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The low shear in W7-AS magnetic configurations leads to global Alfvén eigenmodes (GAE) of both helicities. Thus, low frequency GAEs with the same helicity as toroidal Alfvén eigenmodes (TAE) and elliptical Alfvén eigenmodes (EAE) in tokamaks exist in W7-AS; GAEs that are usually forbidden in tokamaks. Observations of diagnostic signals reveal a rich spectrum of neutral beam injection (NBI) driven GAEs in W7-AS in the frequency range: f(GAE) greater than or equal to 0 kHz and less than or equal to 500 kHz. These GAEs are excited via sideband resonances with NBI ions at low plasma densities and via fundamental resonances at higher plasma densities. A transition in the mode of excitement occurs when the increasing plasma density brings the central local Alfvén velocity down below the maximum tangential injection velocity of the NBI ions.

Additional information

Authors: TEO C-Y, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);WELLER A, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);KONRAD C, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Article: Nuclear Fusion, Vol. 38 (1998) No. 3, pp. 409-417
Record Number: 199810714 / Last updated on: 1998-06-08
Original language: en
Available languages: en
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