Electromagnetic transport components and sheared flows in drift-Alfvén turbulence

Abstract

Results from three-dimensional numerical simulations of drift-Alfvén turbulence in a toroidal geometry with sheared magnetic field are presented. The simulations show a relation between self-generated poloidal shear flows and magnetic field perturbations. For large values of the plasma β we observe an increase of the transport if the viscous damping of the self-generated shear flows is absent. This behavior is in contrast to the standard argument that sheared flows suppress turbulence and transport via a decorrelation mechanism. An explanation of this behavior in terms of the transport related to magnetic flutter is proposed. The characteristics of the E×B flux are investigated using probability density distribution functions (PDFs). Although they are not Gaussian, no signs of algebraic tails in the PDFs are observed. The PDFs of the pointwise transport are found to agree well with a folded Gaussian, while the PDFs of the spatially averaged transport are in good agreement with an extreme value distribution.

Plasma shaping effects on tokamak scrape-off layer turbulence

“…The high plasma collisionality in the tokamak SOL allows neglecting kinetic effects and using a fluid approach to describe plasma dynamics [12,29,40]. Since fluctuations with amplitude and size comparable to the time-averaged values are observed [41], a flux-driven model is necessary to study SOL turbulence.…”

Impact of large island perturbations on turbulent blob transport in tokamaks

“…To overcome these problems the shifted metric procedure 15 has been proposed and is now widely used in the numerical treatments of turbulence models for magnetized plasmas. 13,10,27 Here we follow a similar approach by employing an analytical treatment introducing a third reference system labeled ͑ , , ͒ where the inconvenient nonorthogonality is partially removed. These coordinates are defined by = ; = r;…”

“…The numerical approach implemented has many similarities to previously used schemes. [13][14][15] But for the reason of a self-contained description and due the particular differences in the treatment of field aligned coordinates details of the ATTEMPT code are sketched with special emphasis on the evaluation of parallel gradients.…”

Aspect ratio effects on limited scrape-off layer plasma turbulence

“…It is therefore reasonable to use a fluid [1][2][3] or a gyro-fluid model 4,5 to describe the plasma dynamics in this regime. As the typical amplitude of fluctuations in the SOL is comparable to the background values, one needs a full-n model that does not separate between equilibrium and fluctuation quantities.…”