Properties of the geodesic acoustic mode (GAM) density fluctuations are studiedusing two toroidally separated Langmuir triple-probe arrays on the top of HT-7 tokamak. TheGAM scenario is identified in the potential fluctuations with the toroidally symmetric structure(n= 0) and satisfying the temperature scaling of GAM mode frequency. Some theoretical predictionsabout the mode features of GAM density fluctuations are verified in our experiments:the toroidal mode number of GAM density fluctuations is n=0; its amplitude is consistent withthe theoretical prediction in a factor of 2; the density and potential fluctuations of GAM is inanti-phase at the top of plasma cross-section. Strong nonlinear interactions are found betweenGAM density fluctuations and ambient turbulence (AT). The results support the conclusions thatthe envelope modulation of potential fluctuations is dominantly caused by the direct regulation ofGAM in the generation processing, and the envelope modulation of density fluctuation is due tothe GAM shear effect.
