Orientador: Aruy Marotta / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-03T08:04:27Z (GMT). No. of bitstreams: 1 ParedezAngeles_PabloJenner_M.pdf: 1168016 bytes, checksum: ad72f704ac1f0ed45d1f57e1e5147fd8 (MD5) Previous issue date: 2003 / Resumo: Nesta tese foram obtidas equações generalizadas para a característica tensão-corrente de umatocha de plasma de arco não transferido e de uma tocha de plasma de arco transferido, utilizando o método da Teoria da Similaridade. Para a tocha de arco não transferido, os dados experimentais foram obtidos para ar como gás plasmagênico e na faixa de correntes de 10 a 295 A. Para a tocha de arco transferido, os dados foram obtidos para argônio e faixa de correntes de 300 a 1500 A. A tocha de arco não transferido apresentou característica estática tensão-corrente descendente, enquanto a de arco transferido, a característica obtida foi dinâmica, com comportamento fortemente anômalo, com a presença de histerese, além de possuir ambos os ramos, o descendente e o ascendente. Os testes da tocha de arco transferido foram feitos num forno com paredes refratárias em atmosfera de argônio. Foram obtidas equações generalizadas tendo um, dois e três parâmetros adimensionais independentes, sendo a escolha da melhor equação generalizada baseada no coeficiente de correlação da regressão multilinear. O parâmetro adimensional da voltagem foi considerado como o parâmetro dependente. Em geral, para os parâmetros adimensionais independentes foram utilizados aqueles relacionados com as diversas modalidades de transferência da energia Joule do arco para outras modalidades de energia. Estas foram a convectiva, a radiativa, a turbulenta e a condutiva. As equações generalizadas obtidas para a tocha de arco não transferido apresentaram boa concordância para toda a faixa de dados experimentais. Já as equações para a tocha de arco transferido, devido à grande anomalia observada, foram limitadas à apenas a parte ascendente dos dados experimentais. O estudo experimental, realizado nesta tese pode contribuir para uma melhor compreensão dos fenômenos que ocorrem em tochas de plasma, como também, fornecer uma guia para a engenharia de projeto das tochas / Abstract: In this thesis, generalized equations for the voltage-current characteristics have been obtained for a non transferred arc plasma torch and for a transferred arc plasma torch, using the method of the Theory of the Similarity. For the non transferred arc plasma torch, the experimental data was obtained for air as the plasmagenic gas and for currents of 10 to 295 A. For the transferred arc torch, the experiments were carried out for argon and currents of 300 to 1500 A. The non transferred plasma torch showed a descending voltage-current static characteristic, while the transferred plasma torch, the characteristic was dynamic, with strong anomalous behavior, consisting of the presence of hysteresis, besides possessing both the branches, the descendant and the ascendant. The tests of the transferred torch were carried out in an oven with refractory walls in argon atmosphere. Generalized equations had been obtained having one, two and three independent nondimensional parameters, being the choice of the best generalized equation based in the coefficient of correlation of the multilinear regression. The dimensionless parameter of the voltage was considered as the dependent parameter. In general, for the independent nondimensional parameters have been used those related with the diverse modalities of transference of the Joule energy of the arc to other modalities of energy. These had been the convective one, the radiative, the turbulent and the conductive one. The generalized equations obtained for the non transferred torch showed good agreement for all the range of experimental data. However, the equations for the transferred arc torch, due to their great observed anomaly, had been limited only to the ascending part of the experimental data. The experimental study, carried out in this thesis, might contribute to a better understanding of the phenomena taking place in plasma torches, as well, to provide a guide for their engineering / Mestrado / Física / Mestre em Física

