Spectroscopic study on forbidden magnetic dipole transitions in LHD

Forbidden lines arising from magnetic dipole（M l）transitions among fine-structure levels of highly charged ions have been observed for Al，Ar, Ti, Fe，Kr, Mo and Xe in Large Helical Device（LHD）. A space-resolved 3m normal incidence VUV spectrometer and newly designed double-structure impurity pellets for an impurity pellets injector have been developed for this purpose. The Ml transitions are identified by analyzing their Doppler broademing， temporal intensity behavior and spatial intensity distribution. Wavelengths of these M l transitions are determined with high accuracy and compared with previous experimental and calculated values with detailed spectroscopic analysis of C，Ne and Ar emission lines in range of 250 to 2300Å. The Ml transitions from heavy elements observed here are expected to be useful for visible impurity diagnostics of D-T burning plasmas in the future． The line intensity ratios of the M l transition to the allowed（E l) transition such as 2s22p52P3/2-2P1/2 / 2s22p5 2P3/2-2s2p6 2S1/2 (ArX 5533Å / 165Å，TiXIV 2118Å / 122Å and FeXVIII 975Å / 94Å）and 2s2p 3P1.- 3P2 / 2s2 1S0-2s2p 1P1（ArXV 5944Å / 221Å）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．The effect of fast ions on the M l transition is also considered