Conception et optimisation d’un recirculateur optique pour la source haute brillance de rayons gamma d’ELI-NP

This thesis is about the design and the realization of the optical system of a new gamma-ray source, ELI-NP-GBS (Extreme Light Infrastructure - Nuclear Physics - Gamma Beam Source), which benefits from the recent developments in laser technology, optics and accelerators. The final characteristics that this source aims to reach is one order of magnitude higher in intensity than the actual best Compton machine, HIGS. A new type of optical system has been designed for ELI-NP-GBS. It is a 32 passes system made of two confocal parabolic mirrors and a set of Mirror-Pair Systems. The parabolic reflectors focalize and collimate successively a high intensity laser beam (400 mJ per pulse). The ``dragon-shape'' geometry ensures that the laser beam and electron bunches cross at a constant angle in a unique point. These performances are guaranteed by a few micrometers precision in position alignment, a few microradians precision in orientation alignment and by a few hundreds femtoseconds synchronization between electron bunches and laser pulses for each pass. This alignment and this synchronization is performed by used of dedicated procedures and algorithms. These algorithms have been developed and tested with numerical simulations which take into account the mechanical and optical aspects of the system such as the mechanical pre-alignment, the mirrors' surface deformations, the laser beam polarization, etc. A first proof of principle of the synchronization method has been successful.Cette thèse porte sur la conception et la réalisation du système optique d'une nouvelle source de rayonnement gamma, ELI-NP-GBS (Extreme Light Infrastructure - Nuclear Physics - Gamma Beam Source), qui utilise des développements récents des technologies des lasers, de l'optique et des accélérateurs. Les caractéristiques finales que devra atteindre cette source sont au moins d'un ordre de grandeur, en intensité, supérieur à la meilleure machine Compton actuelle, HIGS. Un nouveau type de système optique a été conçu pour ELI-NP-GBS. Il s'agit d'un système à 32 passages composé de deux miroirs paraboliques confocaux et d'un ensemble de paires de miroirs. Les miroirs paraboliques permettent la focalisation et la collimation successives d'un faisceau laser de haute intensité (400 mJ par impulsion). La géométrie "dragon-shape" garantie que le croisement du faisceau laser avec le faisceau d'électron se produise avec un angle constant en un point unique. De telles performances sont assurées par un alignement des éléments optiques à mieux que quelques micromètres en position et quelques microradians en orientation et une synchronisation de tous les passages avec les paquets d'électrons à mieux que quelques centaines de femtosecondes. Cet alignement et cette synchronisation est obtenue par l'intermédiaire de procédures et d'algorithmes spécialement développés pour ce système. Les algorithmes ont ainsi été développés et testés sur des simulations numériques dédiées prenant en compte les aspects mécaniques et optiques du système tel que les pré-alignements mécaniques, les états de surfaces des miroirs, la polarisation du faisceau laser, etc. Une première preuve de principe de la méthode de synchronisation a été concluante

Hi-sAFe: a 3D agroforestry model for integrating dynamic tree–crop interactions

Agroforestry, the intentional integration of trees with crops and/or livestock, can lead to multiple economic and ecological benefits compared to trees and crops/livestock grown separately. Field experimentation has been the primary approach to understanding the tree–crop interactions inherent in agroforestry. However, the number of field experiments has been limited by slow tree maturation and difficulty in obtaining consistent funding. Models have the potential to overcome these hurdles and rapidly advance understanding of agroforestry systems. Hi-sAFe is a mechanistic, biophysical model designed to explore the interactions within agroforestry systems that mix trees with crops. The model couples the pre-existing STICS crop model to a new tree model that includes several plasticity mechanisms responsive to tree–tree and tree–crop competition for light, water, and nitrogen. Monoculture crop and tree systems can also be simulated, enabling calculation of the land equivalent ratio. The model’s 3D and spatially explicit form is key for accurately representing many competition and facilitation processes. Hi-sAFe is a novel tool for exploring agroforestry designs (e.g., tree spacing, crop type, tree row orientation), management strategies (e.g., thinning, branch pruning, root pruning, fertilization, irrigation), and responses to environmental variation (e.g., latitude, climate change, soil depth, soil structure and fertility, fluctuating water table). By improving our understanding of the complex interactions within agroforestry systems, Hi-sAFe can ultimately facilitate adoption of agroforestry as a sustainable land-use practice

Conception et optimisation d’un recirculateur optique pour la source haute brillance de rayons gamma d’ELI-NP

