Orientador: Aruy Marotta / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-03T02:08:00Z (GMT). No. of bitstreams: 1 Bublievsky_DmitryAlexandrovich_M.pdf: 1177094 bytes, checksum: c681f9fa549216acb2481c1084c3e875 (MD5) Previous issue date: 2003 / Resumo: Nesta tese foi introduzido um novo tipo de técnica de diagnóstico da mancha de arcos elétricos, chamado térmico-espectroscópico. A técnica foi aplicada ao estudo da velocidade de rotação da mancha do arco e da densidade de corrente na mancha. Ambas estão relacionadas com os fenômenos que ocorrem na erosão de eletrodos frios. As medidas foram realizadas em um catodo de cobre não refrigerado, operando em ar, usando uma instalação coaxial magnética. As experiências mostraram que há dois regimes de erosão: micro e macroerosão. Observamos que para o regime de microerosão, a velocidade é sempre maior, e a dispersão da velocidade sempre menor que na macroerosão. Ambos os fatos confirmam a existência de uma força de arraste de superfície ao movimento do arco. Podemos explicar que a fonte dessa força é proveniente dos jatos catódicos no regime de macroerosão, fazendo com que a mancha tenha um movimento descontínuo. As dificuldades das técnicas tradicionais de medida da densidade de corrente na mancha foram superadas, introduzindo-se o conceito de densidade de corrente efetiva na mancha, pela qual mede-se o início da fusão na mancha e não o diâmetro da mancha. O método, baseado no registro espectroscópico temporal da intensidade da linha de emissão do vapor de cobre, juntamente com o registro da evolução da temperatura da superfície do eletrodo, permitiu um grande aumento na sensibilidade de detecção do ponto de transição do regime de micro para macroerosão. A densidade de corrente da mancha, medida como uma função do campo magnético, apresenta um grande crescimento para baixos valores do campo magnético. O estudo experimental realizado nesta tese permite uma melhor compreensão dos fenômenos que ocorrem em manchas de arcos elétricos de eletrodos frios, contribuindo, assim, para uma maior utilização das tochas de plasma / Abstract: In this thesis, we introduced a new type of arc spot diagnostic technique, called thermo-spectroscopic. Attention was concentrated on the study of arc spot rotation velocity and arc spot current density as a function of magnetic field. Both are related to cold electrode erosion phenomena. Measurements were carried out in an uncooled copper cathode in air, using a magnetically driven arc coaxial setup. Experiments have shown that there are two erosion regimes: a micro and a macroerosion one. We observed that for the microerosion regime, velocity was always higher and velocity dispersion lower than for the macroerosion one. Both facts confirm the existence of a surface drag force to the movement of the arc. We could explain that the source of this force is provided by cathode jets in the macroerosion regime, making the spot to move with frequent stops. We overcame the difficulties in traditional techniques in measuring spot current density by introducing the concept of effective arc spot current density, by which we measure the spot fusion onset and not the arc spot diameter. The method, based on the temporal spectroscopic registration of copper vapor atomic line emission intensity, together with the registration of the electrode surface temperature evolution, provided a significative increase in the sensibility of detection of the transition point from micro to macroerosion. The arc spot current density, measured as a function of magnetic field shows a strong increase for low magnetic field values. Experimental study, carried out in this thesis, allows a better understanding of the phenomenon taking place in cold electrode arc spot, thus contributing for a wider utilization of plasma torches / Mestrado / Física / Mestre em Física

Orientador: Paulo Hiroshi Sakanaka / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-16T22:53:19Z (GMT). No. of bitstreams: 1 Shigueoka_Yoshyuki_M.pdf: 1772625 bytes, checksum: 12a5ca824a2d8d727ded428b94802f37 (MD5) Previous issue date: 1979 / Resumo: Foi desenvolvido um modelo de 1 + zero dimensões, borda abrupta na direção r e uma dimensão na direção z, para estudar a dinâmica do q - pinch, com o campo de polarização. Verificou-se que o efeito do raio do plasma sobre a descarga é apreciável, podendo até inverter o sinal do dBz/dt. A influência do fato do solenôide ser de tamanho finito se manifesta como oscilação de grandezas como Bz, R, Ti, etc. ao longo do eixo z. Estas oscilações são as oscilações transpostas de bounce e não constituem nenhuma instabilidade nova / Abstract: It has been developed a (1 + zero) D model, sharp boundary in r and 1D in z, to study dynarnics e - pinches with bias field, in order to calculate bounce oscilations, plasma temperature, effects of plasma radius on the discharge and the influence of finiteness of the q- pinch coil length on the bounce oscilations. It was observed that the effect of plasma radius variation on discharge is appreciable. It can even invert the sign of dBz/dt. The influence of the finite length coil manifested through oscillations of quantities; such as, Bz, R, Ti and Bi along z axis. These oscillations are z simply bounce oscillations transformed into oscillations in z direction, and do not mean a new instability / Mestrado / Física / Mestre em Física

