 |
 |
 |
Abstract. The theory of low frequency instabilities in axisymmetric toroidal plasmas is presented from the point of view of the two-fluids equations, assuming the standard drift wave ordering. Attention is focused on the limit in which neighboring rational surfaces are sufficiently far apart that mode overlapping is non-existent. Owing to field line bending, poloidal side-bands m±1,... coexist with the primary mode m, enhancing noticeably the role of the parallel ion dynamics. The electron and ion branches are investigated accurately under those conditions. It is found that the radial widths of the eigenmodes increase with respect to the slab values; the shear damping rate of the electron branch, respectively the growth rate of the ion branch increases correspondingly. Other interesting results are obtained concerning the frequency, the growth rate and the poloidal variation of the amplitude of the ion mode fluctuations. Those explain the origin of internal transport barriers; they also suggest ways of interpreting fluctuations asymmetries observed in tokamaks and (when collisions are included) the Radiative Improved confinement mode.
IAEA 2001
