No description available.

L'avènement d'une nouvelle génération de lasers ultra-relativistes (d'éclairement supérieur à 10^22 W/cm2), tels le laser APOLLON sur le plateau de Saclay, donnera lieu à un régime d'interaction laser-matière sans précédent, couplant physique des plasmas relativistes et effets électrodynamiques quantiques. Sources de particules et de rayonnements aux propriétés énergétiques et spatio-temporelles inédites, ces lasers serviront, entre autres applications, à la mise au point de nouveaux concepts d'accélérateurs et de diagnostics radiographiques, au chauffage de plasmas denses, comme à la reproduction de configurations astrophysiques en laboratoire. En prévision des futures expériences, les codes particle-in-cell (PIC), qui constituent les outils de référence pour la simulation de l'interaction laser-plasma, doivent être enrichis des processus radiatifs et quantiques propres à ce nouveau régime d'interaction. C'est le cas du code CALDER développé au CEA/DAM, qui modélise désormais l'émission de photons énergétiques et la conversion de ceux-ci en paires électron-positron ; autant d'effets susceptibles d'affecter le bilan d'énergie de l'interaction laser-cible et, plus précisément, le rendement du laser en particules et rayonnements énergétiques. L'objet de ce stage théorique est d'étudier, à l'aide du code CALDER, l'influence de ces processus dans un certain nombre de scénarios physiques en champ extrême (accélération électronique et ionique dans un plasma surcritique, production de rayonnement, génération de choc non-collisionnel…). / Forthcoming multi-petawatt laser systems, such as the French Apollon and European Extreme Light Infrastructure facilities, are expected to deliver on-target laser intensities exceeding 10^22 W/cm^2. A novel regime of laser-matter interaction will ensue, where ultra-relativistic plasma effects are coupled with copious generation of high-energy photons and electron-positron pairs. This will pave the way for many transdisciplinary applications in fundamental and applied research, including the development of unprecedentedly intense, compact particle and radiation sources, the experimental investigation of relativistic astrophysical scenarios and tests of quantum electrodynamics theory.In recent years, most theoretical studies performed in this research field have focused on the impact of synchrotron photon emission and Breit-Wheeler pair generation, both directly induced by the laser field and believed to be dominant at intensities >10^22 W/cm^2. At the lower intensities (≲10^21 Wcm^(-2)) currently attainable, by contrast, photon and pair production mainly originate from, respectively, Bremsstrahlung and Bethe-Heitler/Trident processes, all triggered by atomic Coulomb fields. The conditions for a transition between these two regimes have, as yet, hardly been investigated, particularly by means of integrated kinetic numerical simulations. The purpose of this PhD is precisely to study the aforementioned processes under various physical scenarios involving extreme laser-plasma interactions. This work is carried out using the particle-in-cell CALDER code developed at CEA/DAM which, over the past few years, had been enriched with modules describing the synchrotron and Breit-Wheeler processes.Our first study aimed at extending the simulation capabilities of CALDER to the whole range of photon and positron generation mechanisms arising during relativistic laser-plasma interactions. To this purpose, we have implemented modules for the Coulomb-field-mediated Bremsstrahlung, Bethe-Heitler and Trident processes. Refined Bremsstrahlung and Bethe-Heitler cross sections have been obtained which account for electronic shielding effects in arbitrarily ionized plasmas. Following validation tests of the Monte Carlo numerical method, we have examined the competition between Bremsstrahlung/Bethe-Heitler and Trident pair generations by relativistic electrons propagating through micrometer copper foils. Our self-consistent simulations qualitatively agree with a 0-D theoretical model, yet they show that the deceleration of the fast electrons due to target expansion significantly impacts pair production.We then address the competition between Bremsstrahlung and synchrotron emission from copper foils irradiated at 10^22 Wcm^(-2). We show that the maximum radiation yield (into >10 keV photons) is achieved through synchrotron emission in relativistically transparent targets of a few 10 nm thick. The efficiency of Bremsstrahlung increases with the target thickness, and takes over synchrotron for >2μm thicknesses. The spectral properties of the two radiation processes are analyzed in detail and correlated with the ultrafast target dynamics.Finally, we investigate the potential of nanowire-array targets to enhance the synchrotron yield of a 10^22 Wcm^(-2) femtosecond laser pulse. Several radiation mechanisms are identified depending on the target parameters and as a function of time. A simulation scan allows us to identify the optimal target geometry in terms of nanowire width and interspacing, yielding a ∼10% radiation efficiency. In this configuration, the laser-driven nanowire array rapidly expands to form a quasi-uniform, relativistically transparent plasma. Furthermore, we demonstrate that uniform sub-solid targets can achieve synchrotron yields as high as in nanowire arrays, but that the latter enable a strong emission level to be sustained over a broader range of average plasma density.

