Dissertations / Theses: 'Laser plasma accelerator'

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Kneip, Stefan. "Laser plasma accelerator and wiggler." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/5671.

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This thesis details experimental research of laser-driven electron acceleration from underdense plasmas and the characterisation of the x-ray radiation owing to the transverse oscillatory motion that electrons perform during the acceleration process. Acceleration of monoenergetic electron beams to the GeV level was achieved for the first time in a self-guiding, self-injecting wakefield accelerator in the nonlinear regime, driven by the 200 TW Astra Gemini laser. The laser pulse was shown to be self-guided for 1 cm or more than ten times its Rayleigh range, by measurement of a single filament containing > 30% of the initial laser energy at this distance. The intensity in the guided filament is amplified beyond its initial value, as suggested by the GeV electron energy gain. Three dimensional numerical modeling is in excellent agreement with the experimental findings. In this regime, a beam of tens of keV x-rays emanating from a micrometer source with milliradian divergence, spatial coherence and a peak brightness comparable to third generation light sources was measured on experiments with the 100 TW Hercules laser. The measurements show that, due to their small transverse oscillations, the electron trajectories and their radiation properties resemble the scenario of an electron in a wiggler-type insertion device, with a strength parameter K close to 1. The experimental findings are supported by three dimensional modeling of the electron and x-ray beam. Betatron radiation was also measured with ten times longer and more intense pulses from the Vulcan Petawatt laser. In this case, electron acceleration is strongly driven transversely by the laser and a betatron resonance leads to a tenfold increase in oscillation amplitude. This alters the characteristics of the emitted synchrotron radiation fundamentally, increasing 50-fold the strength parameter and divergence, 10-fold the source size and up to 5-fold the x-ray energy, thereby broadening the electron energy distribution and converting up to 5% of their energy into x-rays. The studies provide evidence for the scalability of self-guided laser wakefield accelerators from 0.1 to 1 GeV. Furthermore the work demonstrates that betatron radiation can help to understand the acceleration process and has characteristics comparable to conventional synchrotron light.

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Maitrallain, Antoine. "Accélération laser-plasma : mise en forme de faisceaux d’électrons pour les applications." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS314/document.

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L'accélération laser plasma (ALP) est le produit de l'interaction non linéaire entre un faisceau laser intense (≈10¹⁸ W/cm²) et une cible gazeuse. Sous certaines conditions, l’onde plasma générée peut piéger et accélérer des électrons jusqu’à des énergies très importantes grâce à des champs accélérateurs élevés (≈ 50 GV/m). Ce processus très prometteur fait l'objet de nombreux travaux au sein de la communauté, qui, après avoir identifié les mécanismes de base, cherche aujourd’hui à améliorer les propriétés de la source (énergie, divergence, reproductibilité...).Les applications de ces faisceaux d'électrons issus de sources ultra-compactes sont variées. Parmi celles-ci, la physique des hautes énergies pour laquelle a été conçu le schéma d'accélération multi-étages. Il s’agit d’un concept basé sur la succession d’étages accélérateurs pour répondre à la problématique de l’augmentation de la longueur d’accélération en vue d’augmenter l’énergie des électrons. Dans sa version de base, un premier étage (injecteur) fournit un faisceau d'électrons d'énergie modérée doté d’une charge très importante. Ce faisceau est alors accéléré vers de plus hautes énergies dans un second étage appelé accélérateur. Cette thèse s'inscrit dans une série de travaux préliminaires aux expériences d'accélération laser-plasma double étages prévues sur la plateforme expérimentale CILEX autour du laser APOLLON 10 PW.Dans ce cadre, une nouvelle cible a été conçue et caractérisée avec le laser UHI100. Les propriétés du faisceau d'électrons ont ensuite été modifiées par mise en forme optique du faisceau laser produisant l'onde de plasma, ainsi que par mise en forme magnétique.Ce dernier dispositif nous a permis de pouvoir utiliser la source pour une application visant à mettre au point un système de dosimétrie adapté au fort débit de dose associé aux électrons issus de l'ALP
Laser plasma acceleration (LPA) comes from the nonlinear interaction between an intense laser beam (≈10¹⁸ W/cm²) and a gas target. The plasma wave which is generated can, trap and accelerate electrons to very high energies due to large accelerating fields (≈ 50 GV/m). Numerous studies have been done on this promising process among our scientific community aiming at understanding the basic mechanisms involved. As a second step, we now try tries to improve the properties of the source (energy, divergence, reproducibility…).Such ultra-compact electronic sources can be used for various applications. Among them, high energy physics for which a specific scheme was designed, based on the multi-stage acceleration. The scheme relies on the addition of successive accelerating modules to increase the effective accelerating length and therefore the final electron energy. In its basic version, a first stage (injector) delivers an electron beam at moderate energy including a high charge. This beam is then further accelerated to high energy through a second stage (accelerator). This thesis is part of preliminary studies performed to prepare the future 2-stages laser plasma accelerator that will be developed on platform CILEX with APOLLON 10 PW laser.In this context, a new target has been designed and characterized with the UHI100 laser. Then the electron beam properties have been adjusted by optical shaping of the laser generating the plasma wave, and also by magnetic shaping.The electron beam, magnetically shaped, has been used for a specific application devoted to the set-up of a new dosimetric diagnostic, dedicated to the measurement of high dose rate delivered by these electrons from LPA

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Bajlekov, Svetoslav. "Towards a free-electron laser driven by electrons from a laser-wakefield accelerator : simulations and bunch diagnostics." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:99f9f13a-d0c2-4dd8-a9a4-13926621c352.

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This thesis presents results from two strands of work towards realizing a free-electron laser (FEL) driven by electron bunches generated by a laser-wakefield accelerator (LWFA). The first strand focuses on selecting operating parameters for such a light source, on the basis of currently achievable bunch parameters as well as near-term projections. The viability of LWFA-driven incoherent undulator sources producing nanojoule-level pulses of femtosecond duration at wavelengths of 5 nm and 0.5 nm is demonstrated. A study on the prospective operation of an FEL at 32 nm is carried out, on the basis of scaling laws and full 3-D time-dependent simulations. A working point is selected, based on realistic bunch parameters. At that working point saturation is expected to occur within a length of 1.6 m with peak power at the 0.1 GW-level. This level, as well as the stability of the amplification process, can be improved significantly by seeding the FEL with an external radiation source. In the context of FEL seeding, we study the ability of conventional simulation codes to correctly handle seeds from high-harmonic generation (HHG) sources, which have a broad bandwidth and temporal structure on the attosecond scale. Namely, they violate the slowly-varying envelope approximation (SVEA) that underpins the governing equations in conventional codes. For this purpose we develop a 1-D simulation code that works outside the SVEA. We carry out a set of benchmarks that lead us to conclude that conventional codes are adequately capable of simulating seeding with broadband radiation, which is in line with an analytical treatment of the interaction. The second strand of work is experimental, and focuses on on the use of coherent transition radiation (CTR) as an electron bunch diagnostic. The thesis presents results from two experimental campaigns at the MPI für Quantenoptik in Garching, Germany. We present the first set of single-shot measurements of CTR over a continuous wavelength range from 420 nm to 7 μm. Data over such a broad spectral range allows for the first reconstruction of the longitudinal profiles of electron bunches from a laser-wakefield accelerator, indicating full-width at half-maximum bunch lengths around 1.4 μm (4.7 fs), corresponding to peak currents of several kiloampères. The bunch profiles are reconstructed through the application of phase reconstruction algorithms that were initially developed for studying x-ray diffraction data, and are adapted here for the first time to the analysis of CTR data. The measurements allow for an analysis of acceleration dynamics, and suggest that upon depletion of the driving laser the accelerated bunch can itself drive a wake in which electrons are injected. High levels of coherence at optical wavelengths indicate the presence of an interaction between the bunch and the driving laser pulse.

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Seggebrock, Thorben. "Conceptual design of a laser-plasma accelerator driven free-electron laser demonstration experiment." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-184314.

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Up to now, short-wavelength free-electron lasers (FEL) have been systems on the scale of hundreds of meters up to multiple kilometers. Due to the advancements in laser-plasma acceleration in the recent years, these accelerators have become a promising candidate for driving a fifth-generation synchrotron light source – a lab-scale free-electron laser. So far, demonstration experiments have been hindered by the broad energy spread typical for this type of accelerator. This thesis addresses the most important challenges of the conceptual design for a first lab-scale FEL demonstration experiment using analytical considerations as well as simulations. The broad energy spread reduces the FEL performance directly by weakening the microbunching and indirectly via chromatic emittance growth, caused by the focusing system. Both issues can be mitigated by decompressing the electron bunch in a magnetic chicane, resulting in a sorting by energies. This reduces the local energy spread as well as the local chromatic emittance growth and also lowers performance degradations caused by the short bunch length. Moreover, the energy dependent focus position leads to a focus motion within the bunch, which can be synchronized with the radiation pulse, maximizing the current density in the interaction region. This concept is termed chromatic focus matching. A comparison shows the advantages of the longitudinal decompression concept compared to the alternative approach of transverse dispersion. When using typical laser-plasma based electron bunches, coherent synchrotron radiation and space-charge contribute in equal measure to the emittance growth during decompression. It is shown that a chicane for this purpose must not be as weak and long as affordable to reduce coherent synchrotron radiation, but that an intermediate length is required. Furthermore, the interplay of the individual concepts and components is assessed in a start-to-end simulation, confirming the feasibility of the envisioned experiment. Moreover, the setup tolerances for a first demonstration experiment are determined, confirming the general practicability. The revealed challenges, besides the energy spread, especially concern the source stability and the precision of the beam optics setup.

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Cipiccia, Silvia. "Compact gamma-ray sources based on laser-plasma wakefield accelerator." Thesis, University of Strathclyde, 2011. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=23936.

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Laser-plasma wakefield accelerator (LWFA) is a promising novel technology that is introducing miniaturization to the accelerator world: the unprecedented gradient of acceleration shrinks the accelerator down to table-top size. Moreover, the LWFA comes with an embedded light source: electrons, while accelerating, undergo betatron oscillatory motion that results in synchrotron radiation emitted in a narrow cone along the direction of propagation. In this thesis we study theoretically and we prove experimentally a new regime of betatron oscillation that occurs when electrons experience the electromagnetic field of the laser during acceleration and oscillate resonantly at the laser frequency or its sub-harmonics. The signature of the harmonically resonant betatron (HRB) regime is a large oscillation amplitude and consequently prolific emission of high energy photons up to the MeV range. The HRB source has unique properties: very short pulse length (~10 fs), small source size (few microns), high peak brightness of the order of 1023 photons/s mm2 mrad2 0.1% B.W., which is comparable with a third generation light source. These properties make the source particularly appealing for the life sciences and medical and security applications. As a part of a future applications project, we give the scaling of the photon energy as a function of laser intensity and plasma density, which could extend toward tens of MeV. The thesis also investigates another gamma-ray source that utilises beams from the LWFA: bremsstrahlung radiation from high energy electrons interacting with metal targets. We study the electron beam and target parameters to optimize the emission process and the gamma-ray beam properties to match potential application requirements, such as radioisotope generation via photonuclear process. The results of a proof of concept experiment are presented and compared with simulations. Finally, we investigate numerically the possibility of generating a converging gamma ray beam based on the bremsstrahlung process. The results are encouraging, and the potential impact of a compact converging gamma-ray beam source is discussed with particular attention to medical applications in cancer treatment.

