Rotation effect on geodesic and zonal flow modes in tokamak plasmas with isothermal magnetic surfaces

Abstract

The electrostatic geodesic mode oscillations are investigated in rotating large aspect ratio tokamak plasmas with circular isothermal magnetic surfaces. The analysis is carried out within the magnetohydrodynamic model including heat flux to compensate for the non-adiabatic pressure distribution along the magnetic surfaces in plasmas with poloidal rotation. Instead of two standard geodesic modes, three geodesic continua are found. The two higher branches of the geodesic modes have a small frequency up-shift from ordinary geodesic acoustic and sonic modes due to rotation. The lower geodesic continuum is a new zonal flow mode (geodesic Doppler mode) in plasmas with mainly poloidal rotation. Limits to standard geodesic modes are found. Bifurcation of Alfvén continuum by geodesic modes at the rational surfaces is also discussed. Due to that, the frequency of combined geodesic continuum extends from the poloidal rotation frequency to the ion-sound band that can have an important role in suppressing plasma turbulence.

Geodesic acoustic modes in tokamak plasmas with a radial equilibrium electric field

“…It is the counterpart of GAM research starting from the fluid model in the case of predominantly poloidal flow. 13,14 The frequencies of both the standard GAMs and the sound wave (SW) increase with respect to the strength of radial electric field but not as strongly as predicted using fluid models. The mode damping rates increase significantly as the electric field increases.…”

“…Moreover, there are different closure choices that may lead to different results using fluid models. 9,13,14 To give a complete description of plasma modes, one has to adopt kinetic equations. This is the motivation of our present research.…”

Geodesic acoustic modes in tokamak plasmas with anisotropic distribution and a radial equilibrium electric field

“…Usually in tokamak plasmas, there is a radial equilibrium electric field, especially near the edge of plasmas. As a consequence, sometimes an equilibrium poloidal mass flow may appear [24,25]. Some investigations have addressed the effect of plasma poloidal flows or radial equilibrium electric fields on the characteristics of GAMs.…”

Drift effects on electromagnetic geodesic acoustic modes

“…Ion heat flux was included in the investigation of equilibrium rotation (poloidal and toroidal) effects on GAMs and ZF and, in the leading order, it has been found that the GAM frequency remains unchanged 44,45 . In the ZF dynamics, however, heat flux must be included, at least for equilibrium with poloidal rotation and isotherm magnetic surfaces 45 .…”