Considerations of ion-temperature-gradient-driven turbulence

For more than a decade, Eulerian simulations of plasma turbulence have been using coordinate systems aligned to the background magnetic field in order to exploit the elongated structure of the turbulent eddies. Here, two possible setups of such field-aligned coordinate systems are studied with regard to their behavior under more extreme conditions such as tokamak edge or stellarator geometries, where large global and/or local shear are encountered. Turbulence codes employing a Fourier expansion are shown to yield correct solutions also for large shear values, given that the radial resolution chosen is large enough. Codes which compute the radial direction in real space, on the other hand, can benefit from the implementation of the shifted metric approach, which may save resolution in the case of large shear.

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“…Refs. [4][5][6][7]), which we will not repeat here. Instead we will give a description of some properties of these coordinate systems.…”

Section: Properties Of Field-aligned Coordinate Systemsmentioning

confidence: 99%

Applicability of different geometry approaches to simulations of turbulence in highly sheared magnetic fields

Told

Jenko

2010

Physics of Plasmas

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“…The second method by which the global drift-wave eigenmodes break into gyroscale vortices is through the nonlinear effect of secondary instabilities (Cowley et al, 1991). Now we consider the descriptions of the cylinderlike single helicity eigenmodes: in the absence of shear flow these modes lock together to form the global (mesoscale) toroidal eigenmodes.…”

Section: Drift-wave Eigenmodes In Toroidal Geometrymentioning

confidence: 99%

Drift waves and transport

1999

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Drift waves occur universally in magnetized plasmas producing the dominant mechanism for the transport of particles, energy and momentum across magnetic field lines. A wealth of information obtained from quasistationary laboratory experiments for plasma confinement is reviewed for drift waves driven unstable by density gradients, temperature gradients and trapped particle effects. The modern understanding of Bohm transport and the role of sheared flows and magnetic shear in reducing the transport to the gyro-Bohm rate are explained and illustrated with large scale computer simulations. The types of mixed wave and vortex turbulence spontaneously generated in nonuniform plasmas are derived with reduced magnetized fluid descriptions. The types of theoretical descriptions reviewed include weak turbulence theory, Kolmogorov anisotropic spectral indices, and the mixing length. A number of standard turbulent diffusivity formulas are given for the various space-time scales of the drift-wave turbulent mixing. [S0034-6861(99)00803-X] CONTENTS

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“…It is a well-established fact that the dominant transport channel of the main ion species in the core region of tokamak devices is ion-temperature-gradient driven (ITG) turbulence. 1,2 Collisions in connection with the toroidal geometry of the magnetic guide field, however, provide another relevant channel: neoclassical transport. 3,4 In contrast to turbulent mechanisms, it does not possess a critical threshold for the driving pressure gradient and also provides a minimal flux level in transport barriers where turbulence is suppressed.…”

Section: Introductionmentioning

confidence: 99%

Interaction between neoclassical effects and ion temperature gradient turbulence in gradient- and flux-driven gyrokinetic simulations

et al. 2016

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Neoclassical and turbulent transport in tokamaks have been studied extensively over the past decades, but their possible interaction remains largely an open question. The two are only truly independent if the length scales governing each of them are sufficiently separate, i.e. if the ratio ρ * between ion gyroradius and the pressure gradient scale length is small. This is not the case in particularly interesting regions such as transport barriers. Global simulations of collisional ion-temperature-gradient-driven microturbulence performed with the nonlinear global gyrokinetic code Gene are presented. In particular, comparisons are made between systems with and without neoclassical effects. In fixed-gradient simulations the modified radial electric field is shown to alter the zonal flow pattern such that a significant increase in turbulent transport is observed for ρ * 1/300. Furthermore, the dependency of the flux on the collisionality changes. In simulations with fixed power input we find that the presence of neoclassical effects decreases the frequency and amplitude of intermittent turbulent transport bursts (avalanches) and thus plays an important role for the self-organisation behaviour.

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Considerations of ion-temperature-gradient-driven turbulence

Cited by 157 publications

References 21 publications

Applicability of different geometry approaches to simulations of turbulence in highly sheared magnetic fields

Applicability of different geometry approaches to simulations of turbulence in highly sheared magnetic fields

Drift waves and transport

Interaction between neoclassical effects and ion temperature gradient turbulence in gradient- and flux-driven gyrokinetic simulations

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