“…The waist diameter of the radiation beam ( ≈ 2 cm ) and the focus position ( focal lenght ≈ 37 cm ) of the antenna were experimentally obtained [ 5 ]. The electron density profile obtained from the ECE radiation were compared with the results obtained from a microwave interferometer installed in TCABR [ 6 ]. The electron density profiles can be approximated by parabolic equation in the form : A gas puffing injection system is normally used in the TCABR tokamak to control the electron density during the discharges.…”
Section: Experimental Aspects Related To the Ece Measurementsmentioning
In tokamak machines with low toroidal magnetic fields and high plasma densities, the accessibility conditions impose restrictions to the detection of the Electron Cyclotron Emission ( ECE ). In these machines, the righthand cutoff condition can be used as an independent method to determine the local electron density from the ECE data in thermal discharges. In this paper is shown the results obatined from the detection of ECE radiation in the TCABR tokamak, in operation at the Institute of Physics of University of São Paulo. The effect of the ECE radiation cutoff was observed for different radial positions of the plasma column. To reach the ECE cutoff condition, the electron density was increased monotonically by the use of an external gas puffing system. For sufficient high densities, the emission at some frequencies is cutoff and the first and the last frequency to be cutoff depends on the shape of the density profile. These measurements do not require the plasma to be optically thick. It was observed that, for a toroidal field BO = 1.14 T , the first cutoff of ECE occurs for a radial position r ∼ = 5 cm . From these measurements the radial electron density was determined. For a symmetric parabolic profile n e = n eo [1 − (r/a) 2 ] α , values of α between 0.86 and 0.97 were experimentally obtained. A good agreement of these values with those obtained from the microwave interferometer measurements ( α ≈ 0.85 ) was found. Therefore, the ECE right-hand cutoff constitutes an independent method to obtain information about the electron density profile.
“…The waist diameter of the radiation beam ( ≈ 2 cm ) and the focus position ( focal lenght ≈ 37 cm ) of the antenna were experimentally obtained [ 5 ]. The electron density profile obtained from the ECE radiation were compared with the results obtained from a microwave interferometer installed in TCABR [ 6 ]. The electron density profiles can be approximated by parabolic equation in the form : A gas puffing injection system is normally used in the TCABR tokamak to control the electron density during the discharges.…”
Section: Experimental Aspects Related To the Ece Measurementsmentioning
In tokamak machines with low toroidal magnetic fields and high plasma densities, the accessibility conditions impose restrictions to the detection of the Electron Cyclotron Emission ( ECE ). In these machines, the righthand cutoff condition can be used as an independent method to determine the local electron density from the ECE data in thermal discharges. In this paper is shown the results obatined from the detection of ECE radiation in the TCABR tokamak, in operation at the Institute of Physics of University of São Paulo. The effect of the ECE radiation cutoff was observed for different radial positions of the plasma column. To reach the ECE cutoff condition, the electron density was increased monotonically by the use of an external gas puffing system. For sufficient high densities, the emission at some frequencies is cutoff and the first and the last frequency to be cutoff depends on the shape of the density profile. These measurements do not require the plasma to be optically thick. It was observed that, for a toroidal field BO = 1.14 T , the first cutoff of ECE occurs for a radial position r ∼ = 5 cm . From these measurements the radial electron density was determined. For a symmetric parabolic profile n e = n eo [1 − (r/a) 2 ] α , values of α between 0.86 and 0.97 were experimentally obtained. A good agreement of these values with those obtained from the microwave interferometer measurements ( α ≈ 0.85 ) was found. Therefore, the ECE right-hand cutoff constitutes an independent method to obtain information about the electron density profile.
“…Mais recentemente, um eletrodo de polarização foi instalado no TCABR para o estudo de regimes de alto confinamento ("modo H"), além de um sistema de Limitador Ergódico Magnético [68] (correspondente a este trabalho) e um sistema de injeção de pastilhas de impurezas (pellets) [67] , instalados para a investigação e controle de instabilidades de disruptura. Basicamente, a densidade de linha das partículas é dado pela seguinte expressão [72] :…”
Section: Iii25 Efeito No Potencial Elétricounclassified
“…No total, há sete cordas disponíveis, mas atualmente, estão instalados apenas 2 fontes de micro-ondas para interferometria. Esquema simplificado do sistema de interferometria utilizado no TCABR [61]…”
O conhecimento dos parâmetros macroscópicos do plasma, tais como a densidade e temperatura, bem como sua evolução e dependência espacial são fundamentais para a compreensão e controle do plasma. Esses parâmetros são essenciais para descrição dos eventos associados a fenômenos de transporte, atividade MHD, estudos de regime de confinamento melhorado (modo H), entre outros. O perfil de temperatura e densidade de íons e elétrons caracteriza um parâmetro extremamente importante em plasmas termonucleares que é o perfil de pressão. Para obter esses perfis foram utilizados os principais diagnósticos disponíveis no tokamak TCABR: espalhamento Thomson, interferometria, reflectometria, ECE e diagnósticos espectroscópicos. O espalhamento Thomson é capaz de determinar o perfil de temperatura e densidade eletrônica durante o disparo; já o diagnóstico ECE é capaz de medir a temperatura eletrônica sob certas condições de descargas. Já os diagnósticos de interferometria e reflectometria medem a densidade eletrônica integrada e a densidade eletrônica local, respectivamente. Por fim, o perfil de temperatura iônica pode ser estimado através do alargamento Doppler das linhas de emissão de impurezas. Tais dados são usados para reconstrução do perfil de pressão, em diferentes tipos de descargas no tokamak, bem como possibilitar a reconstrução do equilíbrio. Não obstante, esses diagnósticos podem fornecer informações como estimativa do Z efetivo do plasma, da velocidade de rotação, e das condições que promovem disrupção no TCABR. Palavras-chaves: perfil de pressão, espalhamento Thomson, equilíbrio MHD, rotação de plasma.
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