Spatial variation of Dα line spectral profile and emission process in the divertor region of JT-60U

Spatial variation of the Dα line spectral profiles emitted from the divertor region has been measured with a high-resolution visible-light spectrometer. The observed Dα line spectral profiles are compared with the calculation of a neutral particle transport code. Good agreement is obtained under the attached-plasma conditions. The components of the observed spectral profiles are identified at each measured position. The dissociative excitation (direct production of D*(n=3) by the dissociation of D2 and D2+) is important near the divertor target. At positions away from the divertor target, the emission due to the electron collisional excitation of the dissociated atoms contributes significantly to both the Dα line intensity and its spectral profile. The contribution of atoms produced by charge exchange and particle reflection are also important in the upstream of the divertor plasma. These fractions increase with the increase in the electron density, broadening the Dα line spectral profile. The Dα line spectral profiles are measured under several plasma conditions. The Dα line spectral profile near the target becomes broader during the ELMy phase. Under the detached-plasma condition, the Dα line spectral profile is symmetric to the line centre and is narrow, dominated by the low-temperature components. A similar feature is observed at the MARFE region. (author)