Fesenyuk O. Alfven eigenmodes and the continuum of the magnetohydrodynamic waves in stellarators.

The spectrum of Alfven waves in stellarators is studied. Alfven modes of a new type, the Alfven eigenmodes induced by the mirror harmonics of the magnetic configuration, are discovered. The plasma pressure is shown to influence their properties considerably. Reduced linear equations of ideal magnetohydrodynamics are derived; these equations are intended, first of all, for studying Alfven eigenmodes in the stellarators with high aspect ratio. They take into account the effects of the plasma pressure and compressibility. The numerical code COBRAS, which calculates the MHD continuum, is developed. Using this code, the MHD continuum in a particular shot of the Wendelstein 7-AS stellarator was calculated. The compressibility effects are shown to be important in the low-frequency part of the MHD continuum. Equations for nonideal Alfven eigenmodes are obtained. They include effects of the finite Larmor radius of the bulk plasma ions and the finite parallel electric field, as well as dissipative mechanisms. Itis shown with the use of these equations that the kinetic Alfven eigenmodes induced by the mirror harmonics of the magnetic configuration do exist in stellarators of the Wendelstein line. The destabilization of these modes by alpha particles arising as a result of fusion reactions is studied.