The turbulence and fluctuation induced transport in the edge plasma of the Tokoloshe tokamak was studied using a Langmuir probe array. In this thesis three separate experiments are presented, each of which examines a particular aspect of the edge plasma. In the first experiment measurements of edge plasma parameters are presented. These include standard parameters (such as Ne, Op , Te, etc.) as well as features such as the velocity shear, T(t) during periods of both high and low Mirnov activity, Te/Te and Q. These are compared with results from other machines as well as predictions of several turbulence theories. It was found that many of the results are very similar to those obtained on other machines and that, since the operating parameter space on Tokoloshe is well within the parameter space described by drift wave theories, resistivity-driven gradient driven turbulence theories do not describe the edge turbulence. In the second experiment external windings are used to produce fields which can slow and lock magnetic islands in the toroidally rotating plasma. Edge parameters are again presented and these results compared with those from the so-called 'reference' plasmas, i.e. ones in which no locking occurred. During locking some parameters are dramatically altered, e.g.Te/Te Standard transport theory ignores the effect of Te/Te since they are usually small in reference discharges. During the locked phase, however, certain measurements used to deduce T and Q are greatly affected by increases in Te/Te. As a result, certain assumptions regarding these measurements are no longer valid. Comparison of results for different island positions (produced by different coils) indicates that the assumption of poloidal and toroidal symmetry of edge conditions is invalid. The third experiment investigates the high frequency (~60 kHz), low amplitude, magnetic oscillation which characterises the locked phase and which exhibits some small degree of correlation with the fluctuations observed on (e.g.) Of'. Since over 80% of the spectral power of Te/Te lies below 70 kHz and since Of /Te depends strongly on Te/Te , it is suggested that the magnetic mode and these large variations in Te, may be due to a similar physical process. / Thesis (Ph.D.)-University of Natal, 1993.

Thesis (M.S.)--West Virginia University, 1998. / Title from document title page. "Fall 1998." Document formatted into pages; contains iii, 28 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 27-28).

Thesis (Ph.D.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Co-Chair: Minami Yoda, Co-Advisor; Committee Co-Chair: Said I. Abdel-Khalik; Committee Member: Donald R. Webster; Committee Member: Narayanan M. Komerath; Committee Member: S. Mostafa Ghiaasiaan; Committee Member: Yogendra Joshi

