Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry

International audienceThe impact of magnetic configuration on edge turbulence properties in circular limiter geometry is investigated using TOKAM3X, a three-dimensional (3D), first-principle, fluid code for edge plasma. The theoretical spatial tilting of magnetic shear on turbulence fluctuations is recovered. Magnetic shear is found to generate or enhance poloidal high/low field sides (HFS/LFS) and up/down asymmetries. A simulation mimicking the impact of an X-point on circular limiter geometry leads to the formation of two transport barriers that are stable in time, thus leading to the improvement of core particle confinement and to reduction of radial turbulent transport. The magnetic shear, which also strongly enhances the E × B shear, is responsible for the barrier formation

Etude numérique des mécanismes gouvernant le transport de la chaleur dans le plasma de bord des Tokamaks

La fusion nucléaire est une solution technologique prometteuse pour une nouvelle source d'énergie. Cependant, utiliser la par fusion nucléaire confinement magnétique comme source d'énergie constitue un challenge scientifique et technologique car cela requière à la fois un bon confinement du plasma de cœur et un contrôle des flux de chaleurs arrivant à la paroi. Ce travail est motivé par la problématique de la gestion des flux de chaleur dans les réacteurs de fusion. Cela est nécessaire pour éviter d'endommager les coûteux composants faisant face au plasma. La compréhension des mécanismes physiques régissant le transport de la chaleur dans le plasma de bord est une tâche critique pour le design des futures machines. Dans ce contexte, il est nécessaire de faire des prédictions fiables de l'étalement de la chaleur dans le but de dimensionner correctement ces futures machines. Cela appelle à un fondement théorique décrivant la manière dont l'énergie s'échappe du plasma. Des études théoriques et expérimentales ont tenté aboutir à cette fin, cependant les mécanismes en jeux ne sont toujours pas clairs. Pour atteindre ce but, la modélisation numérique est un complément nécessaire aux expériences. Ce travail de thèse est dédié à l'étude numérique des différents aspects du transport de la chaleur dans le plasma de bord un utilisant les approches fluides. Une attention particulière est porté à deux mécanismes suspectés de joué un grand rôle dans le transport de la chaleur : le transport intermittent due à la turbulence et le transport convectif à large échelle par les vitesses dérives. Le problème a été traité avec une approche graduelle en utilisant différent outils numériques.Fusion devices are a promising solution for a new source of energy. However, using fusion reaction to produce power within a magnetic confinement is a scientific and technological challenge as it requires a high confinement in the core plasma at the same time as a good control of plasma exhaust on the material walls. This work is motivated by the key problematic of power handling in fusion power plants necessary to avoid damaging the expensive plasma facing components (PFC). The understanding of the physics underlying the heat transport, and more specifically is a critical task for the engineering design of future Tokamak devices. In this context, it is mandatory to make reliable predictions of the power spreading in order to correctly size the future Tokamaks. This calls for a theoretical ground describing the way energy escapes the core plasma through the separatrix and deposits on the PFCs. Some theoretical and experimental studies attempt to achieve such a task, however no definitive conclusion have been drawn yet. To achieve this goal, numerical modelling is a necessary complement to experimental results. This PhD work has been dedicated to the study of the different aspects of the heat transport in the edge plasma using a numerical fluid approach. Special focus was devoted to two types of mechanisms suspected to play an important role in the heat transport: intermittent turbulence; the large-scale convective transport

Hypocoercive estimates on foliations and velocity spherical Brownian motion

International audienc

Effect of mechanical scarification and gibberellins (GA3) on seed germination and growth of Garcinia kola (Heckel)

peer reviewe

Ichtyo3D2 : 3D Teleost skeletal database

International audienceThe application of sampling methods with fine sieve meshes during archaeological excavations has considerably modified the image of the role of fishing in the economy of ancient societies. The use of these field techniques allows, by multiplying the data, a quantitative approach that restores the share of each species in consumption, from the smallest to the largest. The millimetre size of certain remains collected in the samples and the numerous similarities between skeletons of individuals of the same genus, or even of the same family, often make the precise identification of small species difficult. The Ichtyo3D2 project* is a continuation of a preliminary interdisciplinary project (2021) conducted by CCJ-UMR 7299 and CEREGE, which has experimented the use of 3D x-ray micro-CT (Computed Tomography) on vertebrae of three small teleost bones (Chelon saliens, Diplodus sargus, Boops boops). This technique gives us a high spatial resolution (up to submicron) and access to structural information (bone density, deformation, alteration, etc….). We have information such as bone density, age and season of capture which are difficult to detect in any other way and which are necessary for our studies on the exploitation of fisheries resources over the long term. The three-dimensional x-ray imaging analysis (CEREGE) of various skeleton elements made it possible to create an interactive database. This one will be used, ultimately, as an osteological atlas for various small Mediterranean and Black Sea species. The Centre Camille Jullian has an osteotheque that includes a number of small sparids (Diplodus sargus, Sarpa sarpa, Boops boops, Lithognatus mormyrus, Spicara Maena), small mugilids, labridae (Coris julis), serranidae (Seranus cabrilla) whose osteology is very poorly known, illustrated and disseminated. Nevertheless, these species appear on the list of species consumed by different communities over time. They characterise the diet of some social categories.Our objectives with this project are:1)to create a didactic tool for the identification of skeletal elements for any species dedicated to students and researchers interested in the exploitation of marine resources.2)to increase the data sets of interest in several fields of archaeo-ichthyology and more broadly in biology (anatomy, histology of skeletal tissues);3)to characterise the 3D structure (density, shape, porosity, etc.) on various parts of the skeletal elements for the species studied in order to have a better understanding of the conservation parameters of the archaeological remains.This project will also enable the validation of a high-performance technique for saving and replicating bones, whether they belong to a current repository or come from archaeological sites and if they have to be destroyed to carry out biochemical analyses.* The project has received funding from Excellence Initiative of Aix-Marseille University - A*MIDEX, a French "Investissements d’Avenir" programme - Institute for Mediterranean Archaeology ARKAIA (AMX-19-IET-003)

