Дисертації: "Particle accelerator simulation"

1

Goutierre, Emmanuel. "Machine learning-based particle accelerator modeling." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASG106.

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Les accélérateurs de particules reposent sur des simulations de haute précision pour optimiser la dynamique du faisceau. Ces simulations sont coûteuses en ressources de calcul, rendant leur analyse en temps réel difficilement réalisable. Cette thèse propose de surmonter cette limitation en explorant le potentiel de l'apprentissage automatique pour développer des modèles de substitution des simulations d'accélérateurs de particules. Ce travail se concentre sur ThomX, une source Compton compacte, et introduit deux modèles de substitution : LinacNet et Implicit Neural ODE (INODE). Ces modèles sont entraînés sur une base de données développée dans le cadre de cette thèse, couvrant une grande variété de conditions opérationnelles afin d'assurer leur robustesse et leur capacité de généralisation. LinacNet offre une représentation complète du nuage de particules en prédisant les coordonnées de toutes les macro-particules du faisceau plutôt que de se limiter à ses observables. Cette modélisation détaillée, couplée à une approche séquentielle prenant en compte la dynamique cumulative des particules tout au long de l'accélérateur, garantit la cohérence des prédictions et améliore l'interprétabilité du modèle. INODE, basé sur le cadre des Neural Ordinary Differential Equations (NODE), vise à apprendre les dynamiques implicites régissant les systèmes de particules sans avoir à résoudre explicitement les équations différentielles pendant l'entraînement. Contrairement aux méthodes basées sur NODE, qui peinent à gérer les discontinuités, INODE est conçu théoriquement pour les traiter plus efficacement. Ensemble, LinacNet et INODE servent de modèles de substitution pour ThomX, démontrant leur capacité à approximer la dynamique des particules. Ce travail pose les bases pour développer et améliorer la fiabilité des modèles basés sur l'apprentissage automatique en physique des accélérateurs
Particle accelerators rely on high-precision simulations to optimize beam dynamics. These simulations are computationally expensive, making real-time analysis impractical. This thesis seeks to address this limitation by exploring the potential of machine learning to develop surrogate models for particle accelerator simulations. The focus is on ThomX, a compact Compton source, where two surrogate models are introduced: LinacNet and Implicit Neural ODE (INODE). These models are trained on a comprehensive database developed in this thesis that captures a wide range of operating conditions to ensure robustness and generalizability. LinacNet provides a comprehensive representation of the particle cloud by predicting all coordinates of the macro-particles, rather than focusing solely on beam observables. This detailed modeling, coupled with a sequential approach that accounts for cumulative particle dynamics throughout the accelerator, ensures consistency and enhances model interpretability. INODE, based on the Neural Ordinary Differential Equation (NODE) framework, seeks to learn the implicit governing dynamics of particle systems without the need for explicit ODE solving during training. Unlike traditional NODEs, which struggle with discontinuities, INODE is theoretically designed to handle them more effectively. Together, LinacNet and INODE serve as surrogate models for ThomX, demonstrating their ability to approximate particle dynamics. This work lays the groundwork for developing and improving the reliability of machine learning-based models in accelerator physics

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2

Rosencranz, Daniela Necsoiu. "Monte Carlo simulation and experimental studies of the production of neutron-rich medical isotopes using a particle accelerator." Thesis, University of North Texas, 2002. https://digital.library.unt.edu/ark:/67531/metadc3077/.

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The developments of nuclear medicine lead to an increasing demand for the production of radioisotopes with suitable nuclear and chemical properties. Furthermore, from the literature it is evident that the production of radioisotopes using charged-particle accelerators instead of nuclear reactors is gaining increasing popularity. The main advantages of producing medical isotopes with accelerators are carrier free radionuclides of short lived isotopes, improved handling, reduction of the radioactive waste, and lower cost of isotope fabrication. Proton-rich isotopes are the result of nuclear interactions between enriched stable isotopes and energetic protons. An interesting observation is that during the production of proton-rich isotopes, fast and intermediately fast neutrons from nuclear reactions such as (p,xn) are also produced as a by-product in the nuclear reactions. This observation suggests that it is perhaps possible to use these neutrons to activate secondary targets for the production of neutron-rich isotopes. The study of secondary radioisotope production with fast neutrons from (p,xn) reactions using a particle accelerator is the main goal of the research in this thesis.

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3

Feister, Scott. "Efficient Acceleration of Electrons by an Intense Laser and its Reflection." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461225902.

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4

Li, Lulu Ph D. Massachusetts Institute of Technology. "Acceleration methods for Monte Carlo particle transport simulations." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112521.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 166-175).
Performing nuclear reactor core physics analysis is a crucial step in the process of both designing and understanding nuclear power reactors. Advancements in the nuclear industry demand more accurate and detailed results from reactor analysis. Monte Carlo (MC) eigenvalue neutron transport methods are uniquely qualified to provide these results, due to their accurate treatment of space, angle, and energy dependencies of neutron distributions. Monte Carlo eigenvalue simulations are, however, challenging, because they must resolve the fission source distribution and accumulate sufficient tally statistics, resulting in prohibitive run times. This thesis proposes the Low Order Operator (LOO) acceleration method to reduce the run time challenge, and provides analyses to support its use for full-scale reactor simulations. LOO is implemented in the continuous energy Monte Carlo code, OpenMC, and tested in 2D PWR benchmarks. The Low Order Operator (LOO) acceleration method is a deterministic transport method based on the Method of Characteristics. Similar to Coarse Mesh Finite Difference (CMFD), the other acceleration method evaluated in this thesis, LOO parameters are constructed from Monte Carlo tallies. The solutions to the LOO equations are then used to update Monte Carlo fission sources. This thesis deploys independent simulations to rigorously assess LOO, CMFD, and unaccelerated Monte Carlo, simulating up to a quarter of a trillion neutron histories for each simulation. Analysis and performance models are developed to address two aspects of the Monte Carlo run time challenge. First, this thesis demonstrates that acceleration methods can reduce the vast number of neutron histories required to converge the fission source distribution before tallies can be accumulated. Second, the slow convergence of tally statistics is improved with the acceleration methods for the earlier active cycles. A theoretical model is developed to explain the observed behaviors and predict convergence rates. Finally, numerical results and theoretical models shed light on the selection of optimal simulation parameters such that a desired statistical uncertainty can be achieved with minimum neutron histories. This thesis demonstrates that the conventional wisdom (e.g., maximizing the number of cycles rather than the number of neutrons per cycle) in performing unaccelerated MC simulations can be improved simply by using more optimal parameters. LOO acceleration provides reduction of a factor of at least 2.2 in neutron histories, compared to the unaccelerated Monte Carlo scheme, and the CPU time and memory overhead associated with LOO are small.
by Lulu Li.
Ph. D.

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5

Lowe, Robert Edward. "Simulation of electron acceleration at collisionless plasma shocks." Thesis, Queen Mary, University of London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246324.

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6

Day, Hugo Alistair. "Measurements and simulations of impedance reduction techniques in particle accelerators." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/measurements-and-simulations-of-impedance-reduction-techniques-in-particle-accelerators(35666138-5941-4c8b-95b3-7beeb3bdfb24).html.

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Wakefields and the corresponding frequency-domain phenomenon beam coupling impedance have been well studied for a number of years as a source of beam instabilities within particle accelerators. With the development of the Large Hadron Collider (LHC) and the large beam currents stored in the LHC during fills for physics production, wakefield driven instabilities and strong beam induced heating have become a limiting factors in luminosity production due to both instantaneous luminousity and the available time for collisions.In this thesis is presented an in depth study of the beam coupling impedance of two important (from an impedance and operational point of view) devices in the LHC; the collimation system and the injection kicker magnets (MKIs). These systems have both been sources of concern for the beam impedance of the LHC, the collimators due to their large transverse impedance and the MKIs due to the strong heating observed during the increased of beam current during operation in 2011 and 2012. The source of the heating for the MKIs is studied in depth, found to be power lost by the beam to wakefields in the MKIs. Simulations and measurements are used to characterise the impedance and localise the areas responsible for the high impedance, here the beam screen and ferrite yoke of the magnet; improvements are proposed to better screen the ferrite yoke and verified. A new RF damping system using ferrite for the collimation system is studied and compared to the existing RF damping system, focusing on the heating of the damping system. Highlights include a new method for measuring the quadrupolar and constant transverse impedances of an asymmetric structure using a coaxial wire technique is proposed and verified using computational simulations, and a study of the heat loss in a ferrite damped cavity, focusing on the location of the power loss for cavities being damped to varying degrees.

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7

Guyot, Julien. "Particle acceleration in colliding laser-produced plasmas." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS616.

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Les particules chargées énergétiques sont omniprésentes dans l'Univers et sont accélérées par des sources galactiques et extragalactiques. Comprendre l'origine de ces "rayons cosmiques" est crucial en astrophysique et dans le cadre de l'astrophysique de laboratoire à haute densité d'énergie, nous avons développé une nouvelle plate-forme sur les installations laser LULI pour étudier l'accélération de particules. Dans les expériences, la collision de deux plasmas contre-propageant produits par laser génère une distribution non thermique de particules allant jusqu'à 1 MeV d'énergie. L'objectif de ce travail est de fournir un cadre théorique pour comprendre leur origine. Des simulations magnéto-hydrodynamiques avec des particules tests montrent que la collision des plasmas conduit à la croissance de structures caractéristiques de l'instabilité de Rayleigh-Taylor magnétique et à la génération de forts champs électriques. Nous constatons que les particules sont accélérées à des énergies allant jusqu'à quelques centaines de keV en moins de 20 ns, par des interactions répétées avec les perturbations de Rayleigh-Taylor. Les simulations et un modèle d'accélération stochastique reproduisent bien le spectre expérimental. En conclusion, nous avons identifié en laboratoire un nouveau mécanisme d'accélération de particules qui repose sur la croissance de l'instabilité de Rayleigh-Taylor magnétique pour accélérer de manière stochastique les particules. Cette instabilité est fréquente dans les plasmas astrophysiques, avec par exemple les restes de supernovæ et les éjections de masse coronale, et nous suggérons qu'elle peut contribuer à l'accélération de particules dans ces systèmes
Energetic charged particles are ubiquitous in the Universe and are accelerated by galactic and extragalactic sources. Understanding the origin of these "cosmic rays" is crucial in astrophysics and within the framework of high-energy-density laboratory astrophysics we have developed a novel platform on the LULI laser facilities to study particle acceleration in the laboratory. In the experiments, the collision of two laser-produced counter-propagating plasmas generates a distribution of non-thermal particles with energies up to 1 MeV. The aim of this work is to provide a theoretical framework to understand their origin. Magneto-hydrodynamic simulations with test particles show that the plasma collision leads to the growth of bubble and spike structures driven by the magnetic Rayleigh-Taylor instability and the generation of strong electric fields. We find that particles are accelerated to energies up to a few hundred of keV in less than 20 ns, by repeated interactions with these growing magnetic Rayleigh-Taylor perturbations. The simulations and a stochastic acceleration model recover very well the experimentally measured non-thermal energy spectrum. In conclusion, we have identified in the laboratory a new particle acceleration mechanism that relies on the growth of the magnetic Rayleigh-Taylor instability to stochastically energize particles. This instability is very common in astrophysical plasmas, with examples including supernovae remnants and coronal mass ejections, and we suggest that it may contribute to the energization of particles in these systems

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8

Messmer, Peter. "Observations and simulations of particle acceleration in solar flares /." Aachen : Shaker, 2001. http://www.gbv.de/dms/goettingen/338805397.pdf.

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9

Guo, Fan. "Effects of Turbulent Magnetic Fields on the Transport and Acceleration of Energetic Charged Particles: Numerical Simulations with Application to Heliospheric Physics." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/255156.

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Turbulent magnetic fields are ubiquitous in space physics and astrophysics. The influence of magnetic turbulence on the motions of charged particles contains the essential physics of the transport and acceleration of energetic charged particles in the heliosphere, which is to be explored in this thesis. After a brief introduction on the energetic charged particles and magnetic fields in the heliosphere, the rest of this dissertation focuses on three specific topics: 1. the transport of energetic charged particles in the inner heliosphere, 2. the acceleration of ions at collisionless shocks, and 3. the acceleration of electrons at collisionless shocks. We utilize various numerical techniques to study these topics. In Chapter 2 we study the propagation of charged particles in turbulent magnetic fields similar to the propagation of solar energetic particles in the inner heliosphere. The trajectories of energetic charged particles in the turbulent magnetic field are numerically integrated. The turbulence model includes a Kolmogorov-like magnetic field power spectrum containing a broad range of scales from those that lead to large-scale field-line random walk to small scales leading to resonant pitch-angle scattering of energetic particles. We show that small-scale variations in particle intensities (the so-called "dropouts") and velocity dispersions observed by spacecraft can be reproduced using this method. Our study gives a new constraint on the error of "onset analysis", which is a technique commonly used to infer information about the initial release of energetic particles. We also find that the dropouts are rarely produced in the simulations using the so-called "two-component" magnetic turbulence model (Matthaeus et al., 1990). The result questions the validity of this model in studying particle transport. In the first part of Chapter 3 we study the acceleration of ions in the existence of turbulent magnetic fields. We use 3-D self-consistent hybrid simulations (kinetic ions and fluid electrons) to investigate the acceleration of low-energy particles (often termed as "injection problem") at parallel shocks. We find that the accelerated particles always gain the first amount of energy by reflection and acceleration at the shock layer. The protons can move off their original field lines in the 3-D electric and magnetic fields. The results are consistent with the acceleration mechanism found in previous 1-D and 2-D simulations. In the second part of Chapter 3, we use a stochastic integration method to study diffusive shock acceleration in the existence of large-scale magnetic variations. We show that the 1-D steady state solution of diffusive shock acceleration can be significantly modified in this situation. The results suggest that the observations of anomalous cosmic rays by Voyager spacecraft can be explained by a 2-D shock that includes the large-scale magnetic field variations. In Chapter 4 we study electron acceleration at a shock passing into a turbulent magnetic field by using a combination of hybrid simulations and test-particle electron simulations. We find that the acceleration of electrons is greatly enhanced by including the effect of large-scale magnetic turbulence. Since the electrons mainly follow along the magnetic lines of force, the large-scale braiding of field lines in space allows the fast-moving electrons interacting with the shock front multiple times. Ripples in the shock front occurring at various scales also contribute to the acceleration by mirroring the electrons. Our calculation shows that this process favors electron acceleration at perpendicular shocks. We discuss the application of this process in interplanetary shocks and flare termination shocks. We also discuss the implication of this study to solar energetic particles (SEPs) by comparing the acceleration of electrons with that of protons. The intensity correlation of electrons and ions in SEP events indicates that perpendicular or quasi-perpendicular shocks play an important role in accelerating charged particles. In Chapter 5 we summarize the results of this thesis and discuss possible future work.

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10

Lagergren, Mattias. "GPU accelerated SPH simulation of fluids for VFX." Thesis, Linköping University, Visual Information Technology and Applications (VITA), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-57320.

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11

Plewa, Jérémie-Marie. "Etude de l'influence des plasmas dans les diodes à électrons pour la radiographie éclair." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30156/document.

