Estudo espectral das instabilidades MHD no tokamak TCABR

Theodoro, V C

doi:10.11606/d.43.2013.tde-18112014-153714

Cited by 3 publications

(10 citation statements)

References 28 publications

(33 reference statements)

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“…Essa expressão exige o conhecimento do perfil da densidade de corrente J(r) que é uma medida experimental de difícil obtenção e que num tokamak, em geral, não é constante no tempo. Numa situação de equilíbrio, podemos supor um modelo parabólico para J(r) muito comum na literatura [24], dado por:…”

Section: Localização Das Perturbaçõesunclassified

“…Ademais, este trabalho se soma aos esforços anteriores efetuados no laboratório para melhorar a compreensão dos fenômenos magneto-hidrodinâmicos presentes no plasma do TCABR. Dentre as dissertações e teses que foram importantes para este trabalho valem a pena citar: 1) A tese de doutoramento do Dr. Erich Saetone, que estudou as oscilações de Mirnov com o emprego de um conjunto de 24 bobinas de Mirnov numa configuração circular e com distribuição não uniforme das bobinas e que utilizou análise de Fourier no tratamento dos dados [69]; 2) A dissertação de mestrado do Sr. Victor Cominato, estudo sobre instabilidade magneto-hidrodinâmicas utilizando um sistema bolométrico via análise espectral [24]; 3) A tese de doutoramento do Dr. Antônio Fonseca, sobre emissão ciclotrônica do qual o método proposto permitiu a determinação direta da posição e largura das ilhas magnéticas [70] e 4) A tese de doutoramento do Dr. Omar Najera, sobre o perfil tomográfico da emissão da linha Hα [71].…”

Section: Discussões E Conclusãounclassified

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Instabilidades MHD no Tokamak TCABR

Fernandes¹

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This work describes the study of magneto-hydro-dynamic instabilities (MHD) commonly observed in plasma discharges in tokamak TCABR (at Instituto de Física da USP). Two main diagnostics were employed to observe these instabilities: a poloidal set of 24 magnetic coils (Mirnov coils) placed near the plasma border and a detector of emissions in the Ultra Violet and soft X-ray range with 20 channels (SXR system) which improvement of the signal conditioning circuit was done as part of this work. These diagnostics were chosen because they provide complementary information, since the SXR system measures the central part of the plasma column, while the Mirnov coils detect the MHD instabilities in the outer part of the column. The information collected by these diagnoses was submitted to spectral analysis with temporal and spatial resolution, making it possible to determine the evolution of the spectral and spatial characteristics of the observed MHD instabilities. These analyzes revealed that during the initial stage of the plasma formation (when the plasma current is still increasing) magnetic islands with decreasing wave numbers, identified as edge kink modes, are detected in the Mirnov coils. After the plasma formation, when the equilibrium parameters are relatively flat (plateau), oscillations are detected in both Mirnov coils and SXR system, indicating the presence of MHD instability in the whole plasma column. In general, the fluctuations measured by the Mirnov coils have low amplitude corresponding to small magnetic islands, which were identified as tearing modes. On the other hand, the instabilities at the central region were identified as sawteeth oscillations that correspond to periodic relaxations in the internal region of the magnetic surface with safety factor q = 1 and that are accompanied by precursor oscillations which amplitude depends on the phase of the relaxation cycles. Due to this amplitude modulation, frequency satellite peaks appear in the spectrograms of the SXR signals. Furthermore, due to the fact that relaxation cycles are not sinusoidal, harmonics of the relaxation frequency also appear in the spectrograms. However, in many TCABR discharges, the intensity of the oscillations measured by the Mirnov coils increase significantly during the plateau, with affects the frequency of all MHD instabilities, even over the sawteeth in the central region of the column. In all cases, it was observed that during the plateau the frequency of the magnetic islands coincides with the frequency of the sawtooth precursors, although they are two different instabilities located in separated radial positions. This coincidence of frequencies allowed describing the frequency evolution of all measured oscillations by considering only two basic frequencies: the cycles of sawtooth relaxation and the magnetic islands.

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Section: Localização Das Perturbaçõesunclassified

Section: Discussões E Conclusãounclassified

Instabilidades MHD no Tokamak TCABR

Fernandes¹

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“…The bolometer diagnostic [24,25] measures electromagnetic radiation in a wide spectrum range: it covers from near infrared up to low energy x-rays .…”

Section: Optical Diagnosticsmentioning

confidence: 99%

“…Basically, it measures all emitted radiation from the plasma. Description of the last hardware version for this diagnostic in TCABR is found in reference [25]. Figure 1-10 shows its geometric configuration.…”

Section: Optical Diagnosticsmentioning

confidence: 99%

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Emissivity Profiles at TCABR Tokamak

Oliveira¹

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The determination of plasma equilibrium profiles is necessary to evaluate the properties of the confinement and to investigate perturbation effects. Optical diagnostics can be used to determine some of these profiles. However, these diagnostics measure all emitted radiation at a solid angle that illuminate each diagnostic channel through a slit. Therefore, the real measured quantity is the emissivity integrated along the line-of-sight and some unfolding procedure, like Abel's inversion, is commonly used to recover the emissivity profile. In TCABR tokamak, at the Physics Institute of the University of São Paulo, a 24-channel bolometer and a 20-channel soft X-ray optical diagnostics are used to measure the plasma emissivity in wavelength range from 1.0 to 1000 nm, depending on the used filters. In this work, a numerical simulation is used to compute the signal measured by the diagnostics for a given emissivity profile, allowing direct comparison with the experimental data and avoiding the use of the Abel's inversion directly and the numerical difficulties associated with unfolding procedures. By considering TCABR tokamak geometry, spatial coordinates can be related to the normalized linear coordinates of the plasma by imposing a plasma emissivity model that depends on some free parameters, allowing the emissivity resulting in each point can be calculated. Thus, the luminosity of each channel is calculated by the integral of the emissivity modeled in each lineof-sight (Radon Transformation). Emissivity model free parameters are determined by fitting calculated luminosity to measured one. We considered three types of emissivity profiles: a parabolic model in law of power, a Gaussian model and a model based on Bessel functions. We observed that the parabolic profile fits well the bolometer data, while the Gaussian profile is adequate to describe the data obtained with the soft X-ray detector.

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Transporte de impurezas no tokamak TCABR

Fernandes¹

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Dedico esse trabalho ao meu filho, Luís Felippe Tomazini Fernandes.iii Agradecimentos Ao longo desses anos todos de pós-graduação tenho recebido a ajuda e auxílio de inúmeras pessoas de forma que é inegável que o processo de fazer ciência se dá primariamente por relacionamentos humanos. Chegando até aqui, sinto-me compelido a lembrar daqueles que compartilharam comigo seus conhecimentos e experiências.Assim, gostaria de manifestar meu profundo agradecimento, respeito e apreço por meu orientador de doutorado, Prof. Helder José Facundo Severo. Nas incontáveis reuniões e conversas informais por ter me confiado o tema de pesquisa e compartilhado de um ambiente de pesquisa saudável e livre de interferências externas. Aqui também é salutar incluir em meus mais sinceros agradecimentos ao Prof. Ricardo Magnus Osório Galvão cujo caráter exemplar em defesa da ciência e comunidade científica frente às adversidades de cunho ideológico e político é uma marca e influência da qual carregarei como bússola por toda minha carreira acadêmica.

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Estudo espectral das instabilidades MHD no tokamak TCABR

Cited by 3 publications

References 28 publications

Instabilidades MHD no Tokamak TCABR

Instabilidades MHD no Tokamak TCABR

Emissivity Profiles at TCABR Tokamak

Transporte de impurezas no tokamak TCABR

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