Spatial variation of the Dα line spectral profiles emittedfrom the divertor region has been measured with a high-resolutionvisible-light spectrometer. The observed Dα line spectral profiles arecompared with the calculation of a neutral particle transport code. Goodagreement is obtained under the attached-plasma conditions. The components ofthe observed spectral profiles are identified at each measured position. Thedissociative excitation (direct production of D*(n = 3) by thedissociation of D2 and D2+) is important near the divertor target. Atpositions away from the divertor target, the emission due to the electroncollisional excitation of the dissociated atoms contributes significantly toboth the Dα line intensity and its spectral profile. The contributionof atoms produced by charge exchange and particle reflection are alsoimportant in the upstream of the divertor plasma. These fractions increasewith the increase in the electron density, broadening the Dα linespectral profile. The Dα line spectral profiles are measured underseveral plasma conditions. The Dα line spectral profile near thetarget becomes broader during the ELMy phase. Under the detached-plasmacondition, the Dα line spectral profile is symmetric to the linecentre and is narrow, dominated by the low-temperature components. A similarfeature is observed at the MARFE region.
Physics studies of ADITYA & ADITYA-U tokamak plasmas using spectroscopic diagnostics