Alfven eigenmodes and their destabilization by energetic circulating ions in Wendelstein-line stellarators

Instabilities of the Alfven eigenmodes (AEs) that can be driven by circulating energetic ions in optimized stellarators of the Wendelstein line (Helias configurations) are considered. It is stressed that the Alfven instabilities in stellarators may considerably differ from those in tokamaks because specific Alfven eigenmodes and specific resonances of the wave-particle interaction appear when magnetic configurations are non- axisymmetric. An important role of the continuum damping in low-shear stellarators is revealed. Aimed to calculate the continuum damping, a set of resistive magnetohydrodynamic (MHD) equations, which generalize the ideal MHD AE equations obtained in Kolesnichenko et al (Kolesnichenko Ya.I. et al 2001 Phys. Plasmas 8 491), is derived. The derived equations are solved numerically to investigate the damping of the AEs of global character in a Helias reactor