Para o aprimoramento do sistema de aquecimento do plasma por meio de ondas de Alfvén, denominado sistema AWES Alfvén Waves Excitment System, do tokamak TCABR foram construídos, caracterizados, instalados e colocados em operação os diagnósticos para determinação da potência de rádio-freqüência fornecida ao plasma pelo conjunto de antenas para excitação de ondas de Alfvén bem como o circuito processador de sinais para o conjunto de sondas magnéticas, já instaladas dentro da câmara do TCABR, que permitem determinar o espectro de rádio-freqüência gerado pelo conjunto de antenas no interior da câmara de vácuo deste tokamak. Cada conjunto do sistema de diagnóstico de potência é composto por três dispositivos, sendo eles, um sensor de corrente de rádio-freqüência, do tipo bobinas de Rogowski, um sensor de tensão de RF, composto de divisores de tensão acoplados a um circuito processador de sinais e por um circuito multiplicador de sinais capaz de multiplicar os sinais de corrente e tensão de RF e fornecer um sinal proporcional à potência efetivamente fornecida ao plasma. No total foram construídas dez bobinas de Rogowski cujas constantes de sensibilidade são da ordem de 18 mV/A, doze divisores de tensão capazes de reduzir a amplitude de um sinal de 10kV a aproximadamente 5V, seis circuitos processadores de sinais para determinação da tensão de RF e quatro multiplicadores de sinais. Além disso foi construído um circuito processador de sinais capaz de processar o sinal fornecido por quatro sondas magnéticas simultaneamente. Todos os dispositivos elaborados nesse trabalho são capazes de processar sinais de freqüências compreendidas na faixa de 3 a 6MHz e fornecer sinais de baixa freqüência tal que seja possível adquiri-los automaticamente pelo sistema de aquisição de dados do TCABR, denominado TCAqs. Para os procedimentos de calibração e testes de funcionamento dos equipamentos desenvolvidos neste trabalho, estabeleceu-se um Sistema de Calibração Automatizado (SCA) sendo uma de suas partes integrantes um software capaz de comunicar e controlar equipamentos de medição, tais como osciloscópios e geradores de sinais, através de portas de comunicação tipo RS-232 usando a linguagem de comunicação SCPI. Este programa, chamado de SCO, foi inteiramente desenvolvido em software livre e de código aberto para ser usado em sistemas operacionais Unix-Like, como os sistemas GNU/Linux. O código fonte do SCO foi liberado como software livre e com isso registrado sob a licença GNU/GPL. Os procedimentos de calibração uma vez operando sob esse sistema cuja principal característica é a funcionalidade de automação, permitiu a aquisição de uma quantidade de dados muito maior do que aquela que seria possível em procedimentos manuais, resultando assim, em curvas mais confiáveis do ponto de vista estatístico aumentando-se conseqüentemente, de forma considerável, a qualidade das medições. Após extensa caracterização e testes de funcionamento fora e no TCABR concluiu-se que estes dispositivos estão prontos para serem utilizados em campanhas experimentais. / In order to enhance the efficiency of the TCABR\'s Alfvén waves heating system, called AWES - Alfvén Waves Excitement System a diagnostics for determining the radio-frequency power applied to the plasma and a processing circuit for the magnetic coil system was built, characterized, installed and put into operation. The RF diagnostics system was designed to determine the total power that the set of AWES antennas applies to the plasma and, the magnetic coils system is designed to determine the RF spectrum excited by these antennas. Since the magnetic coils are already installed inside the TCABRs vacuum chamber only the signal processing circuit was built for it. The RF power diagnostics set is composed of three devices which are, one RF current sensing device, a set for determining the RF voltage and a multiplying system. A Rogowski coil is used for measuring the RF current. The RF voltage system may be split in two: a couple of voltage dividers and a processing circuit for the potential difference determination. Applying the RF current and voltage signals to the multiplier circuit it is possible to determine the RF power fed to the plasma. In this work a total of ten Rogowski coils, with 18mV/A sensibility constant, as well as twelve voltage dividers, capable of reducing a 10kV signal to approximately 5V signal, six voltage processing circuits and four signal multipliers, were built. Besides that, one demodulator circuit, capable of processing, simultaneously, the signals from four magnetic coils, was built too. All the devices constructed in this project were designed to be able to process signals with frequencies in the range of 3 to 6M Hz and produce a low frequency result signal that may be acquired automatically by the TCABR data acquisition system called TCAqs. For the calibration procedures and operational tests of the equipments developed in this work, it was established an Automated Calibration System (SCA) with a software application as one of its components that is capable of communicating and controlling test instruments, like oscilloscopes and function generators, through the communication port RS-232 and SCPI language. This software, called SCO, was fully developed using free and open source software in order to be used in Unix-Like operational systems like GNU/Linux. As a free software SCO was registered under the GNU/GPL license. The calibration procedures once operating with this system, whose principal characteristics is its automation functionality, allowed us to acquire a great quantity of data, that would have not been possible or practical to do manually. As a consequence, the resulting calibration curves may be considered more accurate, from an statistical point of view which enhanced considerably the quality of the results. After the characterization and detailed tests of all these devices off the TCABR and after the installation of the diagnostics in the TCABR, we may finally conclude they are ready to be used in experimental campaign.

