MHD modes influenced by axial plasma current

Abstract

Summary form only given, as follows. Low frequency MHD modes in a cylindrical plasma surrounded by a vacuum layer are influenced by axial current and, in addition to MHD surface waves propagating on the interface between the plasma and the vacuum layer, unstable kink modes and global Alfven eigenmodes, which may be called discrete Alfven wave or ion-cyclotron wave, are introduced by the axial plasma current. In order to investigate the relation of these MHD modes with the spatial distribution of the axial plasma current, wave equations are derived from the MHD equations with momentum exchange between ions and neutrals and finite ion cyclotron frequency effects. The wave equations clearly show how the axial current changes the cutoffs of the radial wavenumber of shear Alfven wave and compressional Alfven wave and the Alfven resonance. The main findings of the numerical integration of the wave equations are as follows (1) the unstable kink modes and low frequency MHD surface waves are influenced by the total value of the axial current and the helical structure of the magnetic field on the plasma-vacuum interface, (2) the dispersion relations of global Alfven eigenmodes depend on the current density around the central region of the plasma, (3) propagating shear Alfven wave appears for a sufficient value of the axial current density.