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André, Thomas. "Transport et manipulation d’électrons produits par interaction laser plasma sur la ligne COXINEL." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS602/document.

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Les récents progrès en termes de techniques d’accélération par interaction Laser Plasma (LPA) permettent aujourd’hui de générer de forts gradients accélérateurs (GV.m⁻¹); cependant, les faisceaux d’électrons ainsi produits présentent encore une grande dispersion énergie (%) et une divergence élevée (mrad). Le projet COXINEL (ERC Advanced Grant 350014, PI. M.E. Couprie), vise à qualifier, en remplacement d’un accélérateur conventionnel, un accélérateur Laser Plasma, dans le but d’une application de Laser à Électrons Libres. Pour atteindre les propriétés requises, le faisceau d’électrons doit être manipulé à l’aide d’une ligne de transport. Cette ligne est constituée d’un premier triplet de quadrupôles à aimants permanents de gradient variable qui focalise le faisceau et permet la maîtrise de la divergence initiale. Une chicane électromagnétique réduit ensuite la dispersion en énergie par tranche en allongeant longitudinalement le faisceau. Une gamme d’énergie restreinte peut être ensuite sélectionnée via l’insertion d’une fente dans la chicane. Enfin, un quadruplet de quadrupôles électromagnétiques fournit la focalisation finale dans un onduleur. Le travail de thèse porte sur l’étude du transport des faisceaux d’électrons produit par LPA le long de cette ligne. Différents régimes de production d’électrons ont été utilisés : injection par ionisation, cellule de gaz. La maîtrise du transport a été obtenue à l’aide d’une nouvelle méthode d’alignement et de compensation de dérive de pointé initial des électrons en réglant de manière indépendante la position et la dispersion du faisceau à différents endroits de la ligne. Un réglage fin de l’énergie transportée a été effectué en ajustant le gradient des quadrupôles. Les faisceaux produits ont été transportés le long de la ligne et caractérisés en termes de distribution transverse, d’émittance et d’énergie. Les résultats expérimentaux ont ensuite été comparés avec succès aux simulations numériques. Ce travail ouvre la voie à l’observation de rayonnement de l’onduleur, étape préliminaire à une amplification Laser à Électrons Libres
Recent advances in Laser Plasma Acceleration techniques (LPA) are now able to generate strong accelerating gradients (GV.m⁻¹); however the produced electron beam thus still presents a large energy spread (%) and a large divergence (mrad). The COXINEL project (ERC Advanced Grant 350014, PI. M.E. Couprie), aims at qualifying, in replacement of a conventional accelerator, a Laser Plasma Accelerator, for a Free Electrons Laser application. To achieve the required properties, the electron beam must be manipulated using a transport line. This line consists in a first triplet of permanent magnets quadrupoles of variable gradient which focuses the beam and allows for the control of the initial divergence. An electromagnetic chicane then reduces the slice energy spread by lengthening the beam longitudinally. A restricted energy range can then be selected by inserting a slit inside the chicane. Finally, a quadruple of electromagnetic quadrupoles provides the final focus in an undulator. The thesis deals on the study of electron beam transport produced by LPA along this line. Different electron production regimes have been used: ionization injection, gas cell. The transport was controlled using a new alignment and pointing compensation method for the initial electron beam by adjusting independently the beam position and dispersion at different location on the line. A fine adjustment of the transported energy was carried out by adjusting the quadrupole gradient. The produced beam was transported along the line and was characterized in terms of transverse distribution, emittance and energy. Experimental results were then successfully compared with numerical simulations. This work paves the way for the observation of undulator radiation, a preliminary step before Free Electron Laser amplification

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Gonsalves, Anthony J. "Investigation of a hydrogen-filled capillary discharge waveguide for laser-driven plasma accelerator." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442795.

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Seggebrock, Thorben [Verfasser], and Florian [Akademischer Betreuer] Grüner. "Conceptual design of a laser-plasma accelerator driven free-electron laser demonstration experiment / Thorben Seggebrock. Betreuer: Florian Grüner." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1074358740/34.

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Rovige, Lucas. "Optimization, stabilization and optical phase control of a high-repetition rate laser-wakefield accelerator." Electronic Thesis or Diss., Institut polytechnique de Paris, 2022. http://www.theses.fr/2022IPPAE011.

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Cette thèse de doctorat présente le travail expérimental sur le développement d'un accélérateur laser-plasma à haut taux de répétition (kHz) utilisant des impulsions laser de quelques milijoules, et de durée proche du cycle optique. Nous explorons un large ensemble de paramètres expérimentaux pour optimiser l'accélérateur en contrôlant la densité et le profil plasma, la durée des impulsions, le type de gaz et le mécanisme d'injection utilisés dans les expériences. Nous démontrons une amélioration significative des performances, notamment avec d’importants progrès réalisés sur la stabilité et la fiabilité à long terme de l'accélérateur, avec un fonctionnement continu et stable de l'accélérateur pendant plusieurs heures accumulant un record de 18 millions de tirs consécutifs. Ce gain de stabilité est obtenu en utilisant un nouveau type de jet de gaz qui utilise un choc hydrodynamique oblique asymétrique permettant l'injection d’électrons dans le gradient de densité descendant de la région choquée. En utilisant des simulations particle-in-cell, les causes physiques menant à un régime d'accélération optimisé et stable sont établies. L'énergie typique du faisceau d'électrons a également été augmentée d'un facteur deux, jusqu'à 8 MeV, tandis que des divergences divergence mono-tir du faisceau d’électrons aussi faible que 3mrad sont obtenues en utilisant de l'hélium au lieu de l'azote pour créer le plasma. Nous présentons ensuite les résultats d'une première expérience d'application en radiobiologie où notre accélérateur est utilisé pour irradier des cellules cancéreuses, en profitant de la stabilité nouvellement acquise.Dans un second temps, nous étudions les spécificités de l'interaction des impulsions proche du cycle optique avec un plasma sous-dense se produisant dans notre accélérateur, principalement par l'effet de la phase enveloppe-porteuse (CEP). Nous observons et contrôlons expérimentalement pour la première fois les effets CEP dans un accélérateur laser-plasma, qui se manifestent par une dépendance du pointé du faisceau d'électrons à la phase optique initiale du laser. Des variations de charge significatives (jusqu'à 30%) lorsque l'on change la valeur du CEP sont également observées dans certains cas. En effectuant des simulations particle-in-cell, nous expliquons ces effets par une injection périodique hors axe de plusieurs sous-faisceaux d'électrons déclenchée par l'oscillation de l'asymétrie de l'onde plasma dans la direction de polarisation du laser due au glissement de la CEP pendant la propagation. Enfin, nous discutons de résultats préliminaires concernant les effets de la CEP sur le spectre d'énergie des électrons associés à l'injection d'ionisation dans un mélange de gaz hélium-argon
This PhD thesis presents experimental work on the development of a high-repetition rate (kHz) laser-wakefield accelerator using few millijoules, near-single cycle laser pulses. We explore a large set of experimental parameters to optimize the accelerator by controlling the plasma density and profile, pulse duration, type of gas and injection mechanism used in experiments. We demonstrate significant performances improvement, notably with progress made on the long-term stability and reliability of the accelerator with continuous and stable operation of the accelerator for several hours accumulating a record of 18 million consecutive shots. We achieve this gain in stability by using a newly designed type of gas target resulting in an asymmetric hydrodynamic oblique shock enabling injection in the downward density transition of the shock region. Using particle-in-cell simulations, we understand in details the underlying causes leading to an optimized and stable acceleration regime. The typical electron beam energy has also been increased by a factor of two, up to 8 MeV, while a single-shot beam divergence as low as 3mrad is achieved using helium instead of nitrogen to form the plasma. We then present the results of a first application experiment in radiobiology where our accelerator is used to irradiate cancerous cells, taking advantage of the newly acquired stability.Secondly, we study the specificity of the interaction of near-single cycle pulses with an underdense plasma that occurs in our accelerator, mainly through the effect of the carrier-envelope phase (CEP). We observe and control experimentally for the first time CEP effects in a laser-wakefield accelerator, that manifest through a dependence of the electron beam pointing to the laser initial optical phase. We also show significant (up to 30%) charge variations in some cases when changing the value of the CEP. By carrying out particle-in-cell simulations, we explain these effects by the periodic off-axis injection of several electron sub-bunches triggered by the oscillation of the asymmetry of the plasma wave in the laser polarization direction due to the CEP shifting during propagation. Finally, we discuss preliminary results on carrier-envelope phase effects on the electron energy spectrum associated with ionization injection in a helium-argon gas mixture

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Oubrerie, Kosta. "Amélioration de l'efficacité des accélérateurs laser-plasma." Electronic Thesis or Diss., Institut polytechnique de Paris, 2022. http://www.theses.fr/2022IPPAE002.

