Electron Sources from Plasmas

Relativistic electrons are easily generated by self-injection when an intense laser drives a wakefield in a plasma, giving rise to wide electron energy distributions. Several mechanisms involving additional laser beams or different gas composition or distribution can be used to improve the electron beam quality. These mechanisms are introduced and discussed in the perspective of using laser driven electron sources as injectors for plasma accelerators.Comment: 11 pages, contribution to the CAS - CERN Accelerator School: High Gradient Wakefield Accelerators, 11-22 March 2019, Sesimbra, Portuga

Accélération d électrons et rayonnement betatron générés par sillage laser dans des tubes capillaires

Cette thèse porte sur le rayonnement X bêtatron généré par des électrons accélérés par sillage laser plasma dans des tubes capillaires diélectriques. En l état actuel de la technologie des impulsions laser multi-térawatts, on peut produire des faisceaux ayant une intensité crête élevée, de l ordre de 1018 W/cm2 dans le plan focal. Une telle impulsion laser se propageant au sein d un gaz sous-dense conduit à des phénomènes d interaction laser-plasma non-linéaires, tels que la création d une bulle de plasma, i.e. une bulle ne contenant aucun électron, suivant le laser. La séparation spatiale des charges en résultant crée des champs électriques très élevés au sein de la bulle, de l'ordre de 100 GV/m, ce qui offre la possibilité d'accélérer des électrons jusqu'au GeV après seulement quelques centimètres d interaction. En outre, un rayonnement synchrotron ultra-bref, appelé rayonnement bêtatron, est produit lors de l accélération des électrons puisque ces derniers, soumis au champ électrique radial de la bulle plasma, ont une trajectoire oscillante. Cette thèse présente des résultats expérimentaux sur la génération et l'optimisation de faisceaux d'électrons et de leur rayonnement X, en particulier lorsque le tube capillaire est utilisé pour recueillir l'énergie du halo laser dans le plan focal facilitant l autofocalisation du laser sur de longues distances. Des faisceaux d électrons de quelques dizaines de picocoulomb, avec une énergie maximale allant jusqu à 300 MeV, et dont le spectre est soit piqué à haute énergie soit exponentiellement décroissant, ont été produits dans des tubes capillaires de 10 mm de long avec l installation laser du Lund Laser Center (LLC, en Suède) par une impulsion laser de 40 fs d un 16 TW Ti: Saphir. Un rayonnement bêtatron a également été mesuré, il se compose de de photons X dont l énergie est comprise entre 1 et 10 keV et atteint une luminosité maximale d environ 1021 photons/s/mm /mrad /0.1%BW. Cela équivaut à environ 30 fois l intensité des faisceaux générés dans le cas des jets de gaz de longueur 2 mm ne disposant pas de guidage optique externe. La compensation des fluctuations de pointé laser permet de minimiser les fluctuations des propriétés du faisceau d électrons. On obtient des faisceaux d'électrons dont les fluctuations tir-a-tir sont de 1 mrad en pointé, de quelques pourcents en énergie et d environ 20% RMS en charge. La fluctuation en charge du faisceau, qui peut être considérée comme relativement grande, s avère être principalement corrélée à la fluctuation en puissance du laser. De plus, il a été montré que le rayonnement bêtatron pouvait être utilisé pour caractériser le processus d'accélération des électrons en caractérisant le nombre moyen d'oscillations bêtatron effectuées par les électrons à l'intérieur de la bulle plasma. La taille typique des sources de rayonnement X (dimension pour laquelle l intensité gaussienne est égale à 1/e de la valeur crête) est estimée à ~ 2.5 m en utilisant un modèle de diffraction de Fresnel induite par une lame de rasoir. Cela correspond à une émittance RMS normalisée pour le faisceau d'électrons d environ 0,83p mm.mrad. Des simulations tridimensionnelles particle-in-cell (PIC) ont été effectuées et confirment les résultats expérimentaux. Elles indiquent également que les paquets d'électrons générés ainsi que les flashs X directionnels sont ultra-brefs : ~ 10 fs.This dissertation addresses electron acceleration and the associated betatron X-ray radiation generated by laser wakefield inside dielectric capillary tubes. Focusing the state-of-the-art multi-terawatt laser pulses, high peak intensity, of the order of 1018 W/cm2, can be achieved in the focal plane, where a plasma bubble free of electron is formed just behind the laser. Owing to space charge separation ultrahigh electric fields, of the order of 100 GV/m, occur inside the plasma bubble, providing the possibility to accelerate electrons up to GeV-class over merely a centimetre-scale distance. Furthermore, ultra-short synchrotron-like X-ray radiation, known as betatron radiation, is produced simultaneously when the accelerated electrons are transversely wiggled by the radial electric field inside the plasma bubble. This thesis reports experimental results on the generation and optimization of electron and X-ray beams, particularly when a capillary tube is used to collect the energy of laser halos in the focal plane to facilitate the laser keeping self-focused over a long distance. Employing the 40 fs, 16 TW Ti:sapphire laser at the Lund Laser Centre (LLC) in Sweden, either peaked or widely-spread accelerated electron spectra with a typical beam charge of tens of pC were measured with a maximum energy up to 300 MeV in 10 mm long capillary tubes. Meanwhile, betatron X-ray radiation consisting of 1-10 keV photons was measured with a peak brightness of the order of 1021 photons/s/mm2/mrad2/0.1%BW, which is around 30 times higher than that in the case of a 2 mm gas jet without external optical guiding. When the laser pointing fluctuation is compensated, exceptionally reproducible electron beams are obtained with fluctuations of only 1 mrad RMS in beam pointing, a few percent in electron energy, and around 20% RMS in beam charge. The relatively large instability of beam charge is found to be essentially correlated to laser power fluctuation. Moreover, betatron radiation is able to provide the diagnostics about electron acceleration process and average number of betatron oscillations fulfilled by electrons inside the plasma bubble. The typical X-ray source size (waist of Gaussian distribution at 1/e2 intensity) is quantified to be ~2.5 m using Fresnel diffraction induced by a razor blade, which furthermore yields the corresponding normalized RMS emittance of electron beam 0.83p mm mrad. Three dimensional particle-in-cell (PIC) modelings are in good agreement with the experimental findings. The PIC simulations also reveal the generated electron bunches (or X-ray bursts) have pulse durations as short as 10 fs.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Fast laser field reconstruction method based on a Gerchberg-Saxton algorithm with mode decomposition

