Mode coupling in a toroidal sharp-boundary plasma

Mode coupling in the discrete shear-Alfven spectrum of ideal magnetohydrodynamics can be caused either by toroidicity or by noncircularity of the plasma cross-section. The resulting localization of the eigenfunction leads to the formation of gaps in the frequency spectrum. This phenomenon is studied in the strong-coupling regime for both Tokamaks and screw-pinches, and the implications for plasma stability and Alfven wave heating experiments are discussed. (author)