Interpretation of line emissions from helium-like ions in terms of the electron parameters and ion diffusion in Tokamak plasmas

Abstract

A detailed calculation is made of the populations of the excited levels of the helium-like ion O⁶⁺ in a plasma, taking full account of recombination and collisional radiative processes. The results apply equally to equilibrium and non-equilibrium plasmas. Line ratios are identified which are indicative of electron temperature, electron density and the non-equilibrium state of the plasma. Useful diagnostic plots of these line ratios are given in terms of a parameter r describing the relative abundance O⁶⁺/O⁷⁺. Data on the electron parameters, O⁶⁺ line emissions and associated line emissions of O⁵⁺ and O⁷⁺ for the DITE Tokamak facility are used to test the diagnostics model. The interpretation is markedly sensitive to the electron temperature profile. The spatial variation of r from its equilibrium value allows a derivation of the helium-like ion diffusion velocity.