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Pour générer des faisceaux d'électrons à hautes énergies, les accélérateurs conventionnels utilisent des ondes radiofréquences pour accélérer des particules chargées à des vitesses relativistes. Cependant, le champ électrique accélérateur produit est limité à quelques dizaines de mégavolts par mètre, dû notamment à un phénomène de claquage. Il faut donc des installations de très grande taille pour atteindre des énergies suffisamment élevées. Ainsi, l'accélérateur linéaire de Stanford (SLAC), qui est l'accélérateur linéaire le plus long au monde, accélère des électrons jusqu'à 50GeV sur 3.2km. Les accélérateurs laser-plasma peuvent produire des champs électriques dépassant 100 GV/m, soit environ trois ordres de grandeur plus grands que ceux obtenus par les accélérateurs à cavités radiofréquences. Ils pourraient ainsi permettre une diminution drastique de la taille des accélérateurs pour des applications scientifiques, médicales et industrielles. Cependant, plusieurs verrous devront être levés avant que ces applications puissent voir le jour. Il sera notamment nécessaire de démontrer la production efficace de faisceaux d'électrons de haute qualité, à des énergies de plusieurs GeV et à un taux de répétition élevé.Le projet doctoral s’attaque à cette problématique en explorant de nouvelles méthodes pour augmenter l'énergie des faisceaux d'électrons grâce à des techniques qui sont compatibles avec des puissances laser et des taux de répétition élevés et qui peuvent être alliées avec des méthodes d'injection contrôlée. En effet, des faisceaux d'électrons à haute énergie ou avec une injection contrôlée ont été obtenus séparément durant les quinze dernières années, mais jamais de manière combinée. Cette thèse présente les travaux réalisés sur les techniques de guidage ainsi que sur celles d'injection des électrons qui ont permis d'obtenir expérimentalement des faisceaux de bonne qualité à hautes énergies. Ce travail s'est fait notamment au travers de l'optimisation d'une optique nouvellement conçue au Laboratoire d'Optique Appliquée, l'axiparabole, ainsi que sur le développement de jets de gaz spécifiques à l'accélération laser-plasma
To generate high energy electron beams, conventional accelerators use radio frequency waves to accelerate charged particles to relativistic speeds. However, the accelerating electric field produced is limited to a few tens of megavolts per metre, mainly due to a breakdown phenomenon. Very large facilities are therefore needed to reach sufficiently high energies. For example, the Stanford Linear Accelerator (SLAC), which is the world's longest linear accelerator, accelerates electrons up to 50 GeV over a distance of 3.2 km. Laser-Plasma Accelerators can produce electric fields exceeding 100 GV/m, that are about three orders of magnitude larger than those obtained by radiofrequency-cavity accelerators. They could thus allow for a drastic decrease of the size of accelerators for scientific, medical and industrial applications. Yet, several bottlenecks have to be solved before these applications can be really implemented. It is notably necessary to demonstrate the efficient production of high-quality, multi-GeV electron beams at a high-repetition rate.The doctoral project tackles this problem by exploring new methods for increasing the energy of the electron beams thanks to techniques that are compatibles with arbitrarily high laser powers and repetition rates and that can be combined with controlled injection methods. Indeed, high energy or controlled injection electron beams have been obtained separately during the last fifteen years, but never combined. This thesis presents the work carried out on the guiding techniques as well as on the electron injection techniques which allowed to obtain experimentally good quality beams at high energies. This work was done in particular through the optimisation of a new optic designed at the Laboratoire d'Optique Appliquée, the axiparabola, as well as the development of gas jets specific to laser-plasma acceleration

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BOELLA, ELISABETTA. "Ion acceleration driven by intense laser pulses." Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2560337.

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Laser pulses incident on plasma targets are capable of exciting very intense accelerating fields, that allow the acceleration of ions to high energies in very short distances. This is why a lot of interest has been developed on the topic of laser-driven ion acceleration over the past twenty years. Such a compact and affordable ion source would have many potential applications in physics and medicine, but several requirements are still far from being fulfilled. In this thesis two mechanisms of ion acceleration are investigated: shock wave acceleration and Coulomb explosion. Ultraintense lasers shot on plasma targets are capable of driving strong electrostatic shock waves that accelerate the plasma ions to high energies with a narrow energy spectrum. In the present work, the mechanism of shock formation and propagation in near-critical density plasmas is studied in detail. An idealized scenario where shock waves arise from the interpenetration of plasma slabs is studied. A theoretical kinetic model is derived and compared with simulation results. The conditions to accelerate ions to high energies with low energy spread are derived. The role of the laser in exciting shock waves is analyzed. The factors leading to high energy ion beams with narrow energy spectrum obtained in the simpler configuration are verified in this more complex and realistic scenario. A scaling for the ion energy with the pulse intensity is inferred for the ideal case of a plane wave and for a more realistic case of a finite size laser spot. The second mechanism of ion acceleration that has been considered is the Coulomb explosion of pure ion nanoplasmas, an important subject in the field of laser-cluster interaction. In this thesis, a detailed study of Coulomb explosion in hetero-nuclear clusters consisting of different atomic species is carried out. Numerical results indicate that, in the presence of different ion species, lighter ions are accelerated in a quasi-monoenergetic way, in contrast with the well known results on Coulomb explosion of clusters composed by a single ion species, where the energy spectrum is much broader. A study on the formation of shock shells, nonlinear structures that arises during Coulomb explosion of homo-clusters when the initial density exhibits radial non-uniformity, is also presented. The analysis is carried out comparing N-body simulation results, that represent the exact solution since no approximations have been made, to the collisionless kinetic theory. The study shows that there are consistent differences between the real dynamics and the model based on the Vlasov-Poisson equations.

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Subiel, Anna. "Feasibility studies on the application of relativistic electron beams from a laser plasma wakefield accelerator in radiotherapy." Thesis, University of Strathclyde, 2014. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24403.

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Very high energy electrons (VHEEs) (100-250 MeV) have the potential of becoming an alternative modality in radiotherapy because of their improved dosimetry properties compared with X-ray photons, which could confer possible radiobiological benefits. The rapid development of ultra-compact laser-plasma wakefield accelerators (LWFAs) is now providing a potential low cost device for VHEE radiotherapy. These beams have characteristics unlike any other beams currently used for radiotherapy: femotosecond radiation pulses, small field size and energies that exceed electron energies currently used in clinical applications. A set of Monte Carlo (MC) calculations have been performed to study dosimetric properties of VHEEs propagating in water. To assess radiation protection and safety handling issues, the generation of neutrons, induced activity and equivalent doses have been evaluated. A dosimetry system, consisting of EBT2 Gafchromic® film and EPSON Expression 10000XL scanner, for VHEEs has been established. EBT2 Gafchromic film turns out to be a robust dosimeter with a minor energy-dependent response over a broad range of beam energies and modalities, and can be successfully used for dosimetry of very high energy electron beams. The dosimetric measurements have been carried out using three different accelerators: a 20 MeV clinical LINAC, a 165 MeV conventional LINAC and a 135 MeV laser-plasma wakefield accelerator. The measurements have been compared with Monte Carlo simulations using the FLUKA code. Additionally, the set of dose measurements employing IBA CC04 ionisation chamber has been presented. Dosimetric measurements have been complemented by preliminary cancer cell irradiation studies to determine the toxicity and dose response to LWFA VHEEs of two lung cancer cell lines (A549 and H460). The efficacy of VHEEs on in vitro tumour cells has been assessed by clonogenic assay and γ-H2AX assay employing immunofluorescence detection of signalling molecules has been deployed to indicate DNA double-strand breaks and repair.

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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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Desforges, Frédéric. "Injection induite par ionisation pour l’accélération laser-plasma dans des tubes capillaires diélectriques." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112118/document.

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L’interaction d’une impulsion laser, courte (~ 10 - 100 fs) et ultra-intense (> 10^18 W/cm²), avec un plasma sous-dense (< 10^19 cm^-3) peut accélérer, de manière compacte, une fraction des électrons du plasma jusqu’à des énergies relativistes (~ 100 - 300MeV). Ce phénomène, nommé accélération plasma par sillage laser (APSL), pourrait avoir de nombreuses applications telles que le futur collisionneur d’électrons a ultra-hautes énergies. Cependant, cela requiert au préalable des développements supplémentaires afin que l’APSL produise des paquets d’électrons stables et reproductibles avec une excellente qualité, c’est-à-dire de faibles émittances longitudinale et transverses.Au cours de cette thèse, une étude expérimentale de la stabilité et de la reproductibilité des paquets d’électrons auto-injectes a été réalisée dans des tubes capillaires diélectriques, de longueur 8-20mm et de rayon interne 76-89 µm, contenant du H2 pur a une densité électronique de (10 +/- 1, 5)x10^18 cm^-3. Des paquets d’électrons auto-injectes ont été produits, a une cadence de deux tirs par minute, avec une charge accélérée au-delà de 40 MeV de (66+/-7) pC, une énergie moyenne de (65+/-6) MeV, une divergence de (9+/-1) mrad et une fluctuation de pointe de 2,3 mrad. Trois sources de fluctuations et de dérives des propriétés des paquets d’électrons ont été discutées : dérive d’énergie laser, modification du gradient montant de densité électronique et fluctuations du pointé laser. Des contraintes sur le régime de fonctionnement ont été proposées afin d’améliorer la stabilité et la reproductibilité de la source laser-plasma d’électrons.Un mécanisme alternatif d’injection d’électrons dans l’onde de plasma a également été examiné : l’injection induite par ionisation. Une étude expérimentale a montré que les paquets d’électrons accélérés dans un mélange de 99%H2 + 1%N2 ont une charge deux fois plus importante qu’en présence de H2 pur. De plus, une injection plus précoce a été observée pour le mélange de 99%H2 + 1%N2, indiquant que les premiers électrons sont captures selon le mécanisme d’injection induite par ionisation. Une étude complémentaire, utilisant des simulations Particle-In-Cell avec le code WARP, confirment les résultats expérimentaux et suggèrent que l’auto-injection est supprimée par l’injection induite par ionisation
The interaction of a short (~ 10 - 100 fs) and ultra-intense (> 10^18 W/cm²) laser pulse with an underdense (< 10^19 cm^-3) plasma can accelerate, in a compact way, a fraction of the electrons of the plasma toward relativistic energies (~ 100 - 300MeV). This mechanism, called laser wakefield acceleration (LWFA), might have various applications such as the future ultra-high energy electron collider. Prior to this, additional investigations are needed to ensure, through LWFA, a stable and reproducible generation of electron bunches of high quality, i.e. low transverse and longitudinal emittances.In this thesis, the stability and the reproducibility of the electron self-injection were experimentally investigated in 8-20mm long, dielectric capillary tubes, with an internal radius of 76-89 µm, and filled with pure H2 at an electronic density of de (10 +/- 1.5)x10^18 cm^-3. Electron bunches were produced, at a rate of two shots per minute, with an accelerated charge above 40 MeV of (66+/-7) pC, a mean energy of (65+/-6) MeV, a divergence of (9+/-1) mrad, and a pointing fluctuation of 2.3 mrad. Three sources were identified for the fluctuations and drifts of the electron bunch properties: laser energy drift, change of the electron number density upramp, and laser pointing fluctuations. Restrictions on the operating regime were proposed in order to improve the stability and the reproducibility of the laser-plasma electron source.An alternative mechanism of electron injection into the plasma wave was also investigated: the ionization-induced injection. An experimental study demonstrated that electron bunches generated in a mixture of 99%H2 + 1%N2 have twice more accelerated charge than in the case of pure H2. Moreover, the earlier onset of electron injection was observed for the mixture 99%H2 + 1%N2, indicating that the first electrons were trapped under the mechanism of ionization-induced injection. Particle-In-Cell simulations performed with the code WARP confirm the experimental results and suggest that the self-injection was inhibited by the ionization-induced injection

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Wang, Ke. "Design study of a Laser Plasma Wakefield Accelerator with an externally injected 10-MeV electron beam coming from a photoinjector." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS179/document.

