The effects of a non-axisymmetric (3D) equilibrium magnetic field on the linear ion-temperature-gradient (ITG) driven mode are investigated. We consider the strongly driven, toroidal branch of the instability in a global (on the magnetic surface) setting. Previous studies have focused on particular features of non-axisymmetric systems, such as strong local shear or magnetic ripple, that introduce inhomogeneity in the coordinate along the magnetic field. In contrast, here we include non-axisymmetry explicitly via the dependence of the magnetic drift on the field line label α, i.e., across the magnetic field, but within the magnetic flux surface. We consider the limit where this variation occurs on a scale much larger than that of the ITG mode, and also the case where these scales are similar. Close to axisymmetry, we find that an averaging effect of the magnetic drift on the flux surface causes global (on the surface) stabilization, as compared to the most unstable local mode. In the absence of scale separation, we find destabilization is also possible, but only if a particular resonance occurs between the magnetic drift and the mode, and finite Larmor radius effects are neglected. We discuss the relative importance of surface global effects and known radially global effects.
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August 2016
Research Article|
August 22 2016
Geometric stabilization of the electrostatic ion-temperature-gradient driven instability. I. Nearly axisymmetric systems
A. Zocco;
A. Zocco
Max-Planck-Institut für Plasmaphysik
, D-17491, Greifswald, Germany
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G. G. Plunk;
G. G. Plunk
Max-Planck-Institut für Plasmaphysik
, D-17491, Greifswald, Germany
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P. Xanthopoulos;
P. Xanthopoulos
Max-Planck-Institut für Plasmaphysik
, D-17491, Greifswald, Germany
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P. Helander
P. Helander
Max-Planck-Institut für Plasmaphysik
, D-17491, Greifswald, Germany
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Phys. Plasmas 23, 082516 (2016)
Article history
Received:
June 16 2016
Accepted:
August 01 2016
Citation
A. Zocco, G. G. Plunk, P. Xanthopoulos, P. Helander; Geometric stabilization of the electrostatic ion-temperature-gradient driven instability. I. Nearly axisymmetric systems. Phys. Plasmas 1 August 2016; 23 (8): 082516. https://doi.org/10.1063/1.4960993
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