Inductive plasmas are simulated by using a one-dimensional particle-in-cell simulation including Monte Carlo collision techniques (pic/mcc). To model inductive heating, a non-uniform radio-frequency (rf) electric field, perpendicular to the electron motion is included into the classical particle-in-cell scheme. The inductive plasma pic simulation is used to confirm recent experimental results that electric double layers can form in current-free plasmas. These results differ from previous experimental or simulation systems where the double layers are driven by a current or by imposed potential differences. The formation of a super-sonic ion beam, resulting from the ions accelerated through the potential drop of the double layer and predicted by the pic simulation is confirmed with nonperturbative laser-induced fluorescence measurements of ion flow. It is shown that at low pressure, where the electron mean free path is of the order of, or greater than the system length, the electron energy distribution function (eedf) is close to Maxwellian, except for its tail which is depleted at energies higher than the plasma potential. Evidence supporting that this depletion is mostly due to the high-energy electrons escaping to the walls is given. ¶ A new hybrid simulation scheme (particle ions and Boltzmann/particle electrons), accounting for non-Maxwellian eedf and self-consistently simulating low-pressure high-density plasmas at low computational cost is proposed. Results obtained with the “improved” hybrid model are in much better agreement with the full pic simulation than the classical non self-consistent hybrid model. This model is used to simulate electronegative plasmas and to provide evidence supporting the fact that propagating double layers may spontaneously form in electronegative plasmas. It is shown that critical parameters of the simulation were very much aligned with critical parameters of the experiment.

Le caractère éminemment cinétique et hors équilibre de l'interaction laser-plasma et du transport électronique nécessite de résoudre le système complet des équations de Vlasov-Maxwell. Cette thèse se concentre sur les méthodes PIC (‘‘Particle-In-Cell''), et vise à en accroître le régime de fonctionnement. Tout d'abord, nous présentons l'analyse de stabilité linéaire d'un algorithme PIC explicite incluant l'effet de la discrétisation spatio-temporelle. Cette analyse met en exergue l'instabilité d'aliasing, que nous relions au problème, plus général, du chauffage numérique dans les codes PIC en régime surcritique. Nous montrons l'influence bénéfique de la montée en ordre du facteur de forme pour réduire ce chauffage, permettant ainsi d'atteindre des régimes de densité jusque là inaccessibles. Les codes PIC implicites ne sont pas soumis aux mêmes contraintes de stabilité que leurs équivalents explicites. En particulier nous ne sommes plus tenus de résoudre les modes haute fréquence électroniques. Une telle propriété est particulièrement précieuse lorsqu'on modélise l'interaction entre un laser à ultra-haute intensité et un plasma fortement sur-critique. Nous présentons ici l'extension relativiste de la méthode implicite dite directe, en y incluant un paramètre d'amortissement ajustable et des facteurs de forme d'ordre élevé. Ce formalisme a été implémenté dans le code ELIXIRS, 2D en espace et 3D en vitesse. Ce code est validé sur de nombreux problèmes de physique des plasmas, allant de l'expansion d'un plasma à une ou deux températures électroniques, à l'interaction laser-plasma à haut-flux, en passant par les instabilités ‘‘deux faisceaux'' et de filamentation en régime relativiste. Nous montrons notamment la capacité du code à capturer les principales caractéristiques de l'interaction laser-plasma, malgré une discrétisation spatio-temporelle dégradée, autorisant ainsi des gains substantiels en temps de calcul.

No description available.