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Nous étudions l’accélération d’un faisceau d’électrons provenant d’un photoinjecteur RF lorsque celui-ci est injecté dans le champ électrique à très fort gradient crée par un laser de forte puissance dans un plasma. Dans cette thèse la configuration d’une telle expérience est étudiée et des simulations du début à la fin sont présentées. Étant donné qu’un faisceau ultra-court d’électrons (quelques femto secondes) est nécessaire pour atteindre une faible dispersion en énergie dans le plasma, le faisceau d’électrons de 10 MeV provenant du photoinjecteur est comprimé en deux étapes. Le premier étage utilise une chicane coudée qui comprime le paquet d’électrons jusqu’à une durée de 69 fs, puis un deuxième étage qui utilise la méthode de regroupement par différence de célérité dans le plasma et qui comprime le paquet jusqu’à 4 fs avant qu’il ne soit accéléré. Le paquet d’électrons est comprimé transversalement avant d’être injecté dans le plasma. Le paquet d’électrons est focalisé transversalement avant d’être injecté dans le plasma. Une longue cellule plasma est utilisée pour créer le plasma en commençant plusieurs longueurs de Rayleigh avant le plan focal du laser, ce qui permet un regroupement par différence de célérité dans la première partie du plasma avec des contraintes relâchées sur la taille transverse du paquet d’électrons. La cellule plasma s’étend plusieurs longueurs de Rayleigh après le plan focal du laser pour supprimer la divergence angulaire du paquet d’électrons. Nous démontrons que le paquet d’électrons à la sortie du plasma a une énergie de plus d’une centaine de MeV avec une émittance plus petite que 1 µm, une charge plus grande que 7pC et une dispersion en énergie plus petite que 1,5% (largeur à mi-hauteur). Pour étendre la longueur d’accélération nous avons étudié le guidage du laser par un capillaire diélectrique creux et les résultats montrent que même dans le cas optimal le profile Gaussien usuel d’un laser n’est pas optimal, principalement à cause de la diffraction du laser sur les bords à l’entrée du capillaire. Un profile Gaussien aplatit est donc suggéré pour supprimer cette diffraction et il est montré que dans ce cas les électrons peuvent être accélérés sur plus de 10 longueurs de Rayleigh
The acceleration of an externally injected 10MeV electron bunch coming from a RF photoinjector in a high gradient electric ﬁeld excited in a plasma by a high power laser is studied. In this thesis, the conﬁguration of such an experiment is studied and start to end simulations are presented. As an ultrashort electron bunch (several femtoseconds) is required to maintain a low energy spread beam in the plasma, the 10MeV electron bunch coming from the photoinjector is compressed in two stages. The ﬁrst stage is realized using a dogleg chicane which compresses the electron bunch to 69fs, the second stage is realized with velocity bunching in the plasma that further compresses the electron bunch to 3fs before eﬃcient acceleration. The electron bunch is transversely focused with a solenoid before being injected into the plasma. A long cell is used to create a plasma starting several Rayleigh lengths before the laser focal plane, allowing the velocity bunching in the ﬁrst part of the plasma and relaxing constraints on the transverse bunch size. The cell extends several Rayleigh lengths after the laser focal plane to suppress the angular divergence of the electron bunch. We demonstrate that the electron bunch at the exit of the plasma has an energy of more than one hundred MeV, with an emittance smaller than 1 µm, a charge greater than 7pC and a FWHM energy spread smaller than 1.5%. To extend the acceleration section, the guiding of the laser beam with a hollow dielectric capillary is studied, the results show that even in the best matching conditions, the usual laser Gaussian transverse proﬁle is not optimum, mainly because of the diﬀraction of the laser on the edges at the entrance of the capillary, a ﬂattened Gaussian laser proﬁle is then suggested to suppress this diﬀraction and the electrons can be accelerated over more than ten Rayleigh lengths

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Titberidze, Mikheil [Verfasser], and Florian [Akademischer Betreuer] Grüner. "Pilot Study of Synchronization on a Femtosecond Scale between the Electron Gun REGAE and a Laser-Plasma Accelerator / Mikheil Titberidze ; Betreuer: Florian Grüner." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2017. http://d-nb.info/1143868749/34.

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Titberidze, M. [Verfasser], and Florian [Akademischer Betreuer] Grüner. "Pilot Study of Synchronization on a Femtosecond Scale between the Electron Gun REGAE and a Laser-Plasma Accelerator / Mikheil Titberidze ; Betreuer: Florian Grüner." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2017. http://d-nb.info/1143868749/34.

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Weikum, Maria Katharina. "Generation, acceleration and measurement of attosecond electron beams from laser-plasma accelerators." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=29839.

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Accelerator-based light sources are extremely useful machines for investigating matter on a microscopic level, yet their capability for time-resolved research is limited by the femtosecond-scale duration of their radiation pulses. Attosecond beams could enhance these capacities enabling the measurement of most outer shell electron dynamics in molecular and atomic systems. However,one of the main challenges in this direction remains the generation of attosecond-scale electron bunches which can be used for ultrashort radiation generation or as probes themselves. The research presented in this thesis tackles this issue from two angles. First, mechanisms for ultrashort electron beam generation and acceleration in laser wakefield accelerators - as promising,compact accelerator systems - are investigated through particle-in-cell simulations. Bothan optimised electron plasma injector, using upramp-assisted self-injection, and an external injection setup with the plasma stage as an energy booster to a conventionally accelerated beam are capable of providing electron bunches of few hundred attoseconds duration. The externally injected beams are found to be limited in duration, but preserve well the initial high beam quality for energies up to gigaelectronvolts, while in self-injection high beam currents and ultrashort duration can be achieved, yet at some cost to beam quality and stability. As a second research branch, longitudinal beam profile diagnostics with sub-femtosecond resolution are examined as possible means for measuring such ultrashort electron beams. A first proof-of-principle experiment of a novel streaking device is presented and compared with measurements with anX-band radiofrequency deflecting cavity. Additional computational and theoretical studies provide insights into the possibilities and challenges to apply this new diagnostic technique to sub-femtosecond electron beams from conventional and novel accelerators.

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Bischi, Matteo. "X rays from laser-plasma accelerators." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8163/.

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Uno dei maggiori obiettivi della ricerca nel campo degli acceleratori basati su interazione laser-plasma è la realizzazione di una sorgente compatta di raggi x impulsati al femtosecondo. L’interazione tra brevi impulsi laser e un plasma, a energie relativistiche, ha recentemente portato a una nuova generazione di sorgenti di raggi x con le proprietà desiderate. Queste sorgenti, basate sulla radiazione emessa da elettroni accelerati nel plasma, hanno in comune di essere compatte, produrre radiazione collimata, incoerente e impulsata al femtosecondo. In questa tesi vengono presentati alcuni metodi per ottenere raggi x da elettroni accelerati per interazione tra laser e plasma: la radiazione di betatrone da elettroni intrappolati e accelerati nel cosiddetto “bubble regime”, la radiazione di sincrotrone da elettroni posti in un ondulatore convenzionale con lunghezza dell’ordine dei metri e la radiazione ottenuta dal backscattering di Thomson. Vengono presentate: la fisica alla base di tali metodi, simulazioni numeriche e risultati sperimentali per ogni sorgente di raggi x. Infine, viene discussa una delle più promettenti applicazioni fornite dagli acceleratori basati su interazione tra laser e plasma: il Free-electron laser nello spettro dei raggi x, capace di fornire intensità 108-1010 volte più elevate rispetto alle altre sorgenti.

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Biloiu, Ioana A. "Laser induced fluorescence studies of ion acceleration in single and multiple species expanding plasmas." Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10036.

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Thesis (Ph. D.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains xiv, 173 p. : ill. (some col). Vita. Includes abstract. Includes bibliographical references.

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Mollica, Florian. "Interaction laser-plasma ultra-intense à densité proche-critique pour l'accélération d'ions." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX058/document.

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L'interaction d'un laser ultra-intense et ultra-court avec la matière donne naissance à une grande variété de processus issus du couplage des ondes électromagnétiques associées au laser avec les modes du plasma. Ce couplage hautement non-linéaire excite des phénomènes plasmas collectifs capables de produire des champs intenses pouvant atteindre le TV/m. Ces champs ouvrent la possibilité de réaliser des accélérateurs de particules compacts, aussi bien d'électrons que d'ions. Des sources laser-plasma d'ions de plusieurs dizaines de MeV ont été démontré au début des années 2000 et de nombreux mécanismes ont été suggérés depuis afin d'en améliorer les propriétés. Historiquement, les sources d'ions par laser ont été obtenues à partir de cibles solides dîtes sur-denses. L’innovation sur les cibles a été un moteur majeur de l’amélioration de ces sources. Dans la continuité de cette dynamique, l’utilisation de cibles gazeuses a été proposé afin d’alléger les contraintes de contraste laser et de taux de répétition. De récentes démonstrations expérimentales sont venus renforcer l’intérêt pour ces cibles, dîtes sous-denses ou proche critiques, dont la valeur est propice à la propagation, à l’absorption du laser et à la création de structures accélératrices que sont les chocs plasmas et les vortex magnétiques. Les travaux présentés dans cette thèse constituent une exploration expérimentale des paramètres plasmas nécessaires à l’accélération d’ions dans des cibles gazeuses de densité proche-critique. Pour la première fois ces régimes sont explorés avec un laser ultra-intense femtoseconde de 150TW. Une partie des travaux a été consacrée à la réalisation d’une cible innovante, adaptée aux contraintes de densité et de gradients plasma requises par ces régimes. Suivent, les travaux expérimentaux décrivant la propagation du laser et l’accélération d’électrons dans des cibles proche-critiques. Enfin une dernière partie décrit la production d’un faisceau d’atome issue d’une source d’ion laser
Interaction of ultra-intense, ultra-short laser with matter gives rise to a wealth of phenomena, due to the coupling between the electromagnetic field and the plasma. The non-linear coupling excites collective plasma processes able to sustain intense electric fields up to 1TV/m. This property spurred early interest in laser accelerator as compact, next-generation source of accelerated electrons and ions. Laser-driven ion source of several MeV was demonstrated in early 2000 an various mechanisms had been suggest to improve the their properties. These first ion sources have been obtained on solid targets, called “overdense”. Target innovation has driven the improvement of these sources. In the continuity of this dynamic, new gaseous targets had been proposed in order to relax the constraints that solid targets impose on laser contrast and repetition rate. Recent experimental demonstrations of monoenergetic ion acceleration in gas renew the interest in such targets, called under-dense or near-critical because of their intermediate densities. At near-critical density the laser can propagate, but undergoes significant absorbtion, giving rise to the accelerating structures of plasma shocks and magnetic vortex.The work presented in this thesis is an experimental exploration of the plasma conditions required to drive ion acceleration in gaseous near-critical target. For the first time, these regimes are explored with an ultra-intense, femtosecond laser of 150TW. A part of this work has been dedicated to the design of an innovative gas target, suited for plasma density and gradient constraints set by these regimes. Then the experimental works describe laser propagation and electron acceleration in near-critical targets. Finally the last part report the efficient production of an atomic beam from a laser-driven ion source

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Laberge, Michel. "Electron acceleration in a plasma wave above a laser irradiated grating." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30725.