Para o aprimoramento do sistema de aquecimento do plasma por meio de ondas de Alfvén, denominado sistema AWES Alfvén Waves Excitment System, do tokamak TCABR foram construídos, caracterizados, instalados e colocados em operação os diagnósticos para determinação da potência de rádio-freqüência fornecida ao plasma pelo conjunto de antenas para excitação de ondas de Alfvén bem como o circuito processador de sinais para o conjunto de sondas magnéticas, já instaladas dentro da câmara do TCABR, que permitem determinar o espectro de rádio-freqüência gerado pelo conjunto de antenas no interior da câmara de vácuo deste tokamak. Cada conjunto do sistema de diagnóstico de potência é composto por três dispositivos, sendo eles, um sensor de corrente de rádio-freqüência, do tipo bobinas de Rogowski, um sensor de tensão de RF, composto de divisores de tensão acoplados a um circuito processador de sinais e por um circuito multiplicador de sinais capaz de multiplicar os sinais de corrente e tensão de RF e fornecer um sinal proporcional à potência efetivamente fornecida ao plasma. No total foram construídas dez bobinas de Rogowski cujas constantes de sensibilidade são da ordem de 18 mV/A, doze divisores de tensão capazes de reduzir a amplitude de um sinal de 10kV a aproximadamente 5V, seis circuitos processadores de sinais para determinação da tensão de RF e quatro multiplicadores de sinais. Além disso foi construído um circuito processador de sinais capaz de processar o sinal fornecido por quatro sondas magnéticas simultaneamente. Todos os dispositivos elaborados nesse trabalho são capazes de processar sinais de freqüências compreendidas na faixa de 3 a 6MHz e fornecer sinais de baixa freqüência tal que seja possível adquiri-los automaticamente pelo sistema de aquisição de dados do TCABR, denominado TCAqs. Para os procedimentos de calibração e testes de funcionamento dos equipamentos desenvolvidos neste trabalho, estabeleceu-se um Sistema de Calibração Automatizado (SCA) sendo uma de suas partes integrantes um software capaz de comunicar e controlar equipamentos de medição, tais como osciloscópios e geradores de sinais, através de portas de comunicação tipo RS-232 usando a linguagem de comunicação SCPI. Este programa, chamado de SCO, foi inteiramente desenvolvido em software livre e de código aberto para ser usado em sistemas operacionais Unix-Like, como os sistemas GNU/Linux. O código fonte do SCO foi liberado como software livre e com isso registrado sob a licença GNU/GPL. Os procedimentos de calibração uma vez operando sob esse sistema cuja principal característica é a funcionalidade de automação, permitiu a aquisição de uma quantidade de dados muito maior do que aquela que seria possível em procedimentos manuais, resultando assim, em curvas mais confiáveis do ponto de vista estatístico aumentando-se conseqüentemente, de forma considerável, a qualidade das medições. Após extensa caracterização e testes de funcionamento fora e no TCABR concluiu-se que estes dispositivos estão prontos para serem utilizados em campanhas experimentais. / In order to enhance the efficiency of the TCABR\'s Alfvén waves heating system, called AWES - Alfvén Waves Excitement System a diagnostics for determining the radio-frequency power applied to the plasma and a processing circuit for the magnetic coil system was built, characterized, installed and put into operation. The RF diagnostics system was designed to determine the total power that the set of AWES antennas applies to the plasma and, the magnetic coils system is designed to determine the RF spectrum excited by these antennas. Since the magnetic coils are already installed inside the TCABRs vacuum chamber only the signal processing circuit was built for it. The RF power diagnostics set is composed of three devices which are, one RF current sensing device, a set for determining the RF voltage and a multiplying system. A Rogowski coil is used for measuring the RF current. The RF voltage system may be split in two: a couple of voltage dividers and a processing circuit for the potential difference determination. Applying the RF current and voltage signals to the multiplier circuit it is possible to determine the RF power fed to the plasma. In this work a total of ten Rogowski coils, with 18mV/A sensibility constant, as well as twelve voltage dividers, capable of reducing a 10kV signal to approximately 5V signal, six voltage processing circuits and four signal multipliers, were built. Besides that, one demodulator circuit, capable of processing, simultaneously, the signals from four magnetic coils, was built too. All the devices constructed in this project were designed to be able to process signals with frequencies in the range of 3 to 6M Hz and produce a low frequency result signal that may be acquired automatically by the TCABR data acquisition system called TCAqs. For the calibration procedures and operational tests of the equipments developed in this work, it was established an Automated Calibration System (SCA) with a software application as one of its components that is capable of communicating and controlling test instruments, like oscilloscopes and function generators, through the communication port RS-232 and SCPI language. This software, called SCO, was fully developed using free and open source software in order to be used in Unix-Like operational systems like GNU/Linux. As a free software SCO was registered under the GNU/GPL license. The calibration procedures once operating with this system, whose principal characteristics is its automation functionality, allowed us to acquire a great quantity of data, that would have not been possible or practical to do manually. As a consequence, the resulting calibration curves may be considered more accurate, from an statistical point of view which enhanced considerably the quality of the results. After the characterization and detailed tests of all these devices off the TCABR and after the installation of the diagnostics in the TCABR, we may finally conclude they are ready to be used in experimental campaign.

