Abstract
A spectroscopic measurement is performed for a plasma in a rotating radiation belt, which accompanies the complete divertor detachment recently realized in the Large Helical Device (LHD) [J. Miyazawa et al., Nucl. Fusion 46, 532 (2006)]. The population distribution over the exited levels is experimentally determined from the Balmer series line intensities and is compared with the result of the collisional-radiative model calculation to determine the electron temperature Te and density ne. No reasonable pair of Te and ne is found when either the ionizing plasma or the recombining plasma is assumed. A good fitting is obtained under an assumption of the ionization balance plasma with Te = 1.8 eV and ne = 2 × 1020 m-3. These parameters are confirmed through analysis of a high-wavelength-resolution measurement for the Balmer series lines which clearly exhibit the Stark broadening effect.
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