Mechanisms of the energy transfer across the magnetic field by Alfvén waves in toroidal plasmas

Abstract

Physics of the transverse energy transfer by Alfvén waves in toroidal plasmas is elucidated. It is found that, in contrast to the classical Alfvén waves in infinite plasmas, the Alfvén waves in toroidal systems produce plasma compression due to coupling with fast magnetoacoustic waves, which provides the energy transfer. The radial group velocities of the traveling waves constituting the Global Alfvén Eigenmodes and Toroidicity-induced Alfvén Eigenmodes are calculated. It is shown that equations for Alfvén eigenmodes derived in the approximation of vanishing wave field along the equilibrium magnetic field reproduce the longitudinal magnetic field of the wave and lead to correct transverse energy flux. The obtained results explain how Alfvén eigenmodes can provide the spatial energy channeling—the transfer of the energy by these modes from the unstable plasma region to the region where the mode damping dominates.