Validation of Spectroscopic Model for Fe Ions in Non-Equilibrium Ionization Plasma in LHD and Hinode

Abstract

We measured extreme ultraviolet spectra of Fe ions for plasmas produced in the Large Helical Device (LHD) at the National Institute for Fusion Science (NIFS). Iron was injected into the plasmas by using a tracer– encapsulated pellet. By controlling the neutral beam injection pattern, we could produce plasma with a central electron temperature of approximately 500eV, which was suitable for producing Fe XVII ions. We measured seven Fe XVII lines. The intensity ratio for λ of 20.468 to 25.493nm was consistent with the theoretically calculated value of 1.1. This calculated value was determined purely from the branching ratio due to the common upper level of these transitions, although Warren et al. [Astrphys. J. 685, 1277 (2008)] reported a larger ratio of approxinately 2 from Hinode EIS measurements. The other five ratios for Fe XVII lines in our LHD measurements were also consistent with the theoretical ratios calculated with a collisional–radiative model. A preferred atomic dataset for Fe XVII is suggested to obtain better agreement between the measured and calculated ratios.