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La radiographie éclair par faisceau X intense est spécifique en ce sens qu'elle doit permettre de photographier la matière soumise à des conditions extrêmes de densification, de température et de vitesse de déplacement. Le succès de ce type de radiographie repose sur la qualité de la source X qui doit nécessairement être pénétrante (quelques MeV), intense (plusieurs rads), brève (quelques dizaines de ns) et de petite dimension (quelques mm). L'impulsion X est ainsi générée à partir du rayonnement de freinage émis lors de l'interaction avec une cible en métal d'un faisceau focalisé d'électrons de haute énergie (MeV) et de haute intensité (kA). Ce procédé lie très fortement les propriétés du faisceau d'électrons à ceux du faisceau X et donc à la qualité de la radiographie. Dans ce contexte, la thèse porte sur la compréhension de la dynamique du faisceau dans la diode à l'électron (c'est-à-dire juste avant son entrée dans la ligne accélératrice) ainsi que sur la caractérisation du plasma de velours dont sont issus les électrons qui composent le faisceau. Dans un premier temps, la dynamique du faisceau intense d'électrons a été étudiée à l'aide du code LSP reposant sur la méthode " Particle-In-Cell ". Les simulations réalisées ont été comparées avec des mesures effectuées sur l'injecteur d'un accélérateur linéaire à induction, implanté au CEA Valduc sur l'installation Epure. Grâce au modèle de simulation développé, une nouvelle diode à électrons mono-impulsion a été conçue, dimensionnée et réalisée pendant ce travail de thèse afin d'augmenter l'intensité du faisceau d'électrons de 2,0 kA à 2,6 kA permettant ainsi d'améliorer les performances radiographiques de l'installation. Dans un second temps, un modèle permettant d'étudier les mécanismes mis en jeu dans la production du faisceau d'électrons au niveau de plasma de cathode a été développé. Ce dernier est un modèle collisionnel-radiatif (MCR) 0D qui permet de décrire l'évolution de la densité des espèces d'un plasma dont la composition est directement liée aux molécules et atomes désorbés par la cathode de velours. Trois différents mélanges ont été étudiés impliquant de l'hydrogène, de l'oxygène et du carbone dont les proportions ont été estimées par des mesures LIBS (spectroscopie de plasma induit par laser).[...]
Intense X-ray flash radiography is used to take a stop-action picture of a material under extreme conditions like high densification, high temperature and high movement speed. The success of this kind of radiography is based on the quality of the X-ray source which must necessarily be penetrating (some MeV), intense (several rads), short (a few tens of ns) and small (a few mm). The X-ray pulse is generated from the bremsstrahlung radiation emitted during the interaction with a metal target of a focused electron beam of high energy (MeV) and high intensity (kA). This process strongly links the properties of the electron beam to those of the X-ray beam and thus to the quality of the radiography picture. In this context, the thesis is about the electron beam dynamics in the electron diode (i.e. just before electrons move towards the accelerator) as well as about the characterization of the velvet plasma from which electrons are extracted to form the beam. Firstly, the dynamics of the intense electron beam was studied using the LSP code based on the "Particle-In-Cell" method. The simulations were compared to measurements made on the injector of a linear induction accelerator, at the CEA Valduc center on the Epure facility. Based on the developed simulation model, a new single-pulse electron diode was designed, sized and realized during this thesis to increase the intensity of the electron beam from 2.0 kA to 2.6 kA, thus improving the radiographic performances of the facility. In a second step, a model allowing to study the mechanisms involved in the production of the electron beam from the cathode plasma was developed. This latter is a collisional-radiative model (CRM) 0D describing the evolution of the plasma species density of a plasma whose composition is directly related to the molecules and atoms desorbed by the velvet cathode. [...]

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12

Abramowski, Michael. "Atomistic simulations of the uranium/oxygen system." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250187.

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13

Bilgen, Suheyla. "Dynamic pressure in particle accelerators : experimental measurements and simulation for the LHC." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP020.

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L’obtention de très faible pression (UHV) est une condition essentielle pour les accélérateurs de particules de haute énergie et de hautes performances. Par conséquent, la compréhension de l'évolution de la pression dynamique pendant le fonctionnement des accélérateurs est fondamentale afin de trouver des solutions qui permettent de minimiser les hausses de pression induites par de multiples phénomènes présents dans les lignes faisceaux. Pour le LHC, l'apparition d'instabilités peut être due à la succession de plusieurs processus. Tout d’abord, le faisceau de protons de haute intensité ionise le gaz résiduel, produisant des ions positifs (principalement H₂⁺ et CO⁺) ainsi que des électrons qui sont accélérés et qui impactent la paroi en cuivre des tubes de faisceaux. Ensuite, ces interactions induisent : (i) une désorption des gaz absorbés sur les parois, conduisant à des élévations de pression ; (ii) la création de particules secondaires (ions et électrons). Dans ce dernier cas, la production d'électrons secondaires entraîne, par effet d’avalanche, la formation de nuages d’électrons, dont la limitation est l'un des enjeux majeurs de l'anneau de stockage du LHC. Ces nuages génèrent des montées de pression et des dépôts de chaleur sur les parois du collisionneur pouvant conduire à des « quench » d’aimants supraconducteurs. Tous ces phénomènes limitent l'intensité maximale et augmentent l’émittance des faisceaux et donc la luminosité ultime atteignable dans un accélérateur de protons. Ce travail de thèse a pour but d’étudier certains phénomènes fondamentaux qui contrôlent la pression dynamique dans le LHC, à savoir les effets induits par les électrons et les ions, d’une part, et l'influence de la chimie de surface du cuivre constituant les écrans faisceaux, d’autre part. Dans un premier temps, les courants d’électrons et d’ions ainsi que la pression ont été mesurés in situ dans le Secteur Pilote Vide (VPS) situé sur l'anneau du LHC pendant la deuxième période d’exploitation du collisionneur. En analysant ces résultats, une quantité d’ion plus importante que prévu a été détectée et la relation entre les électrons, les ions et les variations de pression a été étudiée. D’autre part, la désorption stimulée par les ions a été mesurée au laboratoire au CERN en utilisant un bâti expérimental dédié. L'influence de la nature, de la masse et de l'énergie des ions incidents interagissant avec les surfaces sur les rendements de désorption ionique a été discutée. De plus, des analyses approfondies de la surface de cuivre constituant l'écran faisceau ont été réalisées dans le laboratoire IJCLab pour identifier le rôle joué par la chimie de surface du cuivre sur le rendement d’émission électronique, les processus de conditionnement de surface et la désorption de gaz stimulée. Le rôle fondamental de composés chimiques sur la surface (contaminants, présence de carbone et d'oxydes natifs) sur le rendement de production des électrons secondaires a été mis en évidence. Enfin, nous avons proposé un code de simulation permettant de prédire les profils de pression dans les chambres à vide des accélérateurs de particules ainsi que leur évolution temporelle. Ce nouveau code de simulation appelé DYVACS (DYnamic VACuum Simulation) est une amélioration du code VASCO développé par le CERN. Il a été appliqué pour simuler la pression dynamique dans le VPS. L'évolution du nuage d'électrons a été implémentée dans le code via des « maps » permettant de calculer l'évolution de la densité des nuages d'électrons. L'ionisation du gaz résiduel par les électrons a également été prise en compte. Finalement, les résultats obtenus avec DYVACS ont été comparés aux mesures de pression enregistrées dans le LHC. Les résultats obtenus à l’issu de ces travaux de thèse, ainsi que les développements expérimentaux et de simulation réalisés, pourront permettre l’étude de la stabilité du vide de futurs accélérateurs de particules tels que HL-LHC ou FCC(ee et hh)
Ultra-High Vacuum is an essential requirement to achieve design performances and high luminosities in high-energy particle colliders. Consequently, the understanding of the dynamic pressure evolution during accelerator operation is fundamental to provide solutions to mitigate pressure rises induced by multiple-effects occurring in the vacuum chambers and leading to beam instabilities. For the LHC, the appearance of instabilities may be due to the succession of several phenomena. First, the high intensity proton beams ionize the residual gas producing positive ions (mainly H₂⁺ or CO⁺) as well as accelerated electrons which impinge the copper wall of the beam pipe. Then, these interactions induce: (i) the desorption of gases adsorbed on the surfaces leading to pressure rises; (ii) the creation of secondary particles (ions, electrons). In this latter case, the production of secondary electrons leads to the so-called “Electron Cloud” build-up by multipacting effect, the mitigation of which being one of the major challenges of the LHC storage ring. Electron clouds generate beam instabilities, pressure rises and heat loads on the walls of beam pipe and can lead to “quench” of the superconducting magnets. All these phenomena limit the maximum intensity of the beams and thus the ultimate luminosity achievable in a proton accelerator. This work aims to investigate some fundamental phenomena which drive the dynamic pressure in the LHC, namely the effects induced by electrons and ions interacting with the copper surface of the beam screens on the one hand and the influence of the surface chemistry of copper on the other hand. First, in-situ measurements were performed. Electron and ion currents as well as pressure were recorded in situ in the Vacuum Pilot Sector (VPS) located on the LHC ring during the RUN II. By analyzing the results, more ions than expected were detected and the interplay between electrons, ions and pressure changes was investigated. Then, the ion-stimulated desorption was studied, using a devoted experimental set-up at the CERN vacuum Lab. The influence of the nature, mass, and energy of the incident ions interacting with the copper surface on the ion-desorption yields was discussed. In addition, extensive surface analyses were performed in the IJCLab laboratory to identify the role played by the surface chemistry on the electron emission yield, surface conditioning processes and the stimulated gas desorption. The fundamental role of the surface chemical components (contaminants, presence of carbon and native oxide layers) on the secondary electron yield was evidenced. Finally, we proposed a simulation code allowing to predict the pressure profiles in the vacuum chambers of particle accelerators as well as their evolution under dynamic conditions (i.e. as a function of time). This new simulation code called DYVACS (DYnamic VACuum Simulation) is an upgrade of the VASCO code developed at CERN. It was applied to simulate the dynamic pressure in the VPS when proton beams circulate into the ring. The electron cloud build-up was implemented in the code via electron cloud maps. The ionization of the residual gas by electrons was also considered. Results obtained with the DYVACS code are compared to pressure measurements recorded during typical fills for physics and a good agreement is obtained. This PhD study has provided interesting results and has allowed the development of new experimental and simulation tools that will be useful for further investigations on the vacuum stability of future particle accelerators such as HL-LHC or FCC (ee and hh)

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14

Soudais, Adrien. "Simulations numériques hybrides de magnétosphères relativistes." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALY029.

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Les magnétosphères relativistes font partie des environnements les plus énergétiques de l'Univers et sont suspectées d'être impliquées dans les noyaux actifs de galaxie, sursauts gamma et binaires X. Elles correspondent à la région proche des objets compacts qui est fortement aimanté et remplie de plasma. Les pulsars sont des étoiles à neutron historiquement détectés grâce à leurs pulsations radio. Ils présentent aussi une émission pulsée intense à travers tout le spectre électromagnétique. Les trous noirs quant à eux n'émettent pas de lumière, l'émission détectée provient de la matière en orbite. Au fil des années, beaucoup de données ont été recueillies sur les deux objets. La collaboration Fermi a récemment publié son troisième catalogue qui recense tous les pulsars émettant en gamma. Ils correspondent aux pulsars les plus énergétiques. Ce dernier catalogue contient deux fois plus de pulsars que le précédent, ce qui permet de tirer des conclusions sur les différentes populations. Où et comment les émissions à haute énergie sont produites est toujours une question ouverte. La découverte par la collaboration HESS d'émissions au TeV pour le pulsar Vela réintroduit la question de l'accéleration de particules aux abords des pulsars. Cette détection vient confirmer une détection plus ancienne aux TeV du pulsar du Crabe et indique que les pulsars sont d'incroyables accélérateurs de particules. Dans le cas des trous noirs, on trouve aussi une forte variabilité du rayonnement gamma. Les développements de la technologie VLBI ont permis à la collaboration Event Horizon Telescope d'imager pour la première fois l'ombre des trous noirs supermassifs, M87* et SgrA*. Les deux images montrent un plasma chaud en orbite et permettent de sonder la physique dans des régimes extrêmes. Pour étudier ces magnétosphères, nous devons nous appuyer sur des simulations numériques afin de prendre en compte toute leur complexité.La modélisation des magnétosphères était d'abord faite en utilisant l'approche sans force. Elle correspond à la limite idéale de la magnétohydrodynamique. Cette méthode nous a permis d'étudier la structure des magnétosphères mais ne permet pas, par construction, de contraindre le rayonnement. La méthode Particle-in-cell est maintenant préférée à cette dernière car elle permet d'obtenir le rayonnement en utilisant directement des particules pour modéliser la magnétosphère. Cependant, la méthode particulaire doit décrire un système à la fois micro- et macro-scopique ce qui est numériquement complexe. Cette grande séparation d'échelle est réduite dans les simulations PIC en rééchelonnant toutes les quantités, tout en conservant la hiérarchie des échelles du problème. Ainsi, les simulations PIC modélisent des systèmes de taille réduite et ne permettent pas une comparaison directe avec les observations.Durant ma thèse, j'ai développé une nouvelle méthode numérique au sein du code Zeltron. Cette méthode combine les approches sans force et PIC de façon simultanée pour modéliser les magnétosphères relativistes. Le but de cette manœuvre est d'accroître la séparation d'échelle des simulations PIC actuelles. Les régions idéales sont alors modélisées pour la méthode sans-force, tant dit que les zones non idéales utilisent la méthode PIC. L'utilisation de la méthode idéale permet d'augmenter la séparation d'échelle de la simulation de manière globale, ce qui impacte aussi les particules. Grâce à cette méthode, j'ai pu augmenter la séparation d'échelle à des valeurs non atteintes par le passé. J'ai démontré que le pulsar milliseconde le plus faible détecté par Fermi est capable d'accélérer des particules jusqu'au TeV. J'ai aussi réussi à valider le processus de rééchelonnage des simulations PIC. Avec ce travail, j'ai prouvé qu'il était possible de développer une méthode sans-force-PIC permettant de faire le pont entre les simulations et les observations
Relativistic magnetospheres represent one of the most energetic environments in the Universe and may be involved in high-energy phenomena such as Active Galactic Nuclei, Gamma-ray Bursts or X-ray binaries. They correspond to the highly magnetized plasma-filled surroundings of a compact object. Pulsars are neutron stars which were first detected via their radio pulsations. They are able to emit across the full electromagnetic spectrum and show strong high-energy signals. Black holes do not emit light but their surrounding does, from radio to gamma-ray wavelengths. The amount of observational data grew a lot in recent years for both pulsars and black holes. The Fermi collaboration published their third catalogue on gamma-ray pulsars, which are the ones emitting at the highest energies. Compared to the previous catalogue, the number of these pulsars more than doubled, making the conclusions on the population even more reliable. How and where this high-energy radiation is coming from is not fully constrained yet. The recent discovery by the HESS collaboration of TeV emission coming from the Vela Pulsar, only confirms a similar detection from the Crab pulsar. This emission only reaffirms the fact that pulsars are incredible particle accelerators. For black holes, the high variability observed in gamma rays is also part of a larger puzzle. Thanks to the development of the Very Large Baseline Interferometry, the Event Horizon Telescope collaboration was able to give the first image of the “shadow'’ of two supermassive black holes, M87* and SgrA*. In the images, the emission is probed down to the horizon scale and gives insights into the physics around black holes. In both pulsar and black hole magnetospheres, the matter is pushed into extreme physical regimes either by the magnetic field (pulsars) or the strong gravity (Lense-Thirring effect of black holes). If we want to study these magnetospheres, we have to rely on numerical simulations to consider the wide range of physical phenomena.The modelling of magnetospheres was originally done using the force-free approach, the ideal limit of magnetohydrodynamics. It allowed us to study the structure of the magnetosphere but was not able to capture radiation by construction. The Particle-in-cell became the next approach used by the community, as the plasma near pulsars and black holes is mostly collisionless. This method directly uses particles to model the magnetosphere and capture particle acceleration. However, it uses microscopic particles to describe global systems. This implies a large-scale separation which is not achievable with the PIC approach, thus they are scaled down while conserving the hierarchy of scales. Consequently, PIC simulations are modelling a reduced system and cannot be used directly to explain the observations.In this thesis, I have developed a new numerical method in the Zeltron code. This method combines the force-free approach and the PIC approach simultaneously to describe relativistic magnetospheres. The goal behind it is to be able to push the scale separation of the simulation as far as possible. The ideal regions of the simulation are treated by the force-free method, while the non-ideal parts are described by the particles. Hiding some regions behind the force-free treatment allowed me to push the parameters of the simulation to a scale separation for the particles never reached before. As a result, I pinpointed the fact that the weakest millisecond pulsar seen by the Fermi collaboration can accelerate particles to TeV energies. Moreover, I highlighted the fact that the rescaling of PIC simulations was valid. With this work, I gave the first proof-of-principle that force-free-PIC methods are doable and can bridge the gap between simulations and observations

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15

Tatomirescu, Emilian-Dragos. "Accélération laser-plasma à ultra haute intensité - modélisation numérique." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0013/document.