Avec la disparition progressive des réserves de carbone fossile, un intérêt tout particulier est aujourd’hui porté sur la valorisation de la biomasse notamment la cellulose. Elle représente une source importante (1,3 Millions de tonnes) et peu onéreuse (< 10 €/kg) de carbone renouvelable. L’utilisation de la cellulose en tant que matière première pour la chimie fine apparait comme une solution attractive tant sur le plan économique qu’environnemental. Néanmoins, la présence de liaisons hydrogène intra et extra réseau lui confère une stabilité élevée (forte cristallinité) la rendant insoluble dans les solvants organiques usuels et dans l’eau. Ainsi, l’hydrolyse de ce polymère en glucose ou oligosaccharides, en présence d’un catalyseur solide est limitée par les interactions catalyseur/cellulose. C’est pourquoi, des prétraitements de la cellulose sont souvent utilisés permettant alors d’augmenter les interactions avec les catalyseurs solides. Toutefois, les méthodes développées dans la littérature sont coûteuses ou néfastes pour l’environnement. L’objectif de cette étude est le développement d’activations physiques de la cellulose, respectueuses de l’environnement, permettant l’hydrolyse de ce polymère en présence d’un catalyseur solide. L’activation de la cellulose est effectuée par ultrasons ou par plasma atmosphérique non thermique. Ces méthodes d’activation permettent d’augmenter considérablement le rendement en glucose en modifiant i) la taille des particules et/ou ii) le degré de polymérisation et/ou iii) la cristallinité de la cellulose. Enfin, à partir des sucres issus de la dépolymérisation de la cellulose, le 5- hydroxyméthylfurfural (molécule plateforme) peut être obtenu. Cette synthèse sera étudiée et plus particulièrement la nature du solvant, qui impacte la sélectivité de cette réaction. Lors de ces travaux, un intérêt tout particulier est porté sur l’utilisation de glycérol et de carbonate de glycérol en tant que solvant. / With the depletion of fossil carbon resources, biomass (including cellulose) is widely introduced in the chemical industry, as a renewable source of carbon. Cellulose is a huge reservoir (1,3 Million tons) of cheap (< 10 €/kg) and non-edible carbon. So use cellulose as raw material has many advantages, as much as economic plan than environmental one. However, due to important inter and intra hydrogen bonds network, cellulose is highly crystalline and thus insoluble in common solvents (including water) and recalcitrant to hydrolysis by heterogeneous catalysis, due to solid/solid interactions. A preliminary step consists in the activation of cellulose to enhance the solid/solid interactions. However, the pretreatments used in the literature are limited by the cost, corrosiveness, and toxicity. The aim of this study is to develop physical pretreatments of cellulose in order to be environmentally friendly and promote cellulose/catalyst interactions. In this manuscript, two physical methods of cellulose activation will be explored. The first involves a sonic treatment and the second implies non-thermal atmospheric plasma technology. These methods lead to an increase of the glucose yield due to the change of i) the particle size, or/and ii) the degree of polymerization or/and iii) the cristallinity. From carbohydrate obtained via the depolymerisation of cellulose, 5-hydroxymethylfurfural (platform molecule) is achieved. This synthesis, including dehydration of fructose, will be studied and especially, the nature of the solvent which is a key point ofthis conversion will be discussed. In this work glycerol or glycerol carbonate-based media were studied, as co-solvent from renewable carbon.

The Generalized Weighted Residual Method (GWRM) is a recently developed time- spectral method for parabolic or hyperbolic initial-value partial differential equations. In this paper, spatial subdomains, used in this method, are analyzed. Subdomains are used to enhance efficiency by dividing entire domains into smaller parts that can be independently solved for and then combined to get the final solution. An automatic grid mapping algorithm for spatial subdomains, called "Compressive Method", is presented and applied to Burgers' viscous equation. The error of the solution, as compared to the analytic solution, is compared for this compressive Method and the uniform grid case. Results show that accuracy can be gained at a small extra cost, using this compressive Method. Conclusions are that this adaptive algorithm shows great potential for further development.

Vigren et al. (2015) presents an integral expression to calculate the ion number density around a low activity comet immersed in the solar wind's convective electric field. A certain parameter of the integral takes values of either 1 or 0 depending on whether a corresponding ion trajectory is feasible or not. The criteria used in the paper has been found not to be strict enough, yielding overestimated ion number densities in the cometary wake. The present project finds two new options for the criteria, one analytical and one numerical. The new numerical condition is tested in the same computations done in the original paper and compares the results of the old and new criteria. The new conditionis found to correct the previous error. / <p>Projektet gjort inom: Fördjupningskurs i fysik - projektkurs, 5.0 hp. Kurskod:1FA566.</p>

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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Orientador: Aruy Marotta / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T12:44:53Z (GMT). No. of bitstreams: 1 Vicente_LuizCarlos_M.pdf: 2101644 bytes, checksum: 68c1a22beb4780709f600ff034f54bf3 (MD5) Previous issue date: 1985 / Resumo: Foi construído um maçarico de plasma para corte e uma fonte de potência, onde realizamos corte de chapas inox de até 16,0 mm de espessura, com velocidade de corte de 0,5 m/min e potência relativamente baixa (~ 8 KW), usando somente argônio como gás de trabalho. Foram feitos estudos qualitativos sobre a entrada do gás em vórtice, pressão dinâmica e também dos diversos problemas encontrados no maçarico de plasma construído, como por exemplo, arco duplo, instabilidade da coluna, etc. Foi estimada a temperatura central da coluna de plasma (T0 ~ 11,4x103 K), usando parâmetros de corte. Fizemos um estudo do comportamento da coluna de plasma, quando esta é confinada por um canal refrigerado, usando a equação de Elenbaas-Heller. A distribuição radial da temperatura na coluna de plasma foi determinada usando espectroscopia. Para isso, construímos um sistema óptico espectral de alta resolução espacial (da ordem de 37,5 mm) e um anodo rotatório. Sendo a coluna não homogênea, foi necessário utilizar a Transformada de Abel para inverter a intensidade lateral medida experimentalmente, para a intensidade radial das linhas espectrais observadas. A temperatura foi determinada pela razão de intensidades relativas das linhas 4300 Þ e 4259 Þ do átomo de argônio, supondo que o plasma se encontra em equilíbrio termodinâmico local. A temperatura central obtida foi de 6x103 K. Essa temperatura, que é quase a metade da estimada acima se deve a que a potência elétrica empregada aqui foi aproximadamente a metade da empregada no corte / Abstract: A plasma-torch for cutting metals and a power supply have been built and are working reliably. The plasma-torch is cutting 16 mm thickness stainless steel with a velocity of 0.5 m/min, using electrical power of 8 KW and argon as working gas. During this work we identified and solved problems like double arc, low dynamic pressure and instabilities which prevented the plasma-torch of working well. We performed calculations using a simple model described by the Elenbaas-Heller equations which showed some of the important qualitative features of the plasma-torch. In order to make spectroscopic measurements a rotatory anode was projected and build. Using this anode, the plasma torch and an optical set-up with a spatial resolution of 37.5 mm we measured the temperature profile of the argon plasma jet. For this purpose we assumed L.T.E. and optically thin plasma conditions and the temperature was found through the relative intensities of argon lines. The center temperature was 6,000 K / Mestrado / Física / Mestre em Física

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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We investigate the dynamic environment of the double asteroid system (65803) Didymoswith its satellite Didymos B for stable trajectories of more than 30 days for a model cubesatcalled APEX, foreseen to visit Didymos with the HERA mission, to be launched in 2023.We find semi-stable orbits with lifetimes up to 15 days under the influence of solar radiationpressure. In comparison, in the absence of solar radiation pressure, orbit trajectories reachlifetimes of up to 90 days. We present the distribution of orbital stability for positionsof initial deployment and the related orbital lifetime for inclinations of i = 0, 6 and 30 to the ecliptic plane of the sun, to investigate expected seasonality of the Didymossystem. The influence on trajectories through solar radiation pressure on the arrangementof the solar panels of APEX is compared to trajectories without solar radiation pressure. Itbecomes clear that the influence of solar radiation pressure is the main variable for stabilityof trajectories and must be further investigated with great care. We also discuss briefly theoperation of APEX in relation to orbital corrections and the limitations for such corrections.