Modern analysis of X-ray spectra is strictly connected with the quality of the atomic data. High-resolution instruments installed at fusion devices such as TEXTOR, TORE SUPRA, NSTX etc. allow us on the other hand to verify the atomic data which describe the different atomic processes [1,2].
He-like spectra of argon have been studied intensively at the tokamak TEXTOR with the aim to test and thus to improve the data for effective excitation of the lines 1s2l-1s2 and the dielectronic satellites 1s2lnl’-1s22l. The effective excitation rates for the lines due to n-1 transitions have been calculated by means of two methods: Coulomb-Born and R-matrix. Both methods have shown agreement to within 4% in a temperature interval 0.5...4.0 keV for all n=2 lines excluding the forbidden line. Here, the deviation reaches 10% for low temperatures of about 0.5 keV.
The atomic data for the dielectronic satellites were obtained in the framework of two main approaches based on Z-expansion of perturbation theory and multi-configurational wave functions. The influence of cascades between the doubly excited states on the intensity of the satellite lines has been intensively studied. Special attention has been paid to the inner-shell excited satellites of n=2 and the group of satellites with n=3 and n=4. Other processes, such as recombination of H-like ions as well as inner-shell ionization of Li-like ions have been also taken into account.
The spectra obtained from the tokamak TEXTOR at substantially different plasma conditions have been compared with theoretical ones based on different sets of atomic data. The deviations for the intensities of the lines were shown to be within 10% for the whole spectral range.

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