Observation of geodesic acoustic mode in SINP-tokamak and its behaviour with varying edge safety factor

The spectral analysis of floating potential fluctuations measured in the edge plasma region (0.87  3). These coherent modes are simultaneously observed in density and radial electric field fluctuation spectra as well. These coherent modes are identified as geodesic acoustic modes (GAMs) having different characteristics over the entire qedge range. In discharges with qedge greater than 3, the local wave number spectra of the mode exhibit the properties of continuum GAM with the observed poloidal and toroidal mode numbers of m ∼ 0 and n ∼ 0, and the mode is radially localized. The observed frequency and its variation with t...