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Axisymmetric global Alfven eigenmodes within the ellipticity-induced frequency gap in the Joint European Torus
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
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Number of Authors: 12262017 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 12, article id 122505Article in journal (Refereed) Published
Abstract [en]

Alfven eigenmodes (AEs) with toroidal mode number n = 0 (i.e., axisymmetric) have been observed in the ellipticity-induced frequency range in the Joint European Torus. The axisymmetric modes are of interest because they can be used to diagnose fast particle energy distributions at the mode location. The modes were identified as global Alfven eigenmodes (GAEs), with the ellipticity of the plasma cross-section preventing strong continuum damping of the modes. The MHD codes CSCAS, MISHKA, and AEGIS were used to compute the n = 0 Alfven continuum, eigenmode structure, and continuum damping. For zero ellipticity, a single mode exists at a frequency below the Alfven continuum branch. This mode has two dominant poloidal harmonics with poloidal mode numbers m = +/- 1 that have the same polarity; therefore, it is an even mode. For finite ellipticity, the continuum branch splits into two branches and the single GAE splits into two modes. An even mode exists below the minimum of the top continuum branch, and the frequency of this mode coincides with the experimentally observed AE frequency. The other mode is found below the lower continuum branch with opposite signs between the two poloidal harmonics (an odd mode structure). This mode was not excited in our experiment. Analytical theory for the n = 0 GAE in an elliptical cylinder shows the n = 0 Alfven continuum agrees with the numerical modelling.

Place, publisher, year, edition, pages
AMER INST PHYSICS , 2017. Vol. 24, no 12, article id 122505
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Fusion, Plasma and Space Physics
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URN: urn:nbn:se:uu:diva-398873DOI: 10.1063/1.5005939ISI: 000418957200039OAI: oai:DiVA.org:uu-398873DiVA, id: diva2:1378731
Note

For complete list of authors see http://dx.doi.org/10.1063/1.5005939

Available from: 2019-12-13 Created: 2019-12-13 Last updated: 2019-12-13Bibliographically approved

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Andersson Sundén, ErikBinda, FedericoCecconello, MarcoConroy, SeanDzysiuk, NataliiaEricsson, GöranEriksson, JacobHellesen, CarlHjalmarsson, AndersPossnert, GöranSjöstrand, HenrikSkiba, MateuszWeiszflog, Matthias

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Andersson Sundén, ErikBinda, FedericoCecconello, MarcoConroy, SeanDzysiuk, NataliiaEricsson, GöranEriksson, JacobHellesen, CarlHjalmarsson, AndersPossnert, GöranSjöstrand, HenrikSkiba, MateuszWeiszflog, Matthias
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Applied Nuclear Physics
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Physics of Plasmas
Fusion, Plasma and Space Physics

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