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Avec les dernières augmentations de l'intensité maximale de laser réalisable grâce à de courtes impulsions à haute puissance (gamme femtoseconde) un intérêt a surgi dans les sources de plasma laser potentiels. Les lasers sont utilisés en radiographie proton, allumage rapide, hadronthérapie, la production de radioisotopes et de laboratoire astrophysique. Au cours de l'interaction laser-cible, les ions sont accélérés par des processus physiques différents, en fonction de la zone de la cible. Tous ces mécanismes ont un point commun: les ions sont accélérés par des champs électriques intenses, qui se produisent en raison de la séparation de forte charge induite par l'interaction de l'impulsion laser avec la cible, directement ou indirectement. Deux principales sources distinctes pour le déplacement de charge peuvent être mis en évidence. Le premier est le gradient de charge provoquée par l'action directe de la force ponderomotive de laser sur les électrons dans la surface avant de la cible, qui est la prémisse pour le processus d'accélération des radiations de pression (RPA). Une deuxième source peut être identifiée comme provenant du rayonnement laser qui est transformée en énergie cinétique d'une population d'électrons relativistes chaud (~ quelques MeV). Les électrons chauds se déplacent et font recirculer à travers la cible et forment un nuage d'électrons relativistes à la sortie de la cible dans le vide. Ce nuage, qui se prolonge pour plusieurs longueurs de Debye, crée un champ électrique extrêmement intense longitudinal, la plupart du temps dirigé le long de la surface normale, ce qui, par conséquent, est la cause de l'accélération d'ions efficace, qui conduit à l'accélération cible normale gaine (TNSA) processus . Le mécanisme TNSA permet d'utiliser des géométries différentes cibles afin de parvenir à une meilleure focalisation des faisceaux de particules de l'ordre de plusieurs dizaines de microns, avec des densités d'énergie élevées. Les électrons chauds sont produits par l'irradiation d'une feuille solide avec une impulsion laser intense; ces électrons sont transportés à travers la cible, la formation d'un champ électrostatique fort, normal à la surface cible. Protons et les ions chargés positivement de la surface arrière de la cible sont accélérés par ce domaine jusqu'à ce que la charge de l'électron est compensée. La densité d'électrons chauds et la température dans le vide arrière dépendent des propriétés géométriques et de composition cibles tels que la courbure de la cible, les structures de mise au point d'impulsion et de microstructure pour l'accélération de protons améliorée. Au cours de ma première année, j'ai étudié les effets de la géométrie de la cible sur le proton et l'ion énergie et la distribution angulaire afin d'optimiser les faisceaux de particules laser accéléré au moyen de deux dimensions (2D) particule-in-cell (PIC) simulations de l'interaction de l'ultra-court impulsions laser avec plusieurs cibles microstructurées. Également au cours de cette année, je l'ai étudié la théorie derrière les modèles utilisés
With the latest increases in maximum laser intensity achievable through short pulses at high power (femtosecond range) an interest has arisen in potential laser plasma sources. Lasers are used in proton radiography, rapid ignition, hadrontherapy, production of radioisotopes and astrophysical laboratory. During the laser-target interaction, the ions are accelerated by different physical processes, depending on the area of the target. All these mechanisms have one thing in common: the ions are accelerated by intense electric fields, which occur due to the separation of high charge induced by the interaction of the laser pulse with the target, directly or indirectly. Two main distinct sources for charge displacement can be identified. The first is the charge gradient caused by the direct action of the laser ponderomotive force on the electrons in the front surface of the target, which is the premise for the pressure ramping acceleration (RPA) process. A second source can be identified as coming from the laser radiation which is transformed into kinetic energy of a hot relativistic electron population (~ a few MeV). The hot electrons move and recirculate through the target and form a cloud of relativistic electrons at the exit of the target in a vacuum. This cloud, which extends for several lengths of Debye, creates an extremely intense longitudinal electric field, mostly directed along the normal surface, which is therefore the cause of effective ion acceleration, which leads to the normal target sheath acceleration (TNSA) process. The TNSA mechanism makes it possible to use different target geometries in order to obtain a better focusing of the beams of particles on the order of several tens of microns, with high energy densities. Hot electrons are produced by irradiating a solid sheet with an intense laser pulse; these electrons are transported through the target, forming a strong electrostatic field, normal to the target surface. Protons and positively charged ions from the back surface of the target are accelerated by this domain until the charge of the electron is compensated. The density of hot electrons and the temperature in the back vacuum depend on the target geometric and compositional properties such as target curvature, pulse and microstructure tuning structures for enhanced proton acceleration. In my first year I studied the effects of target geometry on the proton and energy ion and angular distribution in order to optimize the accelerated laser particle beams by means of two-dimensional (2D) particle -in-cell (PIC) simulations of the interaction of ultra-short laser pulses with several microstructured targets. Also during this year, I studied the theory behind the models used

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16

ROSSI, MARCO. "DEEP LEARNING APPLICATIONS TO PARTICLE PHYSICS: FROM MONTE CARLO SIMULATION ACCELERATION TO PROTODUNE RECONSTRUCTION." Doctoral thesis, Università degli Studi di Milano, 2023. https://hdl.handle.net/2434/951789.

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The thesis arises in the context of deep learning applications to particle physics. The dissertation follows two main parallel streams: the development of hardware-accelerated tools for event simulation in high-energy collider physics, and the optimization of deep learning models for reconstruction algorithms at neutrino detectors. These two topics are anticipated by a review of the literature concerning the recent advancements of artificial intelligence models in particle physics. Event generation is a central concept in high-energy physics phenomenology studies. The state-of-the-art software dedicated to Monte Carlo simulation is often written for general-purpose computing architectures, which allow great flexibility but are not compatible with specialized accelerating devices, such as Graphics Processing Units. The original tools presented in the thesis, PDFFlow and MadFlow, manage to combine these two aspects in Python and require no prior knowledge of specific programming languages for hardware accelerators. The former product, PDFFlow, is a Parton Distribution Functions interpolator, the latter, MadFlow, aims at building a complete tool suite to accelerate the whole event generation framework. The reconstruction pipeline at neutrino detectors is comprised of many different algorithms that work in synergy to extract a high-level representation of detector data. All the most important experiments in neutrino physics are developing software to automatically process and extract this information. This work describes the implementation of deep learning techniques to improve neutrino reconstruction efficiency at the ProtoDUNE-SP detector. Two original contributions are presented concerning raw data denoising and a hit-clustering procedure named "slicing". Both denoising and slicing involve the implementation and the training of novel neural network architectures, based on state-of-the-art models in machine learning, such as feed-forward, convolutional and graph neural networks. They represent a proof of concept that these models are indeed capable of providing an important impact on signal reconstruction at neutrino detectors.

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17

Lehe, Rémi. "Improvement of laser-wakefield accelerators: towards a compact free electron laser." Palaiseau, Ecole polytechnique, 2014. https://tel.archives-ouvertes.fr/tel-01088398/document.

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Lorsque l'on focalise une impulsion laser courte et intense dans un gazsous-dense, celle-ci peut accélérer une fraction des électrons du gaz,et ainsi générer un faisceau d'électrons ayant une énergie de quelquescentaines de MeV. Ce phénomène, connu sous le nom d'accélérationlaser-plasma, pourrait avoir de nombreuses applications,notamment pour la réalisation de sources de rayons Xultra-intenses appelées lasers à électrons libres (LEL). Cependant,ces applications nécessitent que le faisceau d'électrons ait uneexcellente qualité (faible divergence, faible émittance et faible dispersion en énergie). Au cours de cette thèse, différentes solutions ont été développéesafin d'améliorer la qualité des faisceaux d'électrons issus del'accélération laser-plasma. Ce travail est effectué à travers desmodèles analytiques ainsi que dessimulations Particle-In-Cell (PIC). Nous commençons cependant par montrer que les simulations PIC onttendance à surestimer l'émittance du faisceau, en raison de l'effetCherenkov numérique. Afin d'estimer correctement l'émittance ici, nousproposons un algorithme PIC modifié qui n'est pas sujet à l'effetCherenkov numérique. A l'aide de cet algorithme, un nouveau mécanisme permettant de générerle faisceau est observé puis étudié : il s'agit de l'injection optique transverse. Les faisceaux produits par ce mécanisme sontcaractérisés par une forte charge, une faible divergence et une faibleémittance. Par ailleurs, nous proposons un dispositif - la lentille laser-plasma - qui permet defortement réduire la divergence finale des faisceaux. Cesrésultats sont placés dans leur contexte, à travers une discussion despropriétés nécessaires pour un laser à électrons libres compact. Nousmontrons en particulier que les accélérateurs laser-plasma pourraientêtre avantageusement combinés avec des onduleurs laser-plasmainnovants, afin de produire des sources de rayons X intenses
When an intense and short laser pulse propagates through an underdensegas, it can accelerate a fraction of the electrons of the gas, andthereby generate an electron bunch with an energy of a few hundreds ofMeV. This phenomenon, which is referred to as laser-wakefield acceleration, has many potential applications, including the design of ultra-bright X-ray sources known as freeelectron lasers (FEL). However, these applications require the electronbunch to have an excellent quality (low divergence, emittance andenergy spread). In this thesis, different solutions to improve thequality of the electron bunch are developed, both analytically and through the use of Particle-In-Cell (PIC) simulations. It is first shown however that PIC simulations tend to erroneously overestimate the emittance of the bunch, due to the numerical Cherenkov effect. Thus, in order to correctly estimate the emittance, a modified PICalgorithm is proposed, which is not subject to this unphysical Cherenkov effect. Using this algorithm, we observed and studied a new mechanism togenerate the electron bunch: optical transverse injection. This mechanism can produce bunches with ahigh charge, a low emittance and a low energy spread. In addition, wealso proposed an experimental setup - the laser-plasma lens- which can strongly reduce the final divergence of the bunch. Finally, these results are put into context by discussing the propertiesrequired for the design of a compact FEL. It is shown in particularthat laser-wakefield accelerator could be advantageously combinedwith innovative laser-plasma undulators, in order to produce brightX-rays sources

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18

Snyder, Joseph Clinton. "Leveraging Microscience to Manipulate Laser-Plasma Interactions at Relativistic Intensities." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483626346580096.

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19

Rittershofer, Wolf. "Laser wakefield acceleration in tapered plasma channels : theory, simulation and experiment." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:be45ca7d-790c-496c-9e52-160ce4fe277d.

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Laser-plasma accelerators are of great interest because of their ability to sustain extremely large acceleration gradients, enabling compact accelerating structures. Laser-plasma acceleration is realized by using a high-intensity short pulse laser to drive a large plasma wave or wakefield in an underdense plasma. This thesis considers the effect of axial plasma density upramps on laser wakefield acceleration. Theoretical groundwork shows that tapered plasma channels can be used to mitigate one of the main limitations of laser plasma acceleration, that is, dephasing of an electron beam with respect to the plasma wave. It is shown that it is possible to maintain an electron bunch at constant phase in the longitudinal electric fields of the laser wake field. This leads to an increased energy gain of an electron trapped in the wakefield. The required shape of the density slope is difficult to implement in experiments. Therefore, a linear density ramp is also considered which is predicted to also increase the energy gain beyond that possible in a uniform density plasma. Towards an experimental implementation it was studied how a suitable gas density profile can be established in a capillary. This was done employing simulations using the computational fluid dynamics tool kit OpenFoam and comparing these to measurements of the axial density profile based on Raman scattering. It was demonstrated that a linear density ramp could be established by applying different pressures on the capillary gas inlets. The dependence of the density profile on the capillary parameters, such as, capillary diameter and length and inlet diameter were also studied. The results of the simulations and the measurement showed excellent agreement and demonstrate that approximately linear density ramps can be generated by flowing gas along a capillary of constant cross-section Laser wakefield acceleration in plasmas with longitudinally varying density was investigated in an experiment at the Astra Laser at Rutherford Laboratories. The experiment utilised ionisation injection in order to operate in the mildly non-linear regime of laser-wakefield acceleration. The measured electron energies agree well with the theoretical predictions. It was demonstrated that an increase in the energy gain can be obtained by driving the accelerator in a ramped plasma, the electron spectrum is more narrow and the injected charge increases significantly. Measurements of the X-ray spectrum emitted by the betatron motion of the accelerated electron bunch allowed the transverse radius of the bunch to be deduced. These measurements showed that retrieved electron bunch radius is inversely proportional to the longitudinal density gradient, that is a plasma density upramp (downramp) has a decreased (increased) electron bunch radius.

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20

Ball, David, Feryal Özel, Dimitrios Psaltis, and Chi-kwan Chan. "PARTICLE ACCELERATION AND THE ORIGIN OF X-RAY FLARES IN GRMHD SIMULATIONS OF SGR A*." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621230.

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Significant X-ray variability and flaring has been observed from Sgr A* but is poorly understood from a theoretical standpoint. We perform general relativistic magnetohydrodynamic simulations that take into account a population of non-thermal electrons with energy distributions and injection rates that are motivated by PIC simulations of magnetic reconnection. We explore the effects of including these non-thermal electrons on the predicted broadband variability of Sgr A* and find that X-ray variability is a generic result of localizing non-thermal electrons to highly magnetized regions, where particles are likely to be accelerated via magnetic reconnection. The proximity of these high-field regions to the event horizon forms a natural connection between IR and X-ray variability and accounts for the rapid timescales associated with the X-ray flares. The qualitative nature of this variability is consistent with observations, producing X-ray flares that are always coincident with IR flares, but not vice versa, i.e., there are a number of IR flares without X-ray counterparts.

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21

Ngirmang, Gregory Kodeb. "Particle-in-Cell Simulations of the Acceleration of Electrons from the Interaction of a Relativistic Laser Reflecting from Solid Density Targets." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1514985418694386.

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22

Zemzemi, Imene. "High-performance computing and numerical simulation for laser wakefield acceleration with realistic laser profiles." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX111.

