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Um detetor HPGe foi calibrado na faixa de energia 4 a 10 MeV usando fótons provenientes do decaimento do produto da reação 27Al(p, g)28Si em linha, observando as ressonâncias com prótons de energias 992 e 1317 keV. Foram feitas calibrações de energia e eficiência de deteção de fótons e foi analisada a dependência da largura a meia altura dos picos com a meia vida do estado inicial e a energia da transição. Os efeitos do produto da reação estar em movimento, como o efeito Doppler no decaimento em vôo, perda de velocidade do núcleo ao recuar dentro do alvo e energia de recuo são importantes na calibração de energia e análise da largura do pico. A calibração da eficiência depende de outras calibrações: razão entre a área dos picos de absorção total de energia, escapes simples e duplo dos gamas de aniquilação; razão entre a área total do espectro pela área do pico. Os resultados experimentais foram comparados com simulações do espectro usando o código MCNP, sendo que as dimensões internas do detetor, inacessíveis para medição, foram escolhidas de modo a reproduzir parâmetros deduzidos de espectros gama experimentais. A simulação se mostrou capaz de descrever tanto a eficiência para absorção total de energia quanto a razão entre as áreas dos picos de absorção total de energia, escape simples e duplo do gama de aniquilação, mas não foi capaz de descrever a razão entre a área total do espectro e a do pico. / An HPGe detector was calibrated in the 4 to 10 MeV energy range using photons from the decay of the 992 and 1317 keV proton resonances in the reaction 27Al(p, g)28Si on-line. Energy and photon detection efficiencies were calibrated and the dependence of the peak full width at half maximum on the transition energy and initial level half-life was analyzed. The effects of the reaction product motion, like Doppler shift due to in-flight decay, slowing down in the target, and nuclear recoil energy from photon emission, are important for energy calibration and peak width analyses. The efficiency calibration required other calibrations: the full energy peak to single and double escape counting ratios, and total spectrum to peak areas ratio. The experimental results were compared to simulations with MCNP code, where internal detector dimensions, inaccessible to measurement, were chosen in order to fit the experimental gamma spectrum parameters. The simulation was able to explain the full energy peak to single escape and double escape counting ratios, and full-energy peak detection efficiency, but was unable to fit the total spectrum to peak areas ratio.

Um detetor HPGe foi calibrado na faixa de energia 4 a 10 MeV usando fótons provenientes do decaimento do produto da reação 27Al(p, g)28Si em linha, observando as ressonâncias com prótons de energias 992 e 1317 keV. Foram feitas calibrações de energia e eficiência de deteção de fótons e foi analisada a dependência da largura a meia altura dos picos com a meia vida do estado inicial e a energia da transição. Os efeitos do produto da reação estar em movimento, como o efeito Doppler no decaimento em vôo, perda de velocidade do núcleo ao recuar dentro do alvo e energia de recuo são importantes na calibração de energia e análise da largura do pico. A calibração da eficiência depende de outras calibrações: razão entre a área dos picos de absorção total de energia, escapes simples e duplo dos gamas de aniquilação; razão entre a área total do espectro pela área do pico. Os resultados experimentais foram comparados com simulações do espectro usando o código MCNP, sendo que as dimensões internas do detetor, inacessíveis para medição, foram escolhidas de modo a reproduzir parâmetros deduzidos de espectros gama experimentais. A simulação se mostrou capaz de descrever tanto a eficiência para absorção total de energia quanto a razão entre as áreas dos picos de absorção total de energia, escape simples e duplo do gama de aniquilação, mas não foi capaz de descrever a razão entre a área total do espectro e a do pico. / An HPGe detector was calibrated in the 4 to 10 MeV energy range using photons from the decay of the 992 and 1317 keV proton resonances in the reaction 27Al(p, g)28Si on-line. Energy and photon detection efficiencies were calibrated and the dependence of the peak full width at half maximum on the transition energy and initial level half-life was analyzed. The effects of the reaction product motion, like Doppler shift due to in-flight decay, slowing down in the target, and nuclear recoil energy from photon emission, are important for energy calibration and peak width analyses. The efficiency calibration required other calibrations: the full energy peak to single and double escape counting ratios, and total spectrum to peak areas ratio. The experimental results were compared to simulations with MCNP code, where internal detector dimensions, inaccessible to measurement, were chosen in order to fit the experimental gamma spectrum parameters. The simulation was able to explain the full energy peak to single escape and double escape counting ratios, and full-energy peak detection efficiency, but was unable to fit the total spectrum to peak areas ratio.

