Identification and intensity analysis on forbidden magnetic dipole emission lines of highly charged Al, Ar, Ti and Fe ions in LHD

Forbidden lines arising from magnetic dipole (M1) transitions in ground and 2s2p excited configurations of highly charged Al, Ar, Ti and Fe ions have been observed in the large helical device (LHD). Argon was puffed using a piezo-electronic valve and other metallic materials were injected using an impurity pellet injector into LHD plasma for the observation. The M1 transitions in vacuum ultraviolet (VUV) and visible regions are identified by analyzing their Doppler broadening, temporal intensity behavior and spatial intensity distribution. Wavelengths of these M1 transitions are determined with high accuracy and compared with previous experimental and calculated values. The line intensity ratios of the M1 transition to the allowed (E1) transition such as (ArX 5533 Å/165 Å, TiXIV 2118 Å/122 Å and FeXVIII 975 Å/94 Å) and 2s2p - (ArXV 5944 Å/221 Å) are measured as a function of electron density. Results on the ArX and ArXV are compared with a simple level-population calculation. As a result, the density dependence of the ratio is well explained mainly by a competition between two decay processes of the collisional de-excitation and the radiative decay due to the forbidden line emission, although a clear discrepancy between the experimental and calculated absolute values appears for the ArX ratio. Contribution of fast proton impact excitation, which is brought by 180 keV neutral beam injection (NBI) for plasma heating, is also analyzed with the calculation for the F-like ions of ArX, TiXIV and FeXVIII.