La Fermeture de couche N=28 : coexistence de formes et contribution Spin-orbite

One of the fundamental questions, which emerge from the study of nuclei far from stability, concerns the persistance of the magic character of certain configurations of protons and neutrons. From previous measurements arond the N=28 magic number, it appears that this shell closure is especially weakening.In this context, a mass measurement experiment by a time of flight method arond N=28 (Z<20) with the SPEG spectrometer at GANIL has brought some new decisive observations to understand this phenomenum. More than thirty masses have been obtained in the region of interest, 8 of them measured for the first time. The analysis shows clearly the existence of a pseudo-shell closure at N=26. The comparison of these results with shell model and relativistic mean field calculations allow us to attribute the vanishing of the N=28 shell closure to deformation effects and shape coexistence predicted in this region. The evidence of an isomeric state in the 43S in the same experiment and its interpretation by a shell model calculation confirm the analysis of the masses and constitutes the first evidence of shape coexistence around N=28.At the same time, an estimation of the evolution of the contribution of the spin-orbit coupling far from stabilty, partially responsible of the magic numbers sequence, showed that, althought non-negligible, it is not sufficient to explain the vanishing of the shell closure. Through this study, it appeared extremely difficult to separate the contribution of the deformationfrom the one of the spin-orbit coupling in spectroscopic experiments. A feasibility study has thus been undertaken concerning a polarised proton and deuteron target to measure directly the evolution of the spin-orbit potential as a function of the isospin through elastic scattering experiments.Une des questions fondamentales qui émergent de l'étude des noyaux loin de la stabilité concerne la persistance du caractère magique de certaines configurations de protons et de neutrons. A la suite de mesures réalisées autour du nombre magique N = 28 pour des noyaux riches en neutrons, il apparaît que cette fermeture de couche semble particulièrement affaiblie. Dans ce contexte, une expérience de mesures de masses par temps de vol de noyaux autour de N = 28 (Z <20) auprès du spectromètre SPEG au GANIL a apporté des éléments décisifs pour la compréhension de ce phénomène. A l'issue de cette expérience, une trentaine de masses a pu être obtenue dans la zone d'intérêt dont 8 masses jamais mesurées auparavant. L'analyse des masses montre clairement l'existence d'une pseudo-fermeture de couche à N = 26. La comparaison de ces résultats avec des calculs de champ moyen relativiste et de modèle en couches permet d'attribuer la disparition de la fermeture de couche N = 28 à la déformation et aux fortes coexistences de formes prédites dans cette région. La mise en évidence d'un état isomérique dans le 43S et son interprétation par un calcul de modèle en couches confirment l'analyse issue des masses et constitue la première preuve expérimentale d'une coexistence de formes autour de N = 28. Parallèlement, une estimation de l'évolution du couplage spin-orbite loin de la stabilité, partiellement responsable de la séquence des nombres magiques, a montré que, bien que non négligeable, elle ne suffisait pas à expliquer la disparition de la fermeture de couche. A travers cette étude, il est apparu extrêmement difficile de découpler les contributions de la déformation et du couplage spin-orbite dans des expériences de spectroscopie. Une étude de prospective a donc été entreprise sur l'utilisation d'une cible de protons et de deutons polarisés afin de mesurer directement l'évolution du potentiel spin-orbite en fonction de l'isospin à partir de réactions de diffusion élastique

Transport barrier onset and edge turbulence shortfall in fusion plasmas

Turbulent plasmas notably self-organize to higher energy states upon application of additional free energy sources or modification of edge operating conditions. Mechanisms whereby such bifurcations occur have been actively debated for decades. Enhanced confinement occurs at the plasma edge, where a shortfall of predicted turbulence intensity has been puzzling scientists for decades. We show, from the primitive kinetic equations that both problems are connected and that interplay of confined plasma turbulence with its material boundaries is essential to curing the shortfall of predicted turbulence and to triggering spontaneous transport barrier onset at the plasma edge. Both problems determine access to improved confinement and are central to fusion research. A comprehensive discussion of the underlying mechanisms is proposed. These results, highly relevant to the quest for magnetic fusion may also be generic to many problems in fluids and plasmas where turbulence self-advection is active

Neutrino propagation in the Earth and emerging charged leptons with nuPyProp\texttt{nuPyProp}