This thesis is about the design and the realization of the optical system of a new gamma-ray source, ELI-NP-GBS (Extreme Light Infrastructure - Nuclear Physics - Gamma Beam Source), which benefits from the recent developments in laser technology, optics and accelerators. The final characteristics that this source aims to reach is one order of magnitude higher in intensity than the actual best Compton machine, HIGS. A new type of optical system has been designed for ELI-NP-GBS. It is a 32 passes system made of two confocal parabolic mirrors and a set of Mirror-Pair Systems. The parabolic reflectors focalize and collimate successively a high intensity laser beam (400 mJ per pulse). The ``dragon-shape'' geometry ensures that the laser beam and electron bunches cross at a constant angle in a unique point. These performances are guaranteed by a few micrometers precision in position alignment, a few microradians precision in orientation alignment and by a few hundreds femtoseconds synchronization between electron bunches and laser pulses for each pass. This alignment and this synchronization is performed by used of dedicated procedures and algorithms. These algorithms have been developed and tested with numerical simulations which take into account the mechanical and optical aspects of the system such as the mechanical pre-alignment, the mirrors' surface deformations, the laser beam polarization, etc. A first proof of principle of the synchronization method has been successful.Cette thèse porte sur la conception et la réalisation du système optique d'une nouvelle source de rayonnement gamma, ELI-NP-GBS (Extreme Light Infrastructure - Nuclear Physics - Gamma Beam Source), qui utilise des développements récents des technologies des lasers, de l'optique et des accélérateurs. Les caractéristiques finales que devra atteindre cette source sont au moins d'un ordre de grandeur, en intensité, supérieur à la meilleure machine Compton actuelle, HIGS. Un nouveau type de système optique a été conçu pour ELI-NP-GBS. Il s'agit d'un système à 32 passages composé de deux miroirs paraboliques confocaux et d'un ensemble de paires de miroirs. Les miroirs paraboliques permettent la focalisation et la collimation successives d'un faisceau laser de haute intensité (400 mJ par impulsion). La géométrie "dragon-shape" garantie que le croisement du faisceau laser avec le faisceau d'électron se produise avec un angle constant en un point unique. De telles performances sont assurées par un alignement des éléments optiques à mieux que quelques micromètres en position et quelques microradians en orientation et une synchronisation de tous les passages avec les paquets d'électrons à mieux que quelques centaines de femtosecondes. Cet alignement et cette synchronisation est obtenue par l'intermédiaire de procédures et d'algorithmes spécialement développés pour ce système. Les algorithmes ont ainsi été développés et testés sur des simulations numériques dédiées prenant en compte les aspects mécaniques et optiques du système tel que les pré-alignements mécaniques, les états de surfaces des miroirs, la polarisation du faisceau laser, etc. Une première preuve de principe de la méthode de synchronisation a été concluante

Design and optimization of an optical Laser Beam Circulator for the high brillance gamma-ray source of ELI-NP

Cette thèse porte sur la conception et la réalisation du système optique d'une nouvelle source de rayonnement gamma, ELI-NP-GBS (Extreme Light Infrastructure - Nuclear Physics - Gamma Beam Source), qui utilise des développements récents des technologies des lasers, de l'optique et des accélérateurs. Les caractéristiques finales que devra atteindre cette source sont au moins d'un ordre de grandeur, en intensité, supérieur à la meilleure machine Compton actuelle, HIGS. Un nouveau type de système optique a été conçu pour ELI-NP-GBS. Il s'agit d'un système à 32 passages composé de deux miroirs paraboliques confocaux et d'un ensemble de paires de miroirs. Les miroirs paraboliques permettent la focalisation et la collimation successives d'un faisceau laser de haute intensité (400 mJ par impulsion). La géométrie "dragon-shape" garantie que le croisement du faisceau laser avec le faisceau d'électron se produise avec un angle constant en un point unique. De telles performances sont assurées par un alignement des éléments optiques à mieux que quelques micromètres en position et quelques microradians en orientation et une synchronisation de tous les passages avec les paquets d'électrons à mieux que quelques centaines de femtosecondes. Cet alignement et cette synchronisation est obtenue par l'intermédiaire de procédures et d'algorithmes spécialement développés pour ce système. Les algorithmes ont ainsi été développés et testés sur des simulations numériques dédiées prenant en compte les aspects mécaniques et optiques du système tel que les pré-alignements mécaniques, les états de surfaces des miroirs, la polarisation du faisceau laser, etc. Une première preuve de principe de la méthode de synchronisation a été concluante.This thesis is about the design and the realization of the optical system of a new gamma-ray source, ELI-NP-GBS (Extreme Light Infrastructure - Nuclear Physics - Gamma Beam Source), which benefits from the recent developments in laser technology, optics and accelerators. The final characteristics that this source aims to reach is one order of magnitude higher in intensity than the actual best Compton machine, HIGS. A new type of optical system has been designed for ELI-NP-GBS. It is a 32 passes system made of two confocal parabolic mirrors and a set of Mirror-Pair Systems. The parabolic reflectors focalize and collimate successively a high intensity laser beam (400 mJ per pulse). The ``dragon-shape'' geometry ensures that the laser beam and electron bunches cross at a constant angle in a unique point. These performances are guaranteed by a few micrometers precision in position alignment, a few microradians precision in orientation alignment and by a few hundreds femtoseconds synchronization between electron bunches and laser pulses for each pass. This alignment and this synchronization is performed by used of dedicated procedures and algorithms. These algorithms have been developed and tested with numerical simulations which take into account the mechanical and optical aspects of the system such as the mechanical pre-alignment, the mirrors' surface deformations, the laser beam polarization, etc. A first proof of principle of the synchronization method has been successful

