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Title: Investigating the radial structure of axisymmetric fluctuations in the TCV tokamak with local and global gyrokinetic GENE simulations

Axisymmetric (n=0) density fluctuations measured in the TCV tokamak are observed to possess a frequency f<sub>0</sub> which is either varying (radially dispersive oscillations) or a constant over a large fraction of the plasma minor radius (radially global oscillations) as reported in a companion paper [Z. Huang <i>et al.</i>, this issue]. Given that f<sub>0</sub> scales with the sound speed and given the poloidal structure of density fluctuations, these oscillations were interpreted as Geodesic Acoustic Modes, even though f<sub>0</sub> is in fact smaller than the local linear GAM frequency f<sub>GAM</sub> . In this work we employ the Eulerian gyrokinetic code GENE to simulate TCV relevant conditions and investigate the nature properties of these oscillations, in particular their relation to the safety factor profile. Local and global simulations are carried out and a good qualitative agreement is observed between experiments and simulations. By varying also the plasma temperature and density profiles, we conclude that a variation of the edge safety factor alone is not sufficient to induce a transition from global to radially inhomogeneous oscillations, as was initially suggested by experimental results. This transition appears instead to be the combined result of variations in the different plasma profiles, collisionality and finite machine sizemore » effects. In conclusion, simulations also show that radially global GAM-like oscillations can be observed in all fluxes and fluctuation fields, suggesting that they are the result of a complex nonlinear process involving also finite toroidal mode numbers and not just linear global GAM eigenmodes.« less
ORCiD logo [1] ;  [2] ; ORCiD logo [2] ;  [2] ;  [3] ;  [2] ;  [1] ;  [4] ;  [2] ;  [5] ;  [2] ;  [3]
  1. Univ. of California, Los Angeles, CA (United States)
  2. Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne (Switzerland)
  3. Max-Planck Institut fur Plasmaphysik, Garching (Germany)
  4. Princeton Univ., Princeton, NJ (United States)
  5. Univ. of California, Los Angeles, CA (United States); Max-Planck Institut fur Plasmaphysik, Garching (Germany)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Plasma Physics and Controlled Fusion
Additional Journal Information:
Journal Volume: 60; Journal Issue: 3; Journal ID: ISSN 0741-3335
IOP Science
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org:
Country of Publication:
United States
OSTI Identifier: