Abstract
The Heavy ion beam probe (HIBP) is a powerful tool to investigate the potential and density fluctuation of high temperature plasmas. The observations using HIBPs have contributed substentially to the recent rapid progress in the study of zonal flow. In this article, the characteristic of the Geodesic Acoustic Mode (GAM), which is a type of the zonal flow, is introduced on the basis of experimental results using HIBPs. The observed frequency and space structure are quite similar to the theoretical predictions. The influence of the GAM flow on the back ground fluctuation, including the causality, is also observed.