Ultra-high-energy neutrinos serve as messengers of some of the highest energy astrophysical environments. Given that neutrinos are neutral and only interact via weak interactions, neutrinos can emerge from sources, traverse astronomical distances, and point back to their origins. Their weak interactions require large target volumes for neutrino detection. Using the Earth as a neutrino converter, terrestrial, sub-orbital, and satellite-based instruments are able to detect signals of neutrino-induced extensive air showers. In this paper, we describe the software code $\texttt{nuPyProp}$ that simulates tau neutrino and muon neutrino interactions in the Earth and predicts the spectrum of the $\tau$-lepton and muons that emerge. The $\texttt{nuPyProp}$ outputs are lookup tables of charged lepton exit probabilities and energies that can be used directly or as inputs to the $\texttt{nuSpaceSim}$ code designed to simulate optical and radio signals from extensive air showers induced by the emerging charged leptons. We describe the inputs to the code, demonstrate its flexibility and show selected results for $\tau$-lepton and muon exit probabilities and energy distributions. The $\texttt{nuPyProp}$ code is open source, available on github.Comment: 42 pages, 21 figures, code available at https://github.com/NuSpaceSim/nupypro

Geometrical Constraints of Observing Very High Energy Earth-Skimming Neutrinos from Space

International audienceThe detection of very-high-energy (VHE) neutrinos (Eν  10 PeV) is a challenge that future generations of experiments are being designed and constructed to address. One promising method relies on using the Earth as a neutrino target for indirect detection of skimming tau neutrinos interacting within the Earth and producing tau leptons that are able to escape and decay in the atmosphere. The tau decay produces upward-moving Extensive Air Showers (EASs). A space-based or suborbital instrument observing the ground near the Earth limb can search for the beamed Cherenkov signal produced by the up-going EAS resulting from the tau-lepton decay. In this paper, we derive the geometrical constraints for such an observation in general and for the specific case of the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) mission currently under study, focusing on the Cherenkov signal detection. We show that, using reasonable orbital parameters, POEMMA can achieve full-sky coverage to search for potential neutrino sources over the length of its mission. We also show that follow-up of a transient Target-of-Opportunity (ToO), such as a flaring source, can be achieved within an orbit time scale depending on the source location on the celestial sphere and its relative position with respect to the Sun and the Moon

Lateral Deprotometallation-Trapping Reactions on Methylated Pyridines, Quinolines and Quinoxalines Using Lithium Diethylamide

International audienceThe functionalization of methylated azines and diazines has aroused the interest of chemists given the structural diversity that it affords. Hindered lithium dialkylamides have been used to deprotometallate these substrates chemoselectively. In contrast, it can be observed that, despite some promising work, lithium diethylamide has been used very little for this purpose. Our objective here is on the one hand to make an inventory of what reagents have been used to deprotometallate methylpyridines, -quinolines and -quinoxalines, and on the other hand to describe the results obtained by seeking to functionalize a series of substrates with lithium diethylamide (picolines, 2,4-lutidine, methylquinolines and 2-methylquinoxaline). Our efforts to take advantage of the use of an in-situ trap (a zinc chloride chelate) in these reactions are also described

Boundary conditions at the limiter surface obtained in the modelling of plasma wall interaction with a penalization technique

Proceedings of the 19th International Conference on Plasma-Surface Interactions in Controlled FusionInternational audienceIsoardi et al. [1] recently proposed a penalization technique to model solid plasma facing components that treats a solid obstacle as a sink region corresponding to the strong plasma recombination in the solid state material. A major advantage of this approach is that it produces a system that can be solved in an obstacle free domain, thus allowing the use of powerful numerical algorithms. Such a technique implemented in a minimal transport model for ionic density and parallel momentum appeared to exhibit a Mach-1 transition at the boundary layer between the plasma presheath and the limiter region. In this paper, we reconsider this result by analysing the physics of detached plasmas that are governed both by strong recombination and plasma pressure decrease, as imposed by the penalization technique within the limiter region. The analysis provides a unique control parameter A=Γcsmi/ΠA=Γcsmi/Π (Γ being the parallel particles flux, cs the sound speed, mi the ionic mass and Π the total plasma pressure) that allows one to understand the results of the penalization technique for the Mach-1 transition