It is relatively straightforward to establish equilibrium inmagnetically confined plasmas, but the plasma is frequentlysucceptible to a variety of instabilities that are driven bythe free energy in the magnetic field or in the pressuregradient. These unstable modes exhibit effects that affect theparticle, momentum and heat confinement properties of theconfiguration. Studies of the dynamics of several of the mostimportant modes are the subject of this thesis. The studies arecarried out on plasmas in the reversed field pinch (RFP)configuration. One phenomenon commonly observed in RFPs is mode walllocking. The localized nature of these phase- and wall lockedstructures results in localized power loads on the wall whichare detrimental for confinement. A detailed study of the walllocked mode phenomenon is performed based on magneticmeasurements from three RFP devices. The two possiblemechanisms for wall locking are investigated. Locking as aresult of tearing modes interacting with a static field errorand locking due to the presence of a non-ideal boundary. Thecharacteristics of the wall locked mode are qualitativelysimilar in a device with a conducting shell system (TPE-RX)compared to a device with a resistive shell (Extrap T2). Atheoretical model is used for evaluating the threshold valuesfor wall locking due to eddy currents in the vacuum vessel inthese devices. A good correlation with experiment is observedfor the conducting shell device. The possibility of succesfully sustaining discharges in aresistive shell RFP is introduced in the recently rebuiltdevice Extrap T2R. Fast spontaneous mode rotation is observed,resulting in low magnetic fluctuations, low loop voltage andimproved confinement. Wall locking is rarely observed. The lowtearingmode amplitudes allow for the theoretically predictedinternal nonresonant on-axis resistive wall modes to beobserved. These modes have not previously been distinguisheddue to the formation of wall locked modes. The internal andexternal nonresonant resistive wall modes grow on the timescale of the shell penetration time. These growth rates dependon the RFP equilibrium. The internal nonresonant resistive wallmodes dominate in Extrap T2R, especially for shallow reverseddischarges. The external nonresonant modes grow solely in deepreversal discharges. <b>Keywords</b>Nuclear fusion, reversed field pinch, resistiveinstabilities, wall locked modes, tearing modes, resistiveshell modes, field errors, EXTRAP-T2, EXTRAP-T2R, TPE-RX

One of the most demanding engineering issues in Inertial Fusion Energy (IFE) reactors is the design of a reaction chamber that can withstand the intense photons, neutrons and charged particles due to the fusion event. Rapid pulsed deposition of energy within thin surface layers of the fusion reactor components such as the first wall may cause severe surface erosion due to ablation. One particularly innovative concept for the protection of IFE reactor cavity first walls from the direct energy deposition associated with soft X-rays and target debris is the thin liquid film protection scheme. In this concept, a thin film of molten liquid lead is fed through a silicon carbide first wall to protect it from the incident irradiations. Numerous studies have been reported in the literature on the thermal response of the liquid film to the intermittent photon and ion irradiations, as well as on the fluid dynamics and stability of liquid films on vertical and upward-facing inclined surfaces. However, no investigation has heretofore been reported on the stability of thin liquid films on downward-facing solid surfaces with liquid injection through (i.e. normal to the surface of) the bounding wall. This flow models the injection of molten liquid lead over the upper end cap of the reactor chamber. The hydrodynamics of this flow can be interpreted as a variation of the Rayleigh-Taylor instability due to the effect of the bounding wall which is continuously fed with the heavier fluid. In order to gain additional insight into the thin liquid film protection scheme, experiments have been conducted to investigate the critical issues associated with this concept. To this end, an experimental test facility has been designed and constructed to simulate the hydrodynamics of thin liquid films injected normal to the surface of and through downward-facing flat walls. In this doctoral thesis, the effect of different design parameters (film thickness, liquid injection velocity, liquid properties and inclination angle) on liquid film stability has been examined. The results address the morphology of the film free surface, the frequency of droplet formation and detachment, the size and penetration depth of the detached droplets, and the interface wave number. These experimental data have been used to validate a novel mechanistic numerical code based on a level contour reconstruction front tracking method over a wide range of parameters. The results of this investigation will allow designers of IFE power plants to identify appropriate windows for successful operation of the thin liquid film protection concept for different coolants.

The chamber walls in inertial fusion reactors must be protected from the photons and ions resulting from the target explosions. One way this can be accomplished is through a sacrificial liquid wall composed of either liquid jets or thin liquid films. The x-rays produced by the exploding targets deposit their energy in a thin liquid layer on the wall surface or in the surface of liquid jets arrayed to protect the wall. The partially vaporized liquid film/jet forms a protective cloud that expands toward the incoming ionic debris which arrives shortly (a few s) thereafter. The charged particles deposit their energy in the vapor shield and the unvaporized liquid, thereby leading to further evaporation. Re-condensation of the vapor cloud and radiative cooling of the expanding plasma allow the energy deposited in the liquid to be recovered prior to the next target explosion (100ms). Chamber clearing prior to the next explosion represents a major challenge for all liquid protection systems, inasmuch as any remaining liquid droplets may interfere with beam propagation and/or target injection. Therefore, the primary objective of this research is to experimentally examine the interaction between liquid droplets and low- temperature, low-pressure plasmas under conditions similar to those expected following inertial fusion target explosions and the subsequent expansion. The data obtained in this research will be useful in validating mechanistic chamber-clearing models to assure successful beam propagation and target injection for the subsequent explosion.

<p>It is relatively straightforward to establish equilibrium inmagnetically confined plasmas, but the plasma is frequentlysucceptible to a variety of instabilities that are driven bythe free energy in the magnetic field or in the pressuregradient. These unstable modes exhibit effects that affect theparticle, momentum and heat confinement properties of theconfiguration. Studies of the dynamics of several of the mostimportant modes are the subject of this thesis. The studies arecarried out on plasmas in the reversed field pinch (RFP)configuration.</p><p>One phenomenon commonly observed in RFPs is mode walllocking. The localized nature of these phase- and wall lockedstructures results in localized power loads on the wall whichare detrimental for confinement. A detailed study of the walllocked mode phenomenon is performed based on magneticmeasurements from three RFP devices. The two possiblemechanisms for wall locking are investigated. Locking as aresult of tearing modes interacting with a static field errorand locking due to the presence of a non-ideal boundary. Thecharacteristics of the wall locked mode are qualitativelysimilar in a device with a conducting shell system (TPE-RX)compared to a device with a resistive shell (Extrap T2). Atheoretical model is used for evaluating the threshold valuesfor wall locking due to eddy currents in the vacuum vessel inthese devices. A good correlation with experiment is observedfor the conducting shell device.</p><p>The possibility of succesfully sustaining discharges in aresistive shell RFP is introduced in the recently rebuiltdevice Extrap T2R. Fast spontaneous mode rotation is observed,resulting in low magnetic fluctuations, low loop voltage andimproved confinement. Wall locking is rarely observed. The lowtearingmode amplitudes allow for the theoretically predictedinternal nonresonant on-axis resistive wall modes to beobserved. These modes have not previously been distinguisheddue to the formation of wall locked modes. The internal andexternal nonresonant resistive wall modes grow on the timescale of the shell penetration time. These growth rates dependon the RFP equilibrium. The internal nonresonant resistive wallmodes dominate in Extrap T2R, especially for shallow reverseddischarges. The external nonresonant modes grow solely in deepreversal discharges.</p><p><b>Keywords</b>Nuclear fusion, reversed field pinch, resistiveinstabilities, wall locked modes, tearing modes, resistiveshell modes, field errors, EXTRAP-T2, EXTRAP-T2R, TPE-RX</p>

Dans cette thèse, on s'intéresse au contrôle du profil de facteur de sécurité dans un plasma tokamak. Cette variable physique est liée à plusieurs phénomènes dans le plasma, en particulier des instabilités magnétohydrodynamiques (MHD). Un profil de facteur de sécurité adéquat est particulièrement important pour avoir des modes d'opération avancés dans le tokamak, avec haut confinement et stabilité MHD. Pour cela faire, on se focalise sur la commande du gradient du profil de flux magnétique poloidal dans le tokamak. L'évolution de cette variable est donnée par une équation de diffusion avec des coefficients distribuées et temps-variants. En utilisant des techniques de type Lyapunov et les propriétés de stabilité entrée-état du système on propose une loi de commande robuste qui prend en compte des contraintes non-linéaires dans l'action imposées par la physique des actionneurs. / In this thesis, we are interested in the control of the safety factor profile or q-profile in a tokamak plasma. This physical quantity has been found to be related to several phenomena in the plasma, in particular magnetohydrodynamic (MHD) instabilities. Having an adequate safety factor profile is particularly important to achieve advanced tokamak operation, providing high confinement and MHD stability. To achieve this, we focus in controlling the gradient of the poloidal magnetic flux profile. The evolution of this variable is given by a diffusion equation with distributed time-varying coefficients. Based on Lyapunov techniques and the Input-to-State stability properties of the system we propose a robust control law that takes into account nonlinear constraints on the control action imposed by the physical actuators.

