEA FEC 2014 are described. The broadband fluctuations of potential and electron density ne in Ohmic and ECRH regimes are analyzed with Heavy Ion Beam Probing along with fluctuations of poloidal magnetic field Bpol. At the edge, at ρ > 0.8, the dominated GAM peak with frequency 17 kHz in potential fluctuations, and noticeable peak of quasi-coherent density and potential fluctuations with frequency 40-100 kHz and HFHM ~30 kHz are observed. During ECRH of high density n¯e ~ 4 × 1019 m−3 plasmas, the level of broadband fluctuations decreases, but the energy confinement degrades and the GAM amplitude on rises. The bi-spectral analysis of and ne fluctuations demonstrates the existence of statistically significant auto- and cross-bicoherence at the GAM frequency that points out to three-wave interaction between GAM and broadband electrostatic turbulence, while the cross-bicoherence for , ne and Bpol indicates three-wave interaction between GAM and broadband electromagnetic turbulence. These three-wave interactions may be explained by quadratic character of nonlinear GAM generation, e.g. owing to Reynolds stress.