Inertial Alfvén waves occur in plasmas where the Alfvén speed is greater than the electron thermal speed and the scale of wave field structure across the background magnetic field is comparable to the electron skin depth. Such waves have an electric field aligned with the background magnetic field that can accelerate electrons. It is likely that electrons are accelerated by inertial Alfvén waves in the auroral magnetosphere and contribute to the generation of auroras. While rocket and satellite measurements show a high level of coincidence between inertial Alfvén waves and auroral activity, definitive measurements of electrons being accelerated by inertial Alfvén waves are lacking. Continued uncertainty stems from the difficulty of making a conclusive interpretation of measurements from spacecraft flying through a complex and transient process. A laboratory experiment can avoid some of the ambiguity contained in spacecraft measurements. Experiments have been performed in the Large Plasma Device (LAPD) at UCLA. Inertial Alfvén waves were produced while simultaneously measuring the suprathermal tails of the electron distribution function. Measurements of the distribution function use resonant absorption of whistler mode waves. During a burst of inertial Alfvén waves, the measured portion of the distribution function oscillates at the Alfvén wave frequency. The phase space response of the electrons is well-described by a linear solution to the Boltzmann equation. Experiments have been repeated using electrostatic and inductive Alfvén wave antennas. The oscillation of the distribution function is described by a purely Alfvénic model when the Alfvén wave is produced by the inductive antenna. However, when the electrostatic antenna is used, measured oscillations of the distribution function are described by a model combining Alfvénic and non-Alfvénic effects. Indications of a nonlinear interaction between electrons and inertial Alfvén waves are present in recent data.

This thesis is focused on the role of Alfvén waves in the energy transformation and transport in the magnetosphere. Different aspects of Alfvén wave generation, propagation and dissipation are considered. The study involves analysis of experimental data from the Freja, Polar and Cluster spacecraft, as well as theoretical development. An overview of the linear theory of Alfvén waves is presented, including the effects of fnite parallel electron inertia and fnite ion gyroradius, and nonlinear theory is developed for large amplitude Alfvén solitons and structures. The methodology is presented for experimental identification of dispersive Alfvén waves in a frame moving with respect to the plasma, which facilitates the resolution of the space-time ambiguity in such measurements. Dispersive Alfvén waves are identified on field lines from the topside ionosphere up to the magnetopause and it is suggested they play an important role in magnetospheric physics. One of the processes where Alfvén waves are important is the establishment of the field aligned current system, which transports the energy from the reconnection regions at the magnetopause to the ionosphere, where a part of the energy is dissipated. The main mechanism for the dissipation in the top-side ionosphere is related to wave-particle interactions leading to particle energization/heating. An observed signature of such a process is the presence of parallel energetic electron bursts associated with dispersive Alfvén waves. The accelerated electrons (electron beams) are unstable with respect to the generation of high frequency plasma wave modes. Therefore this thesis also demonstrates an indirect coupling between low frequency Alfvén wave and high frequency oscillations.

In this work we investigated the excitation of Alfvén eigenmodes in tokamaks using external antennas to the plasma column. The basic theory of Alfvén waves is revised, including non-ideal effects such as resistivity. Then the theoretical model for excitation Alfvén waves in a cylindrical plasma column, developed by Kurt Appert, is shown in detail, as an introduction to the more complex problem of Alfvén waves in toroidal plasmas. The cylindrical model is implemented in a numerical code, which is used to study the excitation of Global Alfvén Waves (GAWs), below to the so-called Continuum of Alfvén, in TCABR and JET tokamaks, using a realistic description of their antenna systems. In the sequel, it is given a brief description of Toroidal Alfvén eigenmodes (TAEs) that are excited in the gaps of the Continuum of Alfvén created by the periodicity condition of the toroidal configuration. The excitement of these modes in JET tokamak is studied using the codes HELENA, for reconstruction of magneto-hydrodynamic equilibrium, and CASTOR, which calculates the perturbed fields in this equilibrium, coupled with instability or modes excited within the magneto-resistive hydrodynamic model. This study was carried out in order to determine, consistently, the spectrum quality and the eigenmodes associated with TAEs, with different numbers toroidal n, excited by the new JET antenna system. In particular, it was investigated in detail the effect of the phases of the supply currents of the different modules (eight) of the antenna system in the quality of the excited spectrum, using an original method, implemented in this work, based on the CASTOR code. The results indicate that, although the excitation of a certain mode may be a privileged by an optimized choice of phases, satellite modes can also be excited with higher amplitude, so that the purity of the spectrum is not substantially improved. This is the main result obtained in this work. / Neste trabalho é investigada a excitação de modos própios de Alfvén em tokamaks, utilizando antenas externas à coluna de plasma. A teoria básica das ondas de Alfvén é revista, incluindo efeitos não ideais, como resistividade. A seguir, o modelo teórico para excitação de ondas de Alfvén numa coluna cilindrica de plasma, desenvolvido por Kurt Appert, é apresentado em detalhe, como introdução ao problema mais complexo de ondas de Alfvén em plasmas toroidais. O modelo cilindrico é implementado em um código numérico, que é utilizado para estudar a excitação de modos globais de Alfvén (GAWs - Global Alfvén Waves), abaixo do chamado Continuo de Alfvén, nos tokamaks TCABR e JET, utilizando uma descrição realista de seus sistemas de antenas. A seguir é feita uma breve descrição dos auto modos toroidais de Alfvén (TAEs - Toroidal Alfvén Eigenmodes) que são excitados nas brechas do Continuo de Alfvén criadas pela condição de periodicidade em configurações toroidais. A excitação desses modos no tokamak JET é estudada utilizando os códigos HELENA, para reconstrução do equilíbrio magneto-hidrodinâmico, e CASTOR, que calcula os campos perturbados nesse equilíbrio, associados a instabilidades ou modos excitados, dentro do modelo magneto-hidrodinâmico resistivo. Esse estudo foi feito com o objetivo de determinar, de forma consistente, a qualidade do espectro e as auto-funções associadas a TAEs, com diferentes números toroidais n, excitados pelo atual sistema de antenas do JET. Em particular, foi investigado em detalhe o efeito das fases das correntes de alimentação dos diferentes módulos (oito) do sistema de antenas na qualidade do espectro excitado, utilizando um método original, implementado neste trabalho, de utilizar o código CASTOR. Os resultados indicam que embora a excitação de um determinado modo possa ser privilegiado por uma escolha ótima das fases, modos satélites também podem ser excitados com maior amplitude, de modo que a pureza do espectro não é substancialmente melhorada. Este é o principal resultado obtido neste trabalho.