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The acceleration of electrons in a laser produced plasma wave was studied experimentally. A plasma with a modulated density was produced by illuminating a grating with a ruby laser at an intensity of 10¹⁰ W/cm². The plasma expanding above the surface of the grating was diagnosed using interferometry, shadowgraphy and Raman-Nath scattering. The plasma density was found to be modulated with an amplitude of [formula omitted]/n=8% for grating spacings ranging from 6 to 35 µm. A CO₂ laser of intensity 7xlO¹¹ W/cm2 then irradiated this modulated plasma and generated plasma waves. The phase speeds of the plasma waves are v[formula omitted] = ±[formula omitted]k[formula omitted], where k[formula omitted] is the wavenumber of the grating and [formula omitted] is the frequency of the CO₂ laser. Electrons were injected at an energy of 25 keV in one of the plasma waves. In order for the phase speed of the wave to synchronize with the accelerating electrons, a grating with constantly increasing line spacing was used. No conclusive evidence of electron acceleration was obtained, even after the injection energy was increased to 92 keV. This lack of evidence was the result of a large electric field perpendicular to the surface of the grating, which deflected the electrons onto the grating. This detrimental electric field is produced when fast electrons are emitted by the plasma and leave it positively charged. At the low laser intensity used in this experiment, the origin of these electrons could not be identified. Some techniques to remedy this difficulty are proposed.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

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Gangolf, Thomas. "Intense laser-plasma interactions with gaseous targets for energy transfer and particle acceleration." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX110.

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Le plus fréquemment, l’interaction laser-matière est étudiée avec des lasers ayant des longueurs d’onde dans l’infrarouge proche (PIR), car ce sont les lasers qui peuvent générer les impulsions les plus intenses. Pour ces lasers, des cibles de densité allant de 0,05 à 2,5 fois la densité critique sont difficiles à créer mais elles offrent des perspectives intéressantes. Dans cette thèse, des jets d’hydrogène ayant de densité dans ce domaine sont utilisées dans le contexte de deux applications :Premièrement, des ions sont accélérées par choc non-collisionnel (collisionless shock acceleration, CSA). Lors de l’interaction d’une impulsion laser PIR avec une cible légè- rement sur-critique, un faisceau de protons est généré. Il est collimé, dirigé vers l’avant et quasiment monoénergetique. Des simulations indiquent que cela est lié à la formation d’un choc non-collisionnel et à l’accélération des protons par ce choc, en sus de leur accélération par le processus standard dit ”target normal sheath acceleration (TNSA)” qui est effectif en face arrière de la cible. Pour beaucoup d’applications, ces faisceaux de particules quasi-monoénergetiques sont plus appropriés que ceux à spectre large qui sont générés de façon routinière par TNSA.Deuxièmement, de l’énergie est transférée d’une impulsion laser (pump) vers une autre en contrepropagation (seed), par rétrodiffusion Brillouin stimulée, dans le régime de couplage fort (strong coupling-SBS), à des densités entre 0,05 et 0,2 fois la densité critique. Pour des impulsions à large bande (60 nanomètres), le rôle de la pré-ionisation sur la propagation et la rétrodiffusion Brillouin spontanée et stimulée est étudié, en incluant l’influence du chirp. Pour des lasers à bande plus étroite, il est démontré que l’impulsion seed peut être amplifiée par des dizaines de milliJoules, et des signatures d’amplification efficace et d’affaiblissement de l’impulsion laser pompe sont trouvées. Ce concept vise à l’amplification des impulsions laser à des puissances au-delà du seuil de dommage des amplificateurs laser basés sur des matériaux solides
Laser-matter interaction is studied mostly with near-infrared (NIR) lasers as they can generate the most intense pulses. For these lasers, targets between 0.05 to 2.5 times the critical density are challenging to create but offer interesting prospects. In this thesis, novel high-density Hydrogen gas jet targets with densities in this range are used in view of two applications:First, ions are accelerated by collisionless shock acceleration (CSA). Upon interaction of a NIR laser with a slightly overcritical gas jet target, a collimated, quasi-monoenergetic proton beam is generated in forward direction. Simulations indicate the formation of a collisionless shock and acceleration of protons both by the shock and target normal sheath acceleration (TNSA) on the target rear surface under these conditions. These directed, monoenergetic particle bunches are more suitable for many applications than the broadband particle beams already generated routinely.Second, at densities between 0.05 and 0.2 times the critical density, energy is transferred from one laser pulse (pump) to a counterpropagating pulse (seed), via Stimulated Brillouin Backscattering in the strongly-coupled regime (sc-SBS). For the case of broad- band (60 nanometers) pulses, the role of the preionization for pulse propagation and both spontaneous and stimulated Brillouin backscattering are studied, including the influence of the chirp. It is shown that for narrower bandwidths, the seed pulse is ampli- fied by tens of millijoules, and signatures of efficient amplification and pump depletion are found. This concept aims at amplifying laser pulses to powers above the damage thresholds of solid state amplifiers

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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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Flacco, Alessandro. "Experimental study of proton acceleration with ultra-high intensity, high contrast laser beam." École polytechnique, 2010. http://www.theses.fr/2008EPXX0071.

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La production de faisceaux énergétiques d'ions/protons avec des impulsions laser à intensités relativistes (I>10^{18}W/cm^2) a reçu, au cours des dernières années, un intérêt croissant parmi les scientifiques travaillant dans les domaines de l'optique, de la physique des plasmas et des accélérateurs. Une fraction des électrons est chauffée à haute température lors de l'interaction entre une impulsion laser femtoseconde et un plasma surdense. Les ions et les protons sont extraits et accélérés par la séparation de charge qui est produite pendant l'expansion du plasma. Les résultats présentés dans ce manuscrit décrivent la réalisation d'expériences d'accélération d'ions avec un système laser à haute puissance et à haut contraste (XPW). Deux expériences préparatoires sont réalisées, afin d'étudier l'interaction entre le piédestal d'une impulsion laser et une cible. L'expansion d'un plasma créé par laser à intensité moyenne est mesurée par interférométrie; l'évolution de la longueur de son gradient de densité est déduite par les cartes de densité électronique, mesurées à différents instants. La variation de la réflectivité absolue d'une cible mince d'aluminium est mise en corrélation avec la température électronique afin de contrôler le débouché du choc produit par le laser. La corrélation entre les deux expériences est finalement utilisée pour définir le conditions optimales pour l'accélération des protons. Des expériences d'accélération de protons avec un laser à haut contraste, la construction et la validation d'un spectromètre (Galette a Micro-canaux et Parabole Thomson), ainsi que des autres détails sur le montage sont présentés. Les résultats ainsi obtenus montrent que l'amélioration du contraste permet d'utiliser des cibles plus minces et de produire des conditions d'interaction plus stables et contrôlables. Des faisceaux des protons ayant énergie cinétique supérieure à 4MeV sont produits, avec une stabilité tir à tir meilleure de 4% rms. L'accélération des protons avec deux impulsions laser confirme que l'absorption d'énergie laser est augmentée dans le cas des cibles pre-chauffées par une impulsion laser avec les bons paramètres
The production of energetic proton/ion beams with laser pulses at relativistic intensities (I>10^{18}W/cm^2) has received, in the past few years, increasing interest from the scientific community in plasma, optics and accelerator physics. A fraction of electrons is heated to high temperature during the ultrafast interaction between a femtosecond laser pulse and an overdense plasma. Ions and protons are extracted and accelerated by the charge separation set up during the expansion of the plasma. The results presented in this manuscript report on the realization of ion acceleration experiments using a high contrast (XPW) multi-terawatt laser system. Two preparatory experiments are set up, aiming to study the pedestal of a laser pulse interacting with the target. The expansion of a plasma created by a laser at moderate intensity is measured by interferometry; the evolution of the density gradient length is deduced from the electron density maps at different moments. The variation of the absolute reflectivity of a thin aluminium foil is correlated to the electron temperature and is used to monitor the arrival time of the laser produced shock. The crossing between the two experiments is finally used to define the optimum condition for proton acceleration. Proton acceleration experiments with high contrast laser are reported, including the construction and the validation of a real-time, single shot ion spectrometer (Micro-channel Plate and Thomson Parabola), and other details of the realised setup. The obtained results show that the increased contrast enables the use of thinner targets and the production of more stable and controllable interaction conditions. Proton beams with kinetic energy higher than 4 MeV are produced, with a shot-to-shot stability better than 4% rms. Proton acceleration experiment with two laser beams confirms that the laser energy absorption is enhanced when the target is pre-heated by a laser pulse with proper parameters

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Doche, Antoine. "Particle acceleration with beam driven wakefield." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX023/document.