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Le développement des lasers ultra-courts à de hautes intensités a permis l’émergence de nouveaux domaines de recherche en relation avec l’interaction laser-plasma. En particulier, les lasers petawatt femtoseconde ont ouvert la voie vers la possibilité de concevoir une nouvelle génération d’accélérateurs de particules. La modélisation numérique a largement contribué à l’essor de ce domaine d’accélération des électrons par sillage laser. Dans ce contexte, les codes Particle-In-Cell sont les plus répandus dans la communauté. Ils permettent une description fiable de l’interaction laser plasma et surtout de l’accélération par sillage laser.Cependant, une modélisation précise de la physique en jeu nécessite de recourir à des simulations 3D particulièrement coûteuses. Une manière pour accélérer efficacement ce type de simulations est l’utilisation de modèles réduits qui, tout en assurant un gain en temps de calcul très important, garantissent une modélisation fiable du problème. Parmi ces modèles, la décomposition des champs en modes de Fourier dans la direction azimutale est particulièrement adaptée à l’accélération laser plasma.Dans le cadre de ma thèse, j’ai implémenté ce modèle dans le code open-source SMILEI, dans un premier temps, avec un schéma différences finies (FDTD) pour discrétiser les équations de Maxwell. Néanmoins, ce type de solveur peut induire un effet de Cherenkov numérique qui corrompt les résultats de la simulation. Pour mitiger cet artéfact, j’ai également implémenté une version pseudo-spectrale du solveur de Maxwell qui présente de nombreux avantages en termes de précision numérique.Cette méthode est ensuite mise en oeuvre pour étudier l’impact de profils de lasers réalistes sur la qualité du faisceau d’électrons en exploitant des mesures réalisées sur le laser Apollon. Sa capacité à modéliser correctement les processus physiques présents est analysée en déterminant le nombre de modes nécessaires et en comparant les résultats avec ceux issus des simulations 3D en géométrie Cartésienne. Cette étude montre qu’inclure les défauts du laser mène à des différences dans les résultats et que ces derniers dégradent la performance des accélérateurs-laser plasma notamment en termes de quantité de charge injectée. Ces simulations, instructives pour les futures expériences d’accélération d’électrons par le laser Apollon, mettent en avant la nécessité d’inclure les mesures expérimentales dans la simulation et particulièrement celle du front de phase, pour aboutir à des résultats précis
The advent of ultra-short high-intensity lasers has paved the way to new and promising, yet challenging, areas of research in laser-plasma interaction physics. The success of building petawatt femtosecond lasers offers a promising path for designing future particle accelerators and light sources.Achieving this goal intrinsically relies on the combination of experiments and numerical modeling. So far, Particle-In-Cell (PIC) codes have been the ultimate tool to accurately describe the laser-plasma interaction especially in the field of Laser WakeField Acceleration (LWFA). Nevertheless, the numerical modeling of laser-plasma accelerators in 3D can be a very challenging task due to their high computational cost.A useful approach to speed up such simulations consists of employing reduced numerical modes which simplify the problem while retaining a high fidelity.Among these models, Fourier field decomposition in azimuthal modes for the cylindrical geometry is particularly well suited for physical problems with close to cylindrical symmetry, which is the case in LWFA.During my Ph.D., I first implemented this method in the open-source code SMILEI in the Finite Difference Time Domain (FDTD) discretization scheme for the Maxwell solver. However, this kind of solvers may suffer from numerical Cherenkov radiation (NCR). To mitigate this artifact, I also implemented Maxwell’s solver in the Pseudo Spectral Analytical Domain (PSATD) scheme which offers better accuracy of the results.This method is then employed to study the impact of realistic laser profiles from the Apollon facility on the quality of the accelerated electron beam. Its ability to correctly model the involved physical processes is investigated by determining the optimal number of modes and benchmarking its results with full 3D Cartesian simulations. It is shown that the imperfections in the laser pulse lead to differences in the results compared to theoretical profiles. They degrade the performance of laser-plasma accelerators especially in terms of the quantity of injected charge. These simulations, insightful for the future experiments of LWFA that will be held soon with the Apollon laser, put forward the importance of including realistic lasers in the simulation to obtain reliable results

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23

Hsieh, Yikai. "Study on Nonlinear Acceleration of Electrons by Oblique Whistler Mode Waves." Kyoto University, 2018. http://hdl.handle.net/2433/232004.

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24

Owen, Justin. "Simulation of electron beam dyanmics in the 22 MeV accelerator for a coherent electron cooling proof of principle experiment." Thesis, State University of New York at Stony Brook, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1553316.

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Coherent electron cooling (CeC) offers a potential new method of cooling hadron beams in colliders such as the Relativistic Heavy Ion Collider (RHIC) or the future electron ion collider eRHIC. A 22 MeV linear accelerator is currently being built as part of a proof of principle experiment for CeC at Brookhaven National Laboratory (BNL). In this thesis we present a simulation of electron beam dynamics including space charge in the 22 MeV CeC proof of principle experiment using the program ASTRA (A Space charge TRacking Algorithm).

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25

Gerbershagen, Alexander. "CLIC drive beam phase stabilisation." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:ef939ced-40d0-47b6-bcd2-2fac32d0d318.

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The thesis presents phase stability studies for the Compact Linear Collider (CLIC) and focuses in particular on CLIC Drive Beam longitudinal phase stabilisation. This topic constitutes one of the main feasibility challenges for CLIC construction and is an essential component of the current CLIC stabilisation campaign. The studies are divided into two large interrelated sections: the simulation studies for the CLIC Drive Beam stability, and measurements, data analysis and simulations of the CLIC Test Facility (CTF3) Drive Beam phase errors. A dedicated software tool has been developed for a step-by-step analysis of the error propagation through the CLIC Drive Beam. It uses realistic RF potential and beam loading amplitude functions for the Drive and Main Beam accelerating structures, complete models of the recombination scheme and compressor chicane as well as of further CLIC Drive Beam modules. The tool has been tested extensively and its functionality has been verified. The phase error propagation at CLIC has been analysed and the critical phase error frequencies have been identified. The impact of planned error filtering and stabilisation systems for the Drive Beam bunch charge and longitudinal phase has been simulated and the optimal specifications for these systems, such as bandwidth and latency time, have been calculated and discussed. It has been found that a realistic feed-forward system could sufficiently reduce the longitudinal phase error of the Drive Beam, hence verifying that a satisfactory CLIC luminosity recovery system is possible to develop. Alternative designs of the Drive Beam accelerator, the recombination scheme and the phase signal distribution system have also been analysed. Measurements of the CTF3 Drive Beam phase have been performed. The source of the phase and energy errors at CTF3 has been determined. The performance of the phase feed-forward system prototype for CTF3 has been simulated. The prototype's specifications have been defined so that it will provide a sufficient test of the feed-forward correction principle. The prototype based on the defined specifications is currently in development and is to be installed at CTF3 in the second half of 2013.

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26

McEvoy, Erica L., and Erica L. McEvoy. "A Numerical Method for the Simulation of Skew Brownian Motion and its Application to Diffusive Shock Acceleration of Charged Particles." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625664.

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Stochastic differential equations are becoming a popular tool for modeling the transport and acceleration of cosmic rays in the heliosphere. In diffusive shock acceleration, cosmic rays diffuse across a region of discontinuity where the up- stream diffusion coefficient abruptly changes to the downstream value. Because the method of stochastic integration has not yet been developed to handle these types of discontinuities, I utilize methods and ideas from probability theory to develop a conceptual framework for the treatment of such discontinuities. Using this framework, I then produce some simple numerical algorithms that allow one to incorporate and simulate a variety of discontinuities (or boundary conditions) using stochastic integration. These algorithms were then modified to create a new algorithm which incorporates the discontinuous change in diffusion coefficient found in shock acceleration (known as Skew Brownian Motion). The originality of this algorithm lies in the fact that it is the first of its kind to be statistically exact, so that one obtains accuracy without the use of approximations (other than the machine precision error). I then apply this algorithm to model the problem of diffusive shock acceleration, modifying it to incorporate the additional effect of the discontinuous flow speed profile found at the shock. A steady-state solution is obtained that accurately simulates this phenomenon. This result represents a significant improvement over previous approximation algorithms, and will be useful for the simulation of discontinuous diffusion processes in other fields, such as biology and finance.

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27

Meplan, Olivier. "Ondes et particules dans le modèle de l'accélérateur de Fermi : simulation numérique." Université Joseph Fourier (Grenoble ; 1971-2015), 1996. http://www.theses.fr/1996GRE10016.

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Cette these aborde d'un point de vue numerique l'etude de la dynamique quantique de l'accelerateur de fermi qui presente classiquement du chaos: il s'agit d'une particule dans une boite a une dimension dont l'une des parois oscille. Nous etudions d'abord la mecanique classique: nous montrons que le temps du choc d'une particule sur une paroi mobile et l'energie de la particule dans le referentiel de la paroi sont des variables conjuguees et que les sections de poincare dans ces variables sont plus lisibles que les sections stroboscopiques usuelles. Ensuite, la dynamique quantique de ce systeme est etudiee au moyen de deux methodes numeriques: la premiere est une generalisation de la methode kkr dans l'espace-temps ; il suffit de resoudre une equation integrable sur le bord d'un billard espace-temps. La seconde methode est plus rapide et consiste en une succession de propagations libres et de pulses de potentiel. Ceci nous permet de calculer les etats de floquet que nous pouvons d'une part comparer a la dynamique classique grace aux distributions de husimi et d'autre part etudier en fonctions des parametres du systeme. Cette etude nous permet d'illustrer tres clairement certains phenomenes comme la localisation spatiale d'un paquet d'ondes dans un puits vibrant ou l'effet tunnel. Dans le regime adiabatique, nous donnons une formule pour les quasi-energies qui fait apparaitre notamment un terme de phase independant de l'etat (phase adiabatique). Dans ce regime, il existe des situations particuliere ou le spectre de quasi-energies presente une quasi-degenerescence totale. Alors l'energie d'un paquet d'ondes peut croitre de facon significative. Ce phenomene de resonance est tout a fait inattendu pour des oscillations lisses du mur vibrant. La troisieme partie traite de l'evolution d'une onde classique dans l'accelerateur de fermi. Grace a la methode kkr generalisee, nous mettons en evidence un phenomene quelque peu surprenant: dans la plupart des cas (pourvu que le mouvement du mur soit periodique) une onde se localise exponentiellement dans le puits et son energie augmente de facon exponentielle

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28

Rabhi, Nesrine. "Charged particle diagnostics for PETAL, calibration of the detectors and development of the demonstrator." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0339/document.

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Afin de protéger leurs systèmes de détection de l'impulsion électromagnétique géante générée par l'interaction du laser PETAL avec sa cible, les diagnostics de PETAL seront équipés de détecteurs passifs. Pour les ensembles SEPAGE et SESAME, une combinaison d'Imaging Plates (IP) et de couches de protection de matériaux de grand numéro atomique sera utilisée, qui permettra: 1) d'assurer que la réponse des détecteurs sera indépendante de son environnement mécanique proche dans les diagnostics et donc homogène sur toute la détection, 2) de blinder les détecteurs contre les photons de haute énergie produits dans la cible de PETAL. Dans le travail présenté ici, nous avons réalisé des expériences d'étalonnage avec les IPs auprès d'installations générant des électrons, des protons ou des ions, dans le but de couvrir le domaine en énergie cinétique de la détection des particules chargées de PETAL, de 0.1 à 200 MeV. L'introduction a pour but de décrire les méthodes et outils utilisés au cours de cette étude. Le second chapitre présente les résultats de deux expériences réalisées avec des électrons dans le domaine d'énergie cinétique [5-180] MeV. Le troisième chapitre décrit une expérience et ses résultats avec les protons entre 80 et 200 MeV étaient envoyés sur nos détecteurs. Le quatrième chapitre est consacré à une expérience utilisant des protons et des ions entre1 et 22 MeV en énergie de protons et dont l'objectif était l'étude de détecteurs et le test du démonstrateur de SEPAGE. Nous avons utilisé GEANT4 pour l'analyse de nos données et prédire la réponse de nos détecteurs dans le domaine 0.1 à 1000 MeV
In order to protect their detection against the giant electromagnetic pulse generated by the interaction of the PETAL laser with its target, PETAL diagnostics will be equipped with passive detectors. For SESAME and SEPAGE systems, a combination of imaging plate (IP) detectors with high-Z material protection layers will be used to provide additional features such as: 1) Ensuring a response of the detector to be independent of its environment and hence homogeneous over the surface of the diagnostics; 2) Shielding the detectors against high-energy photons from the PETAL target. In this work, calibration experiments of such detectors based on IPs were performed at electron and proton facilities with the goal of covering the energy range of the particle detection at PETAL from 0.1 to 200 MeV. The introduction aims at providing the reader the methods and tools used for this study. The second chapter presents the results of two experiments performed with electrons in the range from 5 to 180 MeV. The third chapter describes an experiment and its results, where protons in the energy range between 80 and 200 MeV were sent onto detectors. The fourth chapter is dedicated to an experiment with protons and ions in the energy range from 1 to 22 MeV proton energy, which aimed at studying our detector responses and testing the demonstrator of the SEPAGE diagnostic. We used the GEANT4 toolkit to analyse our data and compute the detection responses on the whole energy range from 0.1 to 1000 MeV

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29

Last, Jürgen. "Cutout Manager : a stand-alone software system to calculate output factors for arbitrarily shaped electron beams using Monte Carlo simulation." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=116119.

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In external electron beam therapy arbitrarily shaped inserts (cutouts) are used to define the contours of the irradiated field. This thesis describes the implementation and verification of a software system to calculate output factors for cutouts using Monte Carlo simulations. The design goals were: (1) A stand-alone software system running on a single workstation. (2) Task oriented graphical user interface with shape input capability. (3) Implementation on Mac OS XRTM (10A.x Tiger). (4) CPU multicore support by job splitting. (5) EGSnrc (Patch level V4-r2-2-5) for particle transport and dose scoring. (6) Validation for clinical use.
The system, called Cutout Manager, can calculate output factors with 1% statistical error in 20 minutes on Mac Pro computer (Intel XeonRTM, 4 cores). When the BEAMnrc linac model correctly reproduces percentage depth doses in the buildup region and around R100, calculated and measured output factors are in good agreement with precision measurements of circular cutouts at 100 cm source-to-surface distance (SSD) and extended SSD. Cutout Manager simulations are consistent with measurements of clinical cutouts within a 2% error margin.

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30

Ball, David, Feryal Özel, Dimitrios Psaltis, Chi-Kwan Chan, and Lorenzo Sironi. "The Properties of Reconnection Current Sheets in GRMHD Simulations of Radiatively Inefficient Accretion Flows." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/627036.

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Non-ideal magnetohydrodynamic (MHD) effects may play a significant role in determining the dynamics, thermal properties, and observational signatures of radiatively inefficient accretion flows onto black holes. In particular, particle acceleration during magnetic reconnection events may influence black hole spectra and flaring properties. We use representative general relativistic magnetohydrodynamic (GRMHD) simulations of black hole accretion flows to identify and explore the structures and properties of current sheets as potential sites of magnetic reconnection. In the case of standard and normal evolution (SANE) disks, we find that in the reconnection sites, the plasma beta ranges from 0.1 to 1000, the magnetization ranges from 10(-4) to 1, and the guide fields are weak compared with the reconnecting fields. In magnetically arrested (MAD) disks, we find typical values for plasma beta from 10(-2) to 10(3), magnetizations from 10(-3) to 10, and typically stronger guide fields, with strengths comparable to or greater than the reconnecting fields. These are critical parameters that govern the electron energy distribution resulting from magnetic reconnection and can be used in the context of plasma simulations to provide microphysics inputs to global simulations. We also find that ample magnetic energy is available in the reconnection regions to power the fluence of bright X-ray flares observed from the black hole in the center of the Milky Way.

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31

Zamansky, Rémi. "Simulation numérique directe et modélisation stochastique de sous-maille de l'accélération dans un écoulement de canal à grand nombre de Reynolds." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00673464.

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Cette thèse porte sur la caractérisation numérique et la modélisation stochastique de l'accélération du fluide pour l'écoulement en canal à grand nombre de Reynolds. La motivation concerne l'observation et l'analyse des effets de l'intermittence liés aux interactions à longue portée à travers le canal. Dans la première partie, l'accélération est étudiée par simulation numérique directe pour trois différents nombres de Reynolds (180, 590 et 1000). La lognormalité de la norme de l'accélération est observée quelle que soit la distance à la paroi. Un profil universel de la norme de l'accélération est également recherché par analyse dimensionnelle. La seconde partie présente une modélisation stochastique de l'accélération basée sur la décomposition norme/orientation. Le modèle stochastique pour la norme s'appuie sur un processus de fragmentation afin de représenter les interactions à longue portée à travers le canal. Pour l'orientation, l'évolution vers l'isotropie lorsque la distance à la paroi augmente (observée par la DNS) est reproduite grâce à un modèle de marche aléatoire sur une sphère. Ces modèles ont été appliqués à l'approche LES-SSAM (Stochastic Subgrid Acceleration Model) introduite par Sabel'nikov, Chtab et Gorokhovski. Nos calculs montrent que les estimations de la vitesse moyenne, du spectre d'énergie, des contraintes de l'écoulement et de la non-gaussianité des statistiques de l'accélération peuvent être améliorées de façon significative par rapport à la LES classique. L'intérêt de l'approche LES-SSAM, donnant un accès vers la structure intermittente de sous-maille, est illustré dans la dernière partie, par l'étude du transport de particules inertielles ponctuelles par l'écoulement de canal. Cette étude commence par l'analyse par DNS de l'influence des structures de paroi sur la dynamique des particules

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32

Psikal, Jan. "Ion acceleration in small-size targets by ultra-intense short laser pulses (simulation and theory)." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13941/document.

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Cette thèse a pour but l'étude de l’interaction des impulsions laser brèves et ultra-intenses avec des cibles de petite taille. Nous nous intéressons surtout des phénomènes liés à l’accélération des ions aux granges énergies. L'outil principal de cette étude est notre code Particle-in-Cell (PIC) bidimensionnel, qui est capable d'effectuer le calcul du mouvement des particules et de l'évolution des champs en régime relativiste et sans collisions. Ce mémoire présente la théorie de l’accélération d’ions par laser, les simulations numériques des différents régimes d'accélération, ainsi que les algorithmes mis en œuvre dans notre code. Les nouveaux résultats obtenus dans le cadre de cette thèse concernent trois cas principaux: 1) l’interaction des impulsions laser intenses avec des cibles de la masse limitée; 2) l’accélération des protons par laser dans des gouttelettes fines d’eau vaporisé; 3) le transport latéral des électrons chauds dans une feuille mince et son effet sur l’accélération d’ions. Nos études théoriques et les simulations numériques sont appliquées pour l'interprétation des résultats des deux expériences récentes réalisées par les équipes de recherche en Allemagne et en France. Ces expériences montrent une accélération efficace d’ions dans les conditions prévues dans nos travaux théoriques. Le spectre énergétique et le nombre des protons accélérés dans les feuilles minces de la surface limitée et dans les gouttelettes d’eau se comportent conformément aux nos prévisions. Le modèle théorique développé dans cette thèse considère l'accélération des ions en deux étapes. Le champ du laser n'interagit pas directement avec les ions du plasma du à sa masse très élevée. Par contre, les électrons chauds, générés pendant l’interaction de l'impulsion laser avec une cible, produisent les champs électrostatiques importants qui accélèrent les ions aux hautes énergies. Ces champs peuvent être amplifiés si la masse de la cible est suffisamment petite. Nous considérons que la cible a une masse limitée, si toutes ses dimensions sont comparables avec la taille du faisceau laser dans la zone d'interaction. Ces cibles permettent de réduire la dispersion des électrons chauds, et donc d'améliorer la transformation de l'énergie cinétique d'électrons dans l’´energie des ions. Nos simulations numériques indiquent que la taille de cible transverse optimale est égale au diamètre du faisceau laser. Les expériences récentes avec des feuilles minces de la surface limitée ont confirmé que la transformation de l’énergie laser `a l’énergie des ions est plus efficace, l’énergie des ions est plus élevée, et la divergence du faisceau d’ions diminue avec la diminution de la surface de feuille. La physique de l’interaction d'un faisceau laser avec les gouttelettes d’eau est plus complexe, car il faut prendre en compte plusieurs facteurs tels que l'ionisation inhomogène des atomes de la gouttelette et la recombinaison, sa position dans le focus de laser, les collisions des électrons etc. Nous avons modélisé l’interaction de l’impulsion laser avec une gouttelette de diamètre de 100 nm. Dans un petit agrégat des atomes irradié par laser, les électrons sont expulsés par la force pondéromotrice et, pas conséquent, les ions sont accélérés par la force de Coulomb. Nous avons réussi d'expliquer la formation d'un pic dans la fonction de distribution des protons en énergie par l'effet de la répulsion mutuelle entre deux espèces des ions. Finalement, nous avons étudié le transport latéral des électrons dans le cas de l'incidence rasante du faisceau laser sur la cible mince plaine. Avec une série des simulations nous avons démontré qui le transport des électrons accélérés est réalisé par deux mécanismes complémentaires: par le guidage des électrons chauds sur la surface d’avant de la feuille par les champs quasi statiques électrique et magnétique et par la recirculation des électrons entre les faces l'arrière et l'avant de la cible
The presented thesis is based on a theoretical study of the interaction of femtosecond laser pulses with small-size targets and related phenomena, mainly acceleration of ions. We have employed our relativistic collisionless two-dimensional particle-in-cell code to describe the interaction and subsequent ion acceleration. The theory of ion acceleration and related physics (for example, electron heating mechanisms) have been reviewed as well as computational algorithms used in our simulation code. In the thesis, our obtained results are organized into three main parts: 1) interaction of an intense laser pulse with mass-limited targets; 2) laser proton acceleration in a water spray target; 3) lateral hot electron transport and ion acceleration in thin foils. Our theoretical and numerical studies are accompanied with recent experimental results obtained by cooperating research groups on enhanced ion acceleration in thin foils of reduced surface and on proton acceleration in a cloud of water microdroplets. Since the field of nowadays operating lasers is not sufficient to accelerate directly ions to high energies due to their at least 1000 times larger mass-to-charge ratio compared with electrons, the ion acceleration is mediated by hot electrons creating strong electrostatic fields (a population of electrons heated by the laser wave) in targets of sizes higher or comparable with the laser wavelength or by Coulomb force between ions after electron expulsion in small clusters. Due to reduced target dimensions, the mass-limited targets, defined as the targets having all dimensions comparable with the laser spot size, limit the spread of hot electrons and, thus, the electron kinetic energy is transferred to ions more efficiently. We found via 2D PIC simulations that the optimum transverse target size is about the laser beam diameter. The enhancement of proton energy, laser-to-proton conversion efficiency, and narrower ion angular spread have been observed in recent experiments with thin foil sections and have confirmed our previous theoretical studies. The physics of the laser pulse interaction with water spray is rather complex and includes many phenomena (microdroplet ablation by laser prepulse, inhomogeneous droplet ionization, laser focal spot position in the spray, recombination and collisional effects in the surrounding target material, etc.). We have carried out numerical simulations of the laser pulse interaction with a water microdroplet of diameter of 100 nm, which gives an insight into the physics of ion acceleration in the spray. One can observe a pronounced peak in the proton energy spectra at the cutoff energy, which was explained by mutual interaction between protons and oxygen ions. Finally, we have studied two mechanisms of lateral electron transport in a thin foil - the first is due to hot electron guiding along the foil front surface by generated quasi-static electric and magnetic fields, and the second is caused by the hot electron recirculation (reversing of the normal component of electron velocity when the electron propagating through the foil starts to escape into vacuum, while the transverse velocity is largely unaltered). We found that only a small number of electrons can be guided along the foil surface for large incidence angles (60° and more) of the laser beam on the foil surface, whereas the majority of electrons is laterally transported towards foil edges due to the recirculation through the thin foil. However, electrons guided along the surface can be accelerated to several times higher energy than the recirculating electrons, which enhances the energy of accelerated ions from foil edges

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33

Smith, Joseph Richard Harrison. "Advanced Simulations and Optimization of Intense Laser Interactions." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1589302684037632.

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34

Cavallone, Marco. "Application of laser-plasma accelerated beams to high dose-rate radiation biology." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX063.

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Le cancer est la deuxième cause de décès dans le monde, représentant environ un décès sur six en 2018. Parmi les techniques employées de nos jours dans la lutte contre le cancer, l’une des plus utilisées et prometteuses est la radiothérapie, technique consistant en l’utilisation de rayonnements ionisants afin de déposer de l’énergie dans la tumeur pour la traiter. Or, puisque les cellules saines sont également endommagées par les rayonnements, le but de la radiothérapie est d’augmenter la sélectivité du traitement en épargnant autant que possible les tissus sains. L’optimisation de la sélectivité repose sur plusieurs aspects, comprenant l’optimisation spatiale de la dose, la précision de l’imagerie et de la dosimétrie, le type de rayonnement et la structure temporelle utilisée pour délivrer la dose. En particulier, le rôle du débit de dose et du temps d’irradiation n’a pas encore été explorés en détail.Les accélérateurs cliniques délivrent la dose avec un débit de dose d’environ quelques Gy/min, ce qui entraîne des temps d’irradiation de l’ordre de quelques minutes. Si, d’une part, l’effet d’une réduction du débit de dose de l’ordre de cGy/min sur la réponse biologique est bien connu, d’autre part l’effet d’un débit de dose élevé doit encore être éclairci. Recemment, des études in vivo réalisées avec des électrons et des photons produits par des prototypes d’accélérateurs ont montré que l’administration de la dose dans un temps court (<500 ms) et à un débit de dose élevé (>40 Gy/s) augmente la sélectivité du traitement en réduisant le risque d’effets secondaires sur les tissus sains. Bien que les causes de ce phénomène soient encore à l’étude, le protocole FLASH a été testé avec succès sur le premier patient en 2019. Ces résultats soulignent l’importance de la structure temporelle de l’irradiation et les avantages potentiels que les protocoles d’irradiation à haut débit de dose peuvent apporter en clinique. Or, l’utilisation de ces protocoles demande une compréhension plus approfondie des processus physico-chimiques et biologiques déclenchés par un dépôt de dose rapide.Dans ce contexte, les faisceaux de particules accélérées par laser représentent un outil unique pour jeter de la lumière sur les processus qui régissent la réponse biologique suite à une irradiation à haut débit de dose. Ces faisceaux sont produits en focalisant une impulsion laser ultra-courte (~fs) et ultra-intense (1019 W/cm2) sur une cible mince solide ou gazeuse (~μm), ce qui produit des faisceaux de particules ayant une durée de l’impulsion allant de la picoseconde à la femtoseconde. Ces caractéristiques permettent d’atteindre un débit de dose dans l’impulsion de l’ordre de ~109 Gy/s, c’est-à-dire des conditions d’irradiation extrêmement différentes par rapport aux protocoles de traitement conventionnels et FLASH. Pour cette raison, les faisceaux de particules accélérées par laser ont reçu une grande attention au cours des dernières années, mais leur effet biologique est toujours en discussion et d’autres études plus approfondies sont nécessaires.Cette thèse décrit les atouts des Protons Accélérés par Laser (PAL) et des Électrons Accélérés par Laser (EAL) produits par différents types de laser à haute puissance disponibles dans le commerce. En particulier, elle présente des études expérimentales et théoriques réalisées avec trois types de faisceaux permettant différentes modalités temporelles d’administration de la dose. L’objectif est de traiter certains des principaux problèmes liés à l’application de ces sources de particules à la biologie des rayonnements et de montrer des solutions et des techniques viable pour mener des études de radiobiologie systématique. Cela demande une caractérisation précise de ces faisceaux, l’optimisation de la distribution de la dose dans la cible biologique à travers la conception de lignes de transport adaptées et, enfin, l’étude de la réponse des instruments de dosimétrie utilisés en clinique à haut débit de dose
Cancer is the second leading cause of death globally, accounting for an estimated 9.6 million deaths, or one in six deaths, in 2018. Besides surgery and chemotherapy, radiotherapy is one of the major treatment modality. It consists in the use of ionising radiation to kill cancerous cells by depositing energy into the tumour and destroying the genetic material that controls how cells grow and divide. While both cancerous and healthy cells are damaged by radiation, the goal of radiotherapy is to increase the treatment selectivity by sparing as much as possible the healthy tissues. Optimisation of the selectivity reposes on several aspects, including spatial optimisation of the dose, precision of imaging techniques and dosimetry instruments, use of different radiations and temporal structures of dose delivery. In particular, the role of the dose-rate and the total irradiation time has not been extensively explored yet.Clinical accelerators typically deliver the dose with a dose rate around few Gy/min, leading to exposure times in the order of few minutes to deliver a therapeutic dose. While the effect of a reduction of the dose rate in the order of cGy/min is well known, the effect of high-dose rate, fast irradiation on living cells still need to be elucidated. Evidences of an effect of the high dose-rate on the biological response have been recently observed in many studies. In particular, in-vivo studies performed with electrons and photons produced by accelerator prototypes have shown that delivering the prescribed dose in a short exposure time (<500ms) and at a high dose-rate (>40Gy/s) increases the treatment selectivity by reducing the occurrence of secondary effects on healthy tissues compared to conventional treatments with the same total dose. Although theoretical explanations underpinning such phenomenon are still under discussion, the so-called FLASH protocol has been successfully tested with the first human patient in 2019, paving the way for further research in this domain. These important results point out the importance of the dose delivery modality on the treatment selectivity and the potential benefit that high dose-rate protocols may bring to clinics, asking for a deeper understanding of the physico-chemical and biological processes following fast dose deposition.In this scenario, Laser-Driven Particle (LDP) beams represent a unique tool to shed some light on the radiobiological response following high-dose rate irradiation. LDP sources are produced by focusing an ultra-short (~fs) and ultra-intense (1019 W/cm2) laser pulse on a solid or gaseous thin target (~μm), producing proton and electron bunches with duration of respectively a few picoseconds and a few femtoseconds. These characteristics allow the reach of extremely high peak dose-rate in the pulse of the order of ~109 Gy/s in comparison with conventional and FLASH treatment protocols. For this reason, LDP sources have been receiving great attention in the last decade, but their radiobiological effect is still debated and further systematic studies are required.This thesis discusses the potential of both Laser-Accelerated Protons (LAP) and Laser-Accelerated Electrons (LAE) produced by different types of commercially available high-power lasers systems. In particular, it presents experimental and theoretical studies carried out with three different types of LDP beams, i.e. Hz LAPs, single-shot LAPs and kHz LAEs, enabling different temporal modalities of dose delivery. The goal is to address some of the main issues related to the application of such sources to radiation biology and show viable solutions and irradiation protocols to perform systematic radiobiology studies. Such issues include accurate characterisation of the source, optimisation of the dose distribution at the biological target through the design of adapted transport beamlines and investigation of the behaviour of dosimetric instruments for high dose-rate dosimetry

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35

NOBILE, MARCO SALVATORE. "Evolutionary Inference of Biological Systems Accelerated on Graphics Processing Units." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2015. http://hdl.handle.net/10281/75434.

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In silico analysis of biological systems represents a valuable alternative and complementary approach to experimental research. Computational methodologies, indeed, allow to mimic some conditions of cellular processes that might be difficult to dissect by exploiting traditional laboratory techniques, therefore potentially achieving a thorough comprehension of the molecular mechanisms that rule the functioning of cells and organisms. In spite of the benefits that it can bring about in biology, the computational approach still has two main limitations: first, there is often a lack of adequate knowledge on the biological system of interest, which prevents the creation of a proper mathematical model able to produce faithful and quantitative predictions; second, the analysis of the model can require a massive number of simulations and calculations, which are computationally burdensome. The goal of the present thesis is to develop novel computational methodologies to efficiently tackle these two issues, at multiple scales of biological complexity (from single molecular structures to networks of biochemical reactions). The inference of the missing data — related to the three-dimensional structures of proteins, the number and type of chemical species and their mutual interactions, the kinetic parameters — is performed by means of novel methods based on Evolutionary Computation and Swarm Intelligence techniques. General purpose GPU computing has been adopted to reduce the computational time, achieving a relevant speedup with respect to the sequential execution of the same algorithms. The results presented in this thesis show that these novel evolutionary-based and GPU-accelerated methodologies are indeed feasible and advantageous from both the points of view of inference quality and computational performances.

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36

Barge, Alexis. "Propriétés lagrangiennes de l'accélération turbulente des particules fluides et inertielles dans un écoulement avec un cisaillement homogène : DNS et nouveaux modèles de sous-maille de LES." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC012/document.

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Ce travail de thèse porte sur l’étude de l’accélération de particules fluides et inertielles en déplacement dans une turbulence soumise à un gradient de vitesse moyen. L’objectif est de récupérer des données de référence afin de développer des modèles LES stochastiques pour la prédiction de l’accélération de sous-maille et l’accélération de particules inertielles dans des conditions inhomogènes. La modélisation de l’accélération de sous-maille est effectuée à l’aide de l’approche LES-SSAM introduite par Sabel’nikov, Chtab et Gorokhovski[EPJB 80:177]. L’accélération est modélisée à l’aide de deux modèles stochastiques indépendants : un processus log-normal d’Ornstein-Uhlenbeck pour la norme d’accélération et un processus stochastique Ornstein-Uhlenbeck basé sur le calcul de Stratonovich pour les composantes du vecteur d’orientation de l’accélération. L’approche est utilisée pour la simulation de particules fluides et inertielles dans le cas d’une turbulence homogène isotrope et dans un cisaillement homogène. Les résultats montrent une amélioration des statistiques à petites échelles par rapport aux LES classiques. La modélisation de l’accélération des particules inertielles dans le cisaillement homogène est effectuée avec l’approche LES-STRIP introduite par Gorokhovski et Zamansky[PRF 3:034602] et est modélisée avec deux modèles stochastiques indépendants de manière similaire à l’accélération de sous-maille. Nos calculs montrent une amélioration de l’accélération et de la vitesse des particules lorsque le modèle STRIP est utilisé. Enfin dans une dernière partie, nous présentons une équation pour décrire la dynamique de particules ponctuelles de taille supérieure à l’échelle de Kolmogorov dans une turbulence homogène isotrope calculée par DNS. Les résultats sont comparés avec l’expérience et montrent que cette description reproduit bien les propriétés dynamiques des particules
The main objective of this thesis is to study the acceleration of fluid and inertial particles moving in a turbulent flow under the influence of a homogeneous shear in order to develop LES stochastic models that predict subgrid acceleration of the flow and acceleration of inertial particles. Subgrid acceleration modelisation is done in the framework of the LES-SSAM approach which was introduced by Sabel’nikov, Chtab and Gorokhovski[EPJB 80:177]. Acceleration is predicted with two independant stochastic models : a log-normal Ornstein-Uhlenbeck process for the norm of acceleration and an Ornstein-Uhlenbeck process expressed in the sense of Stratonovich calculus for the components of the acceleration orientation vector. The approach is used to simulate fluid and inertial particles moving in a homogeneous isotropic turbulence and in a homogeneous sheared turbulence. Our results show that small scales statistics of particles are better predicted in comparison with classical LES approach. Modelling of inertial particles acceleration is done in the framework of the LES-STRIP which was introduced by Gorokhovski and Zamansky[PRF 3:034602] with two independant stochastic models in a similar way to the subgrid fluid acceleration. Computations of inertial particles in the homogeneous shear flow present good predicitons of the particles acceleration and velocity when STRIP model is used. In the last chapter, we present an equation to describe the dynamic of point-like particles which size is larger than the Kolmogorov scale moving in a homogeneous isotropic turbulence computed by direct numerical simulation. Results are compared with experiments and indicate that this description reproduces well the properties of the particles dynamic

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37

Matsui, Ryutaro. "Study of nonlinear structures and dynamics in collisionless plasmas created by the interaction between high power laser and cluster medium." Kyoto University, 2019. http://hdl.handle.net/2433/242326.

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38

Rassou, Sébastien. "Accélération d'électrons par onde de sillage laser : Développement d’un modèle analytique étendu au cas d’un plasma magnétisé dans le régime du Blowout." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS066/document.

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Une impulsion laser intense se propageant dans un plasma sous-dense (ne< 10¹⁸ W.cm⁻²) et de durée très courte (τ₀< 100 fs), , on atteint le régime de la bulle. Les champs électriques dans ces bulles, de l’ordre de 100 GV/m, peuvent accélérer un faisceau d’électrons jusqu’au GeV sur des distances de l’ordre du centimètre. Dans ce régime, les électrons expulsés par la force pondéromotrice du laser forment une fine et dense couche à la surface d'une cavité d'ions restés immobiles. Les propriétés de ce régime sont examinées par l’intermédiaire d’un modèle analytique, que nous avons développé en nous inspirant du travail de W. Lu et S. Yi. En nous plaçant dans ce régime prometteur, nous avons étudié les mécanismes d’injection et de piégeage dans l'onde de sillage. Dans l’injection optique, les polarisations parallèles ou circulaires positives conduisent respectivement à une injection mettant en jeu du chauffage stochastique, ou à l’injection froide. Un paramètre de similarité est introduit, celui-ci permet de déterminer la méthode d’injection la plus appropriée pour maximiser la charge injectée. Enfin, le modèle analytique présenté en première partie est étendu afin d’étudier l’onde de sillage dans le régime de la bulle lorsqu’un champ magnétique longitudinal initial est appliqué au plasma. Lorsque le plasma est magnétisé deux phénomènes remarquables se manifestent, d'une part une ouverture apparaît à l'arrière de la bulle et d'autre part un mécanisme d'amplification du champ magnétique longitudinale est induit par la variation du flux magnétique. Les prédictions de notre modèle analytique sont confrontées aux résultats de simulations PIC 3D issues du code CALDER-Circ. La conséquence immédiate de la déformation de l'onde de sillage est la réduction, voire la suppression de l'auto-injection. L’application d’un champ magnétique longitudinal, combinée à un choix judicieux des paramètres laser-plasma, permet de réduire la dispersion en énergie des faisceaux d’électrons produits après injection optique
An intense laser pulse propagating in an under dense plasma (ne< 10¹⁸ W.cm⁻²) and short(τ₀< 100 fs), the bubble regime is reached. Within the bubble the electric field can exceed 100 GV/m and a trapped electron beam is accelerated to GeV energy with few centimetres of plasma.In this regime, the electrons expelled by the laser ponderomotive force are brought back and form a dense sheath layer. First, an analytic model was derived using W. Lu and S. Yi formalisms in order to investigate the properties of the wakefield in the blowout regime. In a second part, the trapping and injection mechanisms into the wakefield were studied. When the optical injection scheme is used, electrons may undergo stochastic heating or cold injection depending on the lasers’ polarisations. A similarity parameter was introduced to find out the most appropriate method to maximise the trapped charge. In a third part, our analytic model is extended to investigate the influence of an initially applied longitudinal magnetic field on the laser wakefield in the bubble regime. When the plasma is magnetized two remarkable phenomena occur. Firstly the bubble is opened at its rear, and secondly the longitudinal magnetic field is amplified - at the rear of the bubble - due to the azimuthal current induced by the variation of the magnetic flux. The predictions of our analytic model were shown to be in agreement with 3D PIC simulation results obtained with Calder-Circ. In most situations the wake shape is altered and self-injection can be reduced or even cancelled by the applied magnetic field. However, the application of a longitudinal magnetic field, combined with a careful choice of laser-plasma parameters, reduces the energy spread of the electron beam produced after optical injection

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39

Skwarcan-Bidakowski, Alexander. "Exotic Decays of a Vector-liketop Partner at the LHC." Thesis, Uppsala universitet, Högenergifysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-392988.

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An evaluation of how sensitive some ATLAS searches for new physics are to a new beyond standard model (BSM) vector-like quark (VLQ) and a pseudo Nambu-Goldstone boson (pNGB) scalar. This was done by simulating a signal containing these new particles and making a recast of it onto existing verified ATLAS searches for new physics at center-of-mass (CM) energy of 13 TeV (Run 2) at the Large Hadron Collider (LHC). Signals for recasting were tailored such that their final states would be appropriate in relation to each respective ATLAS search in order to use the same selection criteria as applied in the existing searches. The results are summarized in the form of significances (Z) for each masspoint of the new top-partner and S particle. Significances did not show any expectiation of excluding any masspoint in the examined mass range for the recasts at 95% CL. This suggests that a dedicated search for these particles in the considered masspoints would be required.

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40

Moreau, Julien. "Interaction d’une impulsion laser intense avec un plasma sous dense dans le régime relativiste." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0042/document.

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De part ses nombreuses applications scientifiques et sociétales comme la radiographie protonique ou encore la protonthérapie, l’accélération d’ions par laser suscite un grand intérêt. Cette thèse s’inscrit dans ce cadre et présente une étude de l’interaction d’une impulsion laser d’intensité relativiste avec un plasma de densité modérée. Dans ce régime, le plasma est transparent à l’onde laser et les électrons oscillent à des vitesses relativistes dans le champ de l’onde incidente. Ces conditions sont favorables à un transfert efficace de l’énergie laser vers le plasma, et donc sont intéressantes pour l’accélération d’ions par laser. Ce régime permet également la création de solitons électromagnétiques et acoustiques dont les mécanismes de formation et les propriétés nécessitent une meilleur compréhension. Nous réalisons une étude détaillée de simulations Particle-In-Cell (réalisées avec le code OCEAN) de l’interaction d’une impulsion laser intense avec un plasma sous dense. Nous montrons que la diffusion Raman stimulée (SRS) dans le régime relativiste est le principal processus responsable de l’absorption de l’énergie laser par le plasma et qu’il est, en outre, très efficace puisqu’il permet de transférer près de 70 % de l’énergie de l’impulsion laser aux électrons. Cette instabilité apparaît dans des plasmas dont la densité est nettement supérieure à la densité quart-critique du fait de la diminution de la fréquence plasma électronique et se développe sur des temps très courts. Il permet ainsi un chauffage homogène des électrons tout le long de la propagation de l’impulsion laser à travers le plasma. Ces électrons participent à la détente du plasma, et créent sur ses bords raids un champ électrostatique permettant l’accélération des ions. Ces derniers gagnent 30 % de l’énergie laser initiale. Nous avons aussi développé un modèle simple qui permet de prédire et donc d’optimiser le taux de rétro-diffusion du plasma du fait du développement de l’instabilité SRS. Nous nous intéressons également à la séquence des processus permettant la formation des cavités électromagnétiques. Cette analyse souligne le rôle joué par l’instabilité modulationnelle ou de Benjamin-Feir sur le front de l’impulsion laser qui est divisée en un train de plusieurs solitons électromagnétiques. À l’aide d’une étude détaillée, nous montrons que ces solitons excitent des ondes plasmas dans leur sillage en se propageant dans le plasma, perdent de l’énergie et finissent par être piégés. Ils forment également des dépressions (cavités) des densités électroniques et ioniques du plasma. Ces cavités sont des pièges pour les champs électromagnétiques rayonnés par le plasma (par exemple du fait de l’instabilité SRS) et survivent grâce à un équilibre entre la pression de radiation des champs piégés et les pressions cinétiques électroniques à leurs bords. Ces cavités absorbent une part importante de l’énergie laser mais elles n’en conservent qu’une partie sous forme d’énergie électromagnétique piégée. Le reste de l’énergie permet l’expansion de la cavité, la génération de solitons acoustiques supersoniques et l’accélération de particules
The laser-accelerated ions draw an increasing interest due to their potential applications and to their unique properties. This manuscript presents a study of the interaction between a relativistic intense laser pulse and a low density plasma. In this regime, the plasma is transparent to the laser pulse and electrons oscillate with relativistic velocities in the field of the incident wave. These conditions make the transfer of the laser pulse energy to the plasma efficient, and therefore are interesting for the ion acceleration. This regime generates also electromagnetic and acoustic solitons whose formation mechanisms and properties need to be better understood. We carry out a detailed analysis of Particle-In-Cell simulations (performed with the code OCEAN) of interaction of an intense laser pulse with a low density plasma.We show that the stimulated Raman scattering (SRS) is the main mechanism responsible for the absorption of laser energy in plasma. This process is very efficient : it leads to the transfer of 70 % of the laser pulse energy to electrons. This instability occurs in plasmas with a density larger than the quarter critical one due to the decrease of the electron plasma frequency and develops in a very short time scale. It leads to an homogeneous electron heating all along the distance of propagation of the laser pulse through the plasma. The ions are efficiently accelerated at the plasma edges and can get nearly 30%of the initial laser energy. This study is accompanied by a simple analytical model which is able to predict and so optimize the laser backscattering fraction due to the development of the SRS instability. We also present a sequence of stages which lead to the formation of electromagnetic cavities. This analysis highlights the role of the modulationnal or Benjamin-Feir instability in the front of the laser pulse, which is split in a train of electromagnetic solitons. Our detailed study shows that these solitons excite plasmas waves in their wake, lose energy and are finally trapped in the plasma. They lead to the formation of density depressions (cavities) which may trap the electromagnetic fields produced in the plasma (by the SRS instability, for example). These structures may survive for a long time thanks to an equilibrium of the trapped field radiation pressure and the electronic kinetic pressure at their borders. These cavities absorb an significant part of the laser energy but only a part of it is trapped inside. The remaining part is invested in the cavity expansion, generation of acoustic solitons and acceleration of charged particles

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41

Kerdraon, Denis. "Optimisation par simulation du couplage entre un réacteur sous-critique et sa source de spallation : application à un démonstrateur." Phd thesis, Grenoble INPG, 2001. http://www.theses.fr/2001INPG0089.

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Les réacteurs hybrides, bases sur le couplage entre un accélérateur de particules et un coeur sous-critique via une cible de spallation, présentent des possibilités de réduction de la radiotoxicité des déchets de haute activité et a vie longue promis au stockage. Les différents concepts proposes ces dernières années dans la communauté scientifique montrent la nécessite de réaliser un démonstrateur. Ce travail de thèse a porte sur l'optimisation par simulation Monte Carlo a l'aide du code MCNPX, de la neutronique d'un tel système dans le but de réaliser un réacteur pilote. Tout d'abord, nous avons indique les principales caractéristiques neutroniques d'un réacteur hybride avant de présenter le concept de démonstrateur refroidi au gaz base sur le remontage effectue par la société Framatome ANP. Nous avons caractérise puis optimise la neutronique a travers la géométrie et les matériaux utilises pour ce démonstrateur. Dans le cadre de l'incinération des actinides mineurs, nous avons calcule l'évolution des combustibles envisageables suivant les phases de démonstration prévues. Les grandeurs liées a l'incinération des actinides mineurs sont rapportées. En vue de la transmutation du 99Tc et de l'129I, nous avons calcule les temps caractéristiques et les taux de transmutation a l'équilibre. D'autre part, nous avons analyse le passage du démonstrateur vers un réacteur incinérateur de puissance a partir de critères physiques tels que les facteurs de forme et les niveaux de flux. A partir de cette analyse, des solutions innovantes sont proposées pour améliorer les facteurs de forme d'un incinérateur de puissance. Enfin, dans des perspectives a plus long terme, l'utilisation des réacteurs hybrides dans le cadre de la génération d'233U pour accélérer le démarrage d'une filière de réacteurs a sels fondus basée sur le cycle 232Th/233U a été explorée et s'avère particulièrement efficace
Accelerator Driven Systems (ADS), based on a proton accelerator and a sub-critical core coupled with a spallation target, offer advantages in order to reduce the nuclear waste radiotoxicity before repository closure. Many studies carried out on the ADS should lead to the definition of an experimental plan which would federate the different works in progress. This thesis deals with the neutronic Monte Carlo simulations with the MCNPX code to optimize such a system in view of a pilot reactor building. First, we have recalled the main neutronic properties of an hybrid reactor. The concept of gas-cooled eXperimental Accelerator Driven System (XADS) chosen for our investigations comes from the preliminary studies done by the Framatome company. In order to transmute minor actinides, we have considered the time evolution of the main fuels which could be reasonably used for the demonstration phases. The neutronic parameters of the reactor, concerning minor actinide transmutation, are reported. Also, we have calculated the characteristic times and the transmutation rates in the case of 99Tc and 129I isotopes. We have identified some neutronic differences between an experimental and a power ADS according to the infinite multiplication coefficient, the shape factor and the level of flux to extend the demonstrator concept. We have proposed geometric solutions to keep the radial shape factor of a power ADS acceptable. In the last part, beyond the experimental XADS scope, we have examined the possible transition towards an uranium/thorium cycle based on Molten Salt Reactors using a power ADS in order to generate the required 233U proportion

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42

Breidenich, Jennifer L. "Impact-initiated combustion of aluminum." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54403.

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This work focuses on understanding the impact-initiated combustion of aluminum powder compacts. Aluminum is typically one of the components of intermetallic-forming structural energetic materials (SEMs), which have the desirable combination of rapid release of thermal energy and high yield strength. Aluminum powders of various sizes and different levels of mechanical pre-activation are investigated to determine their reactivity under uniaxial stress rod-on-anvil impact conditions, using a 7.62 mm gas gun. The compacts reveal light emission due to combustion upon impact at velocities greater than 170 m/s. Particle size and mechanical pre-activation influence the initiation of aluminum combustion reaction through particle-level processes such as localized friction, strain, and heating, as well as continuum-scale effects controlling the amount of energy required for compaction and deformation of the powder compact during uniaxial stress loading. Compacts composed of larger diameter aluminum particles (~70µm) are more sensitive to impact initiated combustion than those composed of smaller diameter particles. Additionally, mechanical pre-activation by high energy ball milling (HEBM) increases the propensity for reaction initiation. Direct imaging using high-speed framing and IR cameras reveals light emission and temperature rise during the compaction and deformation processes. Correlations of these images to meso-scale CTH simulations reveal that initiation of combustion reactions in aluminum powder compacts is closely tied to mesoscale processes, such as particle-particle interactions, pore collapse, and particle-level deformation. These particle level processes cannot be measured directly because traditional pressure and velocity sensors provide spatially averaged responses. In order to address this issue, quantum dots (QDs) are investigated as possible meso-scale pressure sensors for probing the shock response of heterogeneous materials directly. Impact experiments were conducted on a QD-polymer film using a laser driven flyer setup at the University of Illinois Urbana-Champaign (UIUC). Time-resolved spectroscopy was used to monitor the energy shift and intensity loss as a function of pressure over nanosecond time scales. Shock compression of a QD-PVA film results in an upward shift in energy (or a blueshift in the emission spectra) and a decrease in emission intensity. The magnitude of the shift in energy and the drop in intensity are a function of the shock pressure and can be used to track the particle scale differences in the shock pressure. The encouraging results illustrate the possible use of quantum dots as mesoscale diagnostics to probe the mechanisms involved in the impact initiation of combustion or intermetallic reactions.

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Hadj-Bachir, Mokrane. "Laser à rayons X ultra-compact Raman XFEL." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0400/document.

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L’obtention d’un Laser à Électrons Libres X (LEL-X) compact est un objectif majeur pour le développement des lasers. Plusieurs schémas prometteurs de LEL-X ont été proposés en utilisant à la fois l’accélération d’électrons dans les plasmas et des onduleurs optiques en régime Compton ou Compton inverse. Nous avons proposé un nouveau concept de LEL-X compact baptisé Raman XFEL, en combinant la physique des LEL en régime Compton, des lasers XUV conventionnels basés sur l’interaction laser plasma, et de l’optique non-linéaire. Nous étudions dans cette thèse les étapes préalables pour déclencher un effet laser à rayons X lors de l’interaction entre un paquet d’électrons libres relativistes et un réseau optique créé par l’interférence transverse de deux impulsions laser intenses. Dans cet objectif j’ai développé un code particulaire baptisé RELIC. Les études menées avec le code RELIC nous ont permis d’étudier la dynamique d’électrons relativistes et les processus d’injection du paquet d’électrons dans le réseau optique. Grâce à RELIC, nous avons distingué de nouveaux régimes d’interaction en fonction des paramètres du paquet d’électrons, ainsi que de la géométrie du réseau optique. Ces études ont été appliquées à l’amplification du rayonnement X et appuyées par des simulations PIC. RELIC a également permis de modéliser et d’analyser la première expérience réalisée en octobre 2015 sur l’installation laser ’Salle Jaune’ au Laboratoire d’Optique Appliquée (LOA). Cette première expérience a été une étape très importante pour la validation des modèles théoriques, et pour la réalisation future d’un laser à électrons libre X Raman
The quest for a compact X-ray laser has long been a major objective of laser science. Several schemes using optical undulators are currently considered, in order to trigger the amplification of back scattered radiation, in Compton or inverse Compton regime. We have proposed a new concept of compact XFEL based on a combination between the physics of free electron lasers, of laser-plasma interactions, and of nonlinear optics. In this thesis, we study the necessary steps to trigger a X-ray laser during the interaction between a free relativistic electron bunch and an optical lattice created by the interference of two intense transverse laser pulses. For this purpose I developed a particular tracking code dubbed RELIC. RELIC allowed us to study the dynamics and injection process of a bunch of relativistic electrons into the optical lattice. Thanks to RELIC, we distinguished several interaction regimes depending on the relativistic electron bunch parameters, and on those of the optical lattice and its geometry. These studies are applied to the X ray amplification and supported by PIC simulations. RELIC also allowed us to model and analyze the first experiment conducted in october 2015 on the ”Salle Jaune” laser facility at LOA. This first experiment was very important to validate our theoretical models, and should prove to be an essential milestone for the development of a Raman X-ray free electron laser

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Galindo, Muñoz Natalia. "Development of direct measurement techniques for the in-situ internal alignment of accelerating structures." Doctoral thesis, Universitat Politècnica de València, 2018. http://hdl.handle.net/10251/100488.

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Анотація:

Las exigentes tolerancias de alineación en los componentes de los futuros colisionadores lineales de partículas requieren el desarrollo de nuevas técnicas de alineación más precisas que las existentes. Este es el caso del Colisionador Lineal Compacto (Compact Linear Collider, CLIC), cuyos objetivos altamente restrictivos de alineamiento alcanzan los 10 um. Para poder lograr el máximo rendimiento del acelerador, es necesario que el posicionamiento de las estructuras que aceleran las partículas y de los campos que las guían cumplan las tolerancias de alineación para dirigir el haz a lo largo de la trayectoria diseñada. Dicho procedimiento consiste en relacionar la posición de los ejes de referencia de cada componente con respecto a objetos externos, o fiduciales, lo cual resulta muy tedioso y económicamente costoso. Los errores sistemáticos y aleatorios se van acumulando en cada paso del proceso y, en consecuencia, la precisión final de alineamiento es todo un desafío. En este contexto, nace el proyecto PACMAN (Particle Accelerator Components Metrology and Alignment to the Nanometre scale), subvencionado por la Unión Europea en el programa FP7 de financiación para la investigación e innovación. El objetivo principal de PACMAN es investigar, desarrollar e implementar una solución integrada alternativa que incorpore todos los pasos de alineación en una misma ubicación, con el objetivo de mejorar la precisión de alineación de los componentes de los aceleradores, en concreto: las estructuras aceleradoras, los cuadrupolos y los monitores de posición de haz. La viabilidad de las soluciones desarrolladas y la precisión de alineamiento alcanzada deben de demostrarse en un banco de pruebas utilizando componentes de CLIC. La estrategia de PACMAN para alcanzar el objetivo técnico se divide en tres pasos. El primero consiste en la fiducialización de los componentes y sus soportes. El segundo paso es el ensamblaje de los componentes en dos tipos de soporte, uno compuesto por un monitor de posición de haz y un cuadrupolo, y otro con cuatro estructuras aceleradoras, tomando como referencia su centro electromagnético. Finalmente, ambos soportes se transportan al túnel para su alineación final utilizando técnicas de hilos tensados. En esta tesis doctoral, se describe el desarrollo de una nueva técnica no destructiva para localizar los ejes electromagnéticos de estructuras aceleradoras y su validación experimental. Para ello, se ha utilizado una estructura aceleradora de CLIC conocida como TD24. Debido a la complejidad mecánica de la TD24, su difícil acceso y su diámetro medio de iris de 5.5 mm, se desarrolla una nueva técnica denominada en esta tesis como 'el método perturbativo' y se realiza una propuesta experimental de validación. El estudio de viabilidad de este método, cumpliendo con los requisitos impuestos de precisión en la medida de 10 um, ha sido realizado con una campaña extensa de simulaciones de campos electromagnéticos en tres dimensiones utilizando la herramienta de software conocida como HFSS. Los resultados de simulación han permitido el desarrollo de un algoritmo muy completo de medidas y han proporcionado las especificaciones técnicas para el diseño conceptual de un banco de pruebas para la medida de los ejes electromagnéticos de la TD24. El preciso ensamblaje del banco de pruebas y sus correspondientes calibraciones, la incorporación de nuevos tratamientos de las medidas en el algoritmo final y la caracterización de fuentes de error en la medida, favorecieron la localización del centro electromagnético en la TD24 con una precisión menor a 1 um con un error estimado menor que 8.5 um, cumplimiendo con los objetivos de precisión establecidos.
In the next generation of linear particle accelerators, challenging alignment tolerances are required in the positioning of the components focusing, accelerating and detecting the beam over the accelerator length in order to achieve the maximum machine performance. In the case of the Compact Linear Collider (CLIC), accelerating structures, beam position monitors and quadrupole magnets need to be aligned in their support with respect to their reference axes with an accuracy of 10 um. To reach such objective, the PACMAN (Particle Accelerator Components Metrology and Alignment to the Nanometer Scale) project strives for the improvement of the current alignment accuracy by developing new methods and tools, whose feasibility should be validated using the major CLIC components. This Ph.D. thesis concerns the investigation, development and implementation of a new non-destructive intracavity technique, referenced here as 'the perturbative method', to determine the electromagnetic axes of accelerating structures by means of a stretched wire, acting as a reference of alignment. Of particular importance is the experimental validation of the method through the 5.5 mm iris-mean aperture CLIC prototype known as TD24, with complex mechanical features and difficult accessibility, in a dedicated test bench. In the first chapter of this thesis, the alignment techniques in particle accelerators and the novel proposals to be implemented in the future linear colliders are introduced, and a detailed description of the PACMAN project is provided. The feasibility study of the method, carried out with extensive electromagnetic fields simulations, is described in chapter 2, giving as a result, the knowledge of the theoretical accuracy expected in the measurement of the electromagnetic axes and facilitating the development of a measurement algorithm. The conceptual design, manufacturing and calibration of the automated experimental set-up, integrating the solution developed to measure the electromagnetic axes of the TD24, are covered in chapter 3. The future lines of research and developments of the perturbative method are also explored. In chapter 4, the most significant results obtained from an extensive experimental work are presented, analysed and compared with simulations. The proof-of-principle is completed, the measurement algorithm is optimised and the electromagnetic centre is measured in the TD24 with a precision less than 1 um and an estimated error less than 8.5 um. Finally, in chapter 5, the developments undertaken along this research work are summarised, the innovative achievements accomplished within the PACMAN project are listed and its impact is analysed.
En la generació pròxima d'acceleradors de partícules lineals, desafiant toleràncies d'alineament és requerit en el posicionament dels components que enfoquen, accelerant i detectant la biga sobre la longitud d'accelerador per tal d'aconseguir l'actuació de màquina màxima. En el cas del Colisionador Compacte Lineal (CLIC), accelerant estructures, monitors de posició de fes i imants necessiten ser alineats en el seu suport amb respectar a les seves destrals de referència amb una precisió de 10 um. Per assolir tal objectiu, el PACMAN (Metrologia de Components de l'Accelerador de partícules i Alineament al Nanometer Escala) projecte s'esforça per la millora de l'actual precisió d'alineament per mètodes nous en desenvolupament i eines, la viabilitat dels quals hauria de ser validada utilitzant els components de CLIC importants. Aquesta tesi concerneix la investigació, desenvolupament i implementació d'un nou no-destructiu tècnica interna, va referenciar ací mentre 'el mètode de pertorbació' per determinar les destrals electromagnètiques d'accelerar estructures mitjançant un cable estès, actuant com a referència d'alineament. De la importància particular és la validació experimental del mètode a través del 5.5 mm iris-roí obertura prototipus de CLIC sabut com TD24, amb característiques mecàniques complexes i accessibilitat difícil, en un banc de prova dedicat. En el primer capítol d'aquesta tesi, les tècniques d'alineament en acceleradors de partícules i les propostes novelles per ser implementades en el futur colisionador lineal és introduït, i una descripció detallada del projecte PACMAN és proporcionat. L'estudi de viabilitat el mètode de pertorbació, va dur a terme amb simulacres de camps electromagnètics extensos, és descrit dins capitol 2, donant com a resultat, el coneixement de la precisió teòrica esperada en la mida de les destrals electromagnètiques i facilitant el desenvolupament d'un algoritme de mida. El disseny conceptual, fabricació i calibratge del conjunt experimental automatitzat-amunt, integrant la solució desenvolupada per mesurar les destrals electromagnètiques del TD24, és cobert dins capitol 3. Les línies futures de recerca i desenvolupaments del mètode és també va explorar. Dins capitol 4, la majoria de resultats significatius van obtenir d'una faena experimental extensa és presentada, analitzat i comparat amb simulacres. La prova-de-el principi és completat, l'algoritme de mida és optimitzat i el centre electromagnètic és mesurat en el TD24 amb una precisió menys d'1 um i un error calculat menys de 8.5 um. Finalment, dins capitol 5, els desenvolupaments empresos al llarg d'aquesta faena de recerca és resumit, les consecucions innovadores van acomplir dins del projecte PACMAN és llistat i el seu impacte és analitzat.
Galindo Muñoz, N. (2018). Development of direct measurement techniques for the in-situ internal alignment of accelerating structures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/100488
TESIS

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45

Jung, Paul Matthew. "Hybrid macro-particle moment accelerator tracking algorithm." Thesis, 2020. http://hdl.handle.net/1828/12036.

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A particle accelerator simulation which straddles the gap between multi-particle and moment codes is derived. The hybrid approach represents the beam using macro-particles which contain discrete longitudinal coordinates and transverse second moments. The discretization scheme for the macro-particles is derived using variational principles, as a natural extension of well known variational approaches. This variational discretization allows for exact transverse emittance conservation. The electrostatic self-potential is discrete in the longitudinal direction and solved semi-analytically in the transverse direction using integrated Green’s functions. The algorithm is implemented and tested against both a moment and multi-particle code.
Graduate

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46

O'Kelly, David Sean 1961. "Operation and reactivity measurements of an accelerator driven subcritical TRIGA reactor." Thesis, 2008. http://hdl.handle.net/2152/3973.

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Experiments were performed at the Nuclear Engineering Teaching Laboratory (NETL) in 2005 and 2006 in which a 20 MeV linear electron accelerator operating as a photoneutron source was coupled to the TRIGA (Training, Research, Isotope production, General Atomics) Mark II research reactor at the University of Texas at Austin (UT) to simulate the operation and characteristics of a full-scale accelerator driven subcritical system (ADSS). The experimental program provided a relatively low-cost substitute for the higher power and complexity of internationally proposed systems utilizing proton accelerators and spallation neutron sources for an advanced ADSS that may be used for the burning of high-level radioactive waste. Various instrumentation methods that permitted ADSS neutron flux monitoring in high gamma radiation fields were successfully explored and the data was used to evaluate the Stochastic Pulsed Feynman method for reactivity monitoring.
text

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47

St, Aubin Joel. "Three dimensional simulation and magnetic decoupling of the linac in a linac-MR system." Phd thesis, 2010. http://hdl.handle.net/10048/1405.

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Real time image guided radiotherapy has been proposed by integrating an in-line 6 MV linear accelerator (linac) to a magnetic resonance (MR) imager in either a parallel or transverse configuration. In either configuration, magnetic interference in the linac is caused by its immersion in the magnetic fringe fields of the MR imager. Thus in order to minimize the effect of the magnetic interference, investigations on linac performance in external magnetic fields was completed through various simulations. Finite difference and finite element methods as well as particle simulations were performed in order to design an electron gun and an in-line 6 MV linac waveguide. Monte Carlo simulations provided calculations of dose distributions in a water tank from the derived electron phase space at the linac target. The entire simulation was validated against measurements taken from a commercial medical in-line 6 MV linac, other simulation programs, and theory. The validated linac simulation was used to investigate linac performance in external magnetic fields. The results of this investigation showed that the linac had a much lower tolerance to transverse magnetic fields compared to longitudinal fields. While transverse magnetic fields caused a global deflection of the electron beam away from the central axis of the waveguide, longitudinal fields changed the optics of the electron gun in a suboptimal way. Both transverse and longitudinal magnetic fields caused excessive beam loss if the field strength was large enough. Heating caused by excessive beam loss in external magnetic fields was shown to have little effect on the resonant frequency of the waveguide, and any change in dosimetry, if it existed, was shown to be easily corrected using the jaws or multileaf collimators (MLCs). It was determined that the low-field parallel configuration linac-MR system investigated did not require any magnetic shielding, so the focus was on shielding the transverse configuration. Using beam loss, MLC motor tolerance to magnetic fields, and MR imager homogeneity as constraints, passive and active magnetic shielding was designed and optimized. Thus through the parallel configuration, or using magnetic shielding, magnetic interference has been reduced to within the linac operational tolerance.
Medical Physics

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48

CROIA, MICHELE. "High gradient ultra-high brightness RF photo-injector optimization." Doctoral thesis, 2018. http://hdl.handle.net/11573/1361108.

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In the pasts decades particle accelerators and especially RF photoinjectors had an impressive development, thanks to which a lot of applications were possible from the industrial one up to the medical use. Historically accelerators were developed for nuclear and particles physics but nowadays only a small part of accelerators are devoted to science, most of them are used for applications. The current request for scientific scope, especially for particle physics, is an higher and higher beam energy. The energy scale of TeV in the center of mass, in the past decades was reached. In the most recent and powerful proton particle accelerator Large Hadron Collider (LHC), was reached the impressive energy value in the center of mass of about 13 TeV and a Luminosity of about 10^34 cm^−2s^−1. The energy request from the scientific community has led to some accelerators project that exceed 50 Km lenght. In order to overcome these accelerator dimensions and especially to reduce costs, a good solution is the plasma acceleration. With this new accelerator technique the accelerating gradients can be a factor 10^3 more intense with respect to the modern RF technology. Nowadays plasma acceleration does not look like a chimera anymore, it was been demonstrated as a proof of principle but a lot of work is still to do in order to reach a good beam quality such that it can be used in accelerator facilities and in applications. Most of the applications in fact demand an high beam quality: ultra low energy spread and ultra high brightness beams. High brightness beams means bunches with an high peak current and a low emittance. These quality parameters are also necessary in order to perform a good matching between beams from accelerator and plasma in the so called external injection scheme for plasma acceleration. For example the energy spread that a bunch acquires during the acceleration is proportional to the length of the bunch that is injected into the plasma. Furthermore with a low transverse emittance the beam can be easily focused in order to reach the transverse matching conditions between beam and plasma. Beam brightness is a fundamental parameter for applications as the Free Electron Laser (FEL) that is able to produce X rays, where the gain length (Lg) is inversely proportional to the electron beam brightness (Lg proportional to B^−1/3) in the Self Amplified Spontaneous Emission (SASE) X-ray regime. These requests in the electron beam quality means that a perfect control of the bunches along the beam line is necessary, starting from the bunch generation in an electron gun up to the accelerator end, especially in the photoinjector region where the beam is not yet relativistic and is in the so called space charge regime. From these requests the beam transport has to be optimized, especially at low energies, performing a fine tuning of the machine parameters and of the positions of the machine elements along the beam line. To do that have to be fixed: a proper position for the first accelerating section, an integrated magnetic field of the gun solenoid, an optimal bunch compression scheme and mostly avoid any misalignments of the accelerating sections and of any magnetic components. In the photoinjector, where the beam is not yet relativistic, any misalignments can generate a transverse kick of the entire beam and a distortion of the beam transverse shape. The bunch can easily degrade its quality parameters in the photoinjector region, which in case of standard applications (e.g. industrial or medical) could be not so detrimental. Differently in case of applications as the ones here discussed (plasma acceleration or FEL) it is a serious matter which compromise the application itself. One of the effects of a low beam quality is a more difficult matching with the linac and subsequently with the plasma channel. In order to meet these stringent beam quality parameter requests, I optimized the beam dynamics of a new ultra high gradient 1.6 cells C-band (5.712 GHz) gun able to reach 240 MV/m as a peak field. By means of the ultra high gradient a better control of the space charge forces inside the bunch is possible. After optimizations on this electron gun a proper emittance compensation scheme was found through simulations with the software General Particle Tracer (GPT). Simulations showed the possibility to have, with a 100 pC beam and an energy of about 150 MeV, an emittance value of about 55 nm and a final beam brightness value of about 5 × 10^16 A/m^2. In order to optimize the present and future SPARC_LAB beam line, I wrote an algorithm able to evaluate transverse misalignments of a gun solenoid with coils powered with opposite currents. This algorithm was checked successfully in a dedicated run at SPARC_LAB. Using this algorithm the estimation of misalignements was about 1 mm and 0.5 mm in the transverse planes. During the SPARC_LAB machine operations we measure a bunch centroid displacement due to the misaligned solenoid. Aligning the solenoid to the found values we will improve the centroid orbit displacement of about 99.4%. Furthermore it will be possible avoid transverse kicks and distortions of the transverse beam shape and emittances i.e. the fundamental parameters to match simultaneously the beam with plasma in both transverse planes. The beam can have different spots and emittances in the x, y transverse planes due to laser on cathode misalignments, or due to some residual misalignements on the gun solenoid or on accelerating sections. I studied the possibility to insert Printed Circuit(PC) skew quadrupoles inside the future SPARC_LAB gun solenoid. By GPT simulations these PC skew quadrupoles will be able to reduce spot differences in the x and y planes, from 14% up to about 1% and a differences in the emittances, in x versus y plane, from 14% up to 5%. A first design of these PC quadrupoles was made, and we are planning to install them in the future SPARC_LAB gun solenoid.

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49

"Particle-in-cell simulations of radiation generation and particle acceleration in plasmas." Thesis, 2009. http://localhost:8080/xmlui/handle/12345678/6474.

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50

Iadarola, Giovanni. "Electron cloud studies for CERN particle accelerators and simulation code development." Tesi di dottorato, 2014. http://www.fedoa.unina.it/9957/13/Giovanni_Iadarola_XXVIciclo.pdf.

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In a particle accelerator free electrons in the beam chambers can be generated by different mechanisms like the ionization of the residual gas or the photoemission from the chamber’s wall due to the synchrotron radiation emitted by the beam. The electromagnetic field of the beam can accelerate these electrons and project them onto the chamber’s wall. According to their impact energy and to the Secondary Electron Yield (SEY) of the surface, secondary electrons can be generated. Especially when the accelerator is operated with closely spaced bunches of positively charged particles, this mechanism can drive an avalanche multiplication process of the electrons with the formation of a so called Electron Cloud (EC) in the chamber. The presence of a large electron density in the beam pipe as well as of a strong electron flux on the chamber’s wall can limit the achievable performance of the accelerator through different effects like transverse instabilities, transverse emittance growth, particle losses, vacuum degradation and heating of the chamber’s surface. EC effects have been recognized among the major performance limitations for the Large Hadron Collider (LHC), presently the world’s largest and most powerful particle accelerator and collider, built by the European Organization for Nuclear Research (CERN) in a 27 km underground tunnel across the Franco-Swiss border near Geneva, Switzerland. EC effects were observed at the LHC during the first three years of beam operation (Run 1, 2010 – 2012), becoming more and more severe while moving to tighter bunch spacing. EC effects with 50 ns bunch spacing could be successfully mitigated through beam induced scrubbing (reduction of the SEY by means of electron bombardment) and this bunch spacing could be used for most of the integrated luminosity production with 7 – 8 TeV Center of Mass (CoM) energy in 2011–12. After the 2013–14 machine shutdown (LS1) the LHC will be able to run at 13–14 TeV CoM energy and it will be necessary to move to the design bunch spacing of 25 ns in order to reach the design luminosity within the pileup limits required by the LHC experiments. Up to now, the 25 ns beam has been used only for test purposes and EC effects proved to be significantly more severe compared to the 50 ns case. The present thesis work addresses EC effects in the LHC and its injector accelerators chain in terms of both numerical simulations and machine experiments. Particular emphasis is put on beams with 25 ns bunch spacing. In particular, the analysis of EC observations in the LHC and its injectors have raised new challenges for the EC build-up simulations. For a correct understanding of machine observations it is often necessary to deal with beams with thousands of bunches and with non-idealities like non-uniform bunch populations and bunch lengths along the beam. Beside the usual simulation scenarios of field free regions and dipole magnets, also more complex situations needed to be addressed, like the EC buildup in quadrupoles or combined function magnets and with two counter-rotating beams in the same chamber. Moreover, the demand for extensive parameter scans gave quite stringent requirements in terms of speed and reliability. CERN’s long experience in the EC build-up simulation, mostly carried out with the ECLOUD code, developed and maintained at CERN since 1997, proved instrumental to respond to the newly arisen needs. However, due to its non-modular structure and to the programming language (FORTRAN 77), the existing ECLOUD code did not appear to be suitable to be extended to fulfill the aforementioned requirements. It was therefore decided to follow a different strategy and write a fully reorganized code, in a more modern and flexible language, considering that the initial effort would be compensated by a significantly increased efficiency in development and debugging. The new code has been called PyECLOUD, since it is almost entirely written in Python and inherits the physical models of the ECLOUD code. During the development we addressed all the known issues of the ECLOUD code were addressed and new features were introduced, necessary to deal with the complex scenarios described above. Modifications on numerical model and implementation were introduced practically everywhere, and key modules of the code, i.e. the MacroParticle (MP) Size Management, the electron space charge evaluation, the MP tracker and the electron/wall interaction have been completely redesigned. The new code has been applied for a full characterization of the EC formation in the main LHC components (including those with the two counter-rotating beams in the same chamber) with respect to different to surface properties (SEY) and beam configurations. In parallel with this modeling and simulation work, an intense experimental activity was carried out, which involved the LHC and the last two synchrotrons of its injector chain, i.e. the Proton Synchrotron (PS) and the Super Proton Synchrotron (SPS), and had three main goals: 1) The qualification of the EC formation in the three accelerators and of its impact on the quality of the proton beam; 2) The collection of experimental data for the validation and the improvement of our simulation models; 3) The definition and experimental validation of possible EC mitigation strategies. As already stated before, at the LHC, EC effects represent the main limitation to the use of the nominal bunch spacing of 25 ns. Experiments with this type of beam took place for the first time in 2011 and more extensively towards the end of the 2012 run. The main goals were to investigate these limitations and to study the process of beam scrubbing as a possible mitigation for future operation. These tests included a 3.5 day scrubbing run at 450 GeV, few test ramps with 25 ns beams in order to study EC effect at high energy (4 TeV), and a pilot physics run with low emittance 25 ns beams. During this period it was possible to collect measurements on several EC observables, e.g. transverse positions for the first seconds after injection, heat load on the cryogenic sections, bunch by bunch intensity, transverse emittance and stable phase. The careful analysis of these data significantly improved our understanding on the EC buildup in the LHC and on its impact on machine performance and beam quality, both at injection and collision energy. Concerning the LHC injectors, both at the PS and at the SPS, several “direct” e-cloud measurements could be collected under different beam conditions (bunch intensity, length, number and spacing) using dedicated devices installed in the rings. Moreover we could observe and qualify the impact of the EC on the vacuum pressure and on the quality of the beams in terms of transverse instabilities, beam losses, emittance growth. For the SPS, the possibility of preparing a dedicated beam for the EC mitigation through beam induced scrubbing has been studied. PyECLOUD simulations have been performed to compare different options and the most promising, the so-called “doublet” beam has been experimentally validated in the accelerator. The thesis is organized in three parts. Part I introduces the main concepts and mechanisms involved in the EC formation and describes in detail our simulation model and its implementation in the PyECLOUD code. Part II addresses the EC effects in the LHC, covering both simulation and experimental studies, with a dedicated chapter focusing on EC effects in the common regions where the two beams share the same chamber. Finally Part III describes simulation and experimental studies on EC effects in the LHC injectors.

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