Nonlinear Excitation of Plasma Convection

Parametric excitations of electrostatic convective cells by drift waves as well as magnetostatic cells by Alfvén waves are considered. The growth rates are calculated for various limits of interest to plasma diffusion studies; our results agree with computer simulations. The problem of crossfield diffusion is also discussed. Finally, the coupling of magnetostatic modes with electrostatic modes is investigated and a variational principle for coalescence of magnetic islands is formulated.