Orientador: Jose Busnardo Neto / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-18T02:46:37Z (GMT). No. of bitstreams: 1 LeiteNeto_JoaquimPaulino_M.pdf: 1599775 bytes, checksum: dc58c3e367168c68f4138d243c3f5510 (MD5) Previous issue date: 1985 / Resumo: Um modelo numérico de dois fluídos, que integra as equações de conservação da massa, do momento e da energia juntamente com as equações de Maxwell, é usado para simular a fase de implosão de três q-pinches: q-pinch Tupã, q-pinch II e q-pinch da Universidade do Texas. Os processos de transporte anômalos (microinstabilidades) são incluídos de maneira auto-consistente, segundo o modelo de Liewer e Krall. Obtém-se perfis de quantidades típicas do plasma tais como densidade, campo magnético, densidade de corrente, temperaturas eletrônica e iônica para vários instantes da implosão. Para o q-pinch de alta densidade (Tupã, com n » 1016cm-3) e para o q-pinch da densidade intermediária (q-pinch II, com n » 1014cm-3), é encontrado que ambos os processos de transporte, o clássico e o anômalo, podem desempenhar um papel importante durante a implosão. O transporte anômalo é dominante na região da camada de corrente e atrás do pistão (onde a corrente e a temperatura são relativamente altas) e o transporte clássico tende a dominar na frente do pistão (onde a densidade é alta e a temperatura relativamente baixa). É demonstrado também que a resistividade anômala aumenta com a massa do íon e que existe um inter-relacionamento entre a resistividade clássica e a resistividade anômala. Para o q-pinch de baixa densidade (Texas, com n » 1012cm-3), o transporte anômalo domina completamente, tanto atrás como na frente do pistão. Neste caso o transporte clássico é desprezível. Os resultados numéricos permitem uma identificação precisa dos fenômenos físicos dominantes nos vários instantes da implosão / Abstract: A two-fluid numerical model, which integrates the mass, momentum and energy conservation equations together with the Maxwell equations, is used to simulate the implosion stage of three q-pinches: q-pinch Tupã (high density), q-pinch II (intermediate density) and the q-pinch of the University of Texas. Anomalous transport processes (microinstabilities) are included self-consistently, following the model of Liewer and Krall. Classical transport processes are introduced according to the model of Braginskii. The profiles of typical plasma quantities such as density, magnetic field, current density, electron temperature and ion temperature are obtained at various stages of the implosion. For a high density q-pinch (n » 1016cm-3) and for na intermediate density q-pinch (n » 1014cm-3) it is found that both transport processes, the classical one and the anomalous one, can play an important role during the implosion. Anomalous transport is dominant in the sheath region and behind the piston (where the current and the temperature are relatively high) and classical transport tends to dominate ahead of the piston (where the density is high and the temperature is relatively low). It is demonstrated also that the anomalous resistivity increases with ion mass and that classical and anomalous resistivities are coupled. For the low density q-pinch (n » 1012cm-3), anomalous transport is completely dominant, both behind and in front of the piston, and classical transport is negligible. These numerical results permit a precise identification of the dominant physical phenomena at the various stages of the implosion / Mestrado / Física / Mestre em Física

Laser-Induced Breakdown Spectroscopy (LIBS) is a method of analytical chemistry that provides a qualitative and quantitative analysis of a sample. The ablation process of a sample is fast and dynamic and the change of plasma in time and space is a question of a few microseconds. An examination that provides a good time and space resolution is necessary to understand better the physical processes. For this reason, the goal of this thesis is to design a basic optomechanic construction for this type of experiment. Furthermore, it is important to check the functionality of this design and to use it for a basic comparison between the spectroscopic and imaging data. Also, the time development of plasma will be observed under different experimental conditions. The goal of this thesis, in general, is to prove that the morphology of plasma is as it is described in available related literature.

