Visible spectroscopic measurements on FTU

Visible spectroscopy has been extensively used in FTU to measure the intensity of the spectral lines of hydrogen, light impurities (C, O, N) and metallic impurities (Ni, Cr, Fe). The plasma light was collected along selected tangential and radial chord views in order to observe the vacuum chamber wall and the limiter respectively. The visible light emitted by atoms and ions was collected by a telescope and focused onto one end of a 1 mm diameter fiber optics. The other end of this quartz fiber with f/3 was directly attached onto the entrance slit of a Monospec27 grating spectrometer with f/3.8 and equipped at the exit slit with an intensified linear diode array. The spectrometer can use 3 different gratings in order to have linear dispersion of 3, 6 and 24 nm/mm. We used in our experiments the second and the third gratings to cover a spectral range of 3000 A and 700 A respectively. The spectrometer has been calibrated in absolute intensity using a calibrated lamp and a lambertian diffuser. The impurity influx has been derived from the absolute line intensity through the calculated value of ionization to photon emission ratio. (author) 3 refs., 6 figs