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  4. Global structure and magnetic components of geodesic acoustic modes in shaped tokamak plasmas
 
conference paper

Global structure and magnetic components of geodesic acoustic modes in shaped tokamak plasmas

Wahlberg, C
•
Graves, J P
2014
Proceeding 41st EPS Conference on Plasma Physics
41st European Physical Society Conference on Plasma Physics

Winsor et al. [1] first derived the geodesic acoustic mode (GAM) to be an elec-trostatic perturbation, localized within a narrow radial region of the plasma. There is, however, recent experimental evidence that the GAM also has a magnetic component with poloidal mode number 𝑚 = 2, existing outside the GAM surface, and even outside the plasma. Such a signal in 𝛿𝐵𝜃, with angular dependence sin2𝜃, has been detected in JT-60U [2] and in TCV [3] (possibly in other machines too), and was predicted theoretically in [4] in a study of the global structure of the corresponding eigenmode within ideal MHD. The ideal MHD model is unable to resolve the detailed fine structure of the GAM, but unlike standard kinetic treatments, it does naturally include the combination of the effects of compressibility, full electromagnetic effects, and mode coupling due to toroidal or shaping geometry effects, which are required to show that the mode has a global structure [5], including a surrounding magnetic halo existing also outside the plasma. While the theory in [4] was developed for toroidally rotating plasmas with circular cross section, the present work extends the analysis in those papers to (static) plasmas with a non-circular cross section. Such an extension of the analysis shows that i) the major effect of plasma shaping on the GAM frequency within the ideal MHD model is a decreasing GAM frequency with elongation, and ii) a non-circular plasma cross section, as well as a finite aspect ratio, induces other Fourier components than 𝑚=2 in the magnetic halo surrounding the GAM surface.

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Type
conference paper
Author(s)
Wahlberg, C
Graves, J P
Date Issued

2014

Published in
Proceeding 41st EPS Conference on Plasma Physics
Start page

P2.047

URL

URL

http://eps2014-berlin.de/

URL

https://crpplocal.epfl.ch/pinboard/papers/144811301.pdf
Editorial or Peer reviewed

NON-REVIEWED

Written at

EPFL

EPFL units
CRPP  
SPC  
Event nameEvent placeEvent date
41st European Physical Society Conference on Plasma Physics

Berlin

23-27 June 2014

Available on Infoscience
March 20, 2015
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/112649
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