Le travail effectué dans le cadre de cette thèse porte sur l’étude des plasmas magnétisés et nonmagnétisés produits par des structures coaxiales qui font office à la fois de propagateur d’onde et de coupleur à impédance adaptée au plasma, mais aussi de sonde d’investigation et de caractérisation de la décharge. Une attention particulière est accordée à l’efficacité de couplage entre l’onde électromagnétique et la décharge et de production d’espèces, et ce pour différentes conditions opératoires : fréquence d’excitation (352 et 2450 MHz),configuration magnétique, géométrie de l’applicateur. L’analyse quantitative et comparative présentée dans ce travail s’appuie aussi bien sur une approche expérimentale que théorique. Les modèles analytiques développés etla simulation électromagnétique réalisée permettent d’extraire à partir des mesures expérimentales, d’une partl ’impédance du plasma décorrélée de celle de la structure de propagation de l’onde, et d’autre part, l’absorption globale et locale de l’onde. Du point de vue expérimental, des techniques et méthodes appropriées ont donc été développées et mises en oeuvre comme, par exemple la méthode de changement de plan d’impédance, ou encore l’auto-interférométrie. L’étude paramétrique, menée sur un domaine de pression étendu sur plusieurs décades(10-4 – 10 Torr) et pour une gamme de puissances allant de un à plusieurs centaines de watts, a permis une investigation minutieuse du type de couplage (capacitif, inductif, résistif) qui est fortement dépendant des caractéristiques de la décharge et donc des paramètres opératoires. Leur mise en corrélation, associée à l’analyse des modes de propagation dans un plasma magnétisé, a permis de localiser avec plus de précision les zones de couplage et d’identifier les principaux mécanismes d’absorption de l’onde mis en jeu. Les principaux résultats obtenus confirment une meilleure efficacité de production d’espèces chargées à une fréquence plus élevée (2450MHz), et la présence d’une population d’électrons chauds plus conséquente ainsi qu’une extension spatiale du plasma lorsque la fréquence est plus faible (352 MHz). Comme la technologie 352 MHz à état solide est plus avantageuse du point de vue du coût des composants, comparée à 2450 MHz, elle pourrait s’avérer intéressante pour des procédés visant la production d’espèces chimiquement actives. Toutefois, le couplage, peu efficace, de type capacitif induit par la diminution de la fréquence, requiert une attention accrue au niveau de la configuration du coupleur. Pour le développement en amont des coupleurs, les résultats issus de ce travail de thèse et les modèles analytiques développés devraient constituer un outil déterminant dans la conception de sources plasma micro-onde performantes. / The work done within the framework of this thesis focuses on the study of magnetized and nonmagnetizedplasmas produced by coaxial structures that serve both as wave propagator and as plasma matchedimpedance coupler but also as investigation and characterization probe of the discharge. Special attention isgiven to the efficiency of coupling between the electromagnetic wave and the discharge and of speciesproduction, for different operating conditions: excitation frequency (352 and 2450 MHz), magnetic configurationand geometry of the applicator. Quantitative and comparative analysis presented in this work is based both on anexperimental and a theoretical approach. Developed analytical models and conducted electromagnetic simulationare set in connection with the experimental measurements in order to determine, on the one hand, the plasmaimpedance de-embedded of the wave propagation structure and, on the other hand, the global and localabsorption of the wave. From the experimental point of view, appropriate techniques and methods have thereforebeen developed and implemented such as, for example, the impedance plane shift method, or autointerferometry.The parametric study, conducted on a pressure range extended over several decades (10-4 - 10Torr) and power ratings from one to several hundred watts, led to a thorough investigation of the coupling type(capacitive, inductive, resistive ) which is highly dependent on the discharge characteristics and thus