<p>When the heavy hydrogen isotopes deuterium (D) and tritium (T) undergo nuclear fusion large amounts of energy are released. At the Joint European Torus (JET) research is performed on how to harvest this energy. Two of the most important fusion reactions, d+d→³He+n (E_n = 2.5 MeV) and d+t→⁴He+n (E_n = 14 MeV), produce neutrons. This thesis investigates how measurements of these neutrons can provide information on the fusion performance.</p><p>The Magnetic Proton Recoil (MPR) neutron spectrometer has operated at JET since 1996. The spectrometer was designed to provide measurements on the 14 MeV neutron emission in DT operation, thereby conveying information on the state of the fuel ions. However, a majority of today’s fusion experiments are performed with pure D fuel. Under such conditions, the measurements with the MPR were severely hampered due to interfering background. This prompted an upgrade of the instrument. The upgrade, described in this thesis, included a new focal plane detector, a phoswich scintillator array, and new data acquisition electronics, based on transient recorder cards. This combination allows for pulse shape discrimination techniques to be applied and a signal to background of 5/1 has been achieved in measurements of the 2.5-MeV neutrons in D experiments. The upgrade also includes a new control and monitoring system, which enables the monitoring and correction of gain variations in the spectrometer’s photo multiplier tubes. Such corrections are vital for obtaining good data quality.</p><p>In addition, this thesis describes a new method for determining the total neutron yield and hence the fusion power by using a MPR spectrometer in combination with a neutron emission profile monitor. The system has been operated at JET both during DT and D experiments. It is found that the systematic uncertainties are considerably lower (≈6 %) than for traditional systems. For a dedicated system designed for the next generation fusion experiments, i.e, ITER, uncertainties of 4 % could be attained.</p><p>Neutron spectroscopy can also be an important tool for determining the neutron emission from residual tritium in D plasmas. This information is combined with other measurements at JET in order to determine the confinement of the 1 MeV tritons from the d+d→t+p reactions.</p>

When the heavy hydrogen isotopes deuterium (D) and tritium (T) undergo nuclear fusion large amounts of energy are released. At the Joint European Torus (JET) research is performed on how to harvest this energy. Two of the most important fusion reactions, d+d→3He+n (En = 2.5 MeV) and d+t→4He+n (En = 14 MeV), produce neutrons. This thesis investigates how measurements of these neutrons can provide information on the fusion performance. The Magnetic Proton Recoil (MPR) neutron spectrometer has operated at JET since 1996. The spectrometer was designed to provide measurements on the 14 MeV neutron emission in DT operation, thereby conveying information on the state of the fuel ions. However, a majority of today’s fusion experiments are performed with pure D fuel. Under such conditions, the measurements with the MPR were severely hampered due to interfering background. This prompted an upgrade of the instrument. The upgrade, described in this thesis, included a new focal plane detector, a phoswich scintillator array, and new data acquisition electronics, based on transient recorder cards. This combination allows for pulse shape discrimination techniques to be applied and a signal to background of 5/1 has been achieved in measurements of the 2.5-MeV neutrons in D experiments. The upgrade also includes a new control and monitoring system, which enables the monitoring and correction of gain variations in the spectrometer’s photo multiplier tubes. Such corrections are vital for obtaining good data quality. In addition, this thesis describes a new method for determining the total neutron yield and hence the fusion power by using a MPR spectrometer in combination with a neutron emission profile monitor. The system has been operated at JET both during DT and D experiments. It is found that the systematic uncertainties are considerably lower (≈6 %) than for traditional systems. For a dedicated system designed for the next generation fusion experiments, i.e, ITER, uncertainties of 4 % could be attained. Neutron spectroscopy can also be an important tool for determining the neutron emission from residual tritium in D plasmas. This information is combined with other measurements at JET in order to determine the confinement of the 1 MeV tritons from the d+d→t+p reactions.

