DOPPLER BROADENING AND MAGNETIC-FIELD EFFECTS ON SOME ION IMPURITY SPECTRA EMITTED IN THE BOUNDARY-LAYER OF A TOKAMAK PLASMA

Examples are presented of Doppler broadening measurements on singlet, doublet and triplet emission spectra from the following impurity ions found in the boundary layer of the TEXTOR tokamak: Cn, CIII, CIV, SiII, and SiIII. The shapes of these spectral lines are significantly influenced by the confining magnetic field of some 2 T, in some cases exhibiting an appreciable Paschen-Back effect which complicates their appearance. It is shown that reliable values for the particular ion temperature can be obtained from the Doppler widths of the various Zeeman components, when the presence of the magnetic field is properly accounted for. Such temperatures derived from partially ionised impurity species should, however, be cautiously interpreted, as the ions in question probably do not exist for long enough in the particular ionisation stage to achieve thermal equilibrium with the background deuterons and protons. This interpretation of our results is supported by a simple one-dimensional model of ionisation and collisional heating processes in the plasma boundary.