of theoperating parameters. Their correlation, combined with the analysis of propagation modes in a magnetizedplasma, has helped locate more accurately the areas of coupling and to identify the main power absorptionmechanisms involved. The main results obtained for the two frequencies confirm a better production efficiencyof charged species at a higher frequency (2450 MHz), the presence of a more substantial hot electron populationand a spatial expansion of the plasma when the frequency is low (352 MHz). As the solid state 352 MHztechnology is more advantageous compared to that at 2450 MHz from the viewpoint of the cost of thecomponents, it could be interesting for processes aiming to produce active chemical species. However itsinefficient coupling, of capacitive type induced by frequency reduction, requires an increased attention at thelevel of coupler configuration. For upstream development of couplers, the analytical models and theexperimental results obtained in this thesis should be a key tool in the design of high-performance microwaveplasma sources.

« La médecine- plasma» est le domaine de recherche décrivant les applications médicales des plasmas, principalement à pression atmosphérique. Les plasmas froids sont un état de la matière caractérisé par la présence d'électrons libres ayant une énergie cinétique de plusieurs eV alors même que les ions et les neutres peuvent être à température ambiante. Cet état transitoire, hors équilibre thermique, produit des espèces chimiques très réactives. L’objectif de ce travail multidisciplinaire a été d’évaluer le potentiel anti-tumoral des plasmas-froids. Deux types de dispositifs ont été conçus et fabriqués par impression 3D: des Décharges à Barrière Diélectrique et des jets plasmas. Des études in-vitro et in-vivo ont été menées avec les lignées cellulaires TC1 et CT26. La production d’espèces réactives produites dans un liquide exposé à un plasma a été étudiée afin de comprendre les résultats in-vitro et de comparer les dispositifs plasma entre eux. Différents dispositifs à plasmas ont été réalisés afin d’étudier in-vivo, l’effet de l’énergie déposée lors du traitement sur la peau et les tumeurs. Afin de limiter l’échauffement cutané et les lésions induites un dispositif refroidi à l’azote liquide a été développé. Enfin, une simulation numérique modélisant les transferts thermiques des tumeurs et tissus sous exposition plasmas a permis de quantifier l’hyperthermie et les lésions associées en validant le modèle sur des résulats expérimentaux. Une revue critique d’études in-vivo de « médecine plasma » publiées dans la littérature est proposée afin d’évaluer le rôle de l’hyperthermie dans les effets thérapeutiques observés. / Plasma-medicine is the field of research describing the medical applications of plasmas, mainly at atmospheric pressure. Cold plasmas are a state of matter characterized by the presence of free electrons with a kinetic energy of several electron volts even though the ions and neutrals may be at room temperature. This transient state, apart from thermal equilibrium, produces highly reactive chemical species. The objective of this multidisciplinary work was to evaluate the anti-tumor potential of cold plasmas. Two types of devices have been designed and manufactured by 3D-printing: Dielectric Barrier Discharge and plasma-jets. In-vitro and in-vivo studies were conducted with TC1 and CT26 cell lines. The production of reactive species produced in a liquid exposed to plasma has been studied in order to understand the in-vitro results and to compare the plasma devices with those of other teams. Various plasma devices have been made to study the effect of the energy deposited during the in-vivo treatment of skin and subcutaneous tumors. A device cooled with liquid nitrogen has been developed to limit skin damage induced by heating. Finally, a numerical simulation modeling the heat transfers of tumors and tissues under plasmas exposure enables to quantify the hyperthermia and the associated lesions by validating the model on experimental results. A critical review of in-vivo plasma-medicine studies published in the literature is proposed to evaluate the role of hyperthermia in the therapeutic effects reported.