Knowledge of the electric field of femtosecond, high intensity laser pulses is of paramount importance to study the interaction of this class of lasers with matter. A novel, hybrid method to reconstruct the laser field from fluence measurements in the transverse plane at multiple positions along the propagation axis is presented, combining a Hermite-Gauss modes decomposition and elements of the Gerchberg-Saxton algorithm. The proposed Gerchberg-Saxton algorithm with modes decomposition (GSA-MD) takes into account the pointing instabilities of high intensity laser systems by tuning the centers of the HG modes. Furthermore, it quickly builds a field description by progressively increasing the number of modes and thus the accuracy of the field reconstruction. The results of field reconstruction using the GSA-MD are shown to be in excellent agreement with experimental measurements from two different high-peak power laser facilities

High-intensity ultrashort laser-induced ablation of stainless steel foil targets in the presence of ambient gas

Ablation depths of stainless steel targets irradiated by 80-fs laser pulses at a flux F ≤ 40 J/cm2 (intensity ≤ 5 × 1014 W/cm2) in the presence of air at atmospheric pressure are experimentally measured. These values are lower than the theoretical predictions for metal targets in vacuum. Results are analyzed on the basis of the role of the ambient gas and of crater formation on the behavior of the ablated material

Efficacy of the Janus kinase 1/2 inhibitor ruxolitinib in the treatment of vasculopathy associated with TMEM173-activating mutations in 3 children

International audienc

Beryllium increases the CD14^dimCD16+ subset in the lung of chronic beryllium disease

CD14dimCD16+ and CD14brightCD16+ cells, which compose a minor population of monocytes in human peripheral blood mononuclear cells (PBMC), have been implicated in several inflammatory diseases. The aim of this study was to investigate whether this phenotype was present as a subset of lung infiltrative alveolar macrophages (AMs) in the granulomatous lung disease, chronic beryllium disease (CBD). The monocytes subsets was determined from PBMC cells and bronchoalveolar lavage (BAL) cells from CBD, beryllium sensitized Non-smoker (BeS-NS) and healthy subjects (HS) using flow cytometry. The impact of smoking on the AMs cell phenotype was determined by using BAL cells from BeS smokers (BeS-S). In comparison with the other monocyte subpopulations, CD14dimCD16+ cells were at decreased frequency in PBMCs of both BeS-NS and CBD and showed higher HLA-DR expression, compared to HS. The AMs from CBD and BeS-NS demonstrated a CD14dimCD16+phenotype, while CD14brightCD16+ cells were found at increased frequency in AMs of BeS, compared to HS. Fresh AMs from BeS-NS and CBD demonstrated significantly greater CD16, CD40, CD86 and HLA-DR than HS and BeS-S. The expression of CD16 on AMs from both CBD and BeS-NS was downregulated significantly after 10μM BeSO4 stimulation. The phagocytic activity of AMs decreased after 10μM BeSO4 treatment in both BeS-NS and CBD, although was altered or reduced in HS and BeS-S. These results suggest that Be increases the CD14dimCD16+ subsets in the lung of CBD subjects. We speculate that Be-stimulates the compartmentalization of a more mature CD16+ macrophage phenotype and that in turn these macrophages are a source of Th1 cytokines and chemokines that perpetuate the Be immune response in CBD. The protective effect of cigarette smoking in BeS-S may be due to the low expression of co-stimulatory markers on AMs from smokers as well as the decreased phagocytic function

Evolution non lineaire des ondes de plasma excitees par conversion de mode auvoisinage de la resonnance de plasma : application aux experiences de modification de l'ionosphere

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc