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Master's Dissertation
DOI
https://doi.org/10.11606/D.43.2022.tde-04042022-130632
Document
Author
Full name
Martim Zurita
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2022
Supervisor
Committee
Guimarães Filho, Zwinglio de Oliveira (President)
Toufen, Dennis Lozano
Viana, Ricardo Luiz
Title in English
Stochastic modeling of turbulent plasma fluctuations applied to the TCABR tokamak
Keywords in English
electrostatic turbulence
ion saturation current
plasma physics
stochastic modeling
tokamaks
Abstract in English
In toroidal devices known as tokamaks, high-temperature plasmas are confined by intense magnetic fields. Nevertheless, this confinement is deteriorated by turbulence at the edge of the devices. This turbulence has an intermittent behavior with the presence of high-amplitude bursts. To describe local measurements of density with bursts, a stochastic pulse train model (SPTM) has been developed since the last decade. For such a model, different categories of background signals have been considered in the literature, namely, backgrounds with Gaussian noises (correlated and uncorrelated) or with small-amplitude pulses. However, until now these models with different background signals weren't simultaneously compared to an experiment. Moreover, there isn't a fitting method for the SPTM that can evaluate all its parameters in a unified and objective way. The present dissertation aims to fulfill these two gaps. Having created the SPTM fit, we applied it to the TCABR tokamak. For this analysis, we utilized measurements of ion saturation current, a signal proportional to the local plasma density. In addition, we introduced to the context of the SPTM two non-linear tools: the complexity-entropy diagram and the determinism from recurrence quantification analysis. With them and the frequency spectrum, we concluded that, for the analyzed experiment, the model with a pulse background described the structure of plasma density fluctuations better than the models with Gaussian noise.
Title in Portuguese
Modelo estocástico de flutuações turbulentas de plasma aplicado ao tokamak TCABR
Keywords in Portuguese
corrente de saturação iônica
física de plasmas
modelagem estocástica
tokamaks
turbulência eletrostática
Abstract in Portuguese
Em dispositivos toroidais conhecidos como tokamaks, plasmas com temperaturas solares são confinados por intensos campos magnéticos. Esse confinamento, todavia, é deteriorado pela turbulência na borda dos dispositivos. Essa turbulência possui um comportamento intermitente marcado pela presença de rajadas de alta amplitude, denominadas como bursts. Para descrever medidas locais de densidade com bursts, um modelo estocástico de trem de pulsos (METP) vem sendo desenvolvido desde a última década. Para tal modelo, foram considerados na literatura diferentes categorias de sinais de fundo, a saber, fundos com diferentes ruídos gaussianos (descorrelacionados e correlacionados) ou com pulsos de pequena amplitude. Entretanto, até o momento esses sinais de fundo não foram comparados simultaneamente a um sinal experimental. Além disso, ainda não há um método de ajuste para o METP que obtenha todos os seus parâmetros de forma unificada e objetiva. A presente dissertação almeja preencher essas duas lacunas. Criado o ajuste do METP, o aplicamos para o tokamak TCABR. Para tal análise, utilizamos medidas de corrente de saturação iônica, um sinal proporcional a densidade local do plasma. Adicionalmente, introduzimos para o contexto do METP duas ferramentas não lineares: o diagrama de complexidade-entropia e o determinismo da análise de recorrência. Com elas e com o espectro de potência, concluímos que, para o experimento analisado, o modelo com fundo de pulsos descreveu a estrutura de flutuações de densidade melhor do que os modelos com ruído gaussiano.
 
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Publishing Date
2022-04-08
 
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