Orientador: Aruy Marotta / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-10T20:43:05Z (GMT). No. of bitstreams: 1 Bubliyeuski_DzmitryAlexandrovich_D.pdf: 2691341 bytes, checksum: 7b8e0d82f84d333a723eb14e64832cf3 (MD5) Previous issue date: 2008 / Resumo: Uma nova técnica de diagnóstico, denominada termo-espectroscópica, foi introduzida neste trabalho para estudo da interação do arco elétrico com o catodo frio de cobre numa instalação coaxial magnética, com catodo não-refrigerado, operando em gases plasmagênicos ar e nitrogênio. A técnica foi aplicada ao estudo da velocidade de rotação da mancha do arco e da densidade efetiva de corrente na mancha. Estes parâmetros têm estreita relação com o fenômeno da erosão de eletrodos frios. A nova técnica combina a técnica óptico-espectroscópica e a técnica térmica, e se baseia na teoria térmica da erosão. Por espectroscopia, registra-se a evolução temporal da intensidade da linha de emissão do vapor de cobre. Pelo método térmico, registra-se a evolução da temperatura da superfície do eletrodo. A técnica permite um grande aumento na sensibilidade de detecção do ponto de transição do regime de micro para macroerosão, através da observação do abrupto aumento da intensidade da linha espectral do cobre. Observamos que para o regime de microerosão, a velocidade é sempre maior, e a dispersão da velocidade sempre menor que na macroerosão. Esse fato confirma a existência de uma força de arraste superficial ao movimento do arco, que pode ser proporcionada pela fusão do eletrodo, por jatos catódicos e/ou por óxidos na superfície do eletrodo. A densidade de corrente na mancha apresenta um grande crescimento para valores baixos do campo magnético e certa saturação para altos valores. Para o ar foi observada uma forte influência dos óxidos na mobilidade da mancha, que é significativamente maior do que com nitrogênio. A diferença entre medidas obtidas no ar e nitrogênio é atribuída ao processo de decomposição de óxidos na superfície, que afeta a determinação correta do ponto de transição. O estudo experimental realizado nesta tese permite uma melhor compreensão dos fenômenos que ocorrem em manchas de arcos elétricos de eletrodos frios / Abstract: In the present work a new diagnostic technique, named thermo-spectroscopic one, was introduced for study of the interaction of the electric arc with a cold copper electrode using the coaxial magnetic installation with non-refrigerated cathode operated in air and nitrogen. The technique was applied to the measurement of the arc spot rotation velocity and the effective spot current density. These parameters have a direct relation with the phenomenon of the cold electrode erosion. The new technique combines the optic-spectroscopic method and the thermal method, and is based on the erosion thermophysical theory. Using spectroscopy, the temporal evolution of the intensity of the copper vapor emission line was registered. Via the thermal method, the evolution of the electrode surface temperature was recorded. By the observation of the abrupt increase of the copper spectral line intensity, the new technique permits a significative increase in the sensibility of the detection of the transition from the microerosion process to the macroerosion one. It was observed that the arc velocity for the microerosion regime is always higher and the velocity dispersion is always lesser then the ones for the macroerosion regime. This fact confirms the existence of the surface drag force to the arc movement, which can be provided by the electrode fusion process, by cathode jets and/or by oxides formed on the electrode surface. The arc spot current density presents a high growth for the low values of the magnetic field and certain saturation for the high values ones. For the air, a strong influence of oxides on the spot mobility was observed, that is more significant then the one for the nitrogen. The difference between the measurements for the air and the nitrogen is attributed to the oxide decomposition process on the electrode surface that affects the correct transition point determination. The experimental study, carried out in this thesis, allows a better understanding of the phenomenon taking place in cold electrode arc spots / Doutorado / Física de Plasmas e Descargas Elétricas / Doutor em Ciências