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Les accélérateurs par onde de sillage plasma produites par faisceaux de particules (PWFA) ou par faisceaux laser (LWFA) appartiennent à un nouveau type d’accélérateurs de particules particulièrement prometteur. Ils permettent d’exploiter des champs accélérateurs jusqu’à cent Gigaélectronvolt par mètre alors que les dispositifs conventionnels se limitent à cent Megaélectronvolt par mètre. Dans le schéma d’accélération par onde de sillage plasma, ou par onde de sillage laser, un faisceau de particules ou une impulsion laser se propage dans un plasma et créé une structure accélératrice dans son sillage : c’est une onde de densité électronique à laquelle sont associés des champs électromagnétiques dans le plasma. L’un des principaux résultats de cette thèse a été la démonstration de l’accélération par onde de sillage plasma d’un paquet distinct de positrons. Dans le schéma utilisé, un plasma de Lithium était créé dans un four, et une onde plasma était excitée par un premier paquet de positrons (le drive ou faisceau excitateur) et l’énergie était extraite par un second faisceau (le trailing ou faisceau témoin). Un champ accélérateur de 1,36 GeV/m a ainsi été obtenu durant l’expérience, pour une charge accélérée typique de 40 pC. Nous montrons également ici la possibilité d’utiliser différents régimes d’accélération qui semblent très prometteurs. Par ailleurs, l’accélération de particule par sillage laser permet quant à elle, en partant d’une impulsion laser femtoseconde de produire un faisceau d’électron quasi-monoénergétique d’énergie typique de l’ordre de 200 MeV. Nous présentons les résultats d’une campagne expérimentale d’association de ce schéma d’accélération par sillage laser avec un schéma d’accélération par sillage plasma. Au cours de cette expérience un faisceau d’électrons créé par laser est refocalisé lors d’une interaction dans un second plasma. Une étude des phénomènes associés à cette plateforme hybride LWFA-PWFA est également présentée. Enfin, le schéma hybride LWFA-PWFA est prometteur pour optimiser l’émission de rayonnement X par les électrons du faisceau de particule crée dans l’étage LWFA de la plateforme. Nous présentons dans un dernier temps la première réalisation expérimentale d’un tel schéma et ses résultats prometteurs
Plasma wakefield accelerators (PWFA) or laser wakefield accelerators (LWFA) are new technologies of particle accelerators that are particularly promising, as they can provide accelerating fields of hundreds of Gigaelectronvolts per meter while conventional facilities are limited to hundreds of Megaelectronvolts per meter. In the Plasma Wakefield Acceleration scheme (PWFA) and the Laser Wakefield Acceleration scheme (LWFA), a bunch of particles or a laser pulse propagates in a gas, creating an accelerating structure in its wake: an electron density wake associated to electromagnetic fields in the plasma. The main achievement of this thesis is the very first demonstration and experimental study in 2016 of the Plasma Wakefield Acceleration of a distinct positron bunch. In the scheme considered in the experiment, a lithium plasma was created in an oven, and a plasma density wave was excited inside it by a first bunch of positrons (the drive bunch) while the energy deposited in the plasma was extracted by a second bunch (the trailing bunch). An accelerating field of 1.36 GeV/m was reached during the experiment, for a typical accelerated charge of 40 pC. In the present manuscript is also reported the feasibility of several regimes of acceleration, which opens promising prospects for plasma wakefield accelerator staging and future colliders. Furthermore, this thesis also reports the progresses made regarding a new scheme: the use of a LWFA-produced electron beam to drive plasma waves in a gas jet. In this second experimental study, an electron beam created by laser-plasma interaction is refocused by particle bunch-plasma interaction in a second gas jet. A study of the physical phenomena associated to this hybrid LWFA-PWFA platform is reported. Last, the hybrid LWFA-PWFA scheme is also promising in order to enhance the X-ray emission by the LWFA electron beam produced in the first stage of the platform. In the last chapter of this thesis is reported the first experimental realization of this last scheme, and its promising results are discussed

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Aniculaesei, Constantin. "Experimental studies of laser plasma wakefield acceleration." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25874.

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This thesis describes experiments thatexplore the possibility of improving the quality of an electron beam obtained from a laser wakefield accelerator (LWFA) by shaping the longitudinal plasma density profile. Different density profiles have been obtained by employing a range of Laval nozzles with different geometries. These are modelled and numerically simulated under different conditions using Fluent 6.3. Density lineouts from simulations for different heights above the nozzle give the plasma density profile for each experimental condition. The plasma density profile is modified by changing the geometry of the nozzle, the interaction point, the laser beam angle relative to the exit plane of the nozzle and pressure of the gas. In this way the leading up-ramp length of the density profile (that interacts first with the laser) has been varied between 0.47 mm to 1.39 mm and the maximum plasma density varied between 1.29 x 1019 cm⁻³ to 2.03 x 1019 cm⁻³. The influence of the density profile parameters on the LWFA process is quantified by monitoring the properties of the generated electron beam. It is shown that the leading ramp of the plasma density profile i.e. the ramp that interacts first with the laser, has a strong influence on the quality of the electron beam. Density profiles with the same peak plasma density but different ramp lengths generate electron beams with a factor of 1.4 difference in charge, 1.1 in electron energy, 2 in pointing and 1.45 in energy spread. Longer ramp lengths enhance the quality of electron beams, which suggest that LWFA injection occurs at the entrance density ramp. Complex density profiles are produced by tilting the nozzle relative to the direction of propagation of the laser. This allows continuous tuning of the peak energy of the electron beam from 135 ± 2MeV up to 171 ± 2MeV. The electron beam energy spread show improvements from 20.7 ± 1.2% to 8.9 ± 0.9%. The charge closely follows the evolution of the energy spread and has a mean value of 0.61 ± 0.16 pC. Experimental results also show that the angular distribution of the electron beam becomes elliptical when the laser focal plane is moved from the edge of the gas jet towards the centre of the density profile. This result is linked to the existence of a distorted LWFA bubble that propagates off-axis therefore affecting the pointing and transverse shape of the electron beam.

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Audet, Thomas. "Développement d'un injecteur pour l'accélération laser plasma multi-étages." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS424/document.

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L’accélération laser plasma (ALP) est un mécanisme d’accélération de particules reposant sur l’interaction d’impulsions laser ultra-intenses, de l’ordre de quelques 10^{18} W/cm², avec un plasma. L’onde plasma générée dans le sillage de l’impulsion laser est associée à des champs électriques de grande amplitude (1 − 100 GV/m). Ces champs électriques de trois ordres de grandeurs supérieurs aux champs maximums supportés dans les cavités radiofréquences des accélérateurs conventionnels constituent le principal point fort de l’ALP, permettant d’envisager des accélérateurs de particules plus compacts. Un important travail pour améliorer les propriétés des paquets d’électrons générés par ALP, leur stabilité et la cadence de tir est cependant nécessaire pour rendre l’ALP compétitive en termes d’applications.Un moyen d’améliorer les propriétés des faisceaux d’électrons consiste à les accélérer dans un régime faiblement non linéaire en plusieurs étapes successives : l’ALP multi-étages. La source laser-plasma d’électrons, ou injecteur, doit générer des paquets d’électrons d’énergie modeste (50 − 100 MeV), de charge la plus importante possible, de faible dimension et de faible divergence. Les électrons doivent alors être injectés dans un second étage purement accélérateur dont l’objectif est d’augmenter leur énergie cinétique.L’objet de cette thèse est le développement d’un injecteur laser plasma pour l’ALP multi-étages. Dans le cadre d’une collaboration autour de l’equipex CILEX et du programme d’ALP à deux étages, un prototype d’injecteur a été construit, ELISA, reposant sur une cellule de gaz de longueur variable. La densité électronique du plasma, qui est un paramètre crucial pour le contrôle du faisceau d’électrons, a été caractérisée à la fois expérimentalement et numériquement. ELISA a été utilisée sur deux installations laser différentes, et les mécanismes physiques déterminant les paramètres des paquets d’électrons produits par ELISA ont été étudiés en fonction des nombreux paramètres expérimentaux. Une gamme de paramètres pertinents pour un injecteur laser plasma a été déterminée.Une ligne de transport et diagnostic magnétique a également été construite, implantée et testée sur l’installation UHI100 du CEA Saclay, permettant à la fois de caractériser plus finement les propriétés des paquets d’électrons générés par ELISA, mais aussi d’évaluer la qualité des paquets d’électrons transportés pour l’injection dans un second étage
Laser wakefield acceleration (LWFA) is a particle acceleration process relying on the interaction between high intensity laser pulses, of the order of 10^{18} W/cm² and a plasma. The plasma wave generated in the laser wake sustain high amplitude electric fields (1-100 GV/m). Those electric fields are three orders of magnitude higher than maximum electric fields in radio frequency cavities and represent the main benefit of LWFA, allowing more compact acceleration. However improvements of the LWFA-produced electron bunches properties, stability and repetition rate are mandatory for LWFA to be usable for applications.A scheme to improve electron bunches properties and to potentially increase the repetition rate is multi-stage LWFA. The laser plasma electron source, called the injector, has to produce relatively low energy (50-100 MeV), but high charge, small size and low divergence electron bunches. Produced electron bunches then have to be transported and injected into a second stage to increase electron kinetic energy.The subject of this thesis is to study and design a laser wakefield electron injector for multi-stage LWFA. In the frame of CILEX and the two-stages LWFA program, a prototype of the injector was built : ELISA consisting in a variable length gas cell. The plasma electronic density, which is a critical parameter for the control of the electron bunches properties, was characterized both experimentally and numerically. ELISA was used at two different laser facilities and physical mechanisms linked to electron bunches properties were studied in function of experimental parameters. A range of experimental parameters suitable for an laser wakefield injector was determined.A magnetic transport and diagnostic line was also built, implemented and tested at the UHI100 laser facility of the CEA Saclay. It allowed a more precise characterization of electron bunches generated with ELISA as well as an estimation of the quality of transported electron bunches for their injection in a second laser wakefield stage

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Gustas, Dominykas. "High-repetition-rate relativistic electron acceleration in plasma wakefields driven by few-cycle laser pulses." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX118/document.

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Le progrès continu de la technologie laser a récemment permis l’avancement spectaculaire d’accélérateurs de particules par onde de sillage. Cette technique permet la génération de champs électriques très forts, pouvant dépasser de trois ordres de grandeurs ceux présents dans les accélérateurs conventionnels. L’accélération résultante a lieu sur une distance très courte, par conséquent les effets de la charge d’espace et de la dispersion de vitesse sont considérablement réduits. Les paquets de particules ainsi générés peuvent alors atteindre des durées de l’ordre de la femtoseconde, qui en fait un outil prometteur pour la réalisation d’expériences de diffraction ultra-rapide avec une résolution inégalée de l’ordre de quelques femtosecondes. La génération de tels paquets d’électrons avec des lasers de 1 J et d’une durée de 30 fs est à présent bien établie. Ces paramètres permettent de produire des faisceaux d’électrons de quelques centaines de MeV, et sont donc inadaptés aux expériences de diffraction. De plus, le taux de répétition de ces lasers de haute puissance est limité à quelques Hz, ce qui est insuffisant pour des expériences exigeant une bonne statistique de mesure. Notre groupe a utilisé un laser de pointe développé au laboratoire par le groupe PCO générant des impulsions de quelques millijoules, d’une durée de 3.4 fs - à peine 1.3 cycle optique - à une cadence de 1 kHz, pour accélérer des électrons par onde de sillage. Ce travail de thèse présente d’une part la première démonstration d’un accélérateur des particules relativistes opéré dans le régime de la bulle à haute cadence. L’utilisation de buses microscopiques a permis l’obtention de charges de dizaines de pC par tir. De plus, cette thèse vise à l’élargissement de notre compréhension des lois d’échelle d’accélération laser-plasma. Nous espérons que notre travail visant à la fiabilisation et l’optimisation de cette source permettra à terme de proposer un instrument accessible et fiable à la communauté scientifique, que ce soit pour la diffraction d’électrons, l’irradiation ultra-brève d’échantillons ou la génération de rayons X
Continuing progress in laser technology has enabled dramatic advances in laser wakefield acceleration (LWFA), a technique that permits driving particles by electric fields three orders of magnitude higher than in conventional radio-frequency accelerators. Due to significantly reduced space charge and velocity dispersion effects, the resultant relativistic electron bunches have also been identified as a candidate tool to achieve unprecedented sub-10 fs temporal resolution in ultrafast electron diffraction (UED) experiments. High repetition rate operation is desirable to improve data collection statistics and thus washout shot-to-shot charge fluctuations inherent to plasma accelerators. It is well known that high-quality electron beams can be achieved in the blowout, or "bubble" regime, which is at present regularly accessed with ≈ 30 fs Joule-class lasers that can perform up to few shots per second. Our group on the contraryutilized a cutting edge laser system producing few-mJ pulses compressed nearly to a single optical cycle (3.4 fs) to demonstrate for the first time an MeV-grade particle accelerator with properties characteristic to the blowout regime operating at 1 kHz repetition rate. We further investigate the plasma density profile and exact laser pulse waveform effects on the source output, and show that using special gas microjets a charge of tens of pC/shot can be achieved. We expect this technique to lead to a generation of highly accessible and robust instruments for the scientific community to conduct UED experiments or to be used for other applications. This work also serves to expand our knowledge on the scalability of laser-plasma acceleration

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Gaul, Erhard Werner. "Fully ionized helium waveguides for laser wakefield acceleration /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004269.

