Geodesic acoustic modes (GAMs) are studied as plasma eigenmodes when an electrostatic potential nearly constant around a magnetic surface is applied to collisionless toroidal plasmas. Besides the standard GAM, a branch of low frequency mode and an infinite series of ion sound wavelike modes are identified. Eigenfrequencies of these modes are obtained analytically and numerically from a linear gyrokinetic model. The finite gyroradius effect is found to enhance the collisionless damping of the standard GAM, while this enhancement is not monotonic as the safety factor varies. Moreover, additional damping due to higher-harmonic resonances becomes important when the safety factor increases. The mode structure of the GAM is also discussed.
We report a series of eigenmodes of the geodesic acoustic mode (GAM), which includes the standard GAM, a branch of low-frequency mode, and a series of ion sound wave-like modes. The case of Ti≫Te is investigated, and eigenfrequencies of these modes are obtained analytically from a linear gyrokinetic model in collisionless plasmas with a rigid constant electrostatic potential around a magnetic surface.
When the Mach number&f, of the poloidal rotation in a tokamak approaches unity, the poloidal variations of plasma density and potential appear to have the characteristics of a shock whose front lies on a plane (ribbon) of a fixed poloidal angle qO. The shock first appears, when 1 -MP 5 $E (E is the inverse aspect ratio), on the inside of the torus at a shock angle q&r if the plasma rotates counterclockwise poloidally, As MP increases, 71~ moves in the direction of the poloidal rotation. At MP = 1, Q = 2~. When MP -1~3 &, the shock angle is at v,, 5: V. The parallel viscosity associated with the shock is collisionality independent, in contrast to the conventional neoclassical viscosity. The viscosity reaches its maximum at M, = 1, which is the barrier that must be overcome to have a poloidal supersonic flow. Strong up-down asymmetric components of poioidal variations of plasma density and potential develop at MP or. 1. In the edge region, the convective poloidal momentum transport weakens the parallel viscosity and facilitates the L-H transition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.