Significant features of low frequency zonal flow and geodesic acoustic mode in the edge plasma of HL-2A tokamak

A three dimensional Langmiur probe array set have completely proven the significant features of low frequency zonal flow (LFZF) and geodesic acoustic mode (GAM) in the HL-2A tokamak plasma by verifying the spatial characteristics and the nonlinear coupling with ambient turbulence. Besides, the radial wave number demonstrated clearly linear dispersion relation for the LFZFs and GAMs, consistently with the theoretical prediction. The spatio-temproal structures of zonal flow effect on ambient turbulence were identified that are similar to those observed in LFZFs and GAMs. The findings provide concrete evidence that the turbulence envelope modulation should be induced by the zonal flows, and strengthen the feasibility of the indirect method to detect the zonal flows through the density fluctuation envelopes that could be measured with various diagnostics. (author)