Toroidal component of velocity for geodesic acoustic modes in the edge plasmas of the J-TEXT tokamak

Abstract

The toroidal component of the velocity for geodesic acoustic modes (GAMs) is first demonstrated. Multiple Langmuir probe arrays set up near the top tokamak of the J-TEXT were utilized for this study. A significant peak at the GAM frequency is observed in Mach number fluctuations. The toroidal velocity for the GAMs is estimated as ∼10–100 m s−1 and increases with the poloidal velocity. The ratio of toroidal component to the poloidal one of the velocity is mainly located in the interval between 0.3 and 1.0. With higher safety factors q, the ratio almost does not change with decreasing the safety factor, whereas it goes up sharply at low q. The coherencies between poloidal electric fields and Mach number fluctuations in turbulence frequency bands are also evaluated, and are higher than those between radial electric fields and Mach number fluctuations.