Kinetic-ballooning-mode theory in general geometry

A systematic procedure for studying the influence of kinetic effects on the stability of MHD ballooning modes is presented. The ballooning mode formalism, which is particularly effective for analysing high-mode-number perturbations of a plasma in toroidal systems, is used to solve the Vlasov-Maxwell equations for modes with perpendicular wavelengths on the scale of the ion gyroradius. The local stability on each flux surface is determined by the solution of three coupled integro-differential equations which include effects due to finite gyroradius, trapped particles, and wave-particle resonances. More tractable forms of these equations are then obtained in the low (ω < ωbi, ωti) and intermediate- (ωbi, ωti < ω < ωbe, ωte) frequency regimes with ωbj and ωtj being the average bounce and transit frequencies of each species. After further simplifying approximations, the kinetic results here are shown to be reducible to the MHD-ballooning-mode equations in the analogous limits, ω ≶ ωs where ωs = cs/Lc, with cs being the acoustic speed and Lc the connection length.