Ichtyo3D2 : 3D Teleost skeletal database

International audienceThe application of sampling methods with fine sieve meshes during archaeological excavations has considerably modified the image of the role of fishing in the economy of ancient societies. The use of these field techniques allows, by multiplying the data, a quantitative approach that restores the share of each species in consumption, from the smallest to the largest. The millimetre size of certain remains collected in the samples and the numerous similarities between skeletons of individuals of the same genus, or even of the same family, often make the precise identification of small species difficult. The Ichtyo3D2 project* is a continuation of a preliminary interdisciplinary project (2021) conducted by CCJ-UMR 7299 and CEREGE, which has experimented the use of 3D x-ray micro-CT (Computed Tomography) on vertebrae of three small teleost bones (Chelon saliens, Diplodus sargus, Boops boops). This technique gives us a high spatial resolution (up to submicron) and access to structural information (bone density, deformation, alteration, etc….). We have information such as bone density, age and season of capture which are difficult to detect in any other way and which are necessary for our studies on the exploitation of fisheries resources over the long term. The three-dimensional x-ray imaging analysis (CEREGE) of various skeleton elements made it possible to create an interactive database. This one will be used, ultimately, as an osteological atlas for various small Mediterranean and Black Sea species. The Centre Camille Jullian has an osteotheque that includes a number of small sparids (Diplodus sargus, Sarpa sarpa, Boops boops, Lithognatus mormyrus, Spicara Maena), small mugilids, labridae (Coris julis), serranidae (Seranus cabrilla) whose osteology is very poorly known, illustrated and disseminated. Nevertheless, these species appear on the list of species consumed by different communities over time. They characterise the diet of some social categories.Our objectives with this project are:1)to create a didactic tool for the identification of skeletal elements for any species dedicated to students and researchers interested in the exploitation of marine resources.2)to increase the data sets of interest in several fields of archaeo-ichthyology and more broadly in biology (anatomy, histology of skeletal tissues);3)to characterise the 3D structure (density, shape, porosity, etc.) on various parts of the skeletal elements for the species studied in order to have a better understanding of the conservation parameters of the archaeological remains.This project will also enable the validation of a high-performance technique for saving and replicating bones, whether they belong to a current repository or come from archaeological sites and if they have to be destroyed to carry out biochemical analyses.* The project has received funding from Excellence Initiative of Aix-Marseille University - A*MIDEX, a French "Investissements d’Avenir" programme - Institute for Mediterranean Archaeology ARKAIA (AMX-19-IET-003)

Drift-driven cross-field transport and Scrape-Off Layer width in the limit of low anomalous transport

The impact of the ∇B-drift in the cross-field transport and its effect on the density and power scrape-off layer (SOL) width in the limit of low anomalous transport is studied with the fluid code SolEdge2D. In a first part of the work, the simulations are run with an isothermal reduced fluid model. It is found that a ∇B-drift dominated regime is reached in all geometries studied (JET-like, ASDEX-like and circular analytic geometries), and that the transition toward this regime comes along with the apparition of supersonic shocks, and a complex parallel equilibrium. The parametric dependencies of the SOL width in this regime are investigated, and the temperature and the poloidal magnetic field are found to be the principal parameters governing the evolution of the SOL width. In the second part of this paper, the impact of additional physics is studied (inclusion of the centrifugal drift, self-consistent variation of temperature and the treatment of the neutral species). The addition of centrifugal drift and neutral species are shown to play a role in the establishment of the parallel equilibrium, impacting the SOL's width. Finally, the numerical results are compared with the estimate of the Goldston's heuristic drift based model (HD-model), which has showed good agreement with experimental scaling laws. We find that the particles SOL's widths in the ∇B-drift dominated regime are, at least, two times smaller than the estimate of the HD-model. Moreover, in the parametric dependencies proposed by the HD-model, only the dependency with B pol is retrieved but not the one on T

Effect of mechanical scarification and gibberellins (GA3) on seed germination and growth of Garcinia kola (Heckel)

Objective: Garcinia kola (Heckel) in general has been shown to have a low germination and this constitutes a real obstacle to any domestication initiative. The experiment was conducted in an attempt to improve seeds germination.Methodology and results: Scarification in combination with Gibberellins (GA3) application and soaking in distillated water was carried out on fresh seeds and sown in two types of soil substrate: sandy topsoil (1/1) and 100 % topsoil. Parameters related to seed germination and seedlings vigour was evaluated. Results indicated that substrate do not affect seed germination and plant vigour. However, the percentage of germination (92.33±3.19) and germination rate (0.013 ±0.00) were highest when scarified seeds were soaked in increasing concentrations of GA3 (10-4 to 10-2 g L-1). In addition, scarified seeds soaked in distillated water have improved percentage of seed germination. Concerning plants vigour, GA3 application increased significantly plant height (11.22±4.31 cm) and plant wingspan (13.35±6.36 cm) against 9.19±4.17 cm and 11.67±6.78 cm for plant height and wingspan in the control.Conclusion and applications of findings: Results suggest that G. kola seeds present seed coat dormancy. Scarification and GA3 application offer possibly an alternative methodology to improve seed germination and seedling vigour for a large-scale production of G. kola seedlings, a prior step of plant species domestication process.Keywords: Garcinia kola, seed coat dormancy, mechanical scarification, GA3, seed germinatio