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This work investigates circulating-particle-induced Alfven instabilities in optimized stellarators of the Wendelstein line [F. Wagner, Trans. Fusion Tech. 33, 67 (1998)]. A general expression for the growth rate of the instabilities is obtained and analyzed. It is shown that the absence of the axial symmetry makes it possible that various types of Alfven eigenmodes will be destabilized; both the kind of destabilized Alfven eigenmodes and the type of the resonances driving the instability may differ from those in tokamaks. In particular, an important role of the helicity-induced resonance is predicted. The discovered new resonances may considerably increase the instability growth rate of both the "gap" modes and the eigenmodes residing below cylindrical Alfven continuum. The upper limits of the local energy losses of circulating alpha-particles caused by various Alfven instabilities in a four-period Helias reactor [C. D. Beidler , in Fusion Energy 2000, 18th International Atomic Energy Agency Conference Proceedings, Sorrento, 2000 (International Atomic Energy Agency, Vienna, 2001), Report IAEA-CN-77/FT/4] are evaluated. It is found that certain destabilized Alfven eigenmodes will affect only alphas with the energy well below 3.5 MeV, which seems to open a possibility to remove the helium ash by exciting the corresponding Alfven eigenmodes by either energetic particles or an antenna system. (C) 2002 American Institute of Physics.
