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.

This paper summarizes experimental results from recent studies on intrinsic rotation at the plasma edge of the TCABR tokamak. These results were obtained after upgrading the number of channels of the rotation diagnostic to three. The measurements were carried out in the collisional (Pfirsch-Schluter) regime and the rotation profiles of the ions were obtained from the Doppler shifts of the impurity carbon lines, CIII (464.74 nm), and CVI (529.06 nm). Results on the correlation between toroidal rotation at the plasma edge and direction of gas injection are also presented. They indicate that the direction of gas injection has a small effect on rotation; the velocity of the background neutral hydrogen is affected by direct momentum transfer from the injected gas (also hydrogen), while the carbon ions' velocity is affected by inward radial friction force between the injected gas atoms and ions, increasing their velocity in the opposite sense of the plasma current.

An overview of intrinsic plasma rotation studies in Ohmic L-mode discharges carried out in the Tokamak Chauffage Alfvén Brésilien (TCABR) tokamak is presented. Measurements of plasma poloidal and toroidal rotation, and a comparison against neoclassical theory, are presented. The results show that poloidal rotation is in good agreement with neoclassical theory while toroidal rotation is found to be anomalous. A new technique that allows for high temporal resolution measurements of plasma rotation is presented. This technique is used to test two models of intrinsic toroidal rotation: the so-called Helander model (Helander et al 2003 Physics of Plasmas 10 4396) and Rozhansky model (Rozhansky 2013 Perpendicular currents and electric fields in fully and partially ionized magnetized plasma Physics of Plasmas 24 101614). As TCABR is a relatively small device, the influence of the neutrals that form the basis of this model is expected to be enhanced. The results indicate that the mechanism proposed by Helander does not contribute significantly to the intrinsic toroidal rotation in TCABR plasmas. The measurements, however, indicate that the frictional force proposed by Rozhansky might be responsible for part of the intrinsic toroidal rotation observed in TCABR plasmas.

The transition from the ohmic heating L-mode to the H-mode in the tokamak TCABR induced by an external electrode biasing is addressed in this work. A gradual improvement in the plasma confinement with the biasing voltage was observed as a result of the enhancement of the E Â B shear flow at the edge. This result was supported by the measurement of plasma parameters in different radial locations by two electrostatic probes. Radial profiles of the electron temperature (from the standard sweeping voltage technique), electron density, and radial electric field, as well as the local turbulence features, were measured. We observed that the electron density profile became steeper as the voltage on the electrode increased, while no significant change in the temperature profile was noticed. In addition, the data were compared with the spectral shift model [G. M. Staebler et al., Phys. Rev. Lett. 110, 055003 (2013)] at different bias voltages, i.e., different E Â B shear flows, showing a good agreement. Particularly, the gradual improvement was held: the higher the biasing voltage, the larger the radial wavenumber shift and so the turbulence suppression. Moreover, by studying the edge radial profile of the mean radial wavenumber, we show that the large shift occurs in the same position where the transport barrier is created.

Long-distance correlations (LDCs) of plasma potential fluctuations in the plasma edge have been investigated in the TCABR tokamak in the regime of edge biasing H-mode using an array of multi-pin Langmuir probes. This activity was carried out as part of the scientific programme of the 4th IAEA Joint Experiment (2009). The experimental data confirm the effect of amplification of LDCs in potential fluctuations during biasing recently observed in stellarators and tokamaks. For long toroidal distances between probes, the cross-spectrum is concentrated at low frequencies f < 60 kHz with peaks at f < 5 kHz, f = 13–15 kHz and f ∼ 40 kHz and low wave numbers with a maximum at k = 0. The effects of MHD activity on the LDCs in potential fluctuation are investigated.