O objetivo do trabalho é a investigação da excitação de ondas no plasma com o uso de uma antena externa e fazer uma análise das ressonâncias de Alfvén encontradas. O sistema de antenas de Alfvén no tokamak TCABR foi desenhado para aquecimento do plasma por meio de ressonâncias. Al em do aquecimento, é possível usar a detecção de ondas excitadas com o uso da antena para objetivos de diagnóstico do plasma, encontrando o valor do perfil de segurança e massa efetiva dos íons. Por causa de uma falha nos diodos do campo toroidal usamos o regime de disparos de limpeza, com campo magnético toroidal mais fraco que de disparos tópicos do TCABR, para os testes do método de excitação e identificação de ressonâncias no plasma. Com o uso do circuito demodulador foram medidas ondas de helicon excitadas com a antena de Alfvén no plasma de limpeza usando as sondas magnéticas e de Langmuir. Com simulação foi possível idênticas as ondas medidas. Há disponível um gerador de frequência variável que foi utilizado junto desse experimento. Ambos os equipamentos se encontram preparados para uso, sendo a próxima etapa usar o plasma tópico de disparo do TCABR, que tem maior densidade que o plasma de limpeza. As medidas realizadas foram um teste para o circuito demodulador e gerador de frequência variável, que teve seu comportamento comparado com os dados de um osciloscópio de alta frequência de amostragem. Os equipamentos do TCABR usados nos experimentos, as antenas e sondas magnéticas, um gerador de baixa potência com frequência variável, um circuito demodulador, sonda de Langmuir e o reflectômetro, que tem alta taxa de amostragem (200MHz) e varredura de frequência na banda de 18 40GHz. São todos descritos na dissertação. Para modelagem das ressonâncias de Alfvén foi feito o cálculo do tensor dielétrico do plasma para o modelo cinético e para o limite magnetohidrodinâmico. Por meio de simulação computacional e cálculos considerando plasma como um fluido de 2 componentes, no caso prótons e elétrons, é possível determinar alguns tipos de onda que podem ser excitadas no plasma e sua relação de dispersão, foram calculadas a onda magnetossônica rápida e a onda global de Alfvén. Determinamos radialmente a posição dos campos eletromagnéticos no plasma. Usando o reactômetro foram medidas as ressonâncias das ondas de Alfvén na borda do plasma induzidas pelas antenas, com o plasma tópico do tokamak, com densidade mais alta e o gerador de alta potência com frequência fixa. O método para achar as ressonâncias nos dados do reflectômetro foi com o uso de sidebands que aparecem em torno da frequência da ressonância não sinal do reflectômetro, que é a frequência do gerador. As sidebands foram analisadas com um espectrograma dos dados. As ondas excitadas na borda do plasma puderam ser identificadas também nas simulações. Os resultados da análise mostram que foi possível medir as ondas no plasma que foram excitadas com o uso das antenas e tanto o circuito demodulador com o uso de sondas magnéticas como o reflectômetro são adequados para se achar ressonâncias no plasma. / The objective of this work is to investigate the excitation of waves in a plasma using an antenna and to analyse the Alfvén resonances found. The Alfvén antenna heating system of the TCABR tokamak was designed to heat the plasma due to resonances. As the diodes of the toroidal field had burned down we used cleaning discharges, with low toroidal magnetic field, to test the excitation method and the identification of plasma resonances. With the demodulator circuit we measured helicon waves excited with the Alfv en antenna in the cleaning plasma using Langmuir and magnetic probes. With computational simulation we found the measured waves. A generator of variable frequency was used in this experiment. Both equipments are prepared for future experiments with the typical plasma of the TCABR, which has higher density than the cleaning plasma. This work was aimed to test to the demodulator circuit and the variable frequency generator, the data obtained were compared to that of a high sampling frequency oscilloscope. It is presented the description of the TCABR equipments used, antenna, magnetic probe, variable frequency generator of low power, demodulator circuit, Langmuir probe and a reflectometer which has a high sampling frequency (200MHZ) and frequency scanning in the range 18 40GHz, and was built in Portugal. In order to have a model of Alfv en resonances we calculated the plasma dieletric tensor both in the kinetic and magnetohydrodynamic limits. With computational simulation and using a two uid model, protons and electrons, it is possible to find some of the excited waves in the plasma and its dispersion relation, we calculated the fast magnetosonic wave and the global Alfvén wave. We found the radial position of the electromagnetic fields in the plasma. With the re ectometer we measured resonances of Alfvén waves induced by the antenna at the plasma border in a typical TCABR tokamak plasma discharge, with higher density and a high power fixed frequency generator. We used sidebands as a method to find out the resonances in the reflectometer data. These sidebands are localized around the resonance frequency, which is the Alfvén wave generator frequency. The sidebands were analysed with spectrograms of the data. The waves excited at the plasma border were also found in the simulation. The analysis results show that we could detect the plasma waves excited with the antennas. The demodulator circuit along with magnetic probes and the reflectometer can be used to find plasma resonances.

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.

One of the most conspicuous problems in space physics for the last decades has been to theoretically describe how the large parallel electric fields on auroral field lines can be generated. There is strong observational evidence of such electric fields, and stationary theory supports the need for electric fields accelerating electrons to the ionosphere where they generate auroras. However, dynamic models have not been able to reproduce these electric fields. This thesis sheds some light on this incompatibility and shows that the missing ingredient in previous dynamic models is a correct description of the electron temperature. As the electrons accelerate towards the ionosphere, their velocity along the magnetic field line will increase. In the converging magnetic field lines, the mirror force will convert much of the parallel velocity into perpendicular velocity. The result of the acceleration and mirroring will be a velocity distribution with a significantly higher temperature in the auroral acceleration region than above. The enhanced temperature corresponds to strong electron pressure gradients that balance the parallel electric fields. Thus, in regions with electron acceleration along converging magnetic field lines, the electron temperature increase is a fundamental process and must be included in any model that aims to describe the build up of parallel electric fields. The development of such a model has been hampered by the difficulty to describe the temperature variation. This thesis shows that a local equation of state cannot be used, but the electron temperature variations must be descibed as a nonlocal response to the state of the auroral flux tube. The nonlocal response can be accomplished by the particle-fluid model presented in this thesis. This new dynamic model is a combination of a fluid model and a Particle-In-Cell (PIC) model and results in large parallel electric fields consistent with in-situ observations.

<p>One of the most conspicuous problems in space physics for the last decades has been to theoretically describe how the large parallel electric fields on auroral field lines can be generated. There is strong observational evidence of such electric fields, and stationary theory supports the need for electric fields accelerating electrons to the ionosphere where they generate auroras. However, dynamic models have not been able to reproduce these electric fields. This thesis sheds some light on this incompatibility and shows that the missing ingredient in previous dynamic models is a correct description of the electron temperature. As the electrons accelerate towards the ionosphere, their velocity along the magnetic field line will increase. In the converging magnetic field lines, the mirror force will convert much of the parallel velocity into perpendicular velocity. The result of the acceleration and mirroring will be a velocity distribution with a significantly higher temperature in the auroral acceleration region than above. The enhanced temperature corresponds to strong electron pressure gradients that balance the parallel electric fields. Thus, in regions with electron acceleration along converging magnetic field lines, the electron temperature increase is a fundamental process and must be included in any model that aims to describe the build up of parallel electric fields. The development of such a model has been hampered by the difficulty to describe the temperature variation. This thesis shows that a local equation of state cannot be used, but the electron temperature variations must be descibed as a nonlocal response to the state of the auroral flux tube. The nonlocal response can be accomplished by the particle-fluid model presented in this thesis. This new dynamic model is a combination of a fluid model and a Particle-In-Cell (PIC) model and results in large parallel electric fields consistent with in-situ observations.</p>