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Walton, Barney Richard. "Optical diagnostics of laser plasma particle acceleration experiments." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418083.

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Shanks, Richard P. "Comprehensive characterisation of laser plasma wakefield accelerated electrons." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18119.

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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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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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Debus, Alexander. "Brilliant radiation sources by laser-plasma accelerators and optical undulators." Forschungszentrum Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-91303.

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This thesis investigates the use of high-power lasers for synchrotron radiation sources with high brilliance, from the EUV to the hard X-ray spectral range. Hereby lasers accelerate electrons by laser-wakefield acceleration (LWFA), act as optical undulators, or both. Experimental evidence shows for the first time that LWFA electron bunches are shorter than the driving laser and have a length scale comparable to the plasma wavelength. Furthermore, a first proof of principle experiment demonstrates that LWFA electrons can be exploited to generate undulator radiation. Building upon these experimental findings, as well as extensive numerical simulations of Thomson scattering, the theoretical foundations of a novel interaction geometry for laser-matter interaction are developed. This new method is very general and when tailored towards relativistically moving targets not being limited by the focusability (Rayleigh length) of the laser, while it does not require a waveguide. In a theoretical investigation of Thomson scattering, the optical analogue of undulator radiation, the limits of Thomson sources in scaling towards higher peak brilliances are highlighted. This leads to a novel method for generating brilliant, highly tunable X-ray sources, which is highly energy efficient by circumventing the laser Rayleigh limit through a novel traveling-wave Thomson scattering (TWTS) geometry. This new method suggests increases in X-ray photon yields of 2-3 orders of magnitudes using existing lasers and a way towards efficient, optical undulators to drive a free-electron laser. The results presented here extend far beyond the scope of this work. The possibility to use lasers as particle accelerators, as well as optical undulators, leads to very compact and energy efficient synchrotron sources. The resulting monoenergetic radiation of high brilliance in a range from extreme ultraviolet (EUV) to hard X-ray radiation is of fundamental importance for basic research, medical applications, material and life sciences and is going to significantly contribute to a new generation of radiation sources and free-electron lasers (FELs).

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Bosi, Marco. "Scaling laws and parallelization schemes in laser-plasma acceleration." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.

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Una sintesi delle dinamiche alla base dell’interazione laser-plasma è presentata insieme ai metodi numerici e algoritmi utilizzati nell'ambiente di simulazione. Il regime TNSA è considerato approfonditamente anche con l’ausilio di modelli teorici, in particolare i risultati del modello 2D confrontati con le simulazioni. Si considera il costo computazionale degli algoritmi e le basi dell'HPC come i vari tipi di parallelismo e lo sfruttamento della cache

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Messner, Philipp [Verfasser]. "Tunable Laser-Plasma Acceleration with Ionization Injection / Philipp Messner." Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2020. http://d-nb.info/1230555242/34.

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Rossi, Francesco <1987&gt. "Numerical and Analytical Methods for Laser-Plasma Acceleration Physics." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6771/1/tesi3.pdf.

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Theories and numerical modeling are fundamental tools for understanding, optimizing and designing present and future laser-plasma accelerators (LPAs). Laser evolution and plasma wave excitation in a LPA driven by a weakly relativistically intense, short-pulse laser propagating in a preformed parabolic plasma channel, is studied analytically in 3D including the effects of pulse steepening and energy depletion. At higher laser intensities, the process of electron self-injection in the nonlinear bubble wake regime is studied by means of fully self-consistent Particle-in-Cell simulations. Considering a non-evolving laser driver propagating with a prescribed velocity, the geometrical properties of the non-evolving bubble wake are studied. For a range of parameters of interest for laser plasma acceleration, The dependence of the threshold for self-injection in the non-evolving wake on laser intensity and wake velocity is characterized. Due to the nonlinear and complex nature of the Physics involved, computationally challenging numerical simulations are required to model laser-plasma accelerators operating at relativistic laser intensities. The numerical and computational optimizations, that combined in the codes INF&RNO and INF&RNO/quasi-static give the possibility to accurately model multi-GeV laser wakefield acceleration stages with present supercomputing architectures, are discussed. The PIC code jasmine, capable of efficiently running laser-plasma simulations on Graphics Processing Units (GPUs) clusters, is presented. GPUs deliver exceptional performance to PIC codes, but the core algorithms had to be redesigned for satisfying the constraints imposed by the intrinsic parallelism of the architecture. The simulation campaigns, run with the code jasmine for modeling the recent LPA experiments with the INFN-FLAME and CNR-ILIL laser systems, are also presented.

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Rossi, Francesco <1987&gt. "Numerical and Analytical Methods for Laser-Plasma Acceleration Physics." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6771/.

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Theories and numerical modeling are fundamental tools for understanding, optimizing and designing present and future laser-plasma accelerators (LPAs). Laser evolution and plasma wave excitation in a LPA driven by a weakly relativistically intense, short-pulse laser propagating in a preformed parabolic plasma channel, is studied analytically in 3D including the effects of pulse steepening and energy depletion. At higher laser intensities, the process of electron self-injection in the nonlinear bubble wake regime is studied by means of fully self-consistent Particle-in-Cell simulations. Considering a non-evolving laser driver propagating with a prescribed velocity, the geometrical properties of the non-evolving bubble wake are studied. For a range of parameters of interest for laser plasma acceleration, The dependence of the threshold for self-injection in the non-evolving wake on laser intensity and wake velocity is characterized. Due to the nonlinear and complex nature of the Physics involved, computationally challenging numerical simulations are required to model laser-plasma accelerators operating at relativistic laser intensities. The numerical and computational optimizations, that combined in the codes INF&RNO and INF&RNO/quasi-static give the possibility to accurately model multi-GeV laser wakefield acceleration stages with present supercomputing architectures, are discussed. The PIC code jasmine, capable of efficiently running laser-plasma simulations on Graphics Processing Units (GPUs) clusters, is presented. GPUs deliver exceptional performance to PIC codes, but the core algorithms had to be redesigned for satisfying the constraints imposed by the intrinsic parallelism of the architecture. The simulation campaigns, run with the code jasmine for modeling the recent LPA experiments with the INFN-FLAME and CNR-ILIL laser systems, are also presented.

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YADAV, MONIKA. "SOME ASPECTS OF LASER-PLASMA INTERACTION FOR ELECTRON ACCELERATION." Thesis, DELHI TECHNOLOGICAL UNIVERSITY, 2021. http://dspace.dtu.ac.in:8080/jspui/handle/repository/18736.

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This thesis focuses on investigation of laser-plasma interaction relevant to electron acceleration to high energies. This work explores various ideas for producing an energetic and good quality electron beam from laser wakefield acceleration (LWFA) in plasmas. In LWFA, a high-intensity laser pulse excites a plasma wave, which propagates behind the laser pulse with the equal speed of the laser group velocity. For efficient accelerations, electrons should be injected into the wakefield. Thus, the wakefield evolution and electron injection both are quite important aspects in LWFA. In order to draw the maximum output from the wakefield structure, which is called wakefield bubble in case of high-intensity laser, the basic understanding behind the factors controlling electron injection into wake structure must be very clear. This thesis work focus toward controlling the electron beam quality by understanding the factors affecting bubble wake evolution. The dependence of beam energy and the beam quality on the shape of the bubble is the main motivation behind this investigation. Particle-in-cell (PIC) simulations are conducted to study the bubble dynamics for optimum electron accelerations. A good quality electron bunch with pC to nC charge are obtained with current laser-plasma parameters. During LWFA, generation of wakefield results in variation of refractive index that may distort the laser pulse shape. Thus, the laser pulse shape may be a significant factor to control the electron beam parameters in LWFA. Various shapes such as q-Gaussian laser pulse and flattened-Gaussian laser pulse have been taken into account to observe the laser pulse effect on electron beam parameters in LWFA. The implications of laser pulse shape was shown to control and optimize the bunch charge as well as the bunch energy. Our insights into the acceleration process might be quite supportive in the future optimization of electron beam stability and quality. The electron bunch generated by LWFA could be used to obtain femtosecond x-rays and subsequent applications in medical sciences.

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Jäckel, Oliver. "Characterisation of ion acceleration with relativistic laser-plasmas." Tönning Lübeck Marburg Der Andere Verl, 2009. http://d-nb.info/995862729/04.

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Ibbotson, Thomas P. A. "An investigation of laser-wakefield acceleration in the hydrogen-filled capillary discharge waveguide." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.560930.

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This thesis describes a detailed investigation into the process of laser-wakefield acceleration (LWFA) for the generation of high-energy electron beams using the hydrogen-filled capillary discharge waveguide. In only the second experiment to be performed using the newly commissioned Astra-Gemini laser at the Rutherford Appleton Laboratory, electron beams were accelerated to energies greater than 0.5 GeV by laser pulses of energy 2.5J and peak power of 30T\~T. The injec- tion and acceleration of electron beams was seen to depend on the state of the plasma channel for axial electron densities less than 2.5 x 1018 cm -3. With the aid of simulations performed using the code WAKE it was found that the plasma channel allows the laser pulse to maintain its self-focussed spot size along the length of the capillary even below the critical power for self-guiding. It was found that the threshold laser energy required for the production of elec- tron beams was reduced by the use of an aperture placed early in the laser system. This was attributed to the increased energy contained in the central part of the focal spot of the laser. A short paper on this work was published in Physical Review Special Topics - Accelerators and Beams and a longer paper was published in the New Journal of Physics. Transverse interferometry was used to measure the electron density of the plasma channel used in the Astra-Gemini experiments. An imaging system was devised which used cylindrical optics to increase the field of view of the capillary longitudinally, whilst maintaining the trans- verse resolution. The measured properties were consistent with previous measurements made by Gonsalves et al. [J]. The observed longitudinal variations in the plasma channel parameters were not found to be significant enough to affect the injection process.