In this thesis the nonlinear effects and heating are studied in inductively coupled plasma (ICP) in a regime of anomalous skin effect (nonlocal regime). In this regime the thermal motion of plasma electrons plays an important role, significantly influencing the processes associated with the penetration of electromagnetic field into plasma, such as the ponderomotive effect and heating of plasma by the field. We have developed a linear kinetic theory that describes the electron dynamics in ICP taking into account the electron thermal motion and collisions of electrons. This theory yields relatively simple expressions for the electron current in plasma, the ponderomotive force, and plasma heating. It describes correctly the thermal reduction of ponderomotive force in the nonlocal regime, which has been previously observed experimentally. It also describes the collisionless heating of plasma due to resonant interaction between the electromagnetic wave and plasma electrons. There is a good overall agreement of the results of our theory with the experimental data on ponderomotive force and plasma heating. Using our theory, we predicted a new effect of reduction of plasma heating compared to the purely collisional value, occurring at low frequencies. This effect has not been previously reported. The nonlinear effects of the electromagnetic field on the electron distribution function and on plasma heating, that are not accounted for in the linear kinetic theory, have been studied using a quasilinear kinetic theory, also developed in this thesis. Within the quasilinear approximation we have formulated the system of equations describing the slow response of plasma electrons to the fast oscillating electromagnetic field. As an example, these equations have been solved in the simplest case of cold plasma with collisions, and the nonlinear perturbation of the electron distribution function and its effect on the plasma heating have been found. It has been shown that the nonlinear modification of plasma heating occurs mainly due to the nonlinear effect of the magnetic component of the electromagnetic field. It has also been shown that at high frequencies the nonlinear effects vanish, and the heating is well described by the linear theory. To verify the predicted new effect of plasma heating reduction at low frequencies, as well as to investigate the nonlinear effect of the magnetic field on plasma heating for arbitrary amplitudes of electromagnetic field in plasma, we have developed a 1d3v Particle-In-Cell (PIC) numerical simulation code with collisions. The collisions were implemented into the PIC code using two different techniques: the direct Monte-Carlo technique for the electron-atom collisions, and the stochastic technique based on the Langevin equation for the electron-electron collisions. The series of numerical simulations by this code confirmed the results of our linear theory, particularly the effect of heating reduction at low frequencies that we predicted theoretically. Also, the nonlinear effects of electromagnetic field on plasma heating were studied using the PIC code in the cases of weak and strong electromagnetic fields. It has been shown that in the case of weak electromagnetic fields (corresponding to weak nonlinearity) the nonlinear effects lead to some enhancement of heating (compared to the linear theory) at low frequencies, followed by a small reduction of heating at higher frequencies. This observed nonlinear perturbation of heating in warm plasma with collisions is similar to that predicted by the quasilinear theory for the case of cold plasma with collisions. In the case of strong electromagnetic fields (corresponding to strong nonlinearity) the nonlinear effects lead to a further reduction of heating (compared to the linear theory) at low frequencies, as shown by the simulation, thus adding to the effect of reduction of heating predicted by the linear theory. The nonlinear effects are shown to vanish at high frequencies, as expected.

