The Eulerian gyrokinetic turbulence code GENE has recently been extended to a full torus code. Moreover, it now provides Krook-type sources for gradient-driven simulations where the profiles are maintained on average as well as localized heat sources for a flux-driven type of operation. Careful verification studies and benchmarks are performed successfully. This setup is applied to address three related transport issues concerning nonlocal effects. First, it is confirmed that in gradient-driven simulations, the local limit can be reproduced -provided that finite aspect ratio effects in the geometry are treated carefully. In this context, it also becomes clear that the profile widths (not the device width) may constitute a more appropriate measure for finite size effects. Second, the nature and role of heat flux avalanches are discussed in the framework of both local and global, flux-and gradient-driven simulations. Third, simulations dedicated to discharges with electron internal barriers are addressed.

Important steps towards the understanding of turbulent transport have been made with the development of the gyrokinetic framework for describing turbulence and with the emergence of numerical codes able to solve the set of gyrokinetic equations. This paper presents some of the main recent advances in gyrokinetic theory and computing of turbulence. Solving 5D gyrokinetic equations requires state-of-the-art high performance computing techniques involving massively parallel computers and parallel scalable algorithms. The various numerical schemes that have been explored until now, Lagrangian, Eulerian and semi-Lagrangian, each have their advantages and drawbacks. A past controversy regarding the finite size effect (finite ρ *) in ITG turbulence has now been resolved. It has triggered an intensive benchmarking effort and careful examination of the convergence properties of the different numerical approaches. Now, both Eulerian and Lagrangian global codes are shown to agree and to converge to the flux-tube result in the ρ * → 0 limit. It is found, however, that an appropriate treatment of geometrical terms is necessary: inconsistent approximations that are sometimes used can lead to important discrepancies. Turbulent processes are characterized by a chaotic behaviour, often accompanied by bursts and avalanches. Performing ensemble averages of statistically independent simulations, starting from different initial conditions, is presented as a way to assess the intrinsic variability of turbulent fluxes and obtain reliable estimates of the standard deviation. Further developments

The response of passing electrons in Ion Temperature Gradient (ITG) and Trapped Electron Mode (TEM) microinstability regimes is investigated in tokamak geometry making use of the flux-tube version of the gyrokinetic code GENE [Jenko et al. 2000 Phys. Plasmas 7 1904]. Results are obtained with two different electron models: 1) fully kinetic, and 2) hybrid, in which passing particles are forced to respond adiabatically while trapped are handled kinetically. Comparing linear eigenmodes obtained with these two models enables to systematically isolate radially fine structures located at corresponding MRS's, clearly resulting from the non-adiabatic passing electron response. The analysis of preliminary non-linear simulations in the ITG regime shows that these fine structures on the non-axisymmetric modes survive in the turbulent phase. Furthermore, through non-linear coupling to axisymmetric modes, they induce modulations in the effective density and ion/electron temperature profiles: flattening at low order MRS's and steepening in between, as was already observed in Ref. [Waltz et al., 2006 Phys. Plasmas 13 052301].

This is a repository copy of Turbulent drag reduction by rotating rings and wall-distributed actuation.

This is a repository copy of Laminar and turbulent flows over hydrophobic surfaces with shear-dependent slip length.