Geodesic acoustic mode observations in the Globus-M spherical tokamak

The results of geodesic acoustic mode (GAM) studies in the spherical torus Globus-M via Doppler reflectometry are presented. The intermittent character of the GAM evolution is similar to the limit-cycle oscillation behavior of zonal flows. The evident correlation between the GAM rotational velocity and both Dα emission and plasma density oscillations is exhibited and discussed. The obtained experimental results are compared with those from tokamaks with large aspect ratios.