In this thesis the nonlinear effects and heating are studied in inductively coupled plasma (ICP) in a regime of anomalous skin effect (nonlocal regime). In this regime the thermal motion of plasma electrons plays an important role, significantly influencing the processes associated with the penetration of electromagnetic field into plasma, such as the ponderomotive effect and heating of plasma by the field. We have developed a linear kinetic theory that describes the electron dynamics in ICP taking into account the electron thermal motion and collisions of electrons. This theory yields relatively simple expressions for the electron current in plasma, the ponderomotive force, and plasma heating. It describes correctly the thermal reduction of ponderomotive force in the nonlocal regime, which has been previously observed experimentally. It also describes the collisionless heating of plasma due to resonant interaction between the electromagnetic wave and plasma electrons. There is a good overall agreement of the results of our theory with the experimental data on ponderomotive force and plasma heating. Using our theory, we predicted a new effect of reduction of plasma heating compared to the purely collisional value, occurring at low frequencies. This effect has not been previously reported. The nonlinear effects of the electromagnetic field on the electron distribution function and on plasma heating, that are not accounted for in the linear kinetic theory, have been studied using a quasilinear kinetic theory, also developed in this thesis. Within the quasilinear approximation we have formulated the system of equations describing the slow response of plasma electrons to the fast oscillating electromagnetic field. As an example, these equations have been solved in the simplest case of cold plasma with collisions, and the nonlinear perturbation of the electron distribution function and its effect on the plasma heating have been found. It has been shown that the nonlinear modification of plasma heating occurs mainly due to the nonlinear effect of the magnetic component of the electromagnetic field. It has also been shown that at high frequencies the nonlinear effects vanish, and the heating is well described by the linear theory. To verify the predicted new effect of plasma heating reduction at low frequencies, as well as to investigate the nonlinear effect of the magnetic field on plasma heating for arbitrary amplitudes of electromagnetic field in plasma, we have developed a 1d3v Particle-In-Cell (PIC) numerical simulation code with collisions. The collisions were implemented into the PIC code using two different techniques: the direct Monte-Carlo technique for the electron-atom collisions, and the stochastic technique based on the Langevin equation for the electron-electron collisions. The series of numerical simulations by this code confirmed the results of our linear theory, particularly the effect of heating reduction at low frequencies that we predicted theoretically. Also, the nonlinear effects of electromagnetic field on plasma heating were studied using the PIC code in the cases of weak and strong electromagnetic fields. It has been shown that in the case of weak electromagnetic fields (corresponding to weak nonlinearity) the nonlinear effects lead to some enhancement of heating (compared to the linear theory) at low frequencies, followed by a small reduction of heating at higher frequencies. This observed nonlinear perturbation of heating in warm plasma with collisions is similar to that predicted by the quasilinear theory for the case of cold plasma with collisions. In the case of strong electromagnetic fields (corresponding to strong nonlinearity) the nonlinear effects lead to a further reduction of heating (compared to the linear theory) at low frequencies, as shown by the simulation, thus adding to the effect of reduction of heating predicted by the linear theory. The nonlinear effects are shown to vanish at high frequencies, as expected.

No description available.

Made available in DSpace on 2014-06-11T19:32:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-06-30Bitstream added on 2014-06-13T19:02:30Z : No. of bitstreams: 1 mitmapillaca_ejd_dr_guara.pdf: 1950757 bytes, checksum: f8081b468d019f4dac4207cfc646916a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Implantação iônica por imersão em plasma com campo magnético (3IPCM) foi investigada usando técnicas numéricas e experimentais. O campo magnético considerado é essencialmente não uniforme e é produzido por duas bobinas magnéticas posicionadas ao redor da câmara de vácuo. O estudo é centrado na análise do efeito de dois dos parâmetros mais importantes: tensão e pressão no processo 3IPCM. Outro tema importante como a dinâmica dos elétrons secundários foi também abordado neste trabalho. Neste contexto, o processo 3IPCM foi pesquisado inicialmente usando o código computacional KARAT. Os resultados numéricos mostraram um incremento da densidade do plasma ao redor do alvo durante a variação dos parâmetros de tensão, pressão e campo magnético considerados. Como consequência deste aumento, um incremento da densidade de corrente iônica sobre o alvo foi observado. Os resultados numéricos mostraram que o sistema de campos cruzados E×B intensifica o processo 3IPCM. Posteriormente, 3IPCM foi realizado experimentalmente. Resultados experimentais mostraram que a densidade de corrente foi incrementada em aproximadamente 100 % em relação ao caso sem campo magnético quando os parâmetros externos foram variados. Todos estes resultados numéricos e experimentais são explicados através do mecanismo de ionização do gás por colisão com os elétrons magnetizados realizando movimento de deriva em campos E×B. Finalmente, para analisar os efeitos do processo 3IPCM no tratamento de materiais foram realizados implantações em amostras de silício. Os resultados mostraram que o processo 3IPCM promove mudanças nas propriedades superficiais das amostras, tornando-as hidrofóbicas. Esta técnica mostra ser atrativa posto que foi possível incrementar a dose e a profundidade de implantação em alta tensão. / Plasma immersion ion implantation (PIII) with magnetic field has been investigated using numerical and experimental methods. The magnetic field in consideration is essentially non-uniform and is generated by two magnetic coils installed outside the PIII vacuum chamber. The study is focused on analysis of the effect of two of the most important process parameters: voltage and gas pressure on the PIII with magnetic field. Another important subject such as the dynamics of secondary electrons has also been considered in this work. In this context, the PIII process with magnetic field has been initially analyzed numerically using the 2.5D computer code KARAT. The numeric results have shown an increase of the plasma density around of the target in the range of the considered parameters, voltage, pressure and magnetic field. As consequence of this an enhancement of the ion current density on the target was observed. The simulation results have demonstrated that the system of crossed E×B fields intensifies the PIII process with magnetic field. Later, the PIII process with magnetic field has been carried out experimentally. Experimental results have shown an increase of the current density in about 100 % in relation to the case without magnetic field when the external parameters have been varied. The numerical and experimental results are explained through the mechanism of gas ionization by collision with electrons drifting in crossed E×B field. Finally, to analyze the effect of the PIII process with magnetic field in material treatment implantation in Silicon samples has been carried out. The results indicate that the PIII process with magnetic field promotes changes of the samples surface properties, turning them hydrophobic. This PIII technique is attractive since it can increase the dose and the depth of implantation at high voltage.

