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Conference Paper

Peculiarities of destabilization of Alfvén modes by energetic ions in stellarators

MPS-Authors
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Weller,  A.
Stellarator Scenario Development (E5), Max Planck Institute for Plasma Physics, Max Planck Society;

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Werner,  A.
W7-X: Physics (PH), Max Planck Institute for Plasma Physics, Max Planck Society;

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Wobig,  H.
Stellarator Theory (ST), Max Planck Institute for Plasma Physics, Max Planck Society;

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Citation

Lutsenko, V. V., Kolesnichenko, Y. I., Yakovenko, Y. V., Fesenyuk, O. P., Weller, A., Werner, A., et al. (2003). Peculiarities of destabilization of Alfvén modes by energetic ions in stellarators. In Fusion Energy 2002. Vienna: International Atomic Energy Agency.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0027-3C23-1
Abstract
A theory of Alfvén instabilities caused by the energetic ions in helical devices is developed, and specific examples relevant to Wendelstein-line stellarators (W7-AS, W7-X, a Helias reactor) are considered. In particular, it is shown that in stellarators there exist specific "non-axisymmetric" resonances, which may strongly affect the instabilities, especially, in W7-X and the Helias reactor, which are characterized by the rotational transform about unity. These resonances are associated with non-axisymmetric components of the magnetic field strength. Destabilization of Alfvén eigenmodes located in specific gaps of helical devices is studied. The effect of plasma rotation on these instabilities is analysed. The Doppler shift of the eigenmodes characterized by several coupled wave numbers is calculated. Instabilities of Energetic Particle Modes (EPM) are discussed. It is shown that the presence of "non-axisymmetric" resonances and additional gaps in the Alfvén continuum of stellarators result in a number of new characteristic frequencies of the EPM modes. An explanation of the temporal evolution of MHD (Alfvénic) activity observed in neutral beam experiments on W7-AS is suggested.