Theoretical Study On The Influence Of Tokamak Plasma Circumferential Rotation On Geodesic Acoustic Modes

Geodesic acoustic modes(GAMs) are toroidally symmetric and nearly poloidally symmetric electrostatic oscillation modes unique to the toroidal plasmas. GAMs have attracted much attention due to that it can scatter drift wave turbulence from long-wavelength unstable domain to short-wavelength stable domain through nonlinear interaction, and thus control and improve the plasma transport. On the other hand, Plasma equilibrium toroidal rotation naturally exists in tokamak plasmas. This paper focuses on the effects of toroidal rotation on the collisional and collisionless damping of the GAM in tokamak plasmas, the main results are as follows:The effects of toroidal rotation on the collisional damping of the GAM shown that the collisional viscous damping rate of the GAM has a tiny increase with the increasing toroidal rotation Mach number under the fluid approximation. In the gyrokinetic formula, it is found that the toroidal rotation could decrease the collisional damping of the GAM in the small safety factor regions and increase the collisional damping of the GAM in the large safety factor regions at low ion collision rate; while at high ion collision rate, the toroidal rotation will increase the collisional damping of the GAM with arbitrary safety factor, and the change quantity of collisional damping rate of the GAM due to the toroidal rotation at high collision rate is larger than that at low collision rate.The effects of toroidal rotation on the collisionless damping of the GAM shown that when only the ion is considered,the GAM frequency will increase with respect to the toroidal rotation Mach number, while the damping rates induced by the ion of the GAM will decreases rapidly with respect to the toroidal rotation Mach number. In addition, the low frequency modes and acoustic branch frequencies and damping rates will decrease with respect to the toroidal rotation Mach number, and the influence of the toroidal rotation on the low frequency modes frequencies and damping rates are very small and can be neglected. After considering the electron dynamics effect, it is found that the toroidal rotation will still increases the GAM frequencies, which is nearly the same as not consider the effect of electron dynamics. And for the collisionless damping of the GAM, it is found that the toroidal rotation can enhance the collisionless damping rate induced by the electron of the GAM significantly due to the increase of the number of resonant electrons. Therefore, when the safety factor is small, the toroidal rotation will decrease the collisionless damping of the GAM, and when the toroidal rotation Mach number is larger enough, the damping rate of the GAM will decrease very slowly and even begin to increase with the increasing toroidal Mach number. When the safety factor is large, the toroidal rotation will greatly increase the collisionless damping of the GAM, and the greater the safety factor or toroidal rotation Mach number is, the greater magnitude of the increase is.