Orientador: Konstantin Georgiev Kostov / Co orientador: Mario Ueda / Banca: Milton Eiji Kayama / Banca: Rogério Pinto Mota / Banca: Munemasa Machida / Banca: Joaquim José Barroso de Castro / Resumo: Implantação iônica por imersão em plasma com campo magnético (3IPCM) foi investigada usando técnicas numéricas e experimentais. O campo magnético considerado é essencialmente não uniforme e é produzido por duas bobinas magnéticas posicionadas ao redor da câmara de vácuo. O estudo é centrado na análise do efeito de dois dos parâmetros mais importantes: tensão e pressão no processo 3IPCM. Outro tema importante como a dinâmica dos elétrons secundários foi também abordado neste trabalho. Neste contexto, o processo 3IPCM foi pesquisado inicialmente usando o código computacional KARAT. Os resultados numéricos mostraram um incremento da densidade do plasma ao redor do alvo durante a variação dos parâmetros de tensão, pressão e campo magnético considerados. Como consequência deste aumento, um incremento da densidade de corrente iônica sobre o alvo foi observado. Os resultados numéricos mostraram que o sistema de campos cruzados E×B intensifica o processo 3IPCM. Posteriormente, 3IPCM foi realizado experimentalmente. Resultados experimentais mostraram que a densidade de corrente foi incrementada em aproximadamente 100 % em relação ao caso sem campo magnético quando os parâmetros externos foram variados. Todos estes resultados numéricos e experimentais são explicados através do mecanismo de ionização do gás por colisão com os elétrons magnetizados realizando movimento de deriva em campos E×B. Finalmente, para analisar os efeitos do processo 3IPCM no tratamento de materiais foram realizados implantações em amostras de silício. Os resultados mostraram que o processo 3IPCM promove mudanças nas propriedades superficiais das amostras, tornando-as hidrofóbicas. Esta técnica mostra ser atrativa posto que foi possível incrementar a dose e a profundidade de implantação em alta tensão. / Abstract: Plasma immersion ion implantation (PIII) with magnetic field has been investigated using numerical and experimental methods. The magnetic field in consideration is essentially non-uniform and is generated by two magnetic coils installed outside the PIII vacuum chamber. The study is focused on analysis of the effect of two of the most important process parameters: voltage and gas pressure on the PIII with magnetic field. Another important subject such as the dynamics of secondary electrons has also been considered in this work. In this context, the PIII process with magnetic field has been initially analyzed numerically using the 2.5D computer code KARAT. The numeric results have shown an increase of the plasma density around of the target in the range of the considered parameters, voltage, pressure and magnetic field. As consequence of this an enhancement of the ion current density on the target was observed. The simulation results have demonstrated that the system of crossed E×B fields intensifies the PIII process with magnetic field. Later, the PIII process with magnetic field has been carried out experimentally. Experimental results have shown an increase of the current density in about 100 % in relation to the case without magnetic field when the external parameters have been varied. The numerical and experimental results are explained through the mechanism of gas ionization by collision with electrons drifting in crossed E×B field. Finally, to analyze the effect of the PIII process with magnetic field in material treatment implantation in Silicon samples has been carried out. The results indicate that the PIII process with magnetic field promotes changes of the samples surface properties, turning them hydrophobic. This PIII technique is attractive since it can increase the dose and the depth of implantation at high voltage. / Doutor