The work presented in this thesis involves experimental and theoretical studies related to plasma properties in high power impulse magnetron sputtering (HiPIMS), and more specifically plasma transport. HiPIMS is an ionized PVD method based on conventional direct current magnetron sputtering (dcMS). In dcMS very little of the sputtered material is ionized since the plasma power density is not high enough. This is not the case for HiPIMS, where a substantial part is ionized, and thus presents many new opportunities for thin film growth. Understanding the dynamics of the charged species in the HiPIMS discharge is therefore of essential value when producing high-quality thin film coatings. In the first part of the work a new type of anomalous electron transport was found. Investigations of the transport resulted in the discovery that this phenomenon could quantitatively be described as being related and mediated by highly nonlinear waves, likely due to the modified two-stream instability (MTSI), resulting in electric field oscillations in the MHz-range (the so-called lower hybrid frequency). Measurements in the plasma confirmed these oscillations as well as trends predicted by the theory of these types of waves. The degree of anomalous transport in the plasma could also be determined by measuring the current density ratio between the azimuthal current density (of which the Hall current density is one contribution) and the discharge current density, Jφ / JD. The results provided important insights into understanding the mechanism behind the anomalous transport. It was furthermore found that the current ratio Jφ / JD is inversely proportional to the transverse resistivity, eta_perpendicular , which governs how well momentum is transferred from the electrons to the ions in the plasma. By looking at the forces involved in the charged particle transport it was expected that the azimuthally rotating electrons would exert a volume force on the ions tangentially outwards from the circular race track region. The effect of having an anomalous transport would therefore be a large fraction of highly energetic ions being transported sideways and lost to the walls. In a series of experiments, deposition rates as well as incoming ion energy distributions were measured directly at the side of the magnetron. It was found that a substantial fraction of sputtered material is transported radially away from the cathode and lost to the walls in HiPIMS as well as dcMS, but more so for HiPIMS giving one possible explanation to why the deposition rate for substrates placed in front of the target is lower for HiPIMS compared to dcMS. Furthermore, the recorded, incoming ion energy distributions confirmed theoretical estimations on this type of transport regarding energy and direction.

A numerical study is done of a plasma in contact with a cold solid surface that is emitting a neutral gas. Two numerical models have been developed to describe the dominant phenomena of surface plasma structures. The first model entails a steady-state, kinetic treatment of the transport equations in one space dimension and one velocity dimension, to determine self-consistently the distribution functions of the interacting species and the electrostatic potential near the solid surface. The dominant phenomena in this region are the ionization of the neutral gas and the acceleration of the resulting ions by the electrostatic field in a pre-sheath region. Other effects involved are a Debye sheath structure between the solid surface and pre-sheath, and collisional trapping and untrapping of electrons in an electrostatic potential well that is predicted in the pre-sheath region. Results are presented from a nondimensional model with a monatomic returning neutral species and for diatomic molecular hydrogen returning from the surface. For each set of physical parameters chosen, a one parameter family of solutions is obtained. The second numerical model involves a steady-state treatment of the transport equations in a (x,v∥,v⊥) phase space for the interacting species. Included in this model are ionization of the refluxing monatomic neutrals, a self-consistently determined electrostatic potential and a nonlinear Fokker-Planck treatment of ion-ion Coulomb collisions. Both the region near the surface dominated by kinetic effects and the region away from the surface in which Coulomb collisional effects are significant are treated. Results are presented which identify the correct physical solution for the region near the surface from the permitted family found with the kinetic model. Additionally, results are shown which span a temperature range from the high temperature kinetic regime where Coulomb collisional effects are negligible, to the low temperature, highly collisional fluid regime. At low temperatures the collisional model agrees well with standard fluid techniques.

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.