Multi-diagnostic approach to geodesic acoustic mode study

Multi-diagnostic approach developed for the GAM research in the spherical tokamak Globus M is described. Doppler backscattering (DBS) method as the tool for the GAM study, together with the diagnostics of plasma density and magnetic field GAM oscillations, were simultaneously used in experiments. The version of the DBS diagnostics with two cut-offs positioned at different poloidal angles of the minor cross-section was employed in Globus-M. For the GAM plasma density oscillation study, the D-alpha emission was observed at different angles to restore the spatial mode structure of the GAM plasma density oscillations. At the same time, the array of Mirnov coils was used for the GAM-like magnetic oscillation study, and that made it possible to restore the magnetic field perturbation spatial structure. The coherent and cross-bicoherence analyzes were employed to identify the interaction between the GAM velocity oscillation and plasma turbulent fluctuations.