Geometrical and profile effects on toroidicity and ellipticity induced Alfvén eigenmodes
The wave structures, eigenfrequencies and damping rates of toroidicity and ellipticity induced Alfvén eigenmodes (TAE, EAE), of low toroidal mode numbers (n), are calculated in various axisymmetric ideal MHD equilibria with the global wave finite element code LION. The importance of safety factor (q) and density (p) profiles on continuum damping rates is analysed. For realistic profiles, several continuum gaps exist in the plasma discharge. Frequency misalignment of these gaps yields continuum damping rates gamma/omega of the order of a few percent. Finite beta(pol) lowers the TAE eigenfrequency. For beta values below the Troyon limit the TAE enters the continuum and can thus be stabilised. Finite elongation allows the EAE to exist but triangularity can have a stablising effect through coupling to the continuum. The localisation of TAE and EAE eigenfunctions is found to increase with the shear and with n. Therefore large shear, through enhanced Landau and collisional damping, is a stabilising factor for TAE and EAE modes.
Bibliographic Reference: Report: LRP 454/92 EN (1992)
Availability: Available from Confédération Suisse, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, 21 avenue des Bains, 1007 Lausanne (CH)
Record Number: 199210875 / Last updated on: 1994-12-02
Original language: en
Available languages: en