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Popp, Antonia. "Dynamics of electron-acceleration in laser-driven wakefields: Acceleration limits and asymmetric plasma waves." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-138159.

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Kamperidis, Christos Antonios. "Investigation of Electron Laser Wakefield Acceleration in Novel Plasma Structures." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485616.

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This thesis presents experimental and simulation results on electron acceleration from the interaction of ultra-intense, ultra-short lasers with underdense plasmas, based on two schemes of the Laser Wakefield Acceleration (LWFA) mechanism. Using the 100 TW laser, in LUll, France, with pulse durations of 500 fsec and intensities' greater than 5.1018 W/cm2 , electron energies of up to 200 MeV,)Here observed. The spectra of the electron beams exhibit a maxwellian distribution, which together-with the recording of the Raman satellites of the laser spectrum suggest that we operate in the Self Modulated-LWFA, making these beams the highest energy observed to date, in that scheme. Total charge estimates suggest that a 1% energy transfer to the electron beam is possible. Occasional non-maxwellian features in the electron spectra, backed up by simulations, suggest that mechanisms other than SM-LWFA are also present in the interaction. Most importantly, self-guiding channels of - cm scales are observed adding a new perspective in achieving a commercially viable LWF accelerator. In the classical short pulse regime of LWFA, the ASTRA (0.6 J, < 50 fsec) laser is used to compare electron acceleration, with and without an external waveguide. Maximum electron energy results in the self-guided regime are only 2x lower compared to the externally guided case. The stability and reproducibility of the beam however, is improved when the external waveguide is used. Electron beams with 200 MeV maximum energy and narrow energy spread are consistently observed. The appearance of these beams is strongly linked with ionisation effects, either from high ion states of waveguide wall material, or recombined gas. A particle tracking code shows that electrons released from ionisation processes within the laser pulse, and hence within the plasma wake, are trapped by the wake and accelerated, pro.ducing a bunch with low energy spread. These lay the basis for future experiments, envisaging improved stability, wall-plug energy transfer efficiency and high brilliance electron beams.

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Nagel, Sabrina Roswitha. "Studies of Electron Acceleration Mechanisms in Relativistic Laser-Plasma Interactions." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4639.

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Laser-plasma interactions have many potential applications, such as medical treatments,x-ray generation, particle acceleration and inertial confinement fusion (ICF).In all of these applications, understanding how laser energy is absorbed by the materialand converted into energetic electrons is very important. Therefore it is vitalto enhance the understanding of how these energetic electrons are created and whatmechanisms influence them. This Thesis comprises experimental studies of electron acceleration mechanismsin laser-plasma interactions, as well as simulations relevant to these experiments. The experiments described were conducted at the Rutherford Appleton Laboratoryutilising the VULCAN laser facility, and investigate laser interactions with both underdenseand overdense plasmas. In the underdense regime, the intensity dependence of the accelerated electronshas been studied experimentally, as well as the impact of the focusing geometry onthe generation of hot electrons. For high intensities, experimental measurementsshow a scaling of the temperature of the electrons with a0. Density and f-numberdependencies of the accelerated electrons are also observed. The effect of laser polarisation and target thickness on the escaping electronsis studied for laser interactions with solid targets, or overdense plasmas. It wasfound that the effective temperature of the electrons depends on both the laserpolarisation and the target thickness. The electron production from ultra-thin foils,and the effect of laser pre-pulse are also investigated.

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Sgattoni, Andrea <1982&gt. "Theoretical and numerical study of the laser-plasma ion acceleration." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3811/1/sgattoni_andrea_tesi.pdf.

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The laser driven ion acceleration is a burgeoning field of resarch and is attracting a growing number of scientists since the first results reported in 2000 obtained irradiating thin solid foils by high power laser pulses. The growing interest is driven by the peculiar characteristics of the produced bunches, the compactness of the whole accelerating system and the very short accelerating length of this all-optical accelerators. A fervent theoretical and experimental work has been done since then. An important part of the theoretical study is done by means of numerical simulations and the most widely used technique exploits PIC codes (“Particle In Cell'”). In this thesis the PIC code AlaDyn, developed by our research group considering innovative algorithms, is described. My work has been devoted to the developement of the code and the investigation of the laser driven ion acceleration for different target configurations. Two target configurations for the proton acceleration are presented together with the results of the 2D and 3D numerical investigation. One target configuration consists of a solid foil with a low density layer attached on the irradiated side. The nearly critical plasma of the foam layer allows a very high energy absorption by the target and an increase of the proton energy up to a factor 3, when compared to the ``pure'' TNSA configuration. The differences of the regime with respect to the standard TNSA are described The case of nearly critical density targets has been investigated with 3D simulations. In this case the laser travels throughout the plasma and exits on the rear side. During the propagation, the laser drills a channel and induce a magnetic vortex that expanding on the rear side of the targer is source of a very intense electric field. The protons of the plasma are strongly accelerated up to energies of 100 MeV using a 200PW laser.

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47

Sgattoni, Andrea <1982&gt. "Theoretical and numerical study of the laser-plasma ion acceleration." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3811/.

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The laser driven ion acceleration is a burgeoning field of resarch and is attracting a growing number of scientists since the first results reported in 2000 obtained irradiating thin solid foils by high power laser pulses. The growing interest is driven by the peculiar characteristics of the produced bunches, the compactness of the whole accelerating system and the very short accelerating length of this all-optical accelerators. A fervent theoretical and experimental work has been done since then. An important part of the theoretical study is done by means of numerical simulations and the most widely used technique exploits PIC codes (“Particle In Cell'”). In this thesis the PIC code AlaDyn, developed by our research group considering innovative algorithms, is described. My work has been devoted to the developement of the code and the investigation of the laser driven ion acceleration for different target configurations. Two target configurations for the proton acceleration are presented together with the results of the 2D and 3D numerical investigation. One target configuration consists of a solid foil with a low density layer attached on the irradiated side. The nearly critical plasma of the foam layer allows a very high energy absorption by the target and an increase of the proton energy up to a factor 3, when compared to the ``pure'' TNSA configuration. The differences of the regime with respect to the standard TNSA are described The case of nearly critical density targets has been investigated with 3D simulations. In this case the laser travels throughout the plasma and exits on the rear side. During the propagation, the laser drills a channel and induce a magnetic vortex that expanding on the rear side of the targer is source of a very intense electric field. The protons of the plasma are strongly accelerated up to energies of 100 MeV using a 200PW laser.

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Beaurepaire, Benoit. "Développement d’un accélérateur laser-plasma à haut taux de répétition pour des applications à la diffraction ultra-rapide d’électrons." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX013/document.

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La microscopie électronique et la diffraction d’électrons ont permis de comprendre l’organisation des atomes au sein de la matière. En utilisant une source courte temporellement, il devient possible de mesurer les déplacements atomiques ou les modifications de la distribution électronique dans des matériaux. A ce jour, les sources ultra-brèves pour les expériences de diffraction d’électrons ne permettent pas d’atteindre une résolution temporelle inférieure à la centaine de femtosecondes (fs). Les accélérateurs laser-plasma sont de bons candidats pour atteindre une résolution temporelle de l’ordre de la femtoseconde. De plus, ces accélérateurs peuvent fonctionner à haut taux de répétition, permettant d’accumuler un grand nombre de données.Dans cette thèse, un accélérateur laser-plasma fonctionnant au kHz a été développé et construit. Cette source accélère des électrons à une énergie de 100 keV environ à partir d’impulsions laser d’énergie 3 mJ et de durée 25 fs. La physique de l’accélération a été étudiée, démontrant entre autres l’effet du front d’onde laser sur la distribution transverse des électrons.Les premières expériences de diffraction avec ce type de sources ont été réalisées. Une expérience de preuve de principe a montré que la qualité de la source est suffisante pour obtenir de belles images de diffraction sur des feuilles d’or et de silicium. Dans un second temps, la dynamique structurelle d’un échantillon de Silicium a été étudiée avec une résolution temporelle de quelques picosecondes, démontrant le potentiel de ce type de sources.Pour augmenter la résolution temporelle à sub-10 fs, il est nécessaire d’accélérer les électrons à des énergies relativistes de quelques MeV. Une étude numérique a montré que l’on peut accélérer des paquets d’électrons ultra-courts grâce à des impulsions laser de 5 mJ et 5 fs. Il serait alors possible d’atteindre une résolution temporelle de l’ordre de la femtoseconde. Finalement, une expérience de post-compression des impulsions laser due à l’ionisation d’un gaz a été réalisée. La durée du laser a pu être réduite d’un facteur deux, et l’homogénéité de ce processus a été étudiée expérimentalement et numériquement
Electronic microscopy and electron diffraction allowed the understanding of the organization of atoms in matter. Using a temporally short source, one can measure atomic displacements or modifications of the electronic distribution in matter. To date, the best temporal resolution for time resolved diffraction experiments is of the order of a hundred femtoseconds (fs). Laser-plasma accelerators are good candidates to reach the femtosecond temporal resolution in electron diffraction experiments. Moreover, these accelerators can operate at a high repetition rate, allowing the accumulation of a large amount of data.In this thesis, a laser-plasma accelerator operating at the kHz repetition rate was developed and built. This source generate electron bunches at 100 keV from 3 mJ and 25 fs laser pulses. The physics of the acceleration has been studied, and the effect of the laser wavefront on the electron transverse distribution has been demonstrated.The first electron diffraction experiments with such a source have been realized. An experiment, which was a proof of concept, showed that the quality of the source permits to record nice diffraction patterns on gold and silicium foils. In a second experiment, the structural dynamics of a silicium sample has been studied with a temporal resolution of the order of a few picoseconds.The electron bunches must be accelerated to relativistic energies, at a few MeV, to reach a sub-10 fs temporal resolution. A numerical study showed that ultra-short electron bunches can be accelerated using 5 fs and 5 mJ laser pulses. A temporal resolution of the order of the femtosecond could be reached using such bunches for electron diffraction experiments. Finally, an experiment of the ionization-induced compression of the laser pulses has been realized. The pulse duration was shorten by a factor of 2, and the homogeneity of the process has been studied experimentally and numerically

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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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Morrison, John T. "Selective Deuteron Acceleration using Target Normal Sheath Acceleration." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365523293.

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Dissertations / Theses on the topic 'Laser plasma accelerator'

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