Parallel shear flow instability in the tokamak edge

Proceedings of the 19th International Conference on Plasma-Surface Interactions in Controlled FusionInternational audienceThe transition between the core and scrape-off layer of a tokamak corresponds to a marked momentum shear layer, owing to sheath acceleration on limiters which drives near-sonic flows along the plasma magnetic field in the scrape-off layer, and a parallel shear flow instability can possibly be triggered. The possibility of this instability driven by the velocity gradient is investigated numerically, using a minimum model of particle and parallel momentum transport in the edge of a tokamak, in a computational domain modelling a limiter plasma with background turbulence modelled as an effective diffusion. It is found that unstable regions can exist in the vicinity of a limiter, in agreement with experimental findings, when momentum radial transport - and therefore coupling between SOL and core flows - is sufficiently weak. Instability is reinforced by core rotation, and is found to be maximum downstream of the limiter (with respect to the core plasma flow)

Modelling SOL flow pattern spreading in the edge plasma

Proceedings of the 18th International Conference on Plasma-Surface Interactions in Controlled Fusion DeviceInternational audienceThe transition region between closed and open magnetic flux surfaces plays a crucial role for tokamak performances. Appropriate understanding of the edge region remains a major challenge owing to several open issues as momentum transport, turbulence overshoot or neutral penetration. We consider here a transport model system to investigate the propagation of parallel momentum from the SOL into the core plasma and vice-versa. The numerical results show that for small values of the radial diffusion coefficient, the density profile decays exponentially from the core to the SOL as predicted by 1D analytical solution. A spreading of the parallel momentum from the SOL to the core is observed, with the presence of non-zero velocities also in the regions far from the SOL. The effect of an imposed rotation of the core plasma is investigated as well as the dynamics of an overdensity imposed in the core plasma

PGPR-Soil Microbial Communities’ Interactions and Their Influence on Wheat Growth Promotion and Resistance Induction against Mycosphaerella graminicola

The efficiency of plant-growth-promoting rhizobacteria (PGPR) may not be consistentlymaintained under field conditions due to the influence of soil microbial communities. The present study aims to investigate their impact on three PGPR-based biofertilizers in wheat. We used the PGPR Paenibacillus sp. strain B2 (PB2), PB2 in co-inoculation with Arthrobacter agilis 4042 (Mix 2), or with Arthrobacter sp. SSM-004 and Microbacterium sp. SSM-001 (Mix 3). Inoculation of PB2, Mix 2, and Mix 3 into non-sterile field soil had a positive effect on root and aboveground dry biomass, depending on the wheat cultivar. The efficiency of the PGPR was further confirmed by the protection they provided against Mycosphaerella graminicola, the causal agent of Septoria leaf blotch disease. PB2 exhibited protection of 37.8%, while Mix 2 showed 47.9% protection in the four cultivars tested. These results suggest that the interactions between PGPR and native soil microbial communities are crucial for promoting wheat growth and protection. Additionally, high-throughput sequencing of microbial communities conducted 7 days after PGPR inoculations revealed no negative effects of PB2, Mix 2, and Mix 3 on the soil microbial community structure. Interestingly, the presence of Arthrobacter spp. appeared to mitigate the potential negative effect of PB2 on bacterial community and foster root colonization by other beneficial bacterial strains

2D modelling of electron and ion temperature in the plasma edge and SOL

Proceedings of the 19th International Conference on Plasma-Surface Interactions in Controlled FusionInternational audienceWe are interested here in modelling the electron and ion temperature fields, Te and Ti respectively, in order to understand the main trends that govern the ratio Ti/Te that is being better documented in the SOL with RFA probes and . The experimental evidence gathered from several devices indicates that this temperature ratio significantly exceeds unity in most data sets that have been analysed, including measurements in the SOL of limiter devices like Tore Supra. Several issues of interest have been addressed with this version of the SOLEDGE-2D code. First, we have analysed the width of the SOL heat channels to the wall components and compared these values to analytical expressions. The key control mechanism of the width of the SOL heat channel is given by a balance between the sheath boundary conditions and the transverse transport. More advanced simulations address the interplay between the edge and SOL plasma allowing one to recover regimes with Ti/Te > 1