Clarifications to the limitations of the s-α equilibrium model for gyrokinetic computations of turbulence

In the context of gyrokinetic flux-tube simulations of microturbulence in magnetized toroidal plasmas, different treatments of the magnetic equilibrium are examined. Considering the Cyclone DIII-D base case parameter set [Dimits et al., Phys. Plasmas 7, 969 (2000)], significant differences in the linear growth rates, the linear and nonlinear critical temperature gradients, and the nonlinear ion heat diffusivities are observed between results obtained using either an $s-\alpha$ or an MHD equilibrium. Similar disagreements have been reported previously [Redd et al., Phys. Plasmas 6, 1162 (1999)]. In this paper it is shown that these differences result primarily from the approximation made in the standard implementation of the $s-\alpha$ model, in which the straight field line angle is identified to the poloidal angle, leading to inconsistencies of order $\varepsilon$ ($\varepsilon=a/R$ is the inverse aspect ratio, $a$ the minor radius and $R$ the major radius). An equilibrium model with concentric, circular flux surfaces and a correct treatment of the straight field line angle gives results very close to those using a finite $\varepsilon$, low $\beta$ MHD equilibrium. Such detailed investigation of the equilibrium implementation is of particular interest when comparing flux tube and global codes. It is indeed shown here that previously reported agreements between local and global simulations in fact result from the order $\varepsilon$ inconsistencies in the $s-\alpha$ model, coincidentally compensating finite $\rho^*$ effects in the global calculations, where $\rho^*=\rho _s / a$ with $\rho_s$ the ion sound Larmor radius. True convergence between local and global simulations is finally obtained by correct treatment of the geometry in both cases, and considering the appropriate $\rho^* \rightarrow 0$ limit in the latter case

Gyrokinetic simulations of microturbulence in tokamak plasmas presenting an electron internal transport barrier, and development of a global version of the GENE code

The abstract goes here

Flux- and gradient-driven global gyrokinetic simulation of tokamak turbulence

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. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3567484

Numerical modelling of the electromagnetic turbulent transport of energetic ions in burning plasmas

We investigate the redistribution of the neutral beam driven current in the presence of small scale turbulence in the ITER steady-state scenario. Gyrokinetic simulations show that anomalous transport of beam ions can be larger than collisional estimates. The impact on the beam driven current in ITER is studied with a single particle following code. The results indicate that the current driven by the 1MeV neutral beam injection is not significantly redistributed by the microturbulent fields. The numerical investigation shows that a larger impact is expected for lower energy neutral beams

Influence of fine scale turbulence on the transport of high energy populations in burning plasmas

Tanzania Veterinary Journal, 2015; 30 (1): 1-10A study was conducted in Chunya District, Tanzania during December 2013 to assess the impact of tsetse fly and trypanosomosis control programme based on use of targets and traps. The trypanosome prevalence was determined by microscopic examination of thick and thin blood smears from 229 cattle selected randomly from 33 households. Additionally a semi-structured questionnaire was administered to heads or representatives of selected households to collect information on cattle- keepers’ knowledge on clinical features, transmission and control of trypanosomosis. Descriptive analysis of the data was done to establish proportions of different attributes and association between variables. Of 229 animals examined, six (2.6%) were positive for trypanosomes indicating significant decrease from baseline level of 13.8% found in 2010 at the beginning of the programme. Two trypanosome species, Trypanosoma vivax and T. congolense were identified in blood samples and vectors collected from the study area were identified as Glossina spp, Tabanus spp and Haematopota spp. Questionnaire results showed that burning of grasses (30.3%), theft of targets and traps (3.0%) and lack of follow up from the programme authority (6.1%) were major constraints that faced the programme. The study has shown a decline in prevalence of trypanosomosis which suggests that the application of traps and screens had a significantr impact on the disease and this warrants a recommendation of extending the trap and screen application technology to other similar tsetse infested areas of Tanzania