Orientador: Munemasa Machida / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-17T22:07:56Z (GMT). No. of bitstreams: 1 Arsioli_BrunoSversut_M.pdf: 7832170 bytes, checksum: 4c771ec7e75b395d3088ed5f46d63820 (MD5) Previous issue date: 2011 / Resumo: O desenvolvimento deste trabalho ocorreu em duas frentes distintas relacionadas à grande área de pesquisa: Fusão Termonuclear Controlada em dispositivos do tipo tokamak. A primeira fase abordou estudos de espectroscopia, tendo como principal motivação o aprimoramento dos métodos de medida e tratamento de dados na área de diagnósticos de plasmas quentes. Os trabalhos consistem no diagnóstico por espectroscopia na região do ultravioleta do vácuo (UVV), realizados nos tokamaks TCABr-USP (Lab. Plasmas USP) e Nova-Unicamp (Lab. de Plasmas IFGW-UNICAMP), e concentraram-se na utilização do detector multicanal do tipo MCP-CCD, acoplado a um espectr ômetro de grade simples McPherson-225 operando na região espectral de 500 a 3200 °A, buscando ordens superiores de difração para o cálculo da temperatura iônica (Ti) via medida do alargamento Doppler (??D). A ideia para o cálculo da Ti é a utilização da relação entre os sinais de ordens superiores de difração (OSD), a fim de reduzir a influência do alargamento instrumental no cálculo do parâmetro ??D, do qual depende a medida de Ti. Também foram coletados dados com fotomultiplicadora, explorando a possibilidade de registrar a evolução temporal (com resolução de 1ms) da intensidade das emissões de algumas das principais impurezas presentes no plasma. Numa segunda fase, realizaram-se estudos do aquecimento do plasma por meio de injeção de partícula neutras (IPN) de alta energia (42-93 keV) no tokamak ASDEX Upgrade (Max-Planck-Institut fur Plasmaphysik; Garching- Alemanha). Tal atividade foi desenvolvida dentro do programa de mestrado em fusão nuclear da União Europeia, ErasmusMundus Fusion-EP, que esteve sob orientação de Dr. Ryter Fran¸cois, e supervisão de Prof. Dr. Stroth Ulrich (Universitat Stuttgart) e Jose Ramon Martin Solis (Universidad Carlos III de Madrid). O tokamak ASDEX Upgrade geralmente opera com plasma de Deutério, sendo a Injeção de Partículas Neutras de Deutério (IPN-D) a principal forma de aquecimento. Para este esquema de operação usual, os perfis de deposição de energia do feixe, ao longo da direção radial, foram extensivamente documentados por meio de cálculos com o código computacional FAFNER. Formulas gerais para os principais parâmetros relacionados à potência depositada e confinamento dos íons rápidos foram desenvolvidas e são rotineiramente utilizadas. No entanto, plasmas de Hélio aquecido por injeção de hidrogênio (IPN-H) e deutério (IPN-D), ocasionalmente são utilizados no ASDEX Upgrade. Uma das motivações para o estudo desse cenário reside na possibilidade de operação do ITER com plasma de hélio, ao menos na fase inicial de baixa ativação. Tal escolha permitiria comissionar os sistemas de controle e diagnóstico sem a necessidade de ativação radioativa das estruturas que compõe o reator, já que as taxas de fusão nuclear seriam mínimas. Até então, a documentação da deposição de potência por IPN em plasma de hélio no tokamak ASDEX Upgrade ainda não havia sido realizada. O objetivo do presente trabalho é a documentação das propriedades de aquecimento por IPN-H e IPN-D em plasma de hélio, utilizando o código FAFNER, sendo de grande interesse viabilizar o uso de uma nova base de dados chamada ADAS. Esta, contém tabelas com coeficientes de atenuação ?s??i adicionais, permitindo levar em conta a presença de átomos excitados no feixe de partículas neutras interagindo com o plasma, o que tem impacto direto sobre a deposição de potência por IPN / Abstract: The development of the present work has happened in two frames strictly related with the research on Thermonuclear Fusion in tokamaks. The first phase was dedicated to studies with spectroscopy, which had as main motivation the development of measurement and data treatment methods concerning hot plasmas diagnostic. Basically, it consisted in UV spectroscopic measurements carried on at TCABr-USP (Lab. Plasmas USP - São Paulo, Brazil) and Nova-Unicamp (Lab. de Plasmas do IFGW-UNICAMP - Campinas, Brazil) tokamaks. The activities were concentrated on the use of a multichannel detector MCP-CCD type, coupled with a single grating spectrometer McPherson-225, allowing VUV spectroscopy at the 500 - 3200°A spectra. The main objective was to look for signals of high diffraction orders aiming to calculate ion temperature via Doppler broadening (??D). The idea for getting precise Ti measurements was to make a relation between high diffraction order (HDO) signals to reduce the influence of the instrumental broadening, which has been accomplished with success. A series of data with photomultiplier was collected at the UV region, exploring the possibility of getting the time evolution of the emission intensity of the main impurities from the plasma. All work carried out on spectroscopy in small size experiments like NOVA tokamak are of great importance. In a second phase, studies related with plasma heating by Neutral Beam Injection (NBI) 42-93 keV were carried out in ASDEX Upgrade tokamak (at Max-Planck-Institut fur Plasmaphysik; Garching-Germany). This activity was developed in the frame of European Union Master Program, ErasmusMundus Fusion-EP, oriented by Dr. Ryter Fran¸cois, and supervised by Prof. Dr. Stroth Ulrich (Universitat Stuttgart) and Prof. Dr.Jose Ramon Martin Solis (Universidad Carlos III de Madrid). The ASDEX Upgrade tokamak is generally operated in deuterium plasma with deuterium Neutral Beam Injection (D-NBI) as main heating. For this usual operation scheme, the heating power deposition has been extensively documented by calculations with the code FAFNER. General fit formulas for the most important parameters related to the power deposition and fast ion content have been developed and are routinely used. However, helium plasmas heated by H-NBI or D-NBI are also occasionally performed in ASDEX Upgrade. One of the motivation for using helium resides in the fact that the low activation phase of ITER might be, at least partly, carried out in helium plasmas. So far, the documentation of the NBI deposition in helium plasmas in ASDEX Upgrade has not been made. The aim of the present work was to document the heating properties of H-NBI and D-NBI for helium plasmas, using the FAFNER code, being of great interest to get FAFNER running with new libraries (ADAS) for the calculation of the stopping rate coefficients ?s??i, allowing to evaluate the influence of excited atoms in the neutral beam. The final goal was to provide a reliable estimate of the main quantities linked to NBI heating in a set of helium discharges, in particular absorbed power, fast ion losses and fast ion energy content / Mestrado / Física de Plasmas e Descargas Elétricas / Mestre em Física

Thermonuclear fusion has potential to offer an economically, environmentally and socially acceptable supply of energy. A promising reactor design to execute thermonuclear fusion is the toroidal magnetic confinement device, tokamak. The tokamak still faces challenges in the major areas which can be categorised into confinement, heating and fusion technology. This thesis addresses the problem of confinement, in particular the role of transport along magnetic field lines perturbed by diverse MHD instabilities.<p><p>Unstable modes such as ideal ballooning-peeling, tearing etc. break closed magnetic surfaces and destroy the axisymmetry of the magnetic configuration in a tokamak, providing deviation of magnetic field lines from unperturbed magnetic surfaces. Radial gradients of plasma parameters have nonzero projections along such lines and drive parallel particle and heat flows which contribute to the radial transport. Such transport can significantly affect confinement as this takes place by the development of neoclassical tearing modes (NTMs) in the core and edge localised modes (ELMs) at the plasma periphery.<p><p>In this thesis, transport of heat through non-overlapped magnetic island chains is first investigated using the 'Optimal path' approach, which is based on the principal of minimum entropy production. This model shows how the effective heat conduction through islands increases with parallel heat conduction and with the perturbation level. A more standard analytical approach for the limit cases of "small" and "large" islands is also presented. Transport of heat through internally heated magnetic islands is next investigated by further development of the 'Optimal path' method. In addition the approach by R. Fitzpatrick, has been extended for this investigation. By application of these approaches to experimental observations made at TEXTOR tokamak, heat flux limit, limiting parallel heat conduction in low collisional plasmas, is elucidated.<p><p>Models to study transport of heat and particles due to ELMs have also been developed. Energy losses during ELMs have been estimated considering contribution from parallel conduction due to electrons and parallel convection of ions, with constant level of the magnetic field perturbation, steady profiles for density and temperature, and by accounting for the heat flux limit. The estimate shows good agreement with experimental observations. The model is developed further by accounting for the time evolution of the perturbation level due to ballooning mode, and of density and temperature profiles. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished