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Master's Dissertation
DOI
10.11606/D.43.2013.tde-03122014-133933
Document
Author
Full name
Wilson Andres Hernandez Baquero
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2013
Supervisor
Committee
Galvao, Ricardo Magnus Osorio (President)
Guimarães Filho, Zwinglio de Oliveira
Kuznetsov, Yurii
Title in Portuguese
Análise espectral de dados experimentais em busca de modos geodésicos de baixa frequência no Tokamak TCABR
Keywords in Portuguese
Física dos plasmas
Modos geodésicos acústicos
Tokamaks
Abstract in Portuguese
O objetivo do presente estudo é a procura de evidências da presença de modos GAM nas descargas do tokamak TCABR, em distintos regimes de operação. As descargas selecionadas foram classicadas segundo a maneira de obter a melhora no connamento do plasma. Nós zemos essa procura nas descargas ôhmicas com incremento espontâneo da densidade do plasma, em descargas onde o plasma foi perturbado externamente pela injeção de ondas de Alfvén e pela alteração do campo elétrico radial via eletrodo de bias. Por causa da natureza eletrostática da oscilação GAM, nas descargas selecionadas foi relevante a presença das sondas eletrostáticas (conhecidas também como sondas de Langmuir). As bobinas de Mirnov foram importantes para identicar as oscilaçes MHD. Diversos métodos de análise espectral e estatístico foram usados na análise dos sinais experimentais como ajuda para identicar os modos GAM. Os métodos usados foram: correlação, espectro de auto-potência, espectro de potência cruzado, coerência e densidade espectral em número de onda e frequência. Para as bobinas de Mirnov, só o espectro de autopot ência foi usado. Os resultados da análise realizada nas descargas com crescimento espontâneo da densidade e nas descargas aquecidas com ondas de Alfvén, não mostram nenhuma presença de GAMs. Nessas descargas somente ocorreu um pequeno incremento na correlação que foi causado pela atividade MHD. Para as descargas com bias, a análise mostra a presença de um modo de f 40KHz, modo que não se observa nas bobinas de Mirnov e que tem simetria poloidal e toroidal.
Title in English
Spectral analysis from experimental data for search of geodesic low frequency modes in the TCABR Tokamak
Keywords in English
Física dos plasmas
Geodesic acoustic mode
Tokamacs
Abstract in English
The goal of the present study is to search for evidences of the presence of GAM modes in plasmas discharges of the TCABR tokamak at dierent operational regimes. The selected discharges were classied according to the way used to obtain plasma improvement of connement. We perform this search in pure ohmic discharges with a spontaneous increment of the plasma density and in discharges where the plasma was externally perturbed by the injection of Alfvén waves and by electrostatic edge biasing. Given the electrostatic nature of the GAM oscillation, in the selected discharges were relevant the presence of electrostatic probes (also known as Langmuir probes). The signals from Mirnov coils was important too, for identify the MHD oscillations. Several statistical and spectral methods were used to analyze the experimental signals in order to helps the identication of the GAM modes, correlation, auto-power spectra, cross-power spectra, coherence and spectral density in wave number and frequency (S(k; f)). For the Mirnov coil just auto-power spectra was used. The results of the analysis performed on the discharges with spontaneous increase of density and for those with Alfvén heating did not show any presence of GAMs. There was just an few increment of the correlation but it was due to the MHD activity. For the discharges with edge biasing, the analysis shows the presence of a f 40kHz mode that was not present in the Mirnov coil and that has toroidal and poloidal symmetry.
 
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WAHBaquero.pdf (7.36 Mbytes)
Publishing Date
2014-12-04
 
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