Plasma spectroscopy for magnetically confined fusion plasma

An emission line of neutral helium λ667.8 nm (21P-31D) is observed with a set of line of sights which covers an entire poloidal cross section of LHD, a heliotron-type fusion experimental device. From the observed Zeeman splittings and the well-known magnetic field structure in the plasma, the emission locations on the line of sight are precisely determined. The distribution of line emissions over the observed poloidal cross section is derived from the results of all the line of sights through a tomographic analysis.Balmer series lines of neutral hydrogen are measured for the rotating radiation body in the Serpens mode [J. Miyazawa et al., Nucl. Fusion 46, 532 (2006)]. The electron temperature and density are derived from the observed spectra with the help of calculations with the collisional-radiative (CR) model. The derived electron density is confirmed with the Stark broadening of several lines from n = 7 to 16 levels, where n is the principal quantum number.We have developed a CR model code for neutral helium based on recently calculated cross section data of electron impact. Six emission lines of neutral helium for the transitions from n = 3 to n = 2 levels are measured for various discharges in LHD and an estimation of the electron temperature and density is attempted from the intensity ratios among three lines, λ667.7 nm (21P-31D), λ706.5 nm (23P-33S), and λ728.1 nm (21P-31S), out of the six lines. Intensities of other three lines, λ388.9 nm (23S-33P), λ501.6 nm (21S-31P), and λ587.6 nm (23P-33D), are calculated with the derived plasma parameters and the agreement with the measured line intensities is found satisfactory