Towards ultimate bandwidth photon sources based on Compton backscattering: Design constraints due to nonlinear effects

International audienceNuclear resonance fluorescence experiments typically require high rates of monochromatic photons due to the narrow linewidth of these resonances. Inverse Compton scattering sources are used to perform these experiments. Their intrinsic excellent monochromaticity is however spoiled by a variety of unavoidable imperfections related to the electron and laser beams. Some projects aim at reaching one per-mille of energy bandwidth, which requires attaining excellent brilliance of the electron beam but also a careful optimization of the laser-beam parameters. In particular, in such a situation, a careful accounting for the nonlinearities induced by a relatively large laser energy has to be considered. In this article, we revisit these nonlinearities with a quantum viewpoint with the goal to provide analytical expressions that can be employed for a very fast optimization of the performance of the source. These expressions were benchmarked against the CAIN event generator with an excellent accuracy in the parameters hypervolume that is of interest in this context. We also show that previously published expression often used to include laser nonlinearities in analytical bandwidth expressions significantly depart from the detailed CAIN simulations. The obtained expression are further used to optimize designs similar to those considered in on-going projects

Alley Cropping Mitigates the Impacts of Climate Change on a Wheat Crop in a Mediterranean Environment: A Biophysical Model-Based Assessment

International audienceIntroduction: Climate change (CC) and the increased occurrence of extreme climatic events pose a serious threat to crop yields and their stability worldwide. This study analyzed the CC mitigation potential of an alley cropping system on crop physiological stresses and growth as compared to a monoculture system. Materials and Methods: Growth of winter durum wheat, cultivated alone (agriculture) and in combination with hybrid walnut (agroforestry), was simulated with the Hi-sAFe agroforestry model, as driven by business-as-usual Intergovernmental Panel on Climate Change (IPCC) projections, split into three scenarios, representing Past (1951–1990), Present (1991–2030), and Future (2031–2070) climatic conditions. Crop growth and the occurrence of thermal, nitrogen, and water stresses were analyzed. Results: Cold-related stresses were modest in Past and almost disappeared over time. Heat, drought, and nitrogen stresses increased about twofold from Past to Future, but were reduced by 20–35% in agroforestry, already with medium-sized trees (diameter at breast height (DBH) of about 10–15 cm). Crop yields in agriculture increased from Past to the end of Present and then remained stable. This moderately decreased with tree age in agroforestry (especially in Future). Discussion: The impact of CC on the crop was buffered in agroforestry, especially for the most extreme climatic events. The mitigation of crop microclimate and the increased stability of crop yields highlight the potential of agroforestry as a CC adaptation strategy

Short pulse laser beam beyond paraxial approximation

International audienceNonparaxial perturbative equations are derived from the scalar wave equation by taking into account spatiotemporal couplings. General solutions are obtained in Fourier space and further transformed back in direct space. They depend on parameters that can be used to match various boundary conditions and the perturbative expansion of any nonparaxial exact solutions. This parametrization is used to study the sensitivity of direct electron acceleration off an ultrashort tightly focused laser pulse to nonparaxial corrections of radially polarized electromagnetic fields

Linearly polarized laser beam with generalized boundary condition and non-paraxial corrections

International audienceLinearly polarized Gaussian beams, under the slowly varying envelope approximation, tightly focused by a perfect parabola modeled with the integral formalism of Ignatovsky are found to be well approximated with a generalized Lax series expansion beyond the paraxial approximation. This allows obtaining simple analytic formulas of the electromagnetic field in both the direct and momentum spaces. It significantly reduces computing time, especially when dealing with the problem of simulating direct laser acceleration. The series expansion formulation depends on integration constants that are linked to boundary conditions. They are found to depend significantly on the region of space over which the integral formulation is fit. Consequently, the net acceleration of electrons initially at rest is extremely sensitive to the chosen set of initial parameters due to the extreme focusing investigated here. This suggests avoiding too tight focusing schemes in order to obtain reliable predictions when the process of interest is sensitive mainly to the field and not the intensity

Compact kW-class enhancement cavity operated at GHz repetition rates for Inverse Compton Scattering sources

International audienceWe report on a compact kW-class optical system composed of a GHz oscillator amplified at high average power and coupled to an optical cavity exhibiting a 250 enhancement factor.</jats:p