Estudos de plasmas a altas temperaturas por espectroscopia visivel e ultravioleta no vacuo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

In this thesis we present results on a wide variety of experiments related to magnetically confined plasma spectroscopy. We discuss the applicability of atomic models to our spectroscopy measurements, spectrometers absolute calibration, as well as the determination of many parameters of the plasma confined in the tokamak NOVA-UNICAMP. For these measurements, we have used two spectrometers, one at visible spectra and the other in the vacuum ultraviolet (VUV) spectra, together with other diagnosis installed in our machine. We have acquired a multichannel detector, consisted basically on a MCP plate connected to a CCD device, for VUV spectrometer, which allowed a very sophisticated diagnosis in our machine. We present in detail the installation and the adjusting process of the above mentioned spectroscopic devices. In this topic, we emphasize the absolute calibration process for different methods: standard lamp, spectral pairs measurements (branching ratio), and as an innovation, the spectral pairs measurements calculating the ground state density (as a function of the temperature). We compare the precision of each method, as well as their applicability. We have developed a new method to obtain more accurate particle confinement time ( t p ) measurements, comparing some hydrogen emissions and the appropriated parameters in Johnson and Hinnov?s tables for our plasma. As a result, we have obtained 1.35 and 2 ms for t p values (in different discharges). More important than calculating t p is the possibility to determine the mean electron density and electron temperature by hydrogen emission (from which we obtain the best radial profiles for these parameters). By the measurements of the absolute emission values and the broadening of these lines, we have calculated the ion density and the ion temperature respectively of the main plasma impurities. We have observed that the oxygen was the main impurity (followed by carbon), as represented by the presence of OIII, OIV and OV, besides the OVI in the second half of the discharge. As typical ion temperatures, we have obtained values between 30 and 60 eV (without any accentuated difference in the values for higher and lower ionization level ions). We have compared the Zeff measurements by three methods: plasma continuous radiation, ion densities sum, and Sptizer formula. For the first method, we have calculated precise gaunt factor values and we have included electronic recombination effects. However, the resulting values for these measurements did not show to be reliable, evidencing the existence of other possible sources (attributed to plasma/wall surface interaction) for the radiation measured. The other two methods have showed close results, mainly in the intermediated times of plasma currents, with values between 2 and 2.5. Finally, we have also analyzed how discharges cleaning and helium discharges influence our plasma conditions. We have observed a great hydrogen dessorption from titanium films in the inner wall vessel, which leads to a great hydrogen flux during the discharge, worsening considerably the plasma conditions

ASSUNTO(S)

espectroscopia visivel espectroscopia ultravioleta no vacuo fisica atomica e molecular tokamaks plasma (gases ionizados)

ACESSO AO ARTIGO

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