Made available in DSpace on 2014-12-17T14:57:38Z (GMT). No. of bitstreams: 1 AdrianoSB.pdf: 1824941 bytes, checksum: 9594a533193a54f04b78499b7820f209 (MD5) Previous issue date: 2007-07-30 / The processing of materials through plasma has been growing enough in the last times in several technological applications, more specifically in surfaces treatment. That growth is due, mainly, to the great applicability of plasmas as energy source, where it assumes behavior thermal, chemical and/or physical. On the other hand, the multiplicity of simultaneous physical effects (thermal, chemical and physical interactions) present in plasmas increases the complexity for understanding their interaction with solids. In that sense, as an initial step for the development of that subject, the present work treats of the computational simulation of the heating and cooling processes of steel and copper samples immersed in a plasma atmosphere, by considering two experimental geometric configurations: hollow and plane cathode. In order to reach such goal, three computational models were developed in Fortran 90 language: an one-dimensional transient model (1D, t), a two-dimensional transient model (2D, t) and a two-dimensional transient model (2D, t) which take into account the presence of a sample holder in the experimental assembly. The models were developed based on the finite volume method and, for the two-dimensional configurations, the effect of hollow cathode on the sample was considered as a lateral external heat source. The main results obtained with the three computational models, as temperature distribution and thermal gradients in the samples and in the holder, were compared with those developed by the Laboratory of Plasma, LabPlasma/UFRN, and with experiments available in the literature. The behavior showed indicates the validity of the developed codes and illustrate the need of the use of such computational tool in that process type, due to the great easiness of obtaining thermal information of interest / O processamento de materiais por plasmas tem crescido bastante nos ?ltimos tempos em diversas aplica??es tecnol?gicas, mais especificamente no tratamento de superf?cies. Esse crescimento se deve, principalmente, pela grande aplicabilidade do plasma como fonte energ?tica. Por outro lado, a multiplicidade de efeitos simult?neos presentes no plasma, (intera??es t?rmicas, qu?micas e f?sicas) aumenta a complexidade para entendimento da sua intera??o com s?lidos. Nesse sentido, como um passo inicial para o desenvolvimento desse tema, o presente trabalho trata da simula??o computacional de aquecimento e resfriamento de amostras de a?o e cobre em ambientes de plasma, considerando-se duas configura??es geom?tricas: catodo oco e catodo planar. Para tal, tr?s modelos computacionais foram desenvolvidos na linguagem Fortran 90: um modelo unidimensional transiente sem suporte (1D,t), um modelo bidimensional transiente sem suporte (2D,t) e um modelo bidimensional transiente (2D,t) que considera a presen?a de um suporte na montagem experimental. Os modelos foram desenvolvidos utilizando-se o m?todo dos volumes finitos e, para as situa??es bidimensionais, o efeito de catodo oco sobre a amostra foi considerado como uma fonte externa de calor lateral. Os resultados obtidos com os tr?s modelos computacionais, como a distribui??o de temperatura nas amostras e nos suportes, os seus gradientes t?rmicos, em fun??o de alguns experimentos de aquecimento e resfriamento desenvolvidos pelo Laborat?rio de Plasma, LabPlasma/UFRN, e de experimentos reportados na literatura, apontam para a validade dos c?digos desenvolvidos e ilustram a necessidade da utiliza??o dessa ferramenta nesse tipo de processo, pela sua facilidade de disponibiliza??o de informa??es t?rmicas de interesse

Mémoire (M.Sc.A)--Université du Québec à Chicoutimi, 1989. / Document électronique également accessible en format PDF. CaQCU

Divertors are in-vessel, plasma-facing, components in magnetic-confinement fusion reactors. Their main function is to remove the fusion reaction ash (α-particles), unburned fuel, and eroded particles from the reactor, which adversely affect the quality of the plasma. A significant fraction (~15 %) of the total fusion thermal power is removed by the divertor coolant and must, therefore, be recovered at elevated temperature in order to enhance the overall thermal efficiency. Helium is the leading coolant because of its high thermal conductivity, material compatibility, and suitability as a working fluid for power conversion systems using a closed high temperature Brayton cycle. Peak surface heat fluxes on the order of 10 MW/m^2 are anticipated with surface temperatures in the region of 1,200°C to 1,500°C. Recently, several helium-cooled divertor designs have been proposed, including a modular T-tube design and a modular finger configuration with jet impingement cooling from perforated end caps. Design calculations performed using the FLUENT® CFD software package have shown that these designs can accommodate a peak heat load of 10 MW/m^2. Extremely high heat transfer coefficients (~50,000 W/(m^2 K)) were predicted by these calculations. Since these values of heat transfer coefficient are considered to be outside of the experience base for gas-cooled systems, an experimental investigation has been undertaken to validate the results of the numerical simulations. Attention has been focused on the thermal performance of the T-tube and the finger divertor designs. Experimental and numerical investigations have been performed to support both divertor geometries. Excellent agreement has been obtained between the experimental data and model predictions, thereby confirming the predicted performance of the leading helium-cooled divertor designs for near- and long-term magnetic fusion reactor designs. The results of this investigation provide confidence in the ability of state-of-the-art CFD codes to model gas